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The recently cloned histamine H(4) receptor is expressed predominantly in haematopoietic cells and has been found to modulate the function of mast cells, eosinophils, dendritic cells and T lymphocytes. It represents an attractive target for pharmacological interventions against a number of inflammatory and autoimmune disorders. In the present work we used two-electrode voltage-clamp to demonstrate histamine H(4) receptor modulation of G protein-coupled inward rectifier potassium (GIRK) channels heterologously expressed in Xenopus oocytes. In accordance with earlier findings in other effector systems, full agonism by histamine and (R)-alpha-methylhistamine, partial agonism by clobenpropit and inverse agonism by thioperamide were observed. Furthermore, in oocytes injected with low amounts of receptor cRNA, clobenpropit apparently acted as a neutral antagonist. We also used the high temporal resolution afforded by this system to study the differential time courses of response deactivation upon ligand washout for clobenpropit and (R)-alpha-methylhistamine. GIRK channels represent a novel effector system for histamine H(4) receptor modulation, which may be of physiological relevance and prove useful in the development of compounds targeting this receptor.

The histamine H(3) receptor mediates inhibitory responses in the nervous system. Here, we demonstrate the coupling of the human histamine H(3) receptor to G protein-coupled inward rectifier potassium (GIRK) channels in Xenopus oocytes, using voltage-clamp. The histamine H(3) receptor agonist (R)-alpha-methylhistamine increased GIRK currents with an EC(50) of 2.5 nM. The response to (R)-alpha-methylhistamine was inhibited by the specific antagonist/inverse agonist clobenpropit. GIRK channels represent a novel effector pathway for the histamine H(3) receptor, also suggesting the use of electrophysiology assays in histamine H(3) receptor drug screening, allowing for the resolution of G protein activation kinetics.

It has been shown that galanin plays a role in central cardiovascular regulation. Galanin administered centrally induces an increase of heart rate and a weak vasodepressor response, whereas the N-terminal galanin fragment (1-15) elicits vasopressor effects and tachycardia. Furthermore, it has been shown that galanin-(1-15), but not galanin-(1-29), decreases the baroreceptor reflex sensitivity. Since these data demonstrate that both galanin and its N-terminal fragment (1-15) exert a different modulation on central cardiovascular control, the aim of this work has been to study if the specific galanin receptor antagonist Galanin-(1-12)-Pro-(Ala-Leu)(2)-Ala]-amide (M40) could modulate their cardiovascular actions. Urethane anaesthetized rats were injected intracisternally and the changes in mean arterial pressure and heart rate were monitored. Two doses of M40 alone have been tested for their cardiovascular effects. With the dose of 1.0 nmol, a significant tachycardia was observed (P<0.001), but 0.1 nmol was ineffective. This suggests a possible agonistic effect for the higher doses of M40. The galanin receptor antagonist M40 at the dose of 0.1 nmol failed to modify the weak vasodepressor effects and tachycardia induced by 3.0 nmol of galanin-(1-29). However, the same dose completely blocked the vasopressor and tachycardic responses elicited by 3.0 nmol of galanin-(1-15). These data show that M40 differentially counteracts the central cardiovascular responses of the galanin fragment and give a functional support for the existence of galanin receptor subtypes within the brainstem. Therefore, the present findings can be explained on the basis that the cardiovascular actions of galanin-(1-29) could be mediated by one type of galanin receptor, whereas a galanin receptor subtype that recognizes N-terminal fragments of galanin may mediate the actions of galanin-(1-15).

We have examined the motor responses to the dopamine D(3) receptor-preferring agonist, S(+)-(4aR,10bR)-3,4,4a, 10b-tetrahydro-4-propyl-2H,5H-1-benzopyranol[4,3-b]-1,4-oxazin+ ++-9-ol ((+)-PD128,907), by non-habituated male rats during postnatal development. (+)-PD128,907 (0.025 and 0.1 mg/kg) increased motor activity (rearing, motility and locomotion) in 14-day-old rats without inducing oral stereotypies. However, in 21-, 28- and 70-day-old rats, (+)-PD128,907 caused a significant reduction in motor activity. This reduction was most pronounced in 70-day-old rats. In addition, the stimulatory effects of (+)-PD128,907 in 14-day-old rats were fully blocked by the dopamine D(3) receptor antagonist 5,6-dimethoxy-2-(di-u-propylamino) indan (U99194A). These results suggest that the motor inhibition mediated by the activation of the dopamine D(3) receptors develops between the second and the third postnatal weeks.

