Hypothalamic neuronal activity associated with onset of pseudopregnancy in the rat

The electrical activity of several hypothalamic sites, before and following cervical stimulation, was examined in an attempt to evaluate the central nervous system processes involved in the induction of pseudopregnancy in the rat. Cervical stimulation, resulting in pseudopregnancy, induced a sequence of neuronal changes at: 3.8, 4.4, 11.6, 20.1, 30.8, 44.5, 51.2, 51.7, 62.4, 85.1 and 111.5 min after stimulation in the preoptic area, lateral hypothalamus, ventromedial hypothalamus, preoptic area, suprachiasmatic nucleus, lateral hypothalamus, preoptic area, ventromedial hypothalamus, lateral hypothalamus and anterior hypothalamus, respectively. These results suggest that the preoptic region contains both the facilitatory neuronal mechanism and also an inhibitory system. The latter could tonically inhibit the expression of the nocturnal prolactin surge. We conclude that the sequence of neuronal events observed in various hypothalamic areas is in part responsible for the process which results in pseudopregnancy.