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Hyperexcitability in the corticostriatal glutamatergic pathway may have a pivotal role in the pathogenesis of Parkinson's disease (PD). Metabotropic glutamate receptors (mGluRs) modulate glutamate transmission by both pre- and postsynaptic mechanisms, making them attractive targets for modifying pathological changes in the corticostriatal pathway. Exercise reportedly alleviates motor dysfunction and induced neuroplasticity in glutamatergic transmission. Here, the mGluR-mediated plasticity mechanism underlying behavioral improvement by exercise intervention was investigated. The experimental models were prepared by 6-hydroxydopamine injection into the right medial forebrain bundle. The models were evaluated with the apomorphine-induced rotation test. Starting 2 weeks postoperatively, exercise intervention was applied to the PD + Ex group for 4 weeks. The exercise-intervention effects on locomotor behavior, glutamate levels, and mGluR (mGluR2/3 and mGluR5) expression in hemiparkinsonian rats were investigated. The results showed that hemiparkinsonian rats have a significant increase in extracellular glutamate levels in the lesioned-lateral striatum. MGluR2/3 protein expression was reduced while mGluR5 protein expression was increased in the striatum. Notably, treadmill exercise markedly reversed these abnormal changes in the corticostriatal glutamate system and promoted motor performance in PD rats. These findings suggest that mGluR-mediated glutamatergic transmission in the corticostriatal pathway may serve as an attractive target for exercise-induced neuroplasticity in hemiparkinsonian rats.

Introduction Parkinson’s Disease (PD) is a progressive neurodegenerative disorder, hallmark of which is loss of nigral dopaminergic neurons. Since a Hypericum polyanthemum extract inhibits monoamine reuptake and some of its constituents present cytotoxic properties, the aim of this study was to evaluate the effect of this extract in an animal PD model. Methods Adult Wistar rats (110 days old) received 6-hydroxydopamine (6-OHDA) infusions into the right medial forebrain bundle. A cyclohexane extract from aerial parts of H. polyanthemum (POL; 90 mg/kg/administration; gavage) was administered in three different regimens. In Regimens 1 and 2, rats received 3 administrations of POL starting 4 or 24 h after 6-OHDA infusion, respectively. In Regimen 3, these administrations were carried out 1 day before any evaluation of ipsilateral rotational activity induced by methylphenidate (MP, 20 mg/kg, i.p.). MP was administered 10, 45, and 85 days after 6-OHDA infusion in all groups. Nigral tyrosine hydroxylase (TH) immunocontent was evaluated 120 days after 6-OHDA infusion in animals submitted to Regimen 2 only. The effect of POL on apomorphine-induced climbing behavior in non-lesioned adult CF1 mice (60 days old) treated with POL was also evaluated. Results Regimen 2 increased MP-induced rotational activity and decreased nigral TH levels in 6-OHDA-lesioned rats. Rotational activity was not altered in regimens 1 and 3. In addition, no change in climbing behavior was observed in non-lesioned mice. Conclusion Together, these results indicate that, in 6-OHDA-lesioned rats, a cyclohexane H. polyanthemum extract potentiates neurotoxicity and MP-induced motor asymmetry depending on the time of administration. In the short term, it seems to not act directly on mice dopaminergic receptors.

The pedunculopontine nucleus (PPN) is connected to spinal, cerebellar and cerebral motor control structures and can be activated with external electrodes. Intrinsic cholinergic neuronal degeneration in the PPN is associated with postural instabilities and gait disturbances (PIGD) in advanced Parkinson's disease (PD). Clinical studies have demonstrated that PPN stimulation may improve PIGD. We investigated this claim and the underlying mechanisms using the 6-hydroxydopamine (6-OHDA) hemilesion model of PD. In this study, gait-related parameters, including the base of support (BOS), stride length, and maximum contact area, were analyzed via CatWalk gait analysis following PPN-low frequency stimulation (LFS) of rats with unilateral 6-OHDA lesions. Additionally, neurotransmitter concentrations in the ventrolateral thalamic nucleus (VL) were measured by microdialysis and liquid chromatography-mass spectrometry (LC-MS). Our data revealed that unilateral 6-OHDA lesions of the medial forebrain bundle (MFB) induced significant gait deficits. PPN-LFS significantly improved the BOS (hindlimb) and maximum contact area (impaired forelimb) scores, whereas no other gait parameters were significantly affected. Unilateral 6-OHDA MFB lesions significantly decreased acetylcholine (ACh) and moderately decreased noradrenaline (NA) concentrations in the VL. PPN-LFS mildly reversed the ACh loss in the VL in the lesioned rats but did not alter the NA levels. Taken together, our data indicate that PPN-LFS is useful for treating gait deficits of PD and that these effects are probably mediated by a rebalancing of ACh levels in the PPN-VL pathway. Thus, our findings provide possible insight into the mechanisms underlying PIGD in PD.