The effects of the systemic (i.p.) administration of the selective adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA) and the selective adenosine A2A receptor agonist sodium 2-p-carboxyethyl)phenylamino-5'-N-carboxamidoadenosine (CGS 21680) on different dopamine receptor agonist-induced behaviours were studied in the male rat. CGS 21680 (1 micromol/kg), but not CPA, was found to counteract the stereotypies induced by the non-selective dopamine receptor agonist apomorphine (0.25 mg/kg s.c.). Low doses of CGS 21680 (0.1 micromol/kg) and high doses of CPA (3 micromol/kg) counteracted yawning induced by the dopamine D2 selective agonist quinpirole (0.05 mg/kg). On the other hand, low doses of CPA (0.3 micromol/kg) antagonized grooming induced by the selective dopamine D1 receptor-selective agonist SKF 38393 (10 mg/kg i.p.), while CGS 21680 was ineffective. These results are consistent with the proposed existence of a selective antagonistic modulation of dopamine D1 and D2 receptors by adenosine A1 and A2A receptors, respectively. The ability of CGS 21680 to counteract apomorphine-induced stereotypies is weaker compared to its previously reported antagonistic effect of amphetamine-induced motor activity. This supports the hypothesis that adenosine A2A receptor agonists may be potential antipsychotic drugs with a low potential for extrapyramidal side effects.

In membrane preparations from rat striatum, where adenosine A2A and dopamine D2 receptors are coexpressed, stimulation of adenosine A2A receptors was found to decrease the affinity of dopamine D2 receptors for dopamine agonists. We now demonstrate the existence of this antagonistic interaction in a fibroblast cell line (Ltk-) stably transfected with the human dopamine D2 (long-form) receptor and the dog adenosine A2A receptor cDNAs (A2A-D2 cells). In A2A-D2 cells, but not in control cells only containing dopamine D2 receptors (D2 cells), the selective adenosine A2A agonist 2-[p-(2-carboxyethyl)-phenethylamino]-5'-N-ethyl-carboxamido adenosine (CGS 21680) induced a 2-3-fold decrease in the affinity of dopamine D2 receptors for dopamine, as shown in competition experiments with dopamine versus the selective dopamine D2 antagonist [3H]raclopride. By contrast, activation of the constitutively expressed adenosine A2B receptors with 5'-N-ethyl-carboxamidoadenosine (NECA) did not modify dopamine D2 receptor binding. In A2A-D2 cells CGS 21680 failed to induce or induced only a small increase in adenosine-3',5'-cyclic-monophosphate (cAMP) accumulation. In D2 cells NECA- or forskolin-induced adenylyl cyclase activation was not associated with any change in dopamine D2 receptor binding. These results indicate that adenylyl cyclase activation is not involved in the adenosine A2A receptor-mediated modulation of the binding characteristics of the dopamine D2 (long-form) receptor.

The present in vivo microdialysis study demonstrated that the subcutaneous injection of modafinil (diphenyl-methyl-sulfinyl-2-acetamide) in doses of 30-300 mg/kg dose dependently increased dopamine release from the intermediate level of the nucleus accumbens along the rostro-caudal axis of the halothane anaesthetized rat. The effect of modafinil in a dose of 100 mg/kg was counteracted by the local perfusion in the nucleus accumbens with the GABAB receptor antagonist phaclofen (beta-p-chlorophenyl-gamma-aminopropyl-phosphonic acid) (50 microM), the GABAA agonist muscimol (3-hydroxy-5-aminomethyl-isoxazolol) (10 microM) and the neuronal GABA reuptake inhibitor SKF89976A (4,4-diphenyl-3-butenyl-nipecotic acid) (0.1 microM), whereas it was increased by the GABAB receptor agonist (-)-baclofen [beta-(p-chlorophenyl-gamma-aminobutyric acid)] (10 microM). In addition, the modafinil-induced increase of dopamine release was associated with a significant reduction of accumbens GABA release. These results suggest that the dopamine releasing action of modafinil in the rat nucleus accumbens is secondary to its ability to reduce local GABAergic transmission, which leads to a reduction of GABAA receptor signaling on the dopamine terminals.

The influence of adenosine A1 (N6-cyclopentyladenosine, CPA) and A2 (2-[4-(2-carboxylethyl)phenethylamino]-5'-N-ethylcarboxamido -adenosine hydrochloride, CGS 21680) receptor agonists on SKF 38393-induced electroencephalographic (EEG) arousal was studied in rabbits. While CPA (0.1 mg/kg i.v.) significantly prevented the EEG effects of SKF 38393, CGS 21680 (0.2 mg/kg i.v.) did not affect them. These results demonstrate that adenosine A1 receptors can modulate dopamine D1 receptor-induced EEG arousal and show, for the first time, that adenosine-dopamine interactions are involved in brain functions other than motor activity.

The mode of coupling between neurotransmitter receptors and G proteins was investigated by agonist-induced high-affinity GTPase activity in rat striatal membranes. There was a simple additive relationship among dopamine-, carbachol-, and gamma-aminobutyric acid (GABA)-sensitive high-affinity GTPase activity in any combination, indicating that the respective receptors stimulated by these agonists (i.e., dopamine D2, pirenzepine-insensitive muscarinic, and GABAB receptors) interact independently with distinct pools of G proteins. Unexpectedly non-additivity was observed between dopamine- and norepinephrine-stimulation. This lack of additivity was apparently due to stimulation of the same dopamine D2 receptors by both dopamine and norepinephrine, since norepinephrine-stimulated high-affinity GTPase activity could be inhibited by dopaminergic but not adrenergic antagonists. The same non-additivity as seen in rat striatum was confirmed in the membranes prepared from cultured mouse fibroblast cells co-transfected with dopamine D2 and adenosine A2A receptors. The implication of the (non-)additivity between receptor-mediated high-affinity GTPase activity was discussed with a consideration of the possible underlying molecular mechanism.

