Effects of vasopressin on noradrenaline-induced cyclic AMP accumulation in rat brain slices

Norepinephrine regulates arginine vasopressin secretion in hypothalamic paraventricular nucleus relating with pain modulation

Our previous study has pointed that arginine vasopressin (AVP) and norepinephrine (NA) are two most important bioactive substances that play a role in hypothalamic paraventricular nucleus (PVN) regulating pain process. The communication was designed to investigate the interaction between AVP and NA in the rat PVN during the pain process. We used the potassium iontophoresis inducing tail-flick to test the pain threshold, PVN push-pull perfusion to collect the samples, high performance chromatography (HPLC) to determine the NA concentration and radioimmunoassay (RIA) to measure the AVP concentration. The results showed that (1) pain stimulation increased both NA and AVP concentrations in the PVN perfusion liquid; (2) PVN administration of l-glutamate sodium increased AVP, not NA concentration in the PVN perfusion liquid; (3) AVP or d(CH(2))(5)Tyr(Et)DAVP (AVP-receptor antagonist) neither changed pain threshold, nor influenced NA concentration in the PVN perfusion liquid; (4) Microinjection of NA into PVN could increase pain threshold in a dose-dependent manner, while PVN administration with phentolamine (alpha-receptor antagonist), not propranolol (beta-receptor antagonist) decreased pain threshold; (5) Administration of NA increased AVP concentration, while phentolamine, not propranolol decreased AVP concentration in the PVN perfusion liquid. These data suggested that it is through alpha-receptor rather than beta-receptor, NA induced PVN secretion of AVP that was delivered to the related brain regions to participate in pain modulation.

Early postnatal appearance of enhanced noradrenaline content in the brain of vasopressin-deficient Brattleboro rat; normal adrenoceptor densities and aberrant influences of vasopressin treatment

The course of postnatal development of noradrenaline (NA) and its unconjugated free metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG), as well as the influence on early chronic vasopressin treatment, were investigated in various brain regions of the hereditary vasopressin-deficient (homozygous di/di) Brattleboro rat. In addition, the densities of the adrenergic receptor subtypes were measured in adult brain. Brain NA levels of di/di pups appeared enhanced already at 7 days of age when compared with data of heterozygous (+/di) controls. This was also seen in areas not known to receive a vasopressinergic input, e.g. the frontal cortex. Levels of MHPG also differed between genotypes, but changes were slight and either a decrease or increase, depending on age and region tested. Saturation analyses of alpha 1-, alpha 2-, and beta-adrenoceptor binding on crude membrane preparations of some brain regions revealed no differences in adulthood. Chronic treatment with vasopressin between 6 and 13 days of age reduced the enhanced NA brain levels throughout the brain of the di/di Brattleboro pups. The known vasopressin-mediated enhancement of NA turnover in adult brain was also measurable in +/di pups of this neonatal period (MHPG/NA ratios), indicating the early maturation of the interaction of vasopressinergic and NAergic systems. However, the dose-response in the di/di Brattleboro rat was biphasic with a decrease at a low dose of vasopressin. Since changes were found throughout the brain, it was concluded that vasopressin deficiency had altered the maturation of NA neurons of the locus coeruleus which may be due to the absence of a presumed inhibitory control of vasopressin on synthesis and storage mechanisms at the perikaryal level.

Effects of intraperitoneal injection of lithium chloride on neurohypophyseal activity: implications for behavioral studies

Intraperitoneal injections of lithium chloride (LiCl) were found to increase the activity of vasopressin-neurons and oxytocin-neurons as indexed by rises in plasma concentrations of vasopressin-associated neurophysin (VP-RNP) and oxytocin-associated neurophysin (OT-RNP). Plasma VP-RNP increased 12 and 4 times basal levels (greater than or equal to 20 fmol/ml) reaching values of 248 +/- 37 fmol/ml (3.0 mEq LiCl/kg body weight) and 89 +/- 10 fmol/ml (1.5 mEq LiCl/kg body weight) at 60 minutes. OT-RNP rose to 37-and 10-times basal levels (greater than or equal to 20 fmol/ml) with peak values of 749 +/- 100 fmol/ml and 188 +/- 48 fmol/ml ten minutes following injection of 3.0 or 1.5 mEq LiCl/kg body weight. Mean arterial pressure increased in response to lithium treatment by 31 +/- 6 mm Hg at 60 minutes in rats receiving 3.0 mEq LiCl/kg and by 22.5 +/- 5 mm Hg at 10 minutes in rats receiving 1.5 mEq LiCl/kg over pretreatment values (125 +/- 3 mm Hg). Heart rate decreased from a pretreatment value of 422 +/- 12 beats/min to 367 +/- 48 beats/min at 10 minutes and to 341 +/- 27 beats/min at 20 minutes for rats treated with the high and low dose of lithium, respectively. These findings suggest that the behavioral effects of LiCl could result from multiple mechanisms and involve its acute release of vasopressin and oxytocin. It is also possible that changes in cardiovascular function may act as cues when LiCl is used as an aversive stimulus.

Vasopressin inhibition of cyclic AMP accumulation and effects on the learned response in inbred mouse strains

The effects of a single injection of arginine vasopressin on the cyclic AMP responses of cerebral cortex slices to noradrenaline, forskolin and 2-chloro-adenosine were tested in six inbred mouse strains. The noradrenaline response was reduced in one strain and that to 2-Cl-adenosine in 2 strains. There was a positive correlation between the differences in the cyclic AMP response to 2-Cl-adenosine between control and AVP-treated mice and the differences in latencies during the extinction period of conditioned avoidance response learning.