D-Amphetamine at low doses suppresses noradrenergic functions.

This study examined the effects of d-amphetamine on the firing rate of hippocampal cells which had been shown to have an inhibitory, noradrenergic input from the nucleus locus coeruleus (LC). d-Amphetamine at low doses of 0.1 mg/kg i.v. or 0.5 mg/kg i.p. increased the firing rates of these cells. With higher doses of d-amphetamine, both increases and decreases in the firing rates of hippocampal cells were observed. These differential effects on the firing rate of hippocampal cells were statistically significant (x2 = 13.32, d.f. = 3, P less than 0.01). The increased firing rate of hippocampal cells produced by the low doses of d-amphetamine was blocked by a prior destruction of the LC indicating that the drug effect was mediated by LC neurons. d-Amphetamine also significantly attenuated the decrement in the firing rates of hippocampal cells produced by LC stimulation (P less than 0.01). These results suggest that low doses of d-amphetamine suppress rather than enhance the actions os norepinephrine.