Effect of central administration of the kappa-opiate receptor agonist U 69.593 on neurohypophyseal hormone levels in blood and cerebrospinal fluid.

Intracerebroventricular (i.c.v.) administration of the kappa-opiate receptor agonist U 69.593 induces a rapid and short lasting suppression of oxytocin (OXT) levels in plasma of water deprived rats, whereas only a tendency towards a suppression of vasopressin (AVP) levels in plasma is observed. No change in neurohypophyseal hormone levels in CSF occurs following i.c.v. administration of U 69.593 at the various times points studied. It is concluded that, upon i.c.v. administration, the suppressive influence of U 69.593 is much weaker than that of the dynorphins and that neurophypophyseal hormone levels in CSF behave differently from those in the peripheral circulation.

The role of limbic vasopressin and oxytocin in social recognition.

Young male rats were exposed two times for 5 min, to older male rats with an interval of 30 min in the anti-vasopressin serum experiments and with an interval of 120 min in the anti-oxytocin serum experiments. The time spent by the older rats with social investigation of the younger animal was scored during the two encounters. In placebo-treated animals the time spent on social investigation of the younger animal during the second encounter at 30 min is significantly shorter than during the first one (social recognition). However, intracerebroventricular or local application of anti-vasopressin serum in the dorsal or ventral hippocampus or in the dorsal septal area, but not in the n. olfactorius, results in similar periods of time spent for social investigation during the two encounters. Thus, endogenous vasopressin in the dorsal and ventral hippocampus and in the dorsal septal region plays a physiological role in social recognition/memory. In placebo-treated rats the time spent on social investigation of the younger animal during the second encounter at 120 min is similar to that during the first encounter. However, local administration of anti-oxytocin serum in the ventral hippocampus, but not in the dorsal hippocampus, nor in the n. olfactorius or the septal area, results in shorter investigation times during the second encounter. Thus, taken together the presence or local release of vasopressin and oxytocin in the ventral hippocampus and that of vasopressin (but not oxytocin) in the dorsal hippocampus and dorsal septal area are of physiological importance for social recognition.

Dynorphin-A and vasopressin release in the rat: a structure-activity study.

The effects on vasopressin (VP) release of three dynorphin-A fragments and two antidynorphin antisera were tested in vivo and in vitro. In vivo, the order of potency to inhibit VP release 30 min upon i.c.v. injection was: dynorphin-A-(1-17) > dynorphin-A-(1-13) > dynorphin-A-(1-8). l.c.v. co-administration of 10 nmoles of the specific endopeptidase-inhibitor cFPAAF-pAB and dynorphin-A-(1-8) also suppressed VP secretion. Dynorphin-A-(1-17) antiserum enhanced VP release 20 and 60 min after i.c.v. injection. The antiserum that recognized dynorphin-A-(1-13) elevated VP plasma levels at 60 min post-injection. In vitro, dynorphin-A-(1-8) suppressed electrically evoked VP release from the isolated neural lobe. VP release was not affected by dynorphin-A-(1-13), dynorphin-A-(1-17), naloxone, or by the anti-dynorphin antisera. These data indicate that dynorphin-A-(1-17), rather than dynorphin-A-(1-8), plays a role in the centrally located control of neurohypophysial VP release, whereas dynorphin-A-(1-8) is involved in the control located in the posterior pituitary. The synthetic intermediate fragment dynorphin-A-(1-13) appears to affect VP release both centrally and peripherally.

Effect of SCH 23390 and quinpirole on novelty-induced grooming behaviour in spontaneously hypertensive rats and Wistar-Kyoto rats.

Grooming behaviour induced by exposure to a novel environment was studied in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). The dopamine D1 receptor antagonist, SCH 23390, and the dopamine D2 receptor agonist, quinpirole, were used to study brain dopamine systems in these rat strains, via their effects on grooming behaviour. The total grooming behaviour displayed in a 50-min observation period was significantly lower in SHR than in WKY. Except for the paw licking component no differences between the two strains were observed in the separate behavioural elements of grooming behaviour. SCH 23390 and quinpirole were found to suppress novelty-induced grooming behaviour of both strains. In SHR, grooming behaviour was less suppressed by SCH 23390, whereas the suppression by quinpirole was more pronounced than in WKY. These results indicate that there are alterations in central dopamine systems in SHR, probably involving changes both in dopamine D1 and D2 receptor mechanisms in the brain.

Neuromedin-induced excessive grooming/scratching behavior is suppressed by naloxone, neurotensin and a dopamine D1 receptor antagonist.

