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The effects of vaginocervical stimulation (VCS) on glutamate (GLU), aspartate (ASP), gamma-aminobutyric acid (GABA), noradrenaline (NA), arginine (ARG) and nitric oxide (NO) (citrulline) release in the nucleus of the solitary tract (nTS) were measured in anaesthetised female rats as a function of the oestrus cycle. During pro-oestrus/oestrus (P/E), but not during met-oestrus/di-oestrus (M/D), VCS significantly increased concentrations of NA, ASP, GLU, NO (citrulline) and GABA, but not ARG. Basal NA concentrations were also increased in P/E. These effects were prevented by bilateral section of either the vagus nerve or pelvic and hypogastric nerves. Vagotomy also significantly decreased basal NO concentrations in M/D and P/E while pelvic and hypogastric nerve section significantly increased GABA concentrations. Our results therefore confirm that the nTS is a relay structure for the visceral afferents sending information from the uterus into the central nervous system. The ability of VCS to trigger classical transmitter release and NO in the female is influenced by the stage of the oestrous cycle and is routed both via the vagus and pelvic/hypogastric nerves.

In vivo microdialysis in urethane anaesthetised rats was used to investigate the effects of substance P (SP) on acetylcholine (ACh) and dopamine (DA) release in the rat striatum. Results showed that SP elicited a dose-dependent increase in ACh release between 1 and 50 pmol/l. The rise in ACh release occurred both during SP administration and for up to 60 min after it. Dose-response curves either based on the initial rise in ACh release, or the total duration of increased release, showed a bell shape with 100 fmol/l and 5 nmol/l doses failing to significantly alter release and a 500 pM dose being less effective than 50 pmol/l. In contrast to this, SP did not significantly alter DA release at doses ranging between 100 fmol/l and 5 nmol/l. There was evidence for a strong desensitisation effect of SP administration since after initial treatment with SP subsequent doses of the peptide, even at very high doses, failed to provoke further changes in ACh still showed the expected increase in release in response to a potassium challenge. Physalaemin and neurokinin A increased ACh release with a similar potency to SP at a 50 pmol/l dose whereas neurokinin B and neuropeptide gamma, while increasing ACh release at a 50 pmol/l dose, were less potent than SP. The effect of SP on ACh release is probably mediated via NK-1 receptors since ACh release in response to SP was reduced in a dose dependent manner by the NK-1 receptor antagonists CP-96,345 and RP-67580.

Microdialysis sampling was used to measure the release of oxytocin (OXY) and monoamine and amino acid transmitters from the region of the medial preoptic area (MPOA) and the bed nucleus of the stria terminalis (BNST) during parturition and suckling in sheep. Results showed that OXY and gamma-aminobutyric acid release increased in both the MPOA and BNST during parturition and suckling. Noradrenaline (NA) release increased in both structures during parturition but not during suckling. Dopamine (DA) release increased in the MPOA and decreased in the BNST during both parturition and suckling. Aspartate release increased in the MPOA during parturition, and the BNST during suckling, and glutamate release increased in the MPOA and BNST at parturition and only in the BNST during suckling. No changes in the release of serotonin or taurine occurred in these structures during parturition or suckling. In a further experiment on 6 estrogen-primed sheep, OXY (10 micrograms/ml) was infused into the MPOA via bilaterally placed microdialysis probes. This treatment inhibited rejection behavior towards lambs, but did not activate positive maternal responses. These OXY infusions also stimulated release of NA. These results show that complex patterns of neurochemical release occur in two closely related areas of the brain, the BNST and MPOA, during parturition when maternal behavior is stimulated. However, while these patterns of release are similar in the two structures, particularly at birth when maternal behavior is stimulated, they are not identical during labor contractions and suckling. The release of oxytocin within the MPOA during parturition may be important for stimulating a reduction in aggression towards lambs, although this action might be mediated via the effect of OXY on NA release.

In order to establish which neurotransmitters may influence the activity of zona incerta neurones in the sheep which respond selectively to the sight or ingestion of food, we have measured the release of amino acid and monoamine neurotransmitters from this region using microdialysis sampling. Co-ordinates for the placement of microdialysis probes in regions of the zona incerta where cells respond to the sight or ingestion of food were first established by making single-unit extracellular recordings. When animals were food-deprived results showed that release of γ-aminobutyric acid (GABA) was increased in response to the sight and ingestion of food but not of aspartate, glutamate, taurine, noradrenaline, dopamine or serotonin. This release of GABA was absent when the animals were shown non-food objects or saw or ingested salt solutions. When the same animals were physiologically sodium-depleted GABA release was evoked by the sight and ingestion of salt solutions and release following the sight and ingestion of food was significantly reduced. These results provide further evidence that GABA is an important neurotransmitter in neural circuits controlling the regulation of food intake.