GTP hydrolyzing activity was assayed by measuring the amount of 32P(i) released from 0.3 microM [gamma-32P]GTP in the membranes prepared from rat brain. 5-Hydroxytryptamine (5-HT) stimulated the high-affinity GTPase activity in hippocampus, but not in striatum, in a concentration-dependent manner with an EC50 value of 18 nM and maximal percent stimulation of 13.9%. This response was mimicked by (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin [(+/-)-8-OH-DPAT], but not by (+/-)-1-(2,5-dimethoxy-4-iodophyenyl)-2-aminopropane [(+/-)-DOI]. These results suggest that 5-HT-stimulated high-affinity GTPase activity of the GTP-binding protein(s) is mediated via 5-HT1A receptor subtype in the rat hippocampus.

The acute or chronic administration of modafinil, (diphenyl-methyl-sulfinyl-2-acetamide, 30 mg/kg s.c.) decreased gamma-amino-butyric acid (GABA) outflow from the cerebral cortex of freely moving guinea pigs and rats. In 5,7-dihydroxytryptamine intracerebroventricularly pretreated guinea pigs, the effect of modafinil on GABA outflow was reversed and the noradrenaline cortical levels increased. Prazosin (35.8 ng/kg i.p.) blocked the drug-induced increase in GABA efflux. In vitro experiments, performed in rat cortical slices, showed that modafinil failed to affect [3H]GABA release and uptake as well as glutamic acid decarboxylase activity. In conclusion, our results suggest that the balance between central noradrenaline and 5-hydroxytryptamine transmission is important for the regulation by modafinil of the GABAergic release in the cerebral cortex.

The modulation of alpha 2-adrenoceptors by neuropeptide Y Y1 and neuropeptide Y Y2 receptor subtypes has been studied in the nucleus tractus solitarii of the male rat. The autoradiographical experiments showed that neuropeptide Y-(1-36), neuropeptide Y-(13-36), a selective neuropeptide Y Y2 receptor agonist, and [Leu31,Pro34]neuropeptide Y, a selective neuropeptide Y Y1 receptor agonist, in the nanomolar range increased the Kd value of the [3H]p-aminoclonidine binding sites in the above rank order of potency without changing the Bmax values. In contrast, in the competition experiments, the neuropeptide Y Y1 and the neuropeptide Y Y2 receptor agonists decreased and increased, respectively, with the same potency the IC50 value of l-adrenaline and especially of clonidine for the alpha 2-adrenoceptor agonist binding sites associated with an increase and a decrease of the B0 value, respectively. Cardiovascular experiments showed that microinjections of clonidine into the nucleus tractus solitarii induced dose-dependent vasodepressor and bradycardiac responses. Threshold doses for vasodepressor effects of neuropeptide Y-(1-36) and of the neuropeptide Y Y1 receptor agonist and for vasopressor effects of the neuropeptide Y Y2 receptor agonist significantly counteracted the vasodepressor action elicited by an ED50 dose of clonidine in the nucleus tractus solitarii, the bradycardiac action of clonidine also being counteracted by the neuropeptide Y Y2 but not the neuropeptide Y Y1 receptor agonist. The present results give indications for the existence of an antagonistic modulation of high affinity alpha 2-adrenoceptors by the neuropeptide Y Y1 and neuropeptide Y Y2 receptor subtype in the nucleus tractus solitarii which may contribute to a reduction of alpha 2-adrenoceptor-mediated cardiovascular depression.

Interactions between alpha 2-adrenoceptors and angiotensin II receptors were evaluated in the nucleus tractus solitarii of the rat by means of quantitative receptor autoradiography and cardiovascular analysis. In binding experiments using l-noradrenaline to compete for [3H]p-aminoclonidine binding sites, angiotensin II (1 nM) increased the IC50 value of l-noradrenaline by 50%. The angiotensin AT1 receptor antagonist, DUP753 (losartan), not only blocked this action but also decreased the IC50 value of l-noradrenaline. The modulatory effect of angiotensin II was also evaluated after addition of both DUP753 and PD123319, an angiotensin AT2 receptor antagonist, and counteraction of the reduction in the IC50 value of l-noradrenaline was observed. In saturation experiments angiotensin II increased the KD and Bmax values of [3H]p-aminoclonidine binding sites, compatible with possible uncoupling of the alpha 2-adrenoceptors. Cardiovascular analysis demonstrated that a threshold dose of angiotensin II (0.05 pmol) counteracted the vasodepressor effect produced by an ED50 dose of l-adrenaline, l-noradrenaline or clonidine coinjected in the nucleus tractus solitarii. DUP753 fully blocked this in vivo modulation of alpha 2-adrenoceptors by angiotensin II. These findings suggest the existence of an antagonistic angiotensin AT1/alpha 2-adrenoceptor interaction in the nucleus tractus solitarii. Therefore, it can be surmised that the activation of angiotensin II AT1 receptors may reduce the transduction of the alpha 2-adrenoceptors and thus the alpha 2-mediated vasodepressor responses.

