Influence of Pseudopregnancy and Sex Hormones on Conditioned Behaviour in Rats

Abstract

Performance of a prelearned conditioned avoidance response (CAR) showed gross deterioration in albino female rats during pregnancy and pseudopregnancy (PSP). To create a PSP-like condition, progesterone and oestradiol were given exogenously, singly and in combination, to different groups of rats. Progesterone alone caused a partial deterioration of behaviour; but when administered in combination with oestradiol, it produced effects on the CAR performance and body weight comparable to those observed in PSP. There was also a good correlation between the behavioural deficits and weight gains resulting from such treatment. Endogenous augmentation of the luteal hormones by prolactin administration in another group produced effects that were comparable to those seen in PSP, although quantitatively poorer. Progesterone, in conjunction with oestrogen, appeared to be responsible for the behavioural deteriorations in the female rats, but was ineffective in the males.

Estrogens and non-reproductive behaviors related to activity and fear

“…Increased acquisition or retention of fear learning, such as in classical conditioning or passive avoidance, is typically considered a positive indicator of fear [63,64]. Two-way active avoidance is an exception, with poorer performance considered a measure of increased fear, and with benzodiazepines improving performance [27,47,65].…”

Expression of FOS, EGR‐1, and ARC in the amygdala and hippocampus of female rats during formation of the intromission mnemonic of pseudopregnancy

“…Pseudopregnancy (PSP) is a neuroendocrine response in which vaginocervical stimulation (VCS) induces a 10-12 day period of daily bicircadian prolactin (PRL) surges. Since the late 1960s, PSP has been understood to involve the establishment of a neural memory or mnemonic for VCS (Everett and Quinn, 1966;Diamond, 1970;Banerjee, 1971;Erskine, 1995). Initiation of PSP requires that estrous females receive a threshold amount of repetitive and intermittent VCS during mating, and the accumulation of VCS over the course of a given mating session suggests that a short-term trace of each stimulus occurs to allow their summation.…”