Postnatal functional development of the dorsal and posteroventral cochlear nuclei of the cat

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Abstract
The postnatal development of firing patterns and response areas was determined for single neurons in the dorsal (DCN) and posteroventral (PVCN) cochlear nuclei of the kitten. Extracellular, single-unit responses to pure-tone stimulation were recorded in ketamine and sodium pentobarbital anesthetized kittens between the ages of 5 and 52 days. Within the first 2 wk of postnatal life threshold is high, first-spike latency is long, and maximal discharge rate is low as compared to older kittens and adult cats. Prior to the end of the 2nd postnatal week the tone-evoked temporal discharge patterns that characterize neurons of the DCN and PVCN in the adult cat are routinely recorded. These patterns, which appear within the first 50 ms of tonal stimulation, include the so-called primarylike, chopper, pauser, buildup, and onset types and their variants. In animals younger than .apprx. 10-12 days of age, the driven activity that occurs later than .apprx. 50 ms after stimulus onset often is not sustained, but breaks up during the stimulus into bursts that are separated by intervals of .apprx. 100-150 ms. Within the first 2 wk of postnatal life, many of the response-area properties of DCN and PVCN neurons are similar to those recorded in adult cats. The excitation and inhibition found within the so-called type II/III, type IV, and type V response areas of the adult occur in this early postnatal period. Apparently many of the cellular mechanisms that underlie the temporal firing patterns and the organization of the response areas of DCN and PVCN neurons are active in the growing, differentiating cochlear nuclei and the emergence of these mechanisms does not depend on afferent activity generated in the cochlea and auditory nerve by the animal''s acoustic environment. If temporal firing patterns and response-area profile remain relatively constant over the life span of the animal, then so must the spatial antitemporal relationships of the inputs that produce and maintain them as these neurons, and the circuits, of which they are a part, grow in size and complexity.