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.