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.

The roles of extrahypothalamic and intrahypothalamic impulses to the medial basal hypothalamus in the control of the pituitary-gonadal-axis.

“…Data of this study are summarized in Table 1 (A, B, C). Table 1 (D) is the data of another experiment (Ishida et al, 1977), which was undertaken to estimate whether each deflection of EVPs was concerned with the direct or pauci-neuronal pathways or the multi-neuronal pathways, based on the et al (1962).…”

“…deflection with 1.5 to 2.5 msec peak-latency of the EVP in response to stimulation of the POA were unaffected by pentobarbital. Therefore, these responses may be mediated through the direct or the pauci-neuronal pathways (discussed in the paper of Ishida et al, 1977). Kawakami and Terasawa (1967) and reported that the amplitude of the hippocampally EVP in the periventricular arcuate nucleus decreased during estrus in the rabbit and that at the same time the amplitude of the amygdaloidly EVP increased.…”

“…The efferent multi-neuronal pathways from the HPC, AMYG and POA, which could be concerned with reflex ovulation except the pathway from the HPC (Ishida et al, 1977), are supposed to be exerted by postcoital changes of pituitarygonadal axis; the HPC-MBH and POA-MBH neuronal system is subjected to negative feedback action and the AMYG-MBH neuronal system subjected to positive feedback action.…”