Fluctuations in somatosensory responsiveness and baseline firing rates of neurons in the lateral striatum of freely moving rats: effects of intranigral apomorphine.

Somatosensory responsiveness and baseline firing rates of 102 striatal neurons were studied in freely moving rats. For individual neurons, mean levels of responsiveness and baseline firing fluctuated unpredictably in direction and magnitude and independently of each other throughout an experiment. Following microinjections of apomorphine into the substantia nigra, which were used as a means of reducing nigral output activity, the magnitude of fluctuations in striatal somatosensory responsiveness significantly increased, while the magnitude of fluctuations in baseline firing was unaltered. The receptive zones of 54 neurons studied in control experiments remained stable, whereas receptive zones changed in 12 of 25 neurons studied after apomorphine microinjection. Normal nigrostriatal dopamine transmission appears to selectively restrict the magnitude of fluctuations in responsiveness of striatal neurons to corticostriatal synaptic input and may exert additional control over afferent projections from cutaneous receptive zones to these neurons.