Gait deficits are important clinical symptoms of Parkinson's disease (PD) but are rarely studied. In this study we made three different rat PD models by administration of 6-hydroxydopamine into caudate putamen (CPU), medial forebrain bundle (MFB) and substantia nigra compact (SNC). We evaluated the gait changes in these models by using a computer-assisted CatWalk system. Correlations of gait parameters with tyrosine hydroxylase protein levels in the CPU and SNC were also investigated. The gait readouts were significantly impaired in both the MFB and SNC groups. However, the MFB group showed a more pronounced impairment than the SNC group. In contrast, only mild and incomplete gait impairment occurred in the CPU group. In addition, some gait parameters demonstrated close correlation with the protein levels of TH. This paper suggests that the 6-hydroxydopamine-induced MFB model is more propitious to study gait dysfunction than the other two models and the CatWalk system can provide reliable and objective criteria to stratify gait changes arising from 6-hydroxydopamine lesioned rats. These findings may hold promise in the study of PD disease progression and new therapeutic methods.

The lateral habenula (LHb) is an important structure involved in various brain functions, because it controls the activity of dopaminergic and serotonergic systems in the midbrain. The impairment of working memory commonly occurs in Parkinson's disease; however, it is not clear whether the LHb involves in the regulation of working memory in rats with unilateral 6-hydroxydopamine lesions of the medial forebrain bundle (MFB). In this study, we found that the MFB lesions in rats decreased choice accuracy as measured by the T-maze rewarded alternation test compared to control rats, indicating the induction of working memory impairment, and decreased dopamine (DA) levels in the medial prefrontal cortex (mPFC), hippocampus and amygdala. Further, rats in the MFB and LHb lesion group showed increased choice accuracy compared to rats in the MFB lesion group, indicating the enhancement of working memory after lesioning the LHb. Neurochemical results found that lesions of the LHb increased DA levels in the mPFC, hippocampus and amygdala in the MFB and LHb lesion group, as well as serotonin (5-HT) level in the mPFC. These findings suggest that DA depletion plays a key role in working memory impairment, and lesions of the LHb improve working memory in the MFB-lesioned rats, which involves in increases in the levels of DA and 5-HT in the mPFC, hippocampus and amygdala. Additionally, the present results may have implications for improving our understanding of the neuropathology and/or treatment of PD.

Factors that trigger emotional expression may be divided into two patterns according to the type of motivation, acquiring reward (pleasure) and avoiding aversion (punishment). Repeated exposure to certain external stimuli accompanied by aberrant motivation may produce psychiatric diseases such as bipolar disorder and addiction via dysregulation of the central nervous system. However, neurobiological underpinnings of such diseases have not been clarified, especially at the neuronal level. In the present study, plasma from rats undergoing intracranial self-stimulation (ICSS) produced neurite outgrowth in PC12-variant cells (PC12m3). Stimulated PC12m3 cells also exhibited heightened activity of the p38 MAPK pathway. These findings indicate that reward states lead to not only morphological changes but also increases in p38 MAPK activity at the neuronal level in the central nervous system.

Our previous study regarding the changes of D(2) receptor in nigrostriatal dopamine system at an early stage (4 weeks after lesion) indicated a different functional activity of striatal D(2) receptor between two different rat parkinsonian models, lesioning with 6-hydroxydopamine in the striatum and in the medial forebrain bundle (MFB). In the present study, we further examined binding of D(2) receptor as well as pre-synaptic dopamine transporter (DAT) at later stages (6 months after lesion) both in the striatal and MFB lesion models. The D(2) receptor binding in MFB model at 6 months after lesion was significantly lower than that at 4 weeks after lesion, albeit it was still higher than the normal side. The D(2) receptor binding in striatal model was decreased to the same extent at both 4 weeks and 6 months after lesion. DAT binding decreased at 6 months after lesion, more profound in MFB model, and the degree of reduction was not different from that at 4 weeks after lesion. These findings indicated different dynamic processes of the D(2) receptor and DAT during a longer time observation in the striatal and MFB lesion models. The dynamic changes of D(2) receptor activity after lesion should be considered when selecting 6-hydroxydopamine-induced rat parkinsonian models.

Depletion of rat brain serotonin (5-hydroxytryptamin, 5-HT) has been widely used to study effects of serotonin and its interaction with other transmitter systems. Various treatment regimes for serotonin depletion have been applied, but the efficacy of these seems to vary considerably. So far, no studies have systematically examined and compared different approaches. The present work combines quantitative and qualitative measurements and compares six different treatment schemes for 5-HT depletion. Treatment outcome was evaluated by HPLC measurements of 5-HT and 5-HIAA concentrations, and by 5-HT and tyrosine hydroxylase immunocytochemistry. The schemes included repeated administration of fenfluramine (FEN) and/or p-chlorophenylalanine (pCPA). The most efficient treatment for rat brain 5-HT depletion was the combined treatment with one daily pCPA (200 mg/kg) injection for 3 days followed by one injection of d,l-FEN (20 mg/kg) on the fourth day, causing a 94.9% brain 5-HT depletion. Immunostaining revealed a distinct brain distribution of the remaining 5-HT, with an almost complete depletion of 5-HT in the cerebral cortex, hippocampus and thalamus, while a substantial amount of 5-HT still was left in the raphe nuclei, the medial forebrain bundle, and the medial eminence. FEN or pCPA treatment alone caused from 68.2 to 94.0% decrease in 5-HT levels. While the pattern of 5-HT depletion using pCPA alone was comparable to the one seen with the combined treatment, the 5-HT depletion using FEN alone showed a different pattern with 5-HT distributed in several brain regions.

