GABA Receptors in the Medial Preoptic Area Modulate the Onset of Oestradiol-Induced Maternal Behaviour in...

We studied the participation of GABA neurotransmission in the medial preoptic area (mPOA) with respect to the onset of the pup retrieval response and nest building. Pregnant female rats were implanted with bilateral cannulae in the mPOA on day 12 of pregnancy and, on day 16, the females were hysterectomised and ovariectomised and given 200 μg/kg of oestradiol benzoate. Two days later, the females received one of the following intracerebral drug treatments: GABA_B agonist baclofen (200 ng); GABA_B antagonist phaclofen (1 μg); GABA_A antagonist bicuculline (60 ng); or physiological saline. Five minutes after intracerebral infusion, three foster pups were introduced into the females' home cage. The subjects were observed for pup grouping (retrieval) during 15 min, after which the pups were left with the female. During the next 12 h, an observation was made every 1 h to determine whether the pups had been grouped (retrieved) or not. The GABA_B agonist baclofen reduced the proportion of females retrieving pups from 4 to 8 h following pup introduction. By contrast, both the GABA_A antagonist bicuculline and the GABA_B antagonist phaclofen enhanced the proportion of females retrieving pups during the first 3 h of observation. The latency to pup retrieval in subjects treated with the GABA_B agonist baclofen was significantly longer than that in subjects given any of the antagonists. All females built a nest but baclofen reduced nest quality. These data show that activation of GABA_B receptors in the mPOA has an inhibitory effect on basic maternal behaviours, whereas blockade of either the GABA_A or GABA_B receptor facilitates pup retrieval. It is possible that reduced GABAergic tone in the mPOA is a key element in the initiation of maternal behaviours in postparturient rats.