Tectal responses to potassium loads and subsequent visual stimuli in the toad, Bufo bufo.

Calling male toads were tested behaviourally for their prey catching responses to wormlike stimuli and assigned to groups of non-hungry and hungry depending on their prey catching motivation before being prepared for visual unit, massed unit and slow potential shift (SPS) recording from the optic tectum. Control recordings to visual stimuli were made before recording the effects of application of isotonic solutions containing concentrations of 0-41 mM K(+). Application of solution was followed by presentation of the visual stimulus while the solution still bathed the tectum. The best tectal responses were made to large square visual stimuli in the non-hungry toads, perhaps because recordings were made in the breeding season. Responses of the tectum to solution addition were significant in the concentration range of 7-17 mM K(+). Hungry toads showed an earlier, smaller response than non-hungry (sexually motivated) animals. When the visual stimulus was presented, there were unit and massed unit responses at all bathing solution concentrations, which were larger in non-hungry animals. These experiments revealed that toads motivated to feed respond earlier than non-hungry toads to application of artificial CSF to the tectum, though non-hungry toads responded best to the subsequent visual stimulus.

Neuronal responses are differentially affected by the polarity of tectal DC stimulation in the toad Bufo bufo.

Male toads were tested behaviourally for their prey catching responses to worm-like stimuli before being prepared for visual unit and slow potential shift (SPS) recording from the optic tectum. The neuronal responses of toads to a prey-like visual stimulus reflected their motivational tendency prior to operations. One second of DC stimulation to the tectum was followed by an SPS of reversed polarity during which time a visual prey-like stimulus was presented. A negative SPS following positive DC stimulation was associated with enhanced neuronal responses to a visual stimulus. The positive SPS that followed negative stimulation was associated with a decline in neural responses below background when a visual stimulus was additionally given. The SPS was largely a result of DC stimulation that interacted with the motivational tendency to produce enhanced neuronal responses, while the potential was negative and vice versa.