Low-dose thrombin given several days before lesioning is neuroprotective in ischemic and hemorrhagic models of stroke, an effect termed thrombin preconditioning (TPC). Here, the ability of TPC to provide protection in a 6-hydroxydopamine (6-OHDA) model of Parkinson's disease (PD) was evaluated. All animals received 10 μg 6-OHDA into the right medial forebrain bundle. Three days prior to 6-OHDA, the animals received either 1 U rat thrombin ( n = 17) or saline ( n = 14) 1 mm above the site of neurotoxin delivery. The animals were then evaluated for neurobehavioral deficits until 21 days post-injection. TPC animals performed significantly better on both a vibrissae-elicited forelimb placing test and a forelimb-use asymmetry test than the saline controls. The animals were then sacrificed for either catecholamine determination by HPLC with electrochemical detection or for histopathology to determine lateral ventricular volume or striatal tyrosine hydroxylase immunoreactivity. Although TPC did not protect against the dopamine depletion associated with this severe model, it did reduce dopaminergic terminal loss and ventricular enlargement as compared to saline-treated animals. This report presents the new finding that preconditioning (and TPC in particular) provides protection in a 6-OHDA PD model. Understanding the mechanisms involved in TPC-mediated protection may stimulate innovative therapeutic regimens.

Auditory evoked potentials (AEPs) were recorded in the motor cortices (MC) with chronically implanted electrodes in the rat. Some of the AEPs in the MC, namely negative potentials on the surface and positive ones at a depth of 2 mm at latencies of about 50-150 ms, were abolished by limited bilateral lesions of the anterior perirhinal cortex (PERa) which was responsive to auditory stimulus, indicating that the AEPs in the MC were at least partially relayed in the PERa. The auditory response in the MC was prominently enhanced when water was supplied or the medial forebrain bundle was stimulated after auditory stimulus. These results indicate that the MC receives the reward associated auditory information from the PERa.

Dopamine (DA) overflow in the mouse nucleus accumbens during intracranial self-stimulation (ICSS) of the median forebrain bundle was estimated by chronoamperometry with removable carbon fibre electrodes. The specificity of the voltammetric signal was confirmed pharmacologically. The parameters of stimulation (50 Hz, 0.5 s train length) allowed us to obtain measurable DA release and to maintain ICSS. Continuous (CR) and fixed-ratio (FR8) schedule of reinforcement showed differing correspondence of the patterns of DA release with the patterns of stimulation/nose-poking. The CR schedule induced a high rate nose-poking and tonic increase in dopamine overflow, which became decreased following the first periods of self-stimulations. The FR schedule induced stable peaks of DA overflow during the entire period of ICSS. We conclude that the availability of a readily-releasable pool of DA in presynaptic terminals determined the pattern of dopamine overflow in the nucleus accumbens during ICSS in mice.

The effect of a unilateral 6-hydroxydopamine (6-OHDA) lesion of the left medial forebrain bundle and 3 weeks treatment with l -DOPA of normal and 6-OHDA lesioned rats on CB1r mRNA expression was investigated by in situ hybridization. A 6-OHDA lesion of nigrostriatal pathway alone, confirmed by the loss of nigral tyrosine hydroxylase mRNA, did not alter CB1r mRNA levels in the dopamine depleted striatum. Similarly, chronic l -DOPA treatment of normal rats had no effect on striatal CB1r mRNA expression. In contrast, chronic l -DOPA treatment of 6-OHDA-lesioned rats significantly increased CB1r mRNA expression in the denervated striatum. These results suggest that the CB1r activity may be altered by l -DOPA's action and this may be related to the treatment of Parkinson's disease.

Rodents with lesion of dopaminergic pathway when receiving repeated l -3,4-dihydroxiphenylalanine ( l -DOPA) treatment develop abnormal involuntary movements called dyskinesia. We demonstrated that nitric oxide synthase (NOS) inhibitors mitigate l -DOPA-induced dyskinesia in rodents. The aim of the present study was to verify if the in vivo preferential neuronal NOS (nNOS) inhibitor 7-nitroindazole (7-NI) affect the expression of the transcription factor FosB/ΔFosB in the lesioned striatum, an indicator of neuronal activity associated with dyskinesia. Male Wistar rats with unilateral microinjection (medial forebrain bundle) of either the neurotoxin 6-hydroxidopamine (6-OHDA; n = 4–6/group) or saline (sham; n = 6/group) were provided with l -DOPA (30 mg/kg plus benserazide 7.5 mg/kg/day, oral gavage), once a day during 22 days. 6-OHDA-lesioned animals developed abnormal involuntary movements (AIMs) classified as axial, limb, orofacial and locomotive dyskinesia and presented FosB/ΔFosB increase in the dopamine-depleted striatum. Administration of 7-NI (30 mg/kg, i.p.), 30 min prior to l -DOPA reduced the severity of AIMs (≈65% for axial, limb and orofacial and 74% for locomotive AIMs scores), without interfering with the rotarod performance. Simultaneously, 7-NI attenuated the expression of FosB/ΔFosB in dopamine-depleted striatum (≈65% in medial and ≈54% in lateral striatum, bregma 0.48 mm). FosB/ΔFosB expression in lateral striatum was correlated with l -DOPA-induced dyskinesia. The findings described here corroborate a new approach to the management of l -DOPA-therapy in Parkinson's disease (PD) treatment.

