Mapping of evoked responses from different areas of hypothalamus on stimulation of spermatic nerve in monkeys.

Stainless steel pedestal was implanted on the skull of 12 adult anesthetized rhesus monkeys, according to the predetermined stereotaxic coordinates of hypothalamus. For recording, conscious monkey was made to sit on its chair in a shielded cage to minimize interfering artifacts. Spermatic nerves were stimulated with concentric needle electrodes inserted into undissected portion of the spermatic cord and evoked responses were recorded from a number of hypothalamic areas. Responses with initial negative and positive phases appeared in the anteromedial and posterior hypothalamic regions respectively. The middle medial portions of hypothalamus showed non-conductive local activity, while the lateral regions at the same anteroposterior co-ordinates gave responses, which showed a positive negative response more on a pattern of primary sensory motor cortex. The results indicate smaller latency zones in medial part and longer latency in anterior and posterior parts, and suggest that hypothalamic excitation occurs via periventricular fiber system.

Neuroendocrine correlates of testosterone-induced changes in brain evoked responses to afferent input.

Evoked responses (ER) to stimulation of spermatic nerve were picked up in conscious monkeys from hypothalamic limbic and cerebral cortical regions. The effect of intravenous injection of testosterone propionate (TPss; 0.4 mg/kg) on ER was examined in the same animal. Hormone administration caused inhibition or potentiation of ER in different regions of brain. The duration of hormone effect also suggested area specificity. A significant, immediate reduction in ER amplitude was produced by hormone injection in the ventromedial nucleus. On the contrary an increase of ER was observed in the anterior hypothalamus and in several limbic areas. Genital sensory motor cortex showed slight potentiation. The results support the hypothesis proposed in earlier EEG studies that TP and genital afferent input probably play a selective role in brain mechanisms underlying organized and integrated expression of reproductive functions.

Effect of glucose on the activity of feeding centres before and after parasagittal cuts between medial and lateral hypothalamus.

Intracarotid administration of isotonic glucose (0.5 ml of 5.4%) in the starving albino rats produced an increase in the multiunit activity (MUA) of ventromedial hypothalamus (satiety centre) and a decrease in the MUA of the lateral hypothalamic area (feeding centre). Intracarotid infusion of normal saline did not change the MUA of any of these centres. Parasagittal knife cuts placed in between the satiety and feeding centres did not affect the responsiveness of these centres to glucose administration as indicated by the recorded multiunit activity.