Effects of Ovulation-Blocking Agents upon the Limbichypothalamic Neuronal Pathways in the Rabbit Brain

Abstract

Female adult rabbits with coaxial bipolar electrodes chronically implanted in the brain were used. Evoked potentials (EVPs) were recorded in the medial basal hypothalamus (MBH) including the median eminence and the arcuate nucleus in response to stimulation of the dorsal hippocampus, medial amygdala and preoptic area. In the present experiment, the influence of ovulation-blocking drugs (pentobarbital, atropine and chlorpromazine) upon those EVPs was investigated.
Since short-latency responses (less than 4.5 msec), which were not consistently observed in those EVPs, were resistent to pentobarbital, they may be considered to be involved in the direct or pauci-neuronal pathways. These pathways were also not depressed in the excitability by atropine and chlorpromazine.
The efferent multi-neuronal pathways from the hippocampus to the MBH were influenced in different ways by pentobarbital, atropine and chlorpromazine, but the efferent multi-neuronal pathways from the amygdala to the MBH were depressed in the excitability by them. On the other hand, the EVPs elicited by preoptic stimulation was hardly affected by those drugs. These findings may suggest that the excitability of the neuronal pathways from the preoptic area to the MBH may be maintained against those agents.
In other words, pentobarbital, atropine and chlorpromazine differ in the manner of action upon the neural mechanism, in spite of their inhibitory effect upon ovulation.
The peak-latency of EVPs was scarcely influenced by those ovulation-blocking agents.
Finally, it is discussed that the multi-neuronal pathways could be concerned with the neural mechanism of copulatory ovulation and that the direct or pauci-neuronal pathways concerned with the electrically stimulated ovulation.