Efferent tectal cells of crucian carp: physiology and morphology

Tectal cells of the crucian carp (Carassius ararssius) showing antidromic responses evoked by rhombencephalic electrical stimulation were physiologically studied and subsequently stained with Lucifer Yellow CH. The stained efferent tectal cells were fusiform, horizontal, and multipolar. The main axon of these efferent tectal cells descended along the wall of the deep tegmentum and could be traced to the motor area below the cerebellum. The axons gave off their collaterals in several brain areas: 1) descending collaterals in the torus semicircularis, dorso-lateral tegmental area and mesencephalic reticular formation and 2) an ascending collateral in the area between the hypothalamus and tegmentum. Fifty percent of the efferent cells were unresponsive to visual stimuli, but some of these cells were activated by visual or tactile stimulation in conjunction with rhombencephalic electrical stimulation. On the other hand, most of the visually active cells were On-transient and movement sensitive with habituation and some were bimodal.