Journal of Neurophysiology, Vol 44, Issue 5 1002-1011, Copyright © 1980 by APS
Cells of origin of medullary projections in central gray of rat mesencephalon
Y. Sakuma and D. W. Pfaff
1. Seventy-four neurons in the central gray of the mesencephalon were
antidromically activated by electrical stimulation of the gigantocellular
and magnocellular nuclei region of the ipsilateral medullary reticular
formation in urethan-anesthetized female rats. An additional eight cells
were located contralaterally. With control of the lordosis reflex
(facilitated from central gray) in mind, each cell was characterized by the
properties of its antidromic response and by its response to pressure
stimulation of the hindquarters of the hindquarters of the animal. 2. The
antidromically activated spikes had constant latencies between 1.0 and 25.5
ms, with a mean of 10.7 +/- 0.7 ms. 3. Cells of origin of the descending
projections were located in all parts of the central gray and adjacent
mesencephalic reticular field except within the inner ring of the central
gray that surrounds the cerebral aqueduct. A particularly dense group of
cells was noted in the ventrolateral aspect of the central gray. Fewer were
found in the dorsal central gray over the cerebral aqueduct. 4. These cells
had very low rates of spontaneous discharge or none at all. No specific
changes in activity could be elicited by lordosis-relevant somatosensory
stimuli. Therefore, these cells appear not to be involved in stimulus-bound
reflexive control of lordosis behavior. Instead, they may be engaged in
mediating influences descending from hypothalamus, known to control
lordosis (see Ref. 48). In turn, they could modulate activity in reflex
arcs completed at lower levels of the neuraxis.