In view of the demonstration of specific binding sites for [125I]galanin-(1-15) in several brain areas including the nucleus of the solitary tract, possibly indicating the existence of multiple galanin receptor subtypes, the effects of intracisternal injections of galanin-(1-15) on cardiovascular parameters were studied. The effects of co-injections of galanin-(1-15) and galanin-(1-29) and co-injections of galanin-(1-15) and the 5-HT1A receptor agonist 8-OH-2-(di-n-propylamino)tetralin (8-OH-DPAT) were also evaluated. Galanin-(1-15) produced a significant increase in mean arterial blood pressure (maximum effect 10% at 3 nmol of galanin-(1-15)) and in heart rate (maximum effect 12% at 1 nmol). When threshold doses of galanin-(1-15) (0.1 nmol) and galanin-(1-29) (3 nmol) were injected simultaneously they elicited an increase in mean arterial blood pressure. The vasodepressor response induced by an ED50 dose of 8-OH-DPAT (6 nmol) was not modulated by a threshold dose of galanin-(1-15), but the increase in heart rate area induced by galanin-(1-15) alone was no longer observed. When threshold doses of both galanin-(1-15) and 8-OH-DPAT (0.3 nmol) were co-injected a vasodepressor response developed and on heart rate a tachycardic response was seen in the peak effects and the overall tachycardic response induced by galanin-(1-15) was sustained. The results show a different role for galanin-(1-15) as compared with galanin-(1-29) in central cardiovascular control.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of local perfusion with the dopamine D1 receptor antagonist SCH 23390 and the dopamine D2 receptor antagonist raclopride on basal and N-methyl-D-aspartate (NMDA) stimulated dopamine, gamma-aminobutyric acid (GABA) and glutamate levels in the dorsolateral striatum were monitored using in vivo microdialysis in the halothane anaesthetized rat. Local perfusion (90 min) with SCH 23390 and raclopride (1 and 10 microM) dose dependently increased basal striatal dopamine release whereas GABA and glutamate dialysate levels were unaffected. Local perfusion (10 min) with the 1 mM concentration of NMDA increased striatal dopamine, GABA and glutamate outflow. However, when perfused together with SCH 23390 (1 microM) NMDA inhibited glutamate efflux. Moreover, in the presence of SCH 23390 (10 microM) the NMDA induced rise in dopamine and GABA levels was partly prevented. On the other hand, raclopride 1 microM enhanced the NMDA stimulated GABA efflux while at 10 microM it partly counteracted the NMDA induced dopamine release. These data demonstrate that NMDA induced changes in striatal neurotransmitter outflow are effectively modified by dopamine D1 and D2 receptor blockade.

[3H] gamma-Aminobutyric acid (GABA) release was studied in rat brain slices in the absence or presence of cholecystokinin-8 (CCK-8). [3H]GABA release under the conditions used was Ca(2+)-dependent and insensitive to the presence of the glial uptake blocker beta-alanine. While the basal release of [3H]GABA was not affected by CCK-8, the K(+)-stimulated release of [3H]GABA was significantly enhanced by 300 nM of CCK-8 in the caudate putamen, the substantia nigra, the hippocampal formation and the parietofrontal cortex. In the cerebral cortex the CCK-8 enhancement of [3H]GABA release was concentration-dependent and abolished by the CCKB receptor antagonists PD135,158 (1.0 nM) and L-365,260 (100 nM). A significant counteraction of the CCK-8 action was also found with the CCKA receptor antagonist L-364,718 (100 nM) but only in concentrations at which both CCKA and CCKB receptors are blocked. No CCK-8 effects on [3H]GABA release were observed when tetrodotoxin was superfused 5 min before the K(+)-induced [3H]GABA release. It is suggested that the enhancing actions of CCK-8 on K(+)-stimulated [3H]GABA release is mainly related to an activation of CCKB receptors.

The effects of neurotensin fragments and of neurotensin itself on the characteristics of neostriatal dopamine D2 agonist binding were studied in competition experiments with dopamine using the D2 antagonist, [3H]raclopride. The biologically active neurotensin-(8-13) fragment, but not the inactive neurotensin-(1-7) fragment, caused a concentration-related increase in the KH and KL values of dopamine with a maximal increase by 110 and 97%, respectively, at 1 nM, while neurotensin-(1-13) only induced such changes at 10 nM. In view of the higher potency and the increased ability of neurotensin-(8-13) versus neurotensin (1-13) to reduce the affinities of the high- and low-affinity states of the neostriatal D2 receptors, the C-terminal neurotensin fragments may be among the endogenous ligands of the neostriatal neurotensin receptors.

