Postnatal development of mesoaccumbens dopamine neurons in the rat: electrophysiological studies

The postnatal development of antidromically identified mesoaccumbens dopamine (MADA) neurons were examined with single-unit electrophysiological techniques. Rats were anesthetized with chloral hydrate. The physiological characteristics of 1-, 2-, 4- and 5-week-old rat pups were compared to adults (7-9-weeks-old). The basal discharge rate, conduction velocity, antidromic latency and discharge patterns of MADA neurons were not significantly different among the 4- and 5-week-old and adult MADA neurons. MADA neurons from 1- and 2-week-old pups, however, had significantly lower mean basal discharge rates and significantly lower mean conduction velocities than MADA neurons from the older animals (i.e., 4-weeks old, 5-weeks old and adults). 1- and 2-week-old MADA neurons were also found to have significantly longer mean antidromic latencies than MADA neurons from older animals. Significantly fewer 1- and 2-week-old MADA neurons were found to discharge in a bursting pattern when compared to MADA neurons from older animals. These results indicate that during early postnatal development MADA neurons are spontaneously active, but still physiologically immature. The results of the present study are discussed in the context of previous developmental electrophysiological studies of nigrostriatal dopamine neurons.