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In order to determine whether serotonergic (5HT) dorsal raphe nucleus (DRN) cells are involved in body sodium status regulation, the effect of a s.c. infusion of either 2 M or 0.15 M NaCl on 5HT DRN neuron firing was studied using single unit extracellular recordings. In separate groups of 2 M and 0.15 M NaCl-infused rats, water intake, oxytocin (OT) plasma concentration, urine and plasma sodium and protein concentrations were also measured. Also, to determine the involvement of particular brain nuclei and neurochemical systems in body sodium overload (SO), animals from both groups were perfused for brain immunohistochemical detection of Fos, Fos-OT and Fos-5HT expression. SO produced a significant increase in serotonergic DRN neuron firing rate compared to baseline and 0.15 M NaCl-infused rats. As expected, 2 M NaCl s.c. infusion also induced a significant increase of water intake, diuresis and natriuresis, plasma sodium concentration and osmolality, even though plasma volume did not increase as indicated by changes in plasma protein concentration. The distribution of neurons along the forebrain and brainstem expressing Fos after SO showed the participation of the lamina terminalis, extended amygdala, supraoptic and paraventricular hypothalamic nuclei in the neural network that controls osmoregulatory responses. Both Fos-OT immunoreactive and plasma OT concentration increased after s.c. hypertonic sodium infusion. Finally, matching the "in vivo" electrophysiological study, SO doubled the number of Fos-5HT immunolabeled cells within the DRN. In summary, the results characterize the behavioral, renal and endocrine responses after body sodium overload without volume expansion and specify the cerebral nuclei that participate at different CNS levels in the control of these responses. The electrophysiological approach also allows us to determine in an "in vivo" model that DRN 5HT neurons increase their firing frequency during an increase in systemic sodium concentration and osmolality, possibly to modulate sodium and water intake/excretion and avoid extracellular volume expansion.

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Cysteamine (CSH), a sulfhydryl agent that promotes disulfide-exchange reactions, was studied for its effects on the immunoreactive (IR) levels and synthesis of oxytocin and vasopressin in the hypothalamus. CSH injection (300 mg/kg s.c.) caused a rapid (1 h) suppression of 35S-cysteine incorporation into hypothalamic arginine vasopressin (VP) and oxytocin (OT). The reduction in labeling persisted for about 8 h; label incorporation was normal within 10 h of CSH administration. The drug did not influence 35S-cysteine incorporation into acid-precipitable protein, nor did it influence 35S-cysteine specific activity in the hypothalamus. In addition, 35S-VP and 35S-OT molecules could not be recovered from hypothalami of CSH-treated rats by subjecting samples to denaturing, reducing and then reoxidizing conditions. Despite the reduction in peptide labeling, CSH treatment produced no alterations in the IR VP and OT contents of hypothalamus or posterior pituitary. These results indicate that CSH causes a true suppression of both VP and OT formation in hypothalamus, and suggest that the effect is either too transient to promote a reduction in endogenous stores of either peptide, or that the drug equally inhibits peptide production and removal (i.e., axonal transport, secretion).

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To investigate the influence of various peptides on control of dehydration-induced drinking, water intake elicited by overnight water deprivation was analyzed in groups of male rats after intracerebroventricular (third ventricle, icv) injection of 2 microliters of normal rabbit serum or an equal volume of antiserum directed against angiotensin II (Ab-AII), atrial natriuretic peptide, vasopressin, or oxytocin. There was no difference in water intake after normal rabbit serum and antiserum injections when water was offered immediately after icv injections. Water intake was greatly reduced by Ab-AII when water was offered 1 hr and 3 hr after icv injection. The other antisera were partially effective only when water was offered 3 hr after icv injection. The dipsogenic effect of icv injection of AII in normally hydrated rats was reduced only by icv injection of Ab-AII 3 hr before and not by the other antisera. Ab-AII injected icv had no effect on the drinking that occurred just before and after the onset of darkness and that was associated with eating (prandial drinking). The results indicate that AII is primarily responsible for dehydration-induced drinking, and the other peptides may play a permissive role since their antisera were partially effective, with longer latencies after antiserum injection, which is perhaps the result of gradual diffusion to effective sites within the hypothalamus. In contrast, endogenous AII appears to play little, if any, role in prandial drinking.

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The effects on ovulation of a specific anti-oxytocin rabbit serum (anti-OT) (50.0 microliters) given by intrabursal injection into the right ovaries of etherized adult female rats at proestrus, were explored by counting the number of ovulated ova present within the right oviducts. Left ovaries were not treated and served as control ovaries. Control rats were treated with male normal rabbit serum (NRS) (50.0 microliters) given by intrabursal injections into the right ovaries of animals at proestrus. Ovulation was induced by injection of human chorionic gonadotrophin (hCG). Anti-OT administered into the right ovarian bursae of proestrous rat ovaries evoked a significant 51% inhibition of ovulation in comparison with that observed in control non-injected left ovaries (p less than 0.01). Also, when the ovulation of right ovaries injected with anti-OT was compared with that of left ovaries injected with NRS, the number of ovulated ova in the right side was significantly smaller (30%) than on the contralateral side (p less than 0.02). However, in rats pre-treated with hCG the intrabursal injection of oxytocin (OT) (50.0 mU/ml) into right and left ovaries failed to alter the number of ovulated ova compared with that of rats receiving intrabursal injections of saline. The basal control and the OT-evoked synthesis and release of endogenous prostaglandin E2 (PGE2) and PGF2 alpha were explored in ovaries isolated from prepuberal rats injected with pregnant mare's serum gonadotrophin (PMSG), two days prior to sacrifice. OT augmented the basal release of PGF2 alpha but did not influence that of PGE2. Moreover, the conversion of exogenous 14C-arachidonic acid (14C-AA) into different prostanoids and into 5-HETE, in the presence and in the absence of added OT (50.0 mU/ml), was studied in rat ovaries isolated in proestrus. The challenge with OT augmented the basal synthesis and release of PGF2 alpha and of 5-HETE from 14C-AA, but failed to influence the formation of products generated via the cyclo-oxygenase pathway, namely 6-keto-PGF1 alpha, PGE2 and thromboxane B2 (TXB2). Therefore, the present results suggest that ovarian OT may play a role in the ovulatory process, via generation of PGF2 alpha to enhance contractions of ovarian smooth muscle and of 5-HETE to promote follicular collagenolysis.

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