Oxytocin affects utilization of noradrenaline in distinct limbic-forebrain regions of the rat brain

Oxytocin and addiction: a review

Neuropeptides affect adaptive central nervous system processes related to opiate ethanol and cocaine addiction. Oxytocin (OXT), a neurohypophyseal neuropeptide synthesized in the brain and released at the posterior pituitary, also is released in the central nervous system (CNS). OXT acts within the CNS and has been shown to inhibit the development of tolerance to morphine, and to attenuate various symptoms of morphine withdrawal in mice. In rats, intravenous self-administration of heroin was potently decreased by OXT treatment. In relation to cocaine abuse, OXT dose-dependently decreased cocaine-induced hyperlocomotion and stereotyped grooming behavior. Following chronic cocaine treatment, the behavioral tolerance to the sniffing-inducing effect of cocaine was markedly inhibited by OXT. Behavioral sensitization to cocaine, on the other hand, was facilitated by OXT. OXT receptors in the CNS--mainly those located in limbic and basal forebrain structures--are responsible for mediating various effects of OXT in the opiate- and cocaine-addicted organism. Dopaminergic neurotransmission--primarily in basal forebrain structures--is another important biochemical mediator of the central nervous system effects of OXT. Tolerance to ethanol (e.g. hypothermia-inducing effect of ethanol) also was inhibited by OXT.

Idazoxan and the effect of intracerebroventricular oxytocin or vasopressin on sodium intake of sodium-depleted rats

The alpha2-adrenergic agonist clonidine and the neuropeptide oxytocin, inhibit sodium intake when injected intracerebroventricularly (i.c.v.). The present work investigates whether (1) vasopressin also inhibits sodium intake when injected i.c.v., and (2) the effect of oxytocin and of vasopressin on sodium intake is affected by i.c.v. injection of idazoxan, an alpha2-adrenergic antagonist. Clonidine (30 nmol), oxytocin (40, 80 nmol) and vasopressin (40, 80 nmol) were injected i.c.v. 20 min prior to a 1.5% NaCl appetite test, in rats depleted of sodium for 24 h by a combination of a single s.c. injection of furosemide (10 mg/rat) and removal of ambient sodium. Every dose of clonidine, oxytocin and vasopressin inhibited the 1.5% NaCl intake. Seizures were observed with the higher dose of vasopressin, but not with either dose of oxytocin. The effect of i.c.v. injection of clonidine (30 nmol), oxytocin (80 nmol) or vasopressin (40 nmol) was partially inhibited by prior i.c.v. injection of idazoxan (160, 320 nmol). The results suggest that the inhibition of 1.5% NaCl intake induced by i.c.v. injection of neuropeptides in sodium-depleted rats depends, in part, on the activation of central alpha2-adrenoceptors.

Aged rats are still responsive to the antidepressant and memory-improving effects of oxytocin

Oxytocin, intraperitoneally injected to 26-month-old male rats 60 min before testing, significantly improved social memory (at doses of 3 and 6 ng/kg) and reduced the duration of immobility in the behavioral despair test (at doses of 50 and 500 micrograms/kg). These results are in agreement with previous data obtained in adult rats and indicate that aging does not compromise the social memory improving and antidepressant-like activities of oxytocin.

Opposite actions of oxytocin and vasopressin in the development of cocaine-induced behavioral sensitization in mice

Subchronic administration of cocaine induces behavioral sensitization (increasing hypermotility) to a challenge dose of the drug administered 72 h after the cessation of treatment. The effects of repeated administration of the neurohypophyseal hormones oxytocin (OXT) and arginine8-vasopressin (AVP) on the development of behavioral sensitization induced by subchronic treatment with cocaine were investigated in mice. Repeated treatment of OXT and AVP did not modify the locomotor stimulatory effect of the challenge dose of cocaine in cocaine-naive control animals. OXT in a dose of 0.5 microgram (sc) augmented the cocaine-induced behavioral sensitization. In contrast, AVP (0.005-0.5 microgram/mouse, sc) dose dependently attenuated the development of sensitization to the hypermotility-inducing effect of cocaine. The results suggest that the behavioral sensitization induced by cocaine can be modulated in opposite directions by neurohypophyseal hormones.