We have previously found, in rat striatal membrane preparations, that stimulation of adenosine A2 receptors (with the selective adenosine A2 receptor agonist CGS 21680) increases the high- and low-affinity dissociation constants and increases the proportion of high-affinity dopamine D2 receptor binding sites labelled with the selective dopamine D2 receptor antagonist [3H]raclopride. As guanine nucleotides and divalent cations (such as Mg2+) are known to regulate the proportion of high-affinity D2 receptor binding sites in opposing ways, interaction experiments with CGS 21680, the GTP analogue Gpp(NH)p and MgCl2 were performed. Our results suggest that these three factors exert significant, though independent, effects on the proportion of high affinity D2 receptors, and that A2 receptors regulate both the affinity of D2 receptors and the transduction of the signal from the D2 receptor to the G-protein.

Combined perfusion of the neostriatum with 1 nM of cholecystokinin octapeptide (CCK-8) and 0.01, 0.1 or 1 nM of neurotensin was done in the halothane-anesthetized rat after systemic apomorphine treatment (0.05 mg/kg, s.c.). Neurotensin (1 nM) plus CCK-8 (1 nM) effectively counteracted the apomorphine-induced inhibition of neostriatal perfusate levels of dopamine (DA). With a constant concentration of CCK-8 (1 nM), the apomorphine-induced inhibition of DA release was counteracted dose relatedly by neurotensin in concentrations of 0.01, 0.1 and 1 nM. The results of binding experiments demonstrated that threshold concentrations of CCK-8 and neurotensin significantly increased the KD values of the high-affinity D2 receptors without significant alterations in the low-affinity D2 receptors or in the proportion of D2 receptors in the high-affinity state. Thus, neurotensin and CCK receptors may regulate synergistically, via intramembrane interactions with the D2 receptors, the binding characteristics and the signal transduction of D2 autoreceptors in the neostriatum. The combined presence of very low concentrations of CCK-8 and neurotensin in the extracellular fluid may be sufficient to regulate D2 receptor transduction, underlining the important role of these peptide receptor interactions with the D2 receptors.

The effects of the Y2 receptor agonist neuropeptide Y NPY-(13-36) on the depolarization-evoked release of [3H]noradrenaline (NA) from synaptosomal preparations of the medulla oblongata, the hypothalamus, the hippocampal formation and the parieto-occipital cortex of the male rat were studied. NPY-(13-36) (0.1-100 nM) caused a concentration-related inhibition of the depolarization-induced release of [3H]NA in all areas studied, except the parieto-occipital cortex. The results indicate that NPY Y2 receptors are present on NA terminals in all areas studied, except the parieto-occipital cortex and inhibit depolarization-evoked [3H]NA release.

The existence and widespread distribution of specific [125I]galanin-(1-15) fragment binding sites in the rat brain was demonstrated by using [125I]galanin-(1-15) as a radioligand in quantitative receptor autoradiographical studies. These binding sites were also present in several areas lacking or having very few [125I]galanin-(1-29) binding sites, such as the dorsal hippocampal formation, the neocortex and the neostriatum. [125I]Galanin-(1-15) binding sites showed a high selectivity for the fragment, since galanin-(1-15) could displace 80% of the binding whereas porcine galanin-(1-29) could only displace 30%. The binding was saturable with a Kd of 0.63 +/- 0.02 nM and a Bmax of 15.3 +/- 1.7 fmol/mg in sections from the dorsal hippocampal formation. Thus, a new type of galanin receptor selective for N-terminal galanin fragments may exist in the rat brain.

The present study was undertaken to evaluate the possible functional implications of the previously demonstrated in vitro interactions between galanin and 5-HT1A receptors. To this end we analysed the interactions between galanin and the 5-HT1A receptor agonist 8-OH-2-(di-n-propylamino)-tetralin (8-OH-DPAT) in central cardiovascular regulation. 8-OH-DPAT given intracisternally (i.c.) produced a dose-dependent reduction of blood pressure, the peak action being 32% at 10 nmol of 8-OH-DPAT. Heart rate and respiration rate were not affected. The vasodepressor action of 8-OH-DPAT was counteracted by the 5-HT1A receptor antagonist 1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl]piperazine (NAN-190). A threshold dose (1 nmol) of galanin given i.c. was shown to enhance the vasodepressor effect of both an ED50 dose and a threshold dose of 8-OH-DPAT. Quantitative receptor autoradiography showed that the IC50 values for [125I]galanin binding sites were reduced in the presence of 8-OH-DPAT (10 nM) by approximately 40% in the dorsal region of the nucleus of the solitary tract, the area postrema, and the raphe pallidus and obscurus nuclei. Galanin (10 nM) also significantly increased the IC50 value for [3H]8-OH-DPAT binding sites within the nucleus of the solitary tract. The results provide evidence for a synergistic interaction between 8-OH-DPAT and galanin in cardiovascular regulation after their central administration, an interaction possibly related to the ability of 8-OH-DPAT to enhance the affinity of the galanin receptor within regions of the medulla oblongata involved in cardiovascular control.

