Spontaneous activity of mediobasal hypothalamic neurons following deafferentations and lesions

In view of the role of extrahypothalamic influences on the hypothalamic regulatory activity, the effects of anterior, anterolateral or posterolateral hypothalamic deafferentations and bilateral medial forebrain bundle (MFB) lesions on the spontaneous single cell activity of neurons in the mediobasal hypothalamus (MBH) were studied in rats under urethane anesthesia. While the deafferentations and particularly the anterior cuts reduced the average rates, MFB lesions increased the rate of firing of MBH neurons, and revealed cyclic activity. These data indicate that normally anterior afferents have mainly a facilitatory, while the MFB projections to the MBH have an inhibitory effect on the spontaneous activity. The possible relation of these alterations to neuroendocrine changes are discussed.