視床下部神経分泌細胞における放出ホルモンの分泌調節機序に関する研究:I. 神経分泌細胞の電気生理学特性と体液性調節について

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Attempts were made to identify hypothalamic neurosecretory cells which participate in the anterior pituitary control with a special reference to the effects of ovarian hormones. Wave forms of the antidromically activated action potentials in the hypothalamus were investigated in the female rats of Wistar strain. The animals of different endocrinological environments, that is, proestrus and diestrus-I of 4-day cyclers; ovariectomized, ovariectomized and estrogen primed, ovariectomized and progesterone primed, were used. The operational procedures were performed under light urethane anesthesia. Different two types of craniotomy were adopted for the preparation. For recordings from the medial basal hypothalamus, the ventral surface of the brain was exposed by parapharyngeal approach, and a bipolar silver ball electrode for the application of electrical stimuli was placed on the surface of the median eminence (ME). Another method was used for recordings of the medial preoptic area (MPO) and the periventricular area of the MPO and the anterior hypothalamus (PVA). In the latter, the parietal surface of the brain was exposed and a side-by-side bipolar electrode for the stimulation was inserted to the arcuate (ARC) -ME region. All the recordings were performed by using glass pipettes which were filled with 0.5 M sodium acetate solution. The solution was added with pontamine sky blue 6B to allow marking recording sites. Stimulatory pulses of 5 msec duration of variable intensity were generated by an electronic stimulator and applied by the above mentioned bipolar electrodes. The antidromic responses and the intensity of the stimuli were observed and photographed on a synchroscope. The following results were obtained : (1) Antidromic responses were recorded from the ARC to the ME stimulation (n=97). The ME-surface stimulation was also effective in inducing antidromic responses in the PVA and 12 responses were observed by this method. The ARC-ME stimulation resulted in 74 antidromic responses in the MPO, and 106 responses in the PVA. These responses showed constant latency and followed to the high frequency stimulation and indicated that these cells send their axons directly to the stimulated sites. (2) The conduction velocity of the axon was calculated from the latency and the distance between the recording and stimulating sites. The calculated velocities were : about 0.2 m/ sec for the ARC cells; 0.4 m/sec for the MPO cells, and 0.3 m/sec for the PVA cells. (3) Most of the responses in the ARC and PVA showed positive-negative biphasic wave form, with a notch in the positive-going phase of each spike, whereas no notch was seen in the all of responses obtained from the MPO. (4) In the ARC and the PVA high frequency repetition of the stimulation induced fractionation of small A-spike and large B-spike at the notch. A-spike component followed exactly to the stimulation of 100 Hz, but a delay or inhibition of B-spike component was occasionally seen to the repetition higher than 10 Hz. (5) Fractionation of A-, and B-components were seen to be affected by hormonal environments of the animal. In the proestrus, B-spike inhibition was not seen in 5 Hz repetition of the stimulatory pulses, whereas in the diestrus-I, inhibition of B-spike was seen in 2 cases among 10 trials with 0.5 Hz repetition. In the ovariectomized rats, estrogen priming increased responsiveness of B-spike formation to high frequency stimuli. On the other hand, suppression of B-spike formation was seen following progesterone treatment. (6) In order to investigate the possible mechanisms of the fractionation of A- and B-components, the effects of train stimulation of 10-100 Hz in the ARC-ME was investigated. Spontaneous activity of the PVA units were seen to be suppressed by the stimulation, not only the B-spike but also the A-spike. Suppression of B-spike amplitude was observed by applying hippocampal stimulation prior to the ME,
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佐久間康夫
横浜市立大学医学部第2生理学教室

視床下部神経分泌細胞における放出ホルモンの分泌調節機序に関する研究:I. 神経分泌細胞の電気生理学特性と体液性調節について

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