A four week sino-aortic denervation produces an increase of adrenaline (A) turnover in the anterior but not the posterior hypothalamus and a selective reduction of dopamine stores in the anterior hypothalamus. Furthermore, the mean arterial blood pressure and heart rate are unchanged in conscious animals, and a selective increase in LH secretion is observed. The activation of a compensatory vasodepressor adrenergic mechanism in the anterior hypothalamus may in part be responsible for the maintenance of a normal mean arterial blood pressure after chronic sino-aortic denervation. The neurochemical changes in the hypothalamic area may also be related to the increase in LH secretion found after chronic sino-aortic denervation.

Catecholamine levels and turnover have been studied in 5 week old male genetically hypertensive (LH) and normotensive (LN) rats of the Sprague-Dawley Lyon strain. The results demonstrate increased hypothalamic adrenaline levels and a reduced adrenaline turnover in the dorsal midline of the medulla oblongata (DCMO) in the LH rats compared with LN control rats. The reduction of adrenaline turnover in the DCMO may contribute to the development of spontaneous hypertension.

Substance P (SP) and the C-terminal sequences octa- and penta-SP produced dose-dependent vasopressor responses, and the action was associated with mild tachycardia. The vasopressor effect of SP was counteracted by the SP antagonist [D-Pro2,D-Phe7,D-Trp9]SP given intracisternally, suggesting that central SP receptors were involved. Experiments with different sodium contents in the vehicle and with naloxone pretreatment indicate that central naloxone-sensitive opiate receptors may exist, capable of modulating the effects of SP receptor activation.

Rat prolactin produces in a dose of 100 micrograms/kg a rapid and marked increase of dopamine turnover in the medial palisade zone of the median eminence and of noradrenaline turnover in the posterior periventricular hypothalamic region as well as a possible minor increase of noradrenaline turnover in the magnocellular part of the paraventricular hypothalamic nucleus of the hypophysectomized male rat. The rat prolactin serum levels measured 2 h following injection were within the upper physiological range of lactating rats. The findings suggest that dopamine in the medial palisade zone may be released as a prolactin inhibitory factor and respond rapidly to increases in serum prolactin levels. Furthermore, rat prolactin can acutely modify noradrenergic mechanisms in discrete areas of the hypothalamus indicating that prolactin can participate in the regulation of types of hypothalamic functions other than regulation of its own secretion.

Rat growth hormone (rGH) (100 micrograms/kg) produced 2-4 h after its i.v. injection a rapid reduction of catecholamine stores and turnover in the subependymal layer and in the medial and lateral palisade zone of the median eminence. It is suggested that rGH may inhibit its own secretion partly via reduction of DA synthesis and release in the median eminence leading to increased somatostatin release and partly via reduced noradrenaline synthesis and turnover in the median eminence leading to reduced secretion of a growth hormone releasing factor.

The ergolene derivative MPME (PTR 17402; (5R,8R)-8-(4-p-methoxyphenyl)-1-piperazynylmethyl-6- methylergolene], a dopamine (DA) receptor agonist acting mainly at DA D-1 receptors linked to dotted types of forebrain DA nerve terminals, induces a characteristic behavioural syndrome consisting of increased locomotion, head-bobbing and sniffing activity without oral stereotypies or increased rearing. Haloperidol and cis-flupenthixol, nonselective DA receptor antagonists, but not selective D-2 receptor antagonists such as remoxipride and sulpiride, could significantly counteract the locomotion and head-bobbing behaviour induced by MPME. In contrast, the sniffing behaviour induced by MPME was only marginally affected by haloperidol and cis-flupenthixol pretreatment. These results suggest that activation of D-1 receptors in the forebrain mainly linked to the dotted types of DA nerve terminals in the striatum, and in the limbic forebrain, can result in behavioural effects which differ from those caused by stimulation of D-2 receptors located mainly within the diffuse types of DA nerve terminal systems.

The effect of five phosphodiesterase (PDE) inhibitors (papaverine, IBMX, theophyllamine, dipyridamol and M & B 22,948) was studied on adenylate cyclase and on cyclic nucleotide phosphodiesterase activities in extracts of rat caudate nucleus. For comparison the effect on DA turnover and on turning behaviour in rats with unilateral lesions of the nigro-neostriatal DA nerurons was studied. Cyclic AMP PDE was inhibited by papaverine, dipyridamol, IBMX, M & B 22,948 and theophyllamine in that order of potency. Cylcic GMP PDE was inhibited by IBMX, papaverine, M & B 22,948 and theophyllamine, but not by dipyridamol. Basal adenylate cyclase washigher if assayed in the presence of papaverine or dipyridamol than if theophyllamine or IBMX was present. The degree of stimulation caused by DA was not significantly influenced by the PDE inhibitors. Papaverine and dipyridamol enhanced DA disappearance in the caudate nucleus and the tuberculum accumbens, but not in the median eminence. Caffeine had no significant effect. Papaverine (1-28 mg/kg) had no signigicant effect on L-dopa (5 mg/kg)-induced turning, and actually inhibited turning induced by the combination of L-dopa (10 mg/kg) and atropine (5 mg/kg). The other four PDE inhibitors all potentiated L-dopa-induced turning. Theophyllamine (20 mg/kg) and IBMX (5 mg/kg) even caused turning when given alone. The data are compatible with the opinion that PDE inhibition leads to an enhanced effect of DA in the caudate nucleus. However, the results also demonstrate that several of the PDE inhibitors have effects on central DA mechanisms that are difficult to explain solely on the basis of PED inhibition.

