Uses of double-pulse stimulation behaviorally to infer refractoriness, summation, convergence, and transmitter characteristics of hypothalamic reward systems

Conducted 5 experiments with 13 male Sprague-Dawley rats. To self-administer strains of pulse pairs, Ss with electrodes in the hypothalamic reward system would press a lever at lower current thresholds or faster latencies, the shorter the intrapair interval--unless the interval was so short that each 2nd pulse fell within the refractory period following the first. By delivering all 2nd pulses to the contralateral reward system, not only was this refractory period limitation on temporal summation circumvented but spatial summation of the 2 reward systems was demonstrated. Evidently, they converge somewhere upon common neurons. Nearby nonreward structures did not share in this convergence. Assuming that the temporal-summation decline at longer intrapair intervals reflected the course of transmitter disposal at the synapse, imipramine and diisopropylfluorophosphate were peripherally administered. These drugs, which retard disposal in adrenergic and cholinergic synapses, respectively, indeed prolonged temporal summation, thus supporting the assumption and implying that adrenergic and cholinergic mechanisms both mediate self-stimulation. (11/2 p ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved).