Nucleus accumbens and preoptic area stimulation: tuberoinfundibular single unit responses, modulation of electrical activity and gonadotrophin secretion.

Single unit activity was recorded from tuberoinfundibular neurones in urethane-anaesthetized pro-oestrous rats. Responses following single shock (0.2 Hz) stimulation of the preoptic area/anterior hypothalamus (PO/AH) or nucleus accumbens (ACB) were recorded and computed for 137 single units. More cells were shown, by antidromic activation, to project to ACB (4 of 77) than to PO/AH (1 of 60). Fewer units were responsive to stimulation of ACB (p less than 0.02), those that were responsive showing a longer latency to the onset of response compared to that following PO/AH stimulation. Significantly (p less than 0.02) more slowly firing cells were found in the group of animals tested with stimulation of PO/AH. Delivery of high frequency stimulation to PO/AH resulted in a 21/2 fold increase in plasma luteinizing hormone (LH) levels (p less than 0.05), whereas ACB-stimulated and control animals showed no increases in plasma LH concentrations. During delivery of the high frequency stimulation only one cell in the ACB group of animals was orthodromically affected (out of five tested). However, in the PO/AH group, five of the seven cells tested showed either excitation or inhibition during stimulation. The possibility that the functional connections demonstrated between ACB and the endocrine hypothalamus are involved in the expression of 'higher' brain functions, recognised during changing endocrine states, is discussed.