Parkinson's disease (PD) is a neurodegenerative disease resulting from progressive loss of dopaminergic nigrostriatal neurons. α-Synuclein protein conformational changes, resulting in cytotoxic/aggregated proteins, have been linked to PD pathogenesis. We investigated a unilateral rotenone-lesioned mouse PD model. Unilateral lesion of the medial forebrain bundle for two groups of male C57 black mice (n=5); adult (6-12 months) group and aged (1.75-2 years) group, was via stereotactic rotenone injection. After 2 weeks post-lesion, phenotypic Parkinsonian symptoms, resting tremor, postural instability, left-handed bias, ipsiversive rotation and bradykinesia were observed and were more severe in the aged group. We investigated protein expression profiles of the post-translational modifier, SUMO-1, and α-synuclein between the treated and control hemisphere, and between adult and aged groups. Western analysis of the brain homogenates indicated that there were statistically significant (p

Prior evidence shows that acupuncture improves symptoms in both Parkinson's disease (PD) patients and animal models. We examined the effects of high-frequency (100 Hz) electroacupuncture (EA) on behavior in a rat PD model induced by medial forebrain bundle (MFB) transection. Neurotransmitters levels in the striatum were measured using in vivo microdialysis and high performance liquid chromatography (HPLC). High-frequency EA stimulation at Dazhui (GV14) and Baihui (GV20) acupoints decreased rotational behavior induced by apomorphine (APO) and improved motor coordination, protected axotomized dopaminergic neurons from degeneration in the substantia nigra (SN), it did not increase striatal dopamine (DA) levels. However, EA stimulation at acupoints significantly decreased the abnormally elevated glutamate (Glu) and acetylcholine (ACh) levels in the lesioned side of striatum. Moreover, the Glu levels correlated significantly with survival ratios of dopaminergic neurons in the SNc and rotational bahavior. These data suggested that behavioral alleviation with EA stimulation may be associated with modulation of neurotransmitters release, such as Glu and ACh in the striatum, rather than with DA restoration.

This study was performed to investigate the effect of intraventricular fetal mesencephalic grafts on the non-lesioned nigro-striatal system of rats with unilateral lesions of dopaminergic neurones in the medial forebrain bundle and to analyze the involvement of the non-lesioned side in functional recovery due to grafts in this model. Grafts placed to the lesioned striatum produced a continuous decrease of apomorphine (APO, 0.25 mg/kg intraperitoneally (i.p.)) and amphetamine (AMPH, 5 mg/kg, i.p.) induced rotations over 7 months after grafting. Using differential pulse voltammetry (DPV) in anaesthetized and pargyline (75 mg/kg, i.p.) pretreated rats we found that 8 months after grafting in the lesioned striatum AMPH (5 mg/kg, i.p.) produced a higher increase of the dopamine (DA) signal (i.e., it became measurable), whereas in the non-lesioned striatum the same treatment produced a smaller increase of the DA signal, both compared to that in sham-grafted controls. After grafting onto the non-lesioned striatum, only a slight decrease of APO-induced rotations was observed, whereas AMPH-induced rotations were increased. In these animals AMPH did not produce a measurable DA signal in the lesioned striatum. The DA signal in the non-lesioned striatum was slightly higher than that of non-grafted controls. These results show clearly that unilateral fetal mesencephalic grafts producing behavioural recovery in the unilateral 6-OHDA model of the rat produce changes at dopaminergic mechanisms in the non-lesioned striatum.

The neurorescuing effect of A68930 (a potent selective D(1) agonist) and its role on the regulation of hypothalamus-pituitary-adrenal (HPA)-axis have been investigated. Acute (AS) and chronic unpredictable (CUS) stress models were used to evaluate the effect of A68930 on HPA-axis regulation in relation to the change in the fiber density and number of immunoreactive (ir) neurons of tyrosine hydroxylase (TH) and glucocorticoid receptor (GR) in the dopamine (DA) and GR rich brain regions in rats. CUS caused a significant decrease in the number of TH ir neurons in the striatum, medial forebrain bundle, ventral tegmental area and substansia nigra and GR in the cortex, striatum and hippocampus as compared to the non-stress controls (NS). Administration of A68930 (0.25mg/kg i.p.) significantly normalized these CUS-induced alterations. We also examined the role of A68930 on stress-induced brain oxidative status. AS enhanced the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) in the cortex and striatum, while CUS reduced the activities of SOD and catalase (CAT) in the cortex, striatum and hippocampus, when compared with NS. Increased GSH-Px activity, with reduced glutathione and increased lipid peroxidation was observed in both AS and CUS in selected brain regions as compared to NS. Administration of A68930 normalized the antioxidant enzyme activities, replenished GSH and decreased the extent of lipid peroxidation. In conclusion, present findings suggest that the stress-induced immunoreactivity of TH and GR in distinct brain regions are modulated by A68930 leading to the normalization of HPA-axis response. Ours results show the therapeutic importance of DA D(1) agonist in stress-induced dopaminergic-related neurological disorders. A68930 also influenced the brain antioxidant machinery probably through the restoration of stress-induced changes in the dopaminergic system and its crosstalk with GR.

