On the blood-brain barrier to peptides: effects of immobilization stress on regional blood supply and accumulation of labelled peptides in the rat brain.

Tritiated arginine-vasopressin (AVP), desglycinamide-vasopressin (DGAVP), chicken gonadotropin releasing hormone (GnRH) or carbetocin were injected intracarotidally into rats exposed to a restraint stress for 60 min. The peptide accumulations were determined in 9-13 brain regions and anterior pituitary. In separate experiments the cerebral blood flow was measured. The blood supply to the brain was decreased in stressed animals as indicated by: 1. significant decrease (17-50%) of cerebral blood flow; 2. diminished accumulation of tritiated AVP in the regions lacking a blood-brain barrier (BBB). Consequently, the values of peptide accumulation were corrected for the changed blood supply. Compared with control animals, restraint stress induced a higher accumulation of AVP (+41%), DGAVP (+60%), carbetocin (+81%) and GnRH (+104%).

The effect of AVP and DGAVP on the exploratory activity of rats.

The effects of [8-L-arginine] vasopressin (AVP) and desglycinamide [8-L-arginine] vasopressin (DGAVP) were tested on the exploratory activity of adult male rats in a novel environment. The inherited individual differences in the non-specific excitability level of the animals were ascertained prior to the drug administration and the rats were then distributed evenly into the experimental groups. One half of each groups contained the less excitable and the other the more excitable animals. The peptides or saline were injected every other day--altogether 4 times--in a dose of 5 micrograms/kg/ml subcutaneously, 40 min before starting the experiments. The exploratory activity in the novel environment was observed for 15 min. AVP and DGAVP, which differ in their peripheral endocrine activities, had opposite effects on the behavior in a novel environment: AVP, with its wide spectrum of peripheral effects, decreased the exploratory activity, whereas DGAVP, with minimal peripheral effects, increased the exploratory activity slightly. This basic response to the administration of peptides was influenced by the type of inherent non-specific excitability level. The depressive action of AVP was more pronounced in the more excitable rats, whereas DGAVP significantly stimulated the less excitable animals. It is concluded that the inhibitory effect of AVP is mainly due to its peripheral endocrine, especially hemodynamic, effects, whereas DGAVP is supposed to increase arousal, which is responsible for differences in the animals' performance with regard to their inherited non-specific excitability levels.

Sexual interaction in adult laboratory rats: importance of female's stimuli and of male's experience.

Precopulatory behaviour of adult male rats towards the passively receptive and towards the ovariectomized females was observed in dyadic interaction, first, at the time when the males were sexually inexperienced and later on after they had gained small and uniform copulatory experience (with a darting female). It was found that precopulatory activity of the sexually inexperienced males towards the ovariectomized female was "higher and richer" than that of males exposed to the passively receptive female. When the males were sexually experienced the frequency of precopulatory behavior increased and the patterns changed only in the animals exposed to the passively receptive female. Precopulatory activity of males weakened during the interaction under all experimental conditions. It is remarkable, however, that the weakening of precopulatory activity of sexually inexperienced males exposed to the ovariectomized female was reinforced again after the female temporarily exhibited behaviour typical of the male. We concluded that both the quality of the female's precopulatory behaviour and the quantity of previous male's experience are the decisive factors in successful interaction.

Sexual behaviour of juvenile male rats injected with lisuride.

Lisuride was reported as drug stimulating sexual behaviour in the adult male rats. It was stated that lisuride is effective through central serotonergic and dopaminergic systems. The present study deals with the effects of lisuride on the sexual behaviour of juvenile Wistar male rats, 43 days old. The animals were injected i.p. with lisuride /0.4 mg/kg/ or saline 40 min prior to testing. When the males were put into a box with the floor prescented by an oestrous female, the males treated with lisuride devoted significantly more time to the sniffing of the scent traces. After a darting female was placed into the box, some of the lisuride injected males initiated copulatory behaviour, even without previous precopulatory behaviour towards her. In noncopulating males treated with lisuride the frequency of precopulatory activities was comparable with those seen in the controls, but the predominance of precopulatory touching the flanks over anogenital exploration was suggested. The results are related to those acquired in the adult animals.