In combined biochemical and functional studies it has been possible to show that ergocornine (0.5-5 mg/kg) and the ergolene derivative (5R,8R)-8-(4-p-methoxyphenyl-1-piperazinylmethyl)-6-methylergolene (PTR 17402; MPME) (0.25-5 mg/kg) reduce in a dose-dependent way brain 5-hydroxytryptamine (5-HT) turnover in rat as evaluated with the tryptophan hydroxylase inhibitor, alpha-propyl-dopacetamide (H 22/54), whereas 2-Br-alpha-ergocryptine (CB 154; Br-EC) had no effect on brain 5-HT turnover. Effects on 5-HT receptor activity were evaluated using the extensor hindlimb reflex of acutely spinalized rats. It was found that ergocornine increased the 5-HT receptor activity independent of presynaptic 5-HT stores and that it didnot have any effects on uptake, retention and spontaneous overflow of 3-H-5-HT in vitro but reduced the fiedl stimulation-induced release of 3-H-5-HT in vitro. Therefore, it is suggested that ergocornine is a 5-HT recpetor-stimulating agent, an effect which may lead to reduction of nervous impulse flow in the 5-HT neurons and subsequently of 5-HT release and turnover. MPME, on the other hand, seems to increase 5-HT receptor release of 5-HT stores, mainly from extragranular sites. Thus, the increase in extensor reflex activity found after MPME was reduced by reserpine and H 22/54 and enhanced by nialamide and in vitro MPME markedly increased 3-H-5-HT overflow in cortical slices of nialamide-pretreated rats and inhibited uptake and retention of 3-H-5-HT (EC50 equals 1.6 times 10-minus 6 M) in cortical slices of normal rats. Inhibition of the 5-HT membrane pump does not seem to be of any major importance, since chlorimipramine was only weakly active on the extensor reflex in the pharmacological models used and since MPME did not block but rather enhanced the 5-HT depletion caused by 4-methyl-alpha-ethyl-m-tyramine. It is suggested that MPME is a releaser of extragranular 5-HT stores leading to increased 5-HT receptor activity and reduction of 5-HT turnover in the same way as indicated for ergocornine. This new ergolene derivative may represent a new class of antidepressant drugs acting via release of extragranular 5-HT stores.

In combined biochemical, histochemical and functional studies on central monoamine neurons it has been shown that a pyrozolyl derivative with a phenyl piperazine side chain (PAP) exerts marked effects on central dopamine (DA) and particularly 5-hydroxytryptamine (5-HT) neurons. The brain 5-HT turnover was reduced with doses down to 0.25 mg/kg, and spontaneous overflow of radioactivity from 3H-5-HT-labelled cortical slices was markedly increased by PAP in a concentration of 10(-6) M. PAP may therefore cause extragranular release of 5-HT stores, since the 5-HT levels were not affected. In agreement with this view, sexual behaviour in the female rat, which is controlled by an inhibitory 5-HT pathway, was inhibited by low doses (0.1-0.5 mg/kg) of PAP. The extensor hindlimb reflex, which is dependent on 5-HT receptor activity, was only increased with higher doses (2.5-10 mg/kg), suggesting that the spinal 5-HT nerve terminals are less sensitive to the releasing action of PAP. A certain direct activation of spinal 5-HT receptors may also be involved, since the actions of PAP in the spinal cord were independent of presynaptic 5-HT stores. The actions of PAP on the DA neurons mainly involve a presynaptic action in the DA nerve terminals leading to increased DA receptor activity. This action may primarily involve a blockade of DA uptake (50% inhibition at 10(-6) M) and/or an extragranular release of DA (two-fold increase in spontaneous overflow at 10(-6) M). The DA turnover was not clearly affected, although a trend to a reduction was observed especially in the nuc, accumbens, probably as a result of a compensatory nervous feedback reducing nervous impulse flow. In agreement with the view mentioned above, PAP mimics amphetamine and not apomorphine in the rotometer model which reveals changes in DA receptor activity. PAP in doses of 0.5-1 mg/kg causes a turning towards the denervated side. The brain noradrenaline (NA) turnover is only significantly increased with somewhat higher doses (5-10 mg/kg) and may be related to NA receptor blockade, since the L-DOPA-induced increase in flexor activity is blocked by PAP in doses down to 0.5 mg/kg. It is suggested that the extragranular release of 5-HT caused by PAP is partly responsible for the inhibition of conditioned avoidance behaviour and the reduction of threatening behaviour found after PAP in low doses (0.05-0.5 mg/kg). In the clinic, PAP may prove to be a new therapeutic tool in the treatment of depressions due to 5-HT deficiency. Its actions on DA terminals may also prove helpful in this respect. When combined with L-DOPA, PAP may also help to alleviate the motor deficits in parkinsonian patients with a moderate degree of degeneration of the DA system in view of its action on DA uptake and/or release.