Cortical and striatal extracellular acetylcholine (ACh), choline (Ch), dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) levels were estimated in samples collected with microdialysis in halothane-anaesthetized rats which had received 0.6 microliter of ibotenic acid (5 micrograms/microliters) into the left nucleus basalis magnocellularis (microdialysis experiments were performed 3-4 weeks after the lesion). Samples were collected under basal (Ringer or Ringer including 10 microM neostigmine) and KCl (100 mM)-stimulated conditions. In the intact frontoparietal cortex and striatum, basal ACh (only detected under neostigmine perfusion) was in the 30 and 300 nM range, respectively. In the same conditions, Ch was in the 0.7 microM range in the cortex and in the 0.2 microM range in the striatum. The inclusion of KCl in the perfusion medium strongly enhanced cortical (greater than 7-fold) and striatal (greater than 10-fold) ACh. KCl only moderately increased striatal (65%) but not cortical Ch. In the lesion side, both basal and stimulated ACh were significantly reduced in the cortex (greater than 60%), but not in the striatum. Ch was not significantly changed in the cortex and striatum. The nucleus basalis lesion also produced a drop in extracellular levels of cortical and striatal DA (40% and 55%, respectively). Neither cortical nor striatal ACh levels were modified by a unilateral DA deafferentation (6-hydroxydopamine lesion into the medial forebrain bundle). However, the destruction of the intrinsic cortical ACh by injection of kainic acid into the frontoparietal cortex produced a 30% decrease in ACh.

The aim of this study was to determine whether striatal glial cells of adult rats with extensive nigro-striatal dopaminergic denervation are induced to contain dopamine by injection of exogenous l-DOPA. At 2 weeks after injection of 6-hydroxydopamine into the medial forebrain bundle of rats, immuno-reactivity of glial cells was detected with antibodies against glial fibrillary acidic protein (GFAP) or ionized calcium binding adapter molecule 1 (Iba1) in the intact and lesioned striatum. Double-labeling immunofluorescence method was secondly performed. In the lesioned striatum, immuno-reactivity of GFAP was significantly increased, whereas immuno-reactivity of Iba1 was significantly increased except for ventral portion. Exogenous l-DOPA induced DA immuno-reactivity in the striatum, which was independently detected from GFAP immuno-positive astroglial cells or Iba1 immuno-positive microglial cells in the intact side as well as in the lesioned side. These findings suggest that the proliferation of glial cells in the striatum is the response to the loss of dopaminergic terminals but the glial cells do not compensate for the lost dopaminergic terminals.

We studied the positron emission tomography (PET) tracer distributions of ligands for dopamine D 1 receptors ([ 11 C]SCH23390) and D 2 receptors ([ 11 C]raclopride) and of the dopamine precursor analog 6-[ 18 F]fluoro- l -3,4-dihydroxyphenylalanine ([ 18 F]FDOPA) in the brain after 6-hydroxydopamine (6-OHDA) lesions of the medial forebrain bundle in rats. The number of methamphetamine-induced rotation was higher at 14 days than at 3 days after the 6-OHDA lesions. The brains of 6-OHDA-treated rats were analyzed by tissue dissection following i.v. bolus of each tracer at 3 days (acute stage) or 3 weeks (chronic stage) postlesion. [ 11 C]Raclopride, but not [ 11 C]SCH23390, showed higher accumulation in the striatum on the lesion side than on the non-lesion (intact) side both at 3 days and 3 weeks postlesion. On the other hand, lower accumulation of [ 18 F]FDOPA was observed in the striatum on the lesion side at 3 days postlesion and in both the striatum and cerebral cortex on the lesion side at 3 weeks postlesion. Our studies demonstrate that an increase in [ 11 C]raclopride and a decrease in [ 18 F]FDOPA uptake in the denervated striatum is evident even at 3 days after the 6-OHDA lesions when the methamphetamine-induced rotational behavior is not established.

In the present study the influence of intraventricular fetal mesencephalic grafts on the elimination rate of extracellular dopamine (DA) in the non-lesioned striatum of previously unilaterally 6-hydroxydopamine (6-OHDA) lesioned rats was investigated. The elimination of DA was measured after electrical stimulation of the medial forebrain bundle in vivo before and after treatment with the high affinity uptake inhibitor GBR 12909 (20 mg/kg i.p.) using fast cyclic voltammetry (FCV). Rotational behavior induced by amphetamine (AMPH, 2 mg/kg i.p.) and tyrosine hydroxylase (TH) immunohistochemistry were used to prove the functional recovery and the ingrowth of the graft, respectively. After grafting, the number of rotations was decreased and TH-positive cells and fibers were found in the grafted striatum. Voltammetric measurements with the aid of a kinetic model revealed a smaller rate constant for the in vivo elimination of extracellular DA in the non-lesioned striatum of grafted rats compared to that of non-grafted controls. This effect was abolished after treatment with GBR 12909. Our results will be discussed in relation to the method used and according to recent investigations of the specific [3H]DA uptake into striatal synaptosomes in vitro. Based on these data we conclude that grafts, placed to the lesioned striatum, reduce the DA uptake rate in the non-lesioned striatum due to the reduction of the number of functional DA transporters

[3H]dihydrotetrabenazine ([3H]TBZOH) was used to label the monoamine vesicular transporter in the rat substantia nigra. An accumulation of neuronal vesicles in the substantia nigra pars compacta was observed after blockade of the fast axonal transport by a microinjection of colchicine (10 micrograms/2 microliters) into the medial forebrain bundle. This accumulation was measured after sustained 2-day pharmacological modifications of the central dopaminergic transmission. It was not modified after s.c. administration of either the direct dopamine (DA) receptor agonist bromocriptine (four injections of 4 or 6 mg/kg) or the DA receptor antagonist haloperidol (four injections of 0.5-1-1.5-2 mg/kg). Thus, it appears that these pharmacological modifications, imposed to the activity of the nigro-striatal dopaminergic system during 2 days, have no consequence on the rate of synthesis of its vesicles.

