Inhibitory retinal efferents from dopaminergic cells in the optic lobe of the octopus

The effect of dopamine (DA) and its related compounds upon retinal activities of the octopus was compared with that of repetitive stimulation of the optic nerve, while recording ERGs and light-elicited spike discharges. Retinal perfusion with DA or its agonist, apomorphine, markedly enhanced ERGs. The effect appeared at about 10(-8) M and saturated at 10(-6) M. Norepinephrine and L-DOPA had very little effect. Intraretinal injections of DA at different depths revealed that the site of DA action was in the plexiform layer. ERGs were also enhanced by optic nerve stimulation, which inhibited spike discharges. This inhibitory effect was particularly evident when discharges were weak. Consequently the inhibitory effect of optic nerve stimulation was exerted predominantly to the peripheral areas of the receptive field of a nerve bundle, thus resulting in a considerable reduction in the size of the receptive field. These observations suggest that the spatial resolution of this animal may be improved by the efferent activity.

A circadian locomotor rhythm in the giant land snail, Achatina fulica

A circadian rhythm in the locomotor behavior of the giant land snail, Achatina fulica, was studied by a running wheel method in a 24 hr light-dark cycle (LD 12:12) and also in constant dim light. The locomotor rhythm could be entrained to the LD cycle, and the entrained rhythm was characterized by the bulk of activity in the dark period, the major activity appeared in the first half of the dark period. In constant dim light the locomotor rhythm free-ran with a period of about 24 hr.

Properties of X- and Y-cells in the rabbit retina

Bevelled glass microelectrodes were used to record spike potentials extracellularly from the ganglion cells of the rabbit retina. Good responses were obtained from the isolated retina or eye-cup preparation for at least 12 hr. Using a contrast reversal stimulus, 63.8% (67/105) of the units showed linear spatial summation (X-cells), and 21.0% (22/105) showed nonlinear spatial summation (Y-cells). The X- and Y-cells in the rabbit retina had physiological properties which were similar to those in cat retina. Directionally selective cells (15.2%) were found to respond poorly, if at all, to the contrast reversal stimulus.

Efferent system in the retina of the frog, Rana catesbiana

Single units were recorded through glass microelectrodes placed on the optic disk or on the retina of the opened eye of the frog (Rana catesbiana). Units were classified as A-, B-, and C-fibers according to conduction velocities. By the method of collision between naturally elicited and electrically elicited impulses, many of the B-fibers and some A- and C-fibers, which showed unusual behavior to photic stimulation, were found to be efferent fibers. Retinal effects of the efferent nerves were studied by repetitive stimulation and cooling of the optic nerve. The effects were found to be both inhibitory and excitatory.