Changes in electrical activity of the brain were studied in 34 Wistar female mature rats (including 3 rats with retrochiasmatic section), following electrical stimulation of the uterine cervix on the day of estrus to induce pseudopregnancy. The macro-micro electrodes were chronically implanted into the various areas of the brain and the multiple unit activity (MUA) was recorded with no behavioral restraint. The results are summarized as follows: For several hours after the cervical stimulation (CS), the MUA in the arcuate nucleus (ARC) decreased, whereas that in the anterior hypothalamic area (AHA) and dorsomedial hypothalamic nucleus (DMH) increased. In contrast, from the 1st day until at least the 4th day, the MUA in the ARC increased, except in the frontal section 6.6 of Albe-Fessard’s atlas, while the MUA in the AHA and medial preoptic area (MPO) decreased. The MUA in the ventromedial hypothalamic nucleus (VMH) decreased immediately following or at least 2 days after the CS. From the 4th day of pseudopregnancy, the DMH, AHA, and hippocampus (HPC) showed a decrease in their MUA. CS failed to establish pseudopregnancy in rats with retrochiasmatic section. In such rats, the MUA in the ARC and AMYG showed almost no change, except for a slight and transient decrease immediately after the stimulation. The bursts of MUA characteristic of cyclic rats were not observed in the pseudo-pregnant rats; when the CS failed to induce pseudopregnancy, the characteristic bursts of MUA were suppressed for about 4 days. Afferent impulses caused by the CS may be conducted to the hypothalamic areas through anterior rather than posterior connections. The MUA changes observed for 3 or 4 days after stimulation seem to represent the brain activity that participates in the establishment of pseudopregnancy. Hormones related to the maintenance of pseudopregnancy, such as prolactin, progesterone, estrogen, and others, may cause the MUA changes on the 4th day of pseudopregnancy and, thereafter, by their feedback action.

Keywords:
Pseudopregnancy, Multiple unit activity, Cervical stimulation, Hypothalamus, Extrahypothalamus
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© 1972 S. Karger AG, Basel
1972
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