The effect of a lack of dopamine (DA) in the striatum upon the K + -evoked release of cholecystokinin (CCK) from superfused rat striatal slices has been studied. Two pharmacological tools were used to deplete the nigrostriatal DA system: administration of α -methyl- p -tyrosine which competitively inhibits DA synthesis and lesions with 6-hydroxydopamine of the medial forebrain bundle. In both cases there was a significant inhibition of the K + -evoked release of CCK. The observed effects might be relevant on pathological conditions implying depletion of the DA system.

The topography of cholinergic neurons has been examined by immunohistochemicall visualization of the acetylcholine synthesizing enzyme, choline acetyltransferase (ChAT), using antisera generated against ChAT of over 95% purity. In the rat forebrain, cholinergic neurons were found in a number of areas including the nucleus tractus diagonalis (Broca), medial septum, medial forebrain bundle, caudate putamen and portions of the globus pallidus.

In view of the importance of the paraventricular nuclei of the hypothalamus (PVN) in the regulation of adrenocortical secretion and the possible role of norepinephrine (NE) in this mechanism, we have studied the effects of injecting the catecholamine neurotoxin 6-hydroxydopamine into the PVN on basal corticosterone (CS) secretion and following ether stress and neural stimuli. PVN NE depletion did not affect the basal and the ether stress-induced rise in CS levels. However, it inhibited significantly the adrenal response to photic, acoustic and sciatic nerve stimulation, suggesting that the PVN NE plays a role in the activation of adrenocortical responses following afferent neural stimuli.

Interruption of the ascending serotonin axons of the medial forebrain bundle (MFB) in the rat brain produced a progressive time-dependent accumulation of imipramine receptors (labeled for autoradiography with [3H]imipramine). The largest accumulation of receptors occurred during the first 12 h at the caudal aspect of the lesion. An electrolytic lesion of the nucleus raphe dorsalis, administered 24 h prior to interruption of the medial forebrain bundle, markedly reduced the number of imipramine receptors on the caudal side of the lesion, while a significant accumulation was still evident on the rostral aspect. These results suggest that imipramine receptors are undergoing the process of orthograde axonal transport to terminals in the forebrain from the neuronal perikarya found in the nucleus raphe dorsalis. These receptors may also be undergoing retrograde transport back to their cell bodies of origin.

In the course of studying the effects of morphine on the escape from electrical stimulation to the rat medial forebrain bundle, we observed that a combination of low doses of morphine and stimulation, neither of which caused stereotypy in the rat, resulted in marked stereotypic behavior that was similar to that seen with high doses of morphine alone. This behavior could be blocked by either naloxone or by the D1 antagonist SCH 23390, but not by the D2 antagonist raclopride. Furthermore, the stereotypy caused by chronically administered high doses of morphine was blocked by naloxone and the D1 antagonist. These results strongly implicate the role of dopamine D1 activation in morphine-induced stereotypies.

The action of dopamine (DA) was studied on rat striatal neurones monosynaptically activated by the substantia nigra (SN) or the medial forebrain bundle (MFB) stimulation. DA, iontophoretically applied, slowly depolarized the membrane cell and decreased the firing rate. The membrane resistance was not modified during DA ejection. Short pulses (up to 300 msec) of DA had no effect on the neurone. These findings suggest that DA is not the fast excitatory transmitter of the nigro-striatum projection, but it plays a different role in this pathway.

In vivo voltammetry was used to monitor dopamine released into the extracellular fluid of the rat striatum by 10-s periods of electrical stimulation of nigrostriatal axons. By varying the interval between stimulations the dynamics of the recovery of the stimulation response has been investigated. The recovery is shown to be differentially affected by dopamine synthesis inhibition at short and long stimulation intervals. The recovery at less than 2 min is independent of dopamine synthesis. Processes in addition to dopamine synthesis must contribute to the recovery of the stimulation response.

Rats pretreated with 6-hydroxydopamine (6-OHDA, 8 micrograms in 4 microliters) in one medial forebrain bundle exhibited an assortment of stereotyped activities and pronounced circling towards the unlesioned side when apomorphine was administered either subcutaneously (0.5 mg/kg), or by discrete stereotaxic injection (5 micrograms in 0.2 microliter) into the caudate nucleus, nucleus accumbens, amygdala, lateral habenula, ventromedial thalamus, substantia nigra zona reticulata, periaqueductal grey or superior colliculus (but not a variety of other areas) ipsilateral to the lesion. These rotational responses were absent in unlesioned animals and, where tested, were attenuated by intraperitoneal haloperidol (0.5 mg/kg). It is suggested that multiple brain sites become sensitive to apomorphine following dopamine depletion by 6-OHDA.