The effects of intracerebroventricular infusions of morphine, oxytocin, and corticotrophin-releasing factor (CRF) on maternal behaviour alone, or in conjunction with vaginocervical stimulation were determined in both nulliparous and multiparous ovariectomized ewes, primed with oestrogen for 3 days proir to testing. Both plasma and cerebrospinal fluid levels of oxytocin were measured under similar conditions, following CRF and morphine treatments. In nulliparous ewes, i.c.v. oxytocin and morphine reduced rejection behaviours, but neither these treatments nor vaginocervical stimulation promoted proceptive acceptance behaviour. Ewes that were maternally experienced showed increases in acceptance and a reduction of rejection behaviours following vaginocervical stimulation or i.c.v. oxytocin. Morphine and CRF potentiated the effects of vaginocervical stimulation on these behaviours. No treatment influenced oxytocin release per se, but i.c.v. morphine increased both peripheral and central release of oxytocin in response to vaginocervical stimulation. The results show that maternal experience is essential for oxytocin to promote proceptive behaviours and that morphine and CRF potentiate the effects of vaginocervical stimulation on acceptance behaviour. Since morphine also potentiated the release of oxytocin in response to vaginocervical stimulation it is difficult to separate the relative contribution of direct versus indirect effects of opiates in potentiating maternal bonding.

The effects of oral ENA713 and CHF2819 (0.5, 1.5 and 4.5 mg/kg), two novel acetylcholinesterase inhibitors, on extracellular concentrations of amino acids in rat hippocampus, were evaluated using in vivo microdialysis. ENA713, at 4.5 mg/kg, but not CHF2819, significantly decreased glutamate, taurine, arginine and citrulline levels, without affecting aspartate concentrations. These results suggest that the modulation of amino acidergic transmission could represent an additional mechanism of action in Alzheimer's disease for some acetylcholinesterase inhibitors.

Intracranial dialysis was used to measure the release of oxytocin (OXY), monoamines and their metabolites and uric acid (UA) from the substantia nigra (SN) and olfactory bulb (OB) of sheep during parturition, suckling, separation from lambs and eating. Results showed that OXY concentrations increased significantly during parturition, suckling and eating in the SN and during parturition and suckling in the OB. Concentrations of dopamine (DA) increased significantly in the SN during suckling and eating and in the OB during parturition and suckling. The dopamine metabolite, homovanillic acid, also increased significantly in the SN during parturition. Concentrations of the noradrenaline metabolite, 4-hydroxy-3-methoxyphenylethan-1,2,-diol (MHPG) and the purine metabolite, UA, were significantly raised during parturition, suckling and separation from the lambs in the SN and increased UA levels were also found during eating. In a separate experiment it was confirmed that OXY was detectable in homogenates of both the SN and the OB. These results show that, in the sheep, OXY and DA release in the SN is associated with maternal and ingestive behaviour whereas similar release in the OB may only be related to maternal behaviour. Release of MHPG in the SN may be associated with maternal behaviour and/or stress.

Concentrations of oxytocin and amino acids were measured in microdialysis samples taken from the olfactory bulbs of 5 conscious, oestrogen-treated ewes before, during and after a 10-min period of vaginocervical stimulation. Results showed that vaginocervical stimulation induced significant increases in concentrations of oxytocin, aspartate, gamma-aminobutyric acid (GABA) and glutamate in dialysis samples. Concentrations of other amino acids measured were not affected. These findings show that vaginocervical stimulation produces significant changes in neurochemical release in the olfactory bulbs of sheep. Such changes may be involved in the induction of maternal behaviour of the olfactory recognition of offspring.

Electrophysiological recordings were made from medial preoptic/anterior hypothalamic (MPOAH) neurones which could be orthodromically excited from the lateral septum (LS) in gonadally intact and castrated male rats. Castration significantly reduced the mean percentage of MPOAH neurones which responded reliably to 0.6 Hz stimulation (from 81.1% to 54.1%) and this could be reversed by testosterone propionate (from 52.5% to 90.1%). Both in the gonadally intact (58.1%) and castrated (53.8%) groups these MPOAH neurones with LS inputs also had inputs from the contralateral fimbria (CFIMB). A further experiment investigated whether these MPOAH neurones responding to LS stimulation had connections with the arcuate/median eminence (ARC/ME) region or the medial forebrain bundle (MFB). Altogether, 23.2% projected directly into the MFB and 9.5% into the ARC/ME. A further 28.4% and 31.6% of these MPOAH neurones received inputs from these respective brain regions. A small population of MPOAH neurones were also found which could be driven antidromically both from the LS and the MFB. Results show that testosterone alters the responsiveness of MPOAH neurones to stimulation of the LS. Since subpopulations of these neurones project to the MFB and ARC/ME the effects of castration on them may reflect both changes in sexual behavior and, for example, gonadotropin release.

