Environmental stimuli but not homeostatic challenges produce apparent increases in dopaminergic activity in the striatum: an analysis by in vivo voltammetry.

Using in vivo voltammetry in rats, we examined the relationship between the electrochemical signal measured in the striatum and the behavioral responses associated with various types of stimulation. Three patterns emerged. First, a series of homeostatic challenges, including abrupt decreases in glucose utilization, blood volume, or arterial blood pressure, were ineffective in altering the electrochemical signal despite the sympathoadrenal response produced by each. Second, intense exteroceptive stimuli, such as an electric shock applied to the tail or placing animals in a shallow ice-water bath, provoked large and abrupt rises in the signal which decayed rapidly. Third, rats eating after a 24-h fast, drinking after a period of dehydration, or presented with novel olfactory or visual stimuli, exhibited much smaller and more gradual rises in the electrochemical signal which were more long-lasting. In each case, the magnitude of the change in electrochemical signal was generally related to the level of behavioral activation, being most prominent when treatments produced a startle response. Those large increases in signal were markedly attenuated by pretreatment with alpha-methyl-p-tyrosine or gamma-butyrolactone, drugs known to decrease the release of dopamine, suggesting that the signal observed was associated with an increase in the activity of central dopaminergic neurons.