Differential pulse voltammetry (DPV) combined with electrically pretreated carbon fibre electrodes has been used to study dopamine (DA)-5-hydroxytryptamine (5-HT) interactions in the striatum of anaesthetised rats. Electrical stimulation of the dorsal raphe (DRN) increased 5HT and decreased DA metabolism in the striatum. Conversely, stimulation of the DA pathway to the striatum was associated with increased DA and decreased 5-HT metabolism. These data support previous studies and demonstrate that there is a functional interaction between DA and 5-HT systems in the striatum. The receptors and other transmitters (if any) involved in this interaction remain to be determined.

The data presented in the present study indicate that the ascending noradrenergic fibers confined to the medial forebrain bundle (MFB) are not essential for the 24-h periodicity characteristic of non-stress plasma corticosterone levels. However, ablation of the MFB did alter the level of the rhythm. MFB-ablated rats presented an overall average which was significantly less than that of controls.

Non-contingent electrical stimulation of the medial forebrain bundle with low current intensities which did not support self-stimulation behavior produced drastic motor activation and sniffing. In addition, self-stimulation was triggered only if current intensities were strong enough to produce aversion when forced-delivered. These results suggest that stimulation of the medial forebrain bundle involves both drive activating and rewarding components and that a sufficient activation of the first component is essential for the maintenance of self-stimulation behavior.

Changes in dopamine (DA) release were measured in microdialysis samples taken from the nucleus accumbens (NAC) of rats pretreated with the DA uptake inhibitor, nomifensine (1 mg/kg, i.p.) during self- or forced stimulation of the medial forebrain bundle (MFB). Self-stimulation of the MFB in nomifensine-pretreated rats caused an increased release of DA in the NAC. In the same rats, similar increases in DA release were also found during forced stimulation, that is, during MFB stimulation in the absence of lever-pressing, but at current and rate parameters identical to those recorded in the previous self-stimulation session. The results indicate that self-stimulation of the MFB activates the mesolimbic DA system; similar neurochemical changes observed during self- and forced stimulation of the MFB suggest that the operant lever-pressing behavior itself did not influence DA release in the NAC.

A method is described for the anatomical identification of groups of neurones likely involved in the elaboration of component acts of a centrally elicited behaviour, when involvement of fibres of passage is suspected. The contraversive circling which accompanied the predatory attack of a cat upon a rat elicited electrical stimulation within the hypothalamic and ventral midbrain trajectory of the medial forebrain bundle (MFB) was used as a model because of the established role played by the nigrostriatal dopamine system in the production of the circling. Following horseradish peroxidase (HRP) injections, made after electrolytic lesion at such MFB sites, substantial numbers of labelled cells were found in the substantia nigra, pars compacta (SNC). In contrast, many fewer SNC neurones were labelled following:(1) HRP injections made after electrolytic lesion at MFB sites at which the elicited predatory behaviour was not accompanied by contraversive circling; and (2) HRP injections made without a prior lesion at MFB sites at which the elicited predatory behaviour was accompanied by contraversive circling.

Visual discrimination learning of stripes vs black were compared in two groups of C57Bl/6J mice, one group (n = 11) bar-pressed for 10 electrical self-stimulations of the brain (ESB) and the other (n = 10) earned a 20 mg pellet of food reward in a T maze. The ESB animals had a stereotaxically placed electrode in the medial forebrain bundle lateral hypothalamic area and the food reward mice had been reduced to 80% body weight. Comparison of ESB to food reinforcement showed fewer trials to criterion in the ESB group for acquisition, reacquisition after one day and retention after 7 days. The results demonstrate sufficiency of ESB to support a pattern of learning and excellent retention in mice.

In rats, brain substance P-like immunoreactivity (SPLI) was examined at different time intervals following hemisections. The SPLI of the frontal cortex ipsilateral to the cut disappeared following hemisections at anterior-posterior levels ranging from the level of the septum to the level of the interpeduncular nucleus. Hemisected brains examined after a 2–8 day survival period showed accumulation of SPLI in axons ascending in the medial forebrain bundle and in axons descending in the internal capsule. It was suggested that the cortical SP projection ascends in the medial forebrain bundle and that the striato-nigral projection descends in the internal capsule.

A retrograde tracer was combined with intracerebral injections of high doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to examine its neurotoxic effects on rat midbrain structures projecting to the striatum. MPTP injections into the substantia nigra pars compacta (SNc) and ventral tegmental area (VTA) caused a huge cell loss in both regions. Furthermore, since MPTP infusions into the medial forebrain bundle produced destruction of dorsal raphe neurons (presumably serotonergic), as well as of dopaminergic SNc/VTA neurons, its neurotoxic effects in the rat are ‘relatively non-selective’ rather than ‘relatively selective’.

