視床下部と飲水行動—飲水と体液制御に対する視床下部神経機構の基礎的研究

Hypothalamus and drinking behaviour—Study of body fluid control in the hypothalamus.

はじめに

　飲水行動は体液の恒常性を維持していくうえで，不可欠な行動である。この行動は，血漿浸透圧および循環血液量などの変動を検知し体内の水分平衡を保つ目的で誘起される一次飲水と，学習や習慣によって起こされる二次飲水とに分けられる。飲水行動は行動の発現から停止まで多くの分野にわたるが，視床下部には，この行動を誘起する受容器があり，統合中枢として働いていると考えられている。本稿では，主に一次飲水とそれによる体液の調節機構を，視床下部による中枢性調節という観点から概説したい。

Drinking is essential behaviour to keep homeo-stasis of body fluid. This drinking behaviour may be called a homeostatic (or primary) drinking, which is triggered by body fluid imbalances. For example, it can be initiated by increase of plasma osmolarity and decrease of blood volume. The hypothalamus has been considered to be receptive and integrative sites for initiation of the behaviour.

The osmoreceptors to detect changes of the plasma osmolarity are distributed in the central and peripheral nervous system. Especially within the hypothalamus, a lot of osmosensitive sites have been observed so far, which exist in the lateral and medial preoptic area, zona incerta, anteroventral third ventricle region (AV3V) and so on. More-over, electrical stimulation and lesion in these sites caused increase or decrease of drinking. Thus, "the thirst center" could be widespread within and near the hypothalamus.