The effect of chronic unpredictable stress on locomotor and exploratory activity in male rats with different endogenous prolactin levels

Abstract

The probable role of prolactin (PRL) on the behavioral responses evoked by chronic unpredictable stress (CUS) was studied in adult male rats. Three experiments were performed examining the effect of CUS on behavioral performance in: (i) intact rats with normal endogenous PRL levels, (ii) rats with high endogenous PRL levels, and (iii) rats with low endogenous PRL levels. Behavioral parameters studied were: locomotion, head-dipping, rearing and grooming. Endocrine parameters studied were: PRL and corticosterone (C) plasma concentrations. In Experiment (i) results showed that CUS inhibited significantly locomotion, head-dipping and rearing activity. No variations in PRL plasma levels were found but a significant increase in C was detected. In Experiment (ii) the hyperprolactinaemia induced by pituitary transplants in the kidney capsule blocked partially the inhibition of locomotion due to CUS. No modifications on head-dipping, rearing and grooming were observed. PRL levels in these rats were consistently high as expected and CUS regimen did not change the hormone concentrations in blood. The C response due to CUS, however was completely blocked in the pituitary-implanted group. In Experiment (iii), repeated treatment with bromocriptine (5 mg/kg i.p.) significantly increased the inhibitory effect of CUS on locomotion, head-dipping and rearing. Grooming was also decreased in CUS-treated rats. PRL levels in these animals was low as expected and the C response due to CUS was significantly increased. Results give support to the concept that PRL may have a regulatory role in CUS.

Behavioural actions of prolactin locally applied into the hippocampus of adult female rats

“…Under strong stressful conditions, PRL increases locomotor activity and present results are in agreement with that found by Drago etal. (1982) and Fracchia et al (1992), who found in different experimental models an augmented motor activity associated with high endogenous PRL levels. The present data tell virtually nothing about the mechanisms of action of PRL in the HPC cells.…”

Influence of the estrous cycle on some non reproductive behaviors and on brain mechanisms in the female rat

“…The falling P4 levels, rather than the absolute concentration of the steroid, can lead to significant changes in the excitability of GABA-containing circuits (see Lovick, 2006). PRL is another putative hormone that may cause the lower scores of anxiety observed at P, since a peak of PRL is observed at this stage (Furudate et al, 1989) and the anti-stress properties of PRL have been well documented (see Fracchia et al, 1992;Torner et al, 2001;Torner, Toschi, Neva, Clapp, & Neumann, 2002;Donner & Handa, 2009).…”