Dissociation of the substrates for medial forebrain bundle self-stimulation and stimulation-escape using a two-electrode stimulation technique.
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Biomedical subjects
C Bielajew
Publications and source records attributed to C Bielajew.
Behavioral methods for inferring anatomical linkage between rewarding brain stimulation sites.
Rats lever pressed for concurrent electrical stimulation of the lateral hypothalamus and ventral tegmentum. The pulse-pair stimulation technique was used, with the first pulse of each pair applied to one electrode and the second to the other electrode; the intrapair interval was varied. The effectiveness of stimulation, measured behaviorally, increased abruptly (within .4 msec) as the intrapair interval was increased in the range from 1.0 to 2.0 msec. These results, which do not resemble single-electrode refractory period results, are interpreted as evidence of collision in the directly stimulated, reward-related neurons linking the two sites. We conclude that self-stimulation of the medial forebrain bundle involves the direct activation of long-axon, longitudinal pathways. Estimates of the conduction velocity in the fibers subserving the collision-like effects are consistent with the properties of small myelinated axons but not central monoaminergic fibers.
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Post-stimulation excitability of mediodorsal thalamic self-stimulation.
The post-stimulation excitability of the substrate for brain stimulation reward in the mediodorsal thalamus was assessed using equal- and unequal-pulse procedures. In 3 rats, refractory periods were found to begin no earlier than 1 ms and to end as late as 10 ms. Using test (T) pulses 1.5 times the amplitude of condition (C) pulses, the contribution of absolute and relative refractory periods was determined in one subject. No change in the slope of the recovery function was obtained in this condition, suggesting that several populations of neurons with different absolute refractory periods compose the behaviorally relevant substrate. A large supernormal contribution, evaluated by increasing the C amplitude to 1.5T, occurred between 3 and 10 ms with a peak at 7.5 ms. These results suggest that mediodorsal thalamic self-stimulation is mediated by a wide range of small, probably unmyelinated fibers.
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