Electrophysiological evidence for central nervous connections of the pigeon's pineal gland.

In the pigeon, Columba livia, single unit electrical activity was recorded from 110 cells in the pineal gland. All the cells were classified according to their responses to single shock stimulation of the habenular nuclei and, of these units, 42 cells were subsequently classified according to their response following stimulation of the optic chiasma. Cells were either activated, inhibited or unaffected by the stimulus. No antidromic responses to the stimulation of either site were observed. Habenula stimulation orthodromically induced both excitatory (50% of the cells) and inhibitory (15%) responses. Approximately half the cells tested were unresponsive to stimulation of the optic chiasma, the responding units all being orthodromically excited. No evidence was found for a relationship between the pattern of response to stimulation at the two sites. The results confirm the presence of a central innervation of the pineal in pigeons but suggest that the two pathways are unlikely to converge and the majority of pineal cells do not receive inputs from both of the routes.