Neuromedin B and neuromedin C were tested for their grooming/scratching-inducing effects and the composition of neuromedin-induced grooming was established by calculating the relative contribution of various grooming elements to the total grooming scores. Excessive grooming induced by neuromedins is characterized by a predominant display of scratching. Since neuromedin C is much more potent than neuromedin B to induce excessive grooming/scratching behavior, it is concluded that the carboxyl-terminal heptapeptide of neuromedin C is important for this effect. Furthermore, it is concluded that dopamine D1 receptors and opiate receptors are involved in this effect since the dopamine D1 receptor antagonist, SCH 23390, as well as the opiate receptor antagonist, naloxone, suppresses or attenuates neuromedin C-induced excessive grooming/scratching behavior.

The opioid receptor subtypes mu and kappa, but not delta, are involved in the control of the vasopressin and oxytocin release in the rat.

The effects of highly selective agonists and antagonists to the mu-, delta- and kappa-opioid receptor subtypes were studied on the vasopressin and oxytocin release in 24 h water-deprived male rats. The delta-agonist [D-Pen2,D-Pen5]enkephalin (dose range 0.01-5 mg/kg) did not affect plasma levels of either hormone 30 min after s.c. administration, whereas the mu-agonist DALDA (H-Tyr-D-Arg-Phe-Lys-NH2) over the same dose range strongly inhibited the release of both vasopressin and oxytocin, an effect that was maximal 30-60 min after s.c. injection. The same effect was found for s.c. administration of the kappa-agonist U-69,593. Intracerebroventricular (i.c.v.) administration of DALDA (0.5 and 5 micrograms/kg) but not U-69,593 suppressed both plasma hormone levels 30 min after injection. Also the effects of selective antagonists were tested over the s.c. dose range of 0.01-1 mg/kg. Whereas both the kappa-selective antagonist nor-binaltorphimine and the relatively mu-selective antagonist naloxone elevated oxytocin plasma levels (peak at 15 and 30 min after injection, respectively), the delta-selective antagonist naltrindole was without any effect. Nor-binaltorphimine, naloxone, and naltrindole did not affect vasopressin release. When the antagonists were administered i.c.v. (dose range 2.5-25 micrograms/kg), only the kappa-antagonist nor-binaltorphimine enhanced oxytocin and vasopressin release 30 min after injection. In conclusion, both mu- and kappa-opioid receptors are involved in the regulation of the secretion of vasopressin and oxytocin from the rat neural lobe; in contrast, delta-opioid receptors do not play a role.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological assessment of the site of action of opioids on the release of vasopressin and oxytocin in the rat.

Naloxone and its congener, methyl naloxone, were given subcutaneously (s.c.) or centrally (i.c.v.) to 24-h water-deprived male rats 30 min prior to decapitation and the effect on plasma levels of vasopressin (VP) and oxytocin (OT) was studied. The potency of s.c. applied methyl naloxone to increase plasma OT levels did not differ from that of naloxone. Injected i.c.v., neither methyl naloxone nor naloxone had a clear effect and they antagonized i.c.v. co-administered dynorphin A-(1-13) equipotently. Methyl naloxone or naloxone, s.c., antagonized the inhibitory action of simultaneous dynorphin A-(1-13) and beta-endorphin-(1-31) given i.c.v., although higher doses of methyl naloxone were required. The data indicate that the sites of inhibition of neurohypophysial hormone release due to beta-endorphin-(1-31) are more likely to be located mostly within the blood-brain barrier, to which methyl naloxone has less ready access, than are the sites of inhibition due to dynorphin A-(1-13).

Solid-phase extraction of plasma vasopressin: evaluation, validation and application.

A new solid-phase extraction method using octyl-silica columns to extract vasopressin-like immunoreactivity from plasma has been developed. The extraction was followed by a radioimmunoassay on the vacuum-dried extracts, which were reconstituted in assay buffer. The total recovery of synthetic vasopressin was ca. 100%. Based on co-elution with synthetic vasopressin after separation by reversed-phase high-performance liquid chromatography of plasma extracts from normal Wistar and Brattleboro rats, and the cross-reactivity of the antiserum used in the radioimmunoassay system, the extracted material was found to be indistinguishable from authentic vasopressin. Unknown experimental samples were interpolated on a standard curve established in "zero" plasma (plasma derived from rats subjected to waterload) spiked with known amounts of synthetic vasopressin, and not on a standard curve established in assay buffer. The limit of detection was 1 fmol of vasopressin equivalent per millilitre. The intra- and inter-assay coefficients of variance were 10-16% and 16%, respectively. The procedure reliably showed that osmotic challenge and 24-h dehydration increased, whereas ethanol ingestion decreased vasopressin-like immunoreactivity plasma levels in the rat, compared with normally hydrated controls.