Single-unit recordings were made from neurones in the zona incerta (ZI) of conscious sheep in response to the sight/visual approach or ingestion of various foods, salts and water. Animals were given parotid fistulae so that effects of sodium appetite, induced by not replacing the sodium lost in the saliva, could be assessed. When sodium depletion was prevented by giving the animals 1% sodium bicarbonate in their drinking water, the majority of cells (45 out of 49) responded most strongly to the sight or visual approach of food compared to water or salt. Four cells responded best to the sight of water, but none to the sight of salt and salt solutions. When a sodium appetite was stimulated, by removing the 1% sodium bicarbonate replacement for 4-6 days, there was a significant change in response profiles of ZI cells. The majority of cells responded most strongly to the sight of salts or salt solutions (35 out of 49) and significantly fewer cells responded most strongly to food (8 out of 49). The number of cells responding primarily to water was not affected (6 out of 49). For 3 cells responding to salts it was shown that, after repeated ingestion of salt over several hours, food became a more potent stimulus. A similar decreased response to foods during sodium depletion, and an increased one to salts, was seen in ZI cells which responded to the ingestion of both solids and liquids. These results show that changing an animal's motivational state produces significant changes in the responses of cells in the ZI responding to the sight or visual approach of substances.(ABSTRACT TRUNCATED AT 250 WORDS)

The sexual behavior of 8, estradiol-treated, ovariectomized common marmosets was recorded prior to and after bilateral radiofrequency lesions of the hypothalamus. Lesions of the anterior hypothalamus, which extended to varying degrees into the medial hypothalamus, virtually abolished proceptive tongue-flicking and staring displays. Tongue-flicking during copulation also decreased, but the females did not show any significant increase in the number of mounts which they refused or terminated with the exception of one animal which had received more extensive damage to the medial hypothalamus. Significant increases in the frequencies of allogrooming and grooming invitations also occurred after the females had been lesioned. Sexual behavior was not significantly altered in 3 females which received sham lesions. These results provide the first direct evidence for a neuroanatomical distinction between hypothalamic mechanisms which regulate proceptivity and receptivity in primates.

Concentrations of monoamines and metabolites and uric acid were measured in sequential 15-min microdialysis samples taken from the area of the supraoptic nucleus (SON) in 9 urethane-anaesthetized rats. A decrease in blood pressure of 40 mm Hg was induced by withdrawing 3-4 ml of blood from an indwelling jugular catheter. This decreased blood pressure was maintained for 30 min and produced a significant rise in the concentrations of noradrenaline (NA) and its metabolite 4-hydroxy-3-methoxyphenylethan-1,2-diol (MHPG) and also in 5-hydroxytryptamine (5-HT) and the purine metabolite uric acid (UA). When blood pressure was returned to normal by replacing the withdrawn blood, the concentrations of NA, MHPG, 5-HT and UA returned to pre-haemorrhage levels within 15 min. No significant changes in concentrations of dopamine and its metabolites were found, and in 7 control animals sampled 1.5-2 mm away from the SON, in the area of the olfactory tubercle, concentrations of NA, MHPG, 5-HT and UA were not significantly altered by haemorrhage-induced decreases in blood pressure.

The effects of intracerebroventricular infusions of naltrexone and phentolamine on the ability of vaginocervical stimulation to induce maternal behaviour, and plasma and cerebrospinal fluid (CSF) levels of oxytocin, were measured in oestrogen-primed ewes. Results showed that naltrexone, but not phentolamine, significantly inhibited maternal behaviour following vaginocervical stimulation. Naltrexone also prevented the CSF increase in oxytocin following vaginocervical stimulation but was without effect on plasma levels. Phentolamine did not prevent either CSF or plasma increases in oxytocin, following vaginocervical stimulation, but reduced basal plasma levels. Results are discussed in terms of an opioid influence on maternal behaviour which may be mediated through a modulation of central oxytocin release.

The time courses of different electrophysiological effects of testosterone on a specific subpopulation of medial preoptic/anterior hypothalamic neurons and sexual behavior were measured in castrated rats. Testosterone reduced the absolute refractory period of those neurons projecting into the medial forebrain bundle with the same time course as it restored maximal responsiveness to orthodromic stimulation of either the lateral septum or the fimbria and sexual responses (5 days). The similar time-courses for these different electrophysiological effects of testosterone argue for a common mechanism of action.

Single unit recordings were made from neurones in the lateral hypothalamus and zona incerta of conscious sheep during the static visual presentation of food or visible approach of food towards the animal's mouth. The ability of this population of neurones to modulate their activity as a result of learning and satiety was investigated together with the extent to which their responsiveness reflected individual food preference. These neurones did not respond to either the sight or visible approach of a nonsense object or a food which they would not eat. Further, when the sight or approach of food which the animal desired to eat was not paired with ingestion the neurones rapidly extinguished their response. The magnitude of the neuronal response and the number of trials to extinction was dependent upon the animal's preference for a particular food: the most preferred food evoking the greatest response and being the most resistant to extinction. Following extinction the neuronal response to the sight or approach of food could be re-established after one or two trials with food reinforcement. If the sheep was repeatedly given the same food to eat the magnitude of the neuronal response and the number of trials to extinction gradually declined until no response occured when the animal refused to eat. These cells could also be induced to respond differentially to the approach of non-food objects dependent upon whether they were associated with a food reward or not. Thus a response could be evoked to the sight or approach of a black bottle if it was associated with a food reward but not to a yellow bottle unassociated with feeding. Acquired neuronal responses to novel foods could also be demonstrated.