Differential effect of short- and long-term lithium treatment on m-CPP-induced neuroendocrine changes in rats

Intravenous administration of the serotonergic agent m-chlorophenylpiperazine (m-CPP) to rats produced increases in plasma prolactin and corticosterone and a decrease in plasma growth hormone concentrations. Short-term (2-4 days) and long-term (21-23 days) lithium treatment did not affect baseline levels of prolactin, corticosterone or growth hormone. Long-term lithium treatment accentuated m-CPP's effect on plasma prolactin and corticosterone but not on growth hormone levels. On the other hand, short-term lithium treatment attenuated m-CPP's effect on plasma corticosterone but not on plasma prolactin or growth hormone levels. These findings demonstrate a differential effect of the duration of lithium treatment on m-CPP-induced neuroendocrine changes. One possible explanation for this differential effect may be that different 5-HT receptor subtypes are involved in mediating different neuroendocrine functions and, furthermore, these different 5-HT receptor subtypes may be affected differentially following lithium treatment. Alternatively, lithium-induced changes in other neurotransmitter systems may be responsible for this differential effect.