Selective attenuation of cocaine-induced stereotyped behaviour by oxytocin: putative role of basal forebrain target sites

The effects of oxytocin (OXT), arginine- and lysine-vasopressin (AVP and LVP) and an OXT-receptor antagonist on cocaine-induced sniffing behaviour were investigated in rats. OXT, but not AVP or LVP injected subcutaneously (s.c.) attenuated cocaine-induced sniffing. The effect of OXT (s.c.) was inhibited by an OXT-receptor antagonist administered intracerebroventricularly (i.c.v.). I.c.v. administration of different doses of OXT in nanogram quantities caused a dose-dependent attenuation of cocaine-induced sniffing. Local cerebral microinjection of OXT into the accumbens nucleus and olfactory tubercle but not into the olfactory nucleus, central amygdaloid nucleus or caudate nucleus, inhibited the cocaine-induced sniffing behaviour. These results demonstrate that OXT selectively attenuates the cocaine-induced stereotyped behaviour through basal forebrain target sites.

Inhibitory influence of oxytocin infusion on contingent negative variation and some memory tasks in normal men

A double-blind study combining electrophysiological and psychometrical approaches was carried out to investigate the central effects of an intravenous oxytocin (OT) infusion in normal men. Contingent negative variation (CNV) was selected as the measure of central cognitive evoked potential, and the psychometric tests measured mood, vigilance and memory. OT infusion induced a significant decrease of CNV amplitude and an increase of post-imperative positive potentials in vertex derivations. A similar effect was still evidenced one week after treatment in frontal derivations, suggesting a long time effect of OT on human brain. No significant influence of OT on mood or vigilance tests was apparent; only one item of a memory test revealed a significant impairment of some mnesic performances. These observations provide new electrophysiological arguments supporting a central action of peripheral OT administration in man.

Oxytocin acts as an antidepressant in two animal models of depression

In the behavioral despair test in mice, oxytocin, i.p. injected 60 min before testing, significantly reduced the duration of immobility at doses of 0.250-1.0 mg/Kg; the effect being similar to that of imipramine (7.5-30 mg/Kg i.p.). A more powerful effect was obtained with a 10-day treatment schedule. In the learned helplessness test, oxytocin (0.500 mg/Kg/day i.p. for 8 days) significantly reduced the escape failures and the latency to escape, the effect being even more intense than that of imipramine (20 mg/Kg/day i.p. for 8 days). These results show a new behavioral effect of oxytocin, and further support its role of CNS regulatory peptide.

Oxytocin diminishes heroin tolerance in mice

Tolerance was induced in mice to the antinociceptive effect of heroin by repeated subcutaneous injections of this narcotic analgesic for 3 days. Pretreatment of mice with daily doses of oxytocin (2-200 micrograms/kg body wt.) resulted in an attenuation of heroin tolerance. A single oxytocin injection prior to the first challenge with heroin was as active in attenuating heroin tolerance as daily treatments with the neuropeptide. A single injection of oxytocin prior to the least heroin challenge also attenuated the expression of tolerance. The neuropeptide failed to modify the acute antinociceptive effect of heroin. It is concluded, therefore, that oxytocin interferes with mechanisms involved in the development and expression of tolerance to heroin.

Pro-Leu-GlyNH2 affects dopamine and noradrenaline utilization in rat limbic-forebrain nuclei

The effects of Pro-Leu-GlyNH2 (PLG), administered i.c.v. in doses of 3.5, 35, 350 and 3500 pmol, were studied on the alpha-MPT-induced disappearance of catecholamines in microdissected rat brain nuclei. PLG, dose-dependently, increased dopamine disappearance in the nucleus caudatus and globus pallidus, whereas a decrease in dopamine disappearance was observed in the nucleus dorsomedialis. Noradrenaline disappearance was decreased in the medial septal nucleus, anterior hypothalamic area and lateral amygdala. A tendency towards an increase in noradrenaline disappearance was observed in the nucl. supraopticus. These data show that PLG has a central site of action. The effects of PLG on dopamine disappearance are comparable to those previously found with vasopressin, while the effects of PLG on noradrenaline utilization show a striking similarity with those previously obtained with oxytocin.