Neurohypophyseal hormones and excessive grooming behaviour.

The pattern of excessive grooming displayed by rats treated with vasopressin and oxytocin was investigated by calculating the frequencies and contribution of the behavioural elements head washing, body grooming, anogenital grooming, paw licking and scratching. In addition, the suppressive effect on peptide-induced grooming of the dopamine D1 receptor antagonist SCH 23390, of neurotensin and of the opiate receptor antagonists naloxone and naloxone-methobromide was studied. The pattern of excessive grooming induced by vasopressin and by oxytocin was characterized by the contribution of most behavioural elements to the total grooming scores. Oxytocin-induced excessive grooming was characterized by a marked increase in the frequency of anogenital grooming. SCH 23390, neurotensin and naloxone, but not naloxone-methobromide, suppressed excessive grooming induced by vasopressin and oxytocin. It is suggested that dopamine D1 receptors as well as opiate receptors located within the blood-brain barrier are involved in the excessive grooming induced by neurhypophyseal hormones.

Dopamine D-1 and D-2 receptor agonists and antagonists and neuropeptide-induced excessive grooming.

The administration of the dopamine D-1 receptor antagonist, SCH 23390, but not of the dopamine D-2 receptor antagonist, sulpiride, suppressed the excessive grooming induced by a new environment or by various neuropeptides. In addition, administration of the dopamine D-1 agonist, SK & F 38393, induced excessive grooming but that of the dopamine D-2 agonist, quinpirole, did not. It is suggested that dopamine D-1 rather than D-2 receptor stimulation is an important mechanism underlying novelty-induced as well as neuropeptide-induced excessive grooming.

Volume-regulated arginine vasopressin release in conscious dogs. Evidence for dopaminergic or opioid modulation?

The possibility of a dopaminergic and/or opioid modulation of the volume-regulated release of AVP was investigated in conscious dogs. Either bromocriptine, 10 micrograms/kg body weight po, or naloxone, 0.1 mg/kg body weight iv, was administered prior to induction of nonhypotensive hypovolemia. Volume contraction of 15 ml/kg body weight was induced gradually, over a period of 30 min. Basal plasma AVP levels in the bromocriptine group were not significantly different from control group values. Bromocriptine administration significantly augmented AVP release following volume contraction. Mean arterial pressure in the bromocriptine group decreased to a slightly, but significantly, lower level than that in the control group. Mean arterial pressures, however, did not adequately explain the magnitude of the AVP response in the bromocriptine group. In the naloxone group, neither baseline levels, nor AVP values following volume contraction, differed significantly from respective control group values. In conclusion, the results suggest the possibility of a stimulatory role for endogenous dopamine in the volume-regulated, but not the basal, release of AVP in conscious dogs.

Grooming behavior induced by substance P.

The intracerebroventricular (i.c.v.) administration of substance P elicits in rats an excessive grooming that is characterized by body grooming, anogenital grooming and scratching. The total grooming scores displayed by rats treated with substance P hardly exceeded 23% of the theoretical maximal grooming score. Substance P-induced excessive grooming was suppressed by pretreatment with naloxone, haloperidol on neurotensin. It is concluded that substance P induces excessive grooming with a pattern different from that of grooming elicited by other peptides.

Radioimmunoassay of desglycinamide-arginine vasopressin and its application in a pharmacokinetic study in the rat.

The purpose of this investigation was to develop a sensitive and selective radioimmunoassay for Desglycinamide-Arginine Vasopressin (DGAVP). DGAVP was extracted from rat plasma after protein precipitation, using Sep-Pak C18 cartridges and 50 mM glycine buffer/methanol (10:90) solution. Extraction recovery was 73 +/- 14% (mean +/- S.D.; n = 11) and good linearity was achieved in the concentration range of 0.25-128 pg/tube. Instantaneous tracer addition resulted in a detection limit of 250 fg/tube, whereas 24 hours preincubation and delayed tracer addition resulted in a detection limit of 100 fg/tube. Intra-assay variation ranged between 7.4% and 10.0% depending on the peptide concentration and inter-assay variation was 13.2%. Using this procedure, plasma pharmacokinetics of DGAVP in the rat were determined after IV administration. DGAVP plasma concentration showed a rapid distribution phase (t1/2 = 1.0 +/- 0.2 min) and a somewhat slower elimination phase (t1/2 = 7.2 +/- 2.1 min). High clearance values (CLss = 97 +/- 30 ml.min-1) suggest rapid metabolism by amino- and carboxy-peptidases.

