A Golgi analysis of caudate neurons in rats exposed to carbon monoxide.

Interneurons of the caudate nucleus have been reported in the literature to respond to deafferentation by reduction in dendritic spines. In the studies reported here, caudate interneurons have been examined using the Golgi technique and increased numbers of spines were found in adult rats exposed to carbon monoxide as neonates. The development of spines on the caudate neurons was delayed for several days after an acute anoxic episode in 5-day-old rats exposed to carbon monoxide to the point of respiratory arrest. By the time the rats were 6 weeks old the caudate neurons had recovered to the point where they had essentially normal numbers of spines. At later ages (2- and 7-months old) the number of spines was greater in rats exposed perinatally to carbon monoxide than in control rats of the same age. The development of abnormal numbers of spines coincided with the time of recovery of rats from behavioral hyperactivity induced by carbon monoxide. The increased spines on the caudate neurons of the adult rats (7-months old) can be explained as a compensatory response to increased afferent flow to the caudate during the period of juvenile hyperactivity which reaches a peak at 6 weeks of age. It is proposed that the return to normal activity in the adult may be a consequence of increased activity of the caudate nucleus.