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.

Visual responses of morphologically identified tectal neurons in the crucian carp.

Tectal neurons of the crucian carp were functionally and morphologically identified by recording their electrical activity and simultaneously injecting dye (Procion yellow). Among intrinsic tectal neurons, visual neurons successfully stained with dye were pyramidal, pyriform and uncategorized neurons. The stained intrinsic tectal neurons were classified into 4 types, according to their visual response properties, i.e. sustained, dimming, transient and other response types. In 23 stained neurons we studied, no correlation was established between response properties and morphology of tectal neurons. In stained pyramidal neurons, the following receptive field (RF) organization could be recognized: (1) on-center, off-surround; off-center, on-surround; both with a small RF; and (2) excitatory or inhibitory center only, with a large RF.