Osmolality-regulated arginine vasopressin release in conscious dogs. Evidence for dopaminergic or opioid modulation?

Experiments were performed in conscious dogs, in order to study the possibility of dopaminergic or opioid modulation of the osmolality-regulated release of AVP. Hypertonic saline (20%), infused during a period of 2 h at a rate of 0.03 ml.kg-1.min-1, induced a significant AVP response, which was not influenced by prior administration of bromocriptine or naloxone. Data presented in this report, therefore, are not in support of a dopaminergic or opioid modulation of the osmolality-regulated AVP release in dogs. The results demonstrate a great consistency in individual plasma osmolality-plasma AVP relationships, next to a large inter-individual variation.

Vasopressin levels in the cerebrospinal fluid of rats with lesions of the paraventricular and suprachiasmatic nuclei.

The circadian rhythm and dehydration-induced response of vasopressin (AVP) levels in rat cerebrospinal fluid (CSF) were studied after lesions had been made in the paraventricular (PVN) and suprachiasmatic (SCN) nuclei. The rhythmic fluctuation of AVP levels in CSF was abolished after SCN lesions, whereas lesions of the PVN had no effect. Dehydration seems to increase AVP levels in CSF of both sham-operated and lesioned animals. These data further suggest that the circadian rhythm of AVP in CSF is preferentially generated by SCN. In contrast, several areas of the brain may contribute to the overall AVP levels in CSF, both under normal physiological conditions and under osmotic stress.

Some characteristics of TRH-induced grooming behavior in rats.

Intracerebroventricular administration of TRH induces excessive grooming behavior that is characterized by an important contribution of the elements scratching and paw licking. As compared with other grooming inducing peptides, the pattern of TRH-induced grooming resembles that induced by beta-endorphin rather than those elicited by ACTH or bombesin. TRH-induced excessive grooming is suppressed by pretreatment with haloperidol, naloxone or neurotensin. Haloperidol suppresses TRH-induced grooming in a general way, whereas the suppressive effect of the other drugs is mainly due to a selective reduction of TRH-induced excessive scratching. Combined treatments of rats with TRH and a submaximal dose of ACTH, bombesin or beta-endorphin do not result in higher grooming scores than with single peptide treatment. Excessive grooming elicited by water immersion is not affected by TRH. It is concluded that TRH is undoubtedly an excessive grooming inducing peptide. In situations where excessive grooming is elicited by other peptides or by water immersion, TRH does not further activate the operating systems involved in the existing excessive grooming.

Effects of osmotic stimuli on vasopressin levels in the CSF of rats.

Arginine-vasopressin (AVP) levels and osmolality were measured in the CSF of rats during 5 days of osmotic stimulation. Dehydration increased AVP levels about 3-fold but did not affect the circadian rhythm of AVP. During dehydration, AVP levels in CSF increased as osmolality increased. Neither AVP levels nor osmolality changed significantly in the CSF of rats receiving 2% NaCl as drinking water. The increased AVP values in CSF may reflect activated release of AVP in the central nervous system during dehydration. Our data also suggest that the AVP release connected with the regulation of osmotic changes may be separate from the mechanism that regulates the circadian rhythm of AVP in the CSF of rats.

Excessive grooming induced by somatostatin or its analog SMS 201-995.

Intracerebroventricular (i.c.v.) administration of somatostatin or SMS 201-995 induces excessive grooming behavior in rats. The grooming inducing effect of somatostatin is rather weak, as doses of 300 ng or less did not result in increased total grooming scores. In contrast a dose of 10 ng SMS 201-995 already significantly increased the total grooming scores. However, doses of 100 ng and more did not further increase the total grooming scores reached with a 50 ng dose of this peptide. Systemic administration of SMS 201-995 in doses up to 900 micrograms did not result in excessive grooming behavior. The patterns of excessive grooming induced by i.c.v. SMS 201-995 and somatostatin were characterized by a predominant display of scratching. Since peptide-induced scratching is mainly due to activation of opiate receptor systems it is suggested that opiate receptors are involved in the behavioral response to SMS 201-995 and somatostatin administration. This suggestion is further supported by the suppressive effect of naloxone on excessive grooming induced by these peptides. Haloperidol and neurotensin also suppress the excessive grooming induced by somatostatin but not that induced by SMS 201-995. Finally, tolerance developed to the grooming-inducing effect of SMS 201-995 and somatostatin. In addition there was cross tolerance between somatostatin and SMS 201-995.