A method for averaging response latency patterns of antidromically excited neurons.

Electrical stimulation of the axon evokes an action potential which travels antidromically (backwards) up the cell body, where it can be recorded with a microelectrode. Since the antidromic invasion implies no synaptic transmission between the stimulation and recording sites, its recording is frequently used in neurophysiology to identify axonal projections of different neurons (e.g., 4,5). The extracellular recording of antidromic invasion of the cell body can provide, besides anatomical information , data about synaptic inputs impinging on the neuron. Examining respiratory neurons, Merrill (5) demonstrated that the temporal pattern of their antidromic invasion latencies correlates with the polarization of the soma. When the axon was stimulated with a constant frequency, the antidromic latency (AL) measured to the somato-dendritic (SD) spike varied regularly with respiratory cycle (to 0.5 ms) and was found shorter during the period of synaptic excitation of the neuron. Merrill's recording technique was based on a dot display of antidromic responses. The technique of direct recording of AL variations has been also used for estimation of the excitability changes in other neurons, namely preganglionic sympathetic neurons (3) or spinal motoneurons (2). In this