Tail vein injections of [3H]N-propylnorapomorphine ([3H]NPA) in male mice resulted in a dose-related accumulaton of radioactivity in the following brain regions: striatum (max), olfactory tubercle and cerebellum (min). The specific binding was saturable with increasing concentrations of the drug and stereospecifically displaced by (+) butaclamol. Dopamine agonist (apomorphine, NPA and bromocriptine) and antagonists (spiperone, haloperidol, (+) butaclamol and I-sulpiride) all caused dose-dependent prevention of [3H]NPA binding. Mianserin, phenoxybenzamine and propranolol did not prevent the in vivo [3H]NPA binding suggesting that [3H]NPA binds specifically to dopamine receptors in the striatum and the olfactory tubercle of the mouse.

Beta-Endorphin (0.9--2.0 nmol), morphine (11--250 nmol) and D-ala2-met-enkephalinamide (17--33 nmol) administered intracisternally produced preferential vasodepressor responses and bradycardia. Leu- (1.8--180 nmol), met-enkephalin (17--520 nmol) and alpha-endorphin (5.7--57 nmol) administered in the same way produced preferential vasopressor effects and the latter two peptides also produced bradycardia. Results obtained with naloxone (300 nmol) given intracisternally indicate that the pressor and depressor actions as well as the bradycardia are mediated through opiate receptors. The results indicate that opioid peptides may be involved in central cardiovascular control.

l-Glutamate but not methyl-D-aspartate (NMDA) or quisqualate ( Quis ) (10(-6 M) in vitro with or without preincubation increased significantly the KD value of the [3H]N-propylnorapomorphine ( [3H]NPA) binding sites by 21 and 36% respectively in striatal membranes of rat without influencing the striatal [3H]spiperone binding sites. The number of striatal [3H]NPA binding sites was not changed by l-glutamate (10(-6) and 10(-5) M) in vitro. There may thus exist interactions between striatal glutamate receptors -- not related to excitatory amino-acid receptors of the NMDA or the QUIS type -- and high affinity striatal DA receptors.

With the indirect immunofluorescence technique TRH-containing nerve terminals were found in the medial part of the external layer of the median eminence, the dorsomedial nucleus and the perifornical area, in extrahypothalmic nuclei such as nucleus accumbens, the lateral septal nucleus and in several motor nuclei of the brain stem and spinal cord. These findings suggest that TRH may act both as a hormone, released into the portal vessels, as well as a neurotransmitter or modulator, released at synapses in discrete regions of the brain and spinal cord.

The effects of acute audiogenic stress, with or without simultaneous nicotine treatment (0.3 mg/kg i.v.), on catecholamine levels in discrete dopamine and noradrenaline nerve terminal systems of the hypothalamus, and on the secretion of adenohypophyseal hormones and of corticosterone, were studied using quantitative microfluorometric evaluations of catecholamine stores and radioimmunoassays for the determination of serum hormone levels. Audiogenic stress and nicotine induced very rapid and discrete decreases in noradrenaline levels in the subependymal layer (SEL), in the parvocellular part of nuc. paraventricularis hypothalamic (PA FP) and in the posterior periventricular hypothalamic systems, (PV II); the decreases were apparent 2 min following the onset of treatment. Increases of arterial blood pressure were observed after nicotine treatment but could not have been a major factor in producing the changes in catecholamine levels. These changes in NA levels may be related to the nicotine- and stress-induced increases of ACTH (SEL and PA FP) and prolactin secretion (PV II) found in the present experiments. Stress enhanced the rapid but variable increase in vasopressin secretion induced by nicotine, suggesting one possible mechanism by which stress combined with smoking can contribute to the development of increased arterial blood pressure and finally to sustained hypertension.

Acute sino-aortic denervation produces an acute reduction of adrenaline stores in the anterior and posterior hypothalamus and a reduction of noradrenaline stores in the dorsal midline area of the caudal medulla oblongata. Furthermore, removal of baroreflex afferents results in an increase of adrenaline turnover in the DCMO but not in the hypothalamus. The present findings give evidence for participation of adrenergic mechanisms in central baroreflex regulation. The findings can be interpreted according to the adrenaline vasodepressor hypothesis of hypertension.

The effect of intracerebroventricular injections of pertussis toxin were investigated on the neuropeptide Y-induced modulation of alpha 2-adrenoceptor binding in membranes from the dorsomedial medulla oblongata of the rat. Concentration-response experiments showed that neuropeptide Y reduced the binding affinity of the alpha 2-agonist, p-[3H]aminoclonidine, with a maximal effect of 30% at 3-30 nM. Pertussis toxin treatment (10 micrograms, 24 h) counteracted this modulation, without reducing the binding of neuropeptide Y to its own receptor. The results indicate that pertussis toxin-sensitive G-proteins are essential for the mediation of the intramembrane interaction between neuropeptide Y receptors and alpha 2-adrenoceptors.