Crayfish antennal neuropil. II. Periodic bursting elicited by sensory stimulation and extrinsic current in interneurons.

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Abstract
Intracellular recordings were obtained in vivo from interneurons near the antennal neuropil of the crayfish [Procambarus clarkii] brain. Repetitive periodic bursting was elicited by proprioceptive, tactile, and visual stimuli in higher order interneurons. The burst period was 400-700 ms. The burst arose from successively augmenting compound EPSP [excitatory postsynaptic potential]. These EPSP suggested the recruitment of one or several presynaptic neurons during the expression of repetitive bursting. Bursting with a similar period was elicited by extrinsic current. Variations in outward current could produce variations in burst repetition rate over a narrow range. Sensory stimuli produced a modest acceleration of burst repetition rate. The bursting interneurons were recurrently connected to other neurons. These connections were revealed by: delayed bursts of synaptic potentials following brief current pulses to an impaled neuron; cross-correlation of simultaneously monitored cells; and marked nonlinearities in the current-frequency characteristic of these neurons. The periodic activity probably arises from weak intrinsic pacemaker properties in the interneurons, and bursting is reinforced by recurrent connections in the brain.