SEGREGATION OF BEHAVIOR-SPECIFIC SYNAPTIC INPUTS TO A VERTEBRATE NEURONAL OSCILLATOR

Although essential for understanding the mechanisms underlying sensori motor integration and motor control of behaviors, very little is known about the degree to which different behaviors share neural elements o f the sensorimotor command chain by which they are controlled. Here, w e provide, to our knowledge, the first direct physiological evidence t hat various modulatory premotor inputs to a vertebrate central pattern generator, the pacemaker nucleus in gymnotiform electric fish, carryi ng distinctly different behavioral information, can remain segregated from their various sites of origin in the diencephalon to the synaptic termination sites on different target neurons in the medullary pacema ker nucleus. During pharmacological activation of each of the premotor inputs originating from the three prepacemaker nuclei so far identifi ed, we determined in vivo the changes in input resistance in the neuro nal elements of the pacemaker nucleus, i.e., relay cells and pacemaker cells. We found that each input yields significantly different effect s on these cells; the inputs from the two diencephalic prepacemaker nu clei, PPnC and PPnG, which resulted in increased oscillator activity, caused significantly lower input resistances in relay and pacemaker ce lls, respectively, exhibiting drastically different time courses. The input from the sublemniscal prepacemaker nucleus, which resulted in re duced oscillator activity, however, caused a significant increase in i nput resistance only in relay cells. Considering that the sensory path ways processing stimuli yielding these behaviors are separated as well , this study indicates that sensorimotor control of different behavior s can occur in strictly segregated channels from the sensory input of the brain all through to the synaptic input level of the final premoto r command nucleus.