The influence of serotonin (5-hydroxytryptamine; 5-HT) innervation on peptide-containing neurons in the rat suprachiasmatic nucleus (SCN) was investigated by peroxidase-anti-peroxidase (PAP) immunocytochemistry. The 5-HT neuronal system was chemically severed by 5,6-dihydroxytryptamine (5,6-DHT) injection into the medial forebrain bundle bilaterally. After this treatment, a marked decrease of vasoactive intestinal peptide (VIP)-like immunoreactivity in neuronal perikarya occurred in the SCN corresponding to a decrease in number of 5-HT immunoreactive fibers and terminals. However, no alteration of arginine-vasopressin-like immunoreactivity was detected between 5,6-DHT-treated animals and the controls. It is speculated that VIP-like immunoreactive neurons play an important role in the SCN under the influence of strong 5-HT innervation.

Axonal projections from neurons located in the medial and lateral septal nuclei (MSN and LSN) were traced autoradiographically. The MSN projected bilaterally via a midline route to the diagonal band of Broca (DBB), the preoptic area (POA), the suprachiasmatic (SCN), paraventricular (PVN), ventromedial (VHM) and arcuate (ARC) nuclei including the median eminence (fiberous zone). Lateral coursing fibers traveled with the medial forebrain bundle (MFB) to the supraoptic (SON) and pre- and supra-mammillary nuclei. The majority of LSN axons projected to, and terminated in, the MSN. Fibers projected ipsilaterally through the POA, SON, SCN, ARC, ME and MMN with axonal projections observed throughout the MFB. In summary, the neurons of the MSN project to the medial hypothalamic nuclei via a midline route while LSN axons projected strongly to the MSN with the remaining ribers coursing along the ipsilateral MFB to terminate in several hypothalamic nuclei. These data indicate that a direct septo-hypothalamic pathway exists in the rat.

Biodegradable controlled-release systems constitute an exciting new technology for drug delivery to the central nervous system (CNS). The present study describes functional and histochemical observations, indicating that implantation of DA microcapsules into striatal tissue assures a prolonged release of the transmitter in situ. This technology has considerable potential for basic and possibly also clinical research.

The paraventriculo-spinal projection of the Syrian hamster was characterized by retrograde labelling of neuronal perikarya in the paraventricular nucleus of the hypothalamus (PVN) following injection of True blue tracer into the intermediolateral cell column of the thoracic spinal cord. Injection of the excitatory neurotoxin, N-methyl- d,l -aspartic acid into the region of the PVN spared magnocellular neurones and fibres of passage but destroyed parvocellular neurones of the paraventriculo-spinal pathway. Hamsters bearing complete bilateral lesions of the parvocellular PVN failed to show the typical nocturnal increase in pineal melatonin content. These data indicate the importance of the paraventriculo-spinal projection in the central control of pineal melatonin synthesis.

The intrinsic neurons of the medial forebrain bundle were unilaterally destroyed, in rats, through local injection of ibotenic acid (4 micrograms in 0.5 microliter). Ten days later, electrodes were bilaterally implanted, one in the lesioned lateral hypothalamus, the other into the contralateral hypothalamus. Firstly, self-stimulation was studied with stimulation of each electrode separately. Later on, the effect of non-contingent electrical stimulation on evoked locomotor activity in the open-field was analysed for each electrode. While self-stimulation of the lesion area was greatly depressed in comparison with the unlesioned lateral hypothalamus, the increase in locomotor activity produced by stimulation, at the intensity applied, was the same whether the stimulated hypothalamus was lesioned or not.

The nucleus raphe magnus and rostral parts of the nucleus raphe obscurus were found to have extensive efferent projections: a major ascending non-serotonergic (5-HT) projection through the median forebrain bundle, and a descending system consisting of both 5-HT and non-5-HT neurons. Differences in the localizations of their cells of origin suggest that they form two distinct efferent systems from the caudal medullary raphe nuclei.

The frequency response of nigrostriatal neurones to electrical stimulation of the median forebrain bundle was investigated in vivo using high-speed cyclic voltammetry to measure the evoked striatal dopamine overflow. It was found that the nerves could follow 25-50 Hz stimulation for at least 10 s, whereas the neurones were unable to respond to high frequencies (100-200 Hz) for more than 1-3 s. Accommodation, due to incomplete re-equilibration of ionic fluxes between successive stimuli, provides a possible explanation for these findings.

The specific binding sites for strychnine-insensitive [ 3 H]glycine were already demonstrable at prenatal stages and had increased to the adult level by postnatal day (PN) 10. This ontogenic increase was found to be due to an augmentation of B max without changes in k d of the [ 3 H]glycine binding. Moreover, there was no shift in inhibition of the binding due to glycine, d -serine, l -serine and HA-966 (1-hydroxy-3-aminopyrrolid-2-one) after birth. These findings are consistent with the view that there is an increase in density in the absence of the glycine recognition site associated with N- methyl- d -aspartate receptor/ion channel complex in rat forebrain during ontogenic development.

Following unilateral transection of the medial forebrain bundle (MFB) within the anterior hypothalamic-preoptic region of cats, the biting attack upon a rat elicited by ipsilateral posterior hypothalamic or ventral midbrain stimulation is eliminated, although the cat continues to approach from 2.8 metres away to within several centimetres of the rat. In contrast, both the approach to and biting attack upon a rat elicited by contralateral posterior hypothalamic and ventral midbrain stimulation are unchanged. The results suggest that specific aspects (biting, approach) of the elicited behaviour may be mediated by neural effects which proceed along anatomically distinct components of the ascending as well as the descending MFB.