title: "Temporal summation decay" in hypothalamic self-stimulation: threshold changes at long intrapair intervals due to axonal subnormal periods.
abstract: Rats were trained to bar press for trains of conditioning (C) and test (T) pulses delivered via lateral hypothalamic electrodes. As intrapair (C-T) intervals increased from 10 ms to 100 ms, the frequency of pulses required for self-stimulation increased, similar to results of Smith and Coons (1970). This effect was observed only for electrode placements where self-stimulation was obtained at frequencies below 16 Hz and currents of 600 microA and higher. The effect was larger when the train duration was increased from 0.5 s to 2.0 s. The threshold increase was abolished when the T pulses were greater in current than the C pulses but not when C pulses were larger than T pulses. The larger T pulses also removed relative refractory period effects at a C-T interval of 1.0 ms. Therefore, the increase in required current or frequency at long C-T intervals appears to be due to a decline in axonal excitability (i.e., the subnormal period) rather than a decay in synaptic temporal summation. Possible flaws in other reports of paired-pulse "temporal summation decay" at long C-T intervals using 2 electrodes are discussed.
authors.affiliation: Department of Psychology, University of Toronto, Ontario, Canada.
authors.forename: J S
authors.initials: JS
authors.lastname: Yeomans
mesh_terms: D000818:Animals; D001369:Axons / Q000502:physiology*; D001931:Brain Mapping; D004292:Dominance, Cerebral / Q000502:physiology; D004558:Electric Stimulation; D007026:Hypothalamic Area, Lateral / Q000502:physiology*; D008297:Male; D008474:Medial Forebrain Bundle / Q000502:physiology*; D009413:Nerve Fibers, Myelinated / Q000502:physiology; D009474:Neurons / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time / Q000502:physiology*; D012653:Self Stimulation / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology*; D014697:Ventromedial Hypothalamic Nucleus / Q000502:physiology