Chronic administration of desipramine or nialamide decreases wet-dog shakes in rats produced by the TRH-analog MK-771

Repeated treatment with amitriptyline or electroconvulsive shock does not affect thyrotropin releasing hormone receptors in discrete rat brain structures

We studied the effect of repeated treatment with amitriptyline (10 mg/kg, p.o., twice daily for 14 days) or electroconvulsive shock (ECS) (once daily for 10 days) on the thyrotropin-releasing hormone (TRH) content and TRH receptors in the cerebral cortex, nucleus accumbens, striatum and septum of the rat. Repeated amitriptyline did not significantly affect the density or affinity of TRH receptors in the examined structures, but caused a marked increase in the TRH content in the striatum and nucleus accumbens. Long-term treatment with ECS reduced the density and affinity of TRH receptors in the septum only, but it increased the TRH concentration in the cerebral cortex and striatum. These results, together with the literature data, indicate that there is no simple relationship between the brain content (and release) of TRH and the functional sensitivity of TRH receptors on one hand, and the density of these receptors on the other.

The effect of repeated administration of antidepressant drugs on the thyrotropin-releasing hormone (TRH) content of rat brain structures

The present study investigated the effect of repeated treatment with the antidepressant drugs imipramine, amitryptyline, citalopram and mianserin (10 mg/kg PO, twice daily for 14 days) on levels of thyrotropin-releasing hormone (TRH) in several brain structures (cerebral cortex, amygdala + pyriform cortex, hippocampus, nucleus accumbens, striatum and hypothalamus) of the rat. Amitriptyline caused a marked increase in the TRH content in the striatum and nucleus accumbens. Citalopram and mianserin produced a smaller but significant increase in the TRH content in the striatum only, while imipramine did not significantly affect the TRH concentrations in any of the brain structures. None of the antidepressant drugs administered acutely significantly affected the TRH concentrations in the nucleus accumbens or the striatum. These results indicate that changes in brain TRH induced by antidepressant drugs are not related to their therapeutic activity.

The effect of repeated treatment with antidepressant drugs on the thyrotropin-releasing hormone (TRH)-induced hyperthermia in mice

The effect of acute (single dose) or repeated (twice daily, for 14 days) administration of 10 mg kg-1 p.o. of imipramine, amitriptyline, citalopram or mianserin has been examined on the hyperthermia induced by thyrotropin-releasing hormone (TRH) (40 mg kg-1 i.p., 2, or 2 and 72 h after single or last dose of antidepressants, respectively) in mice. Both imipramine and amitriptyline, given repeatedly, potentiated the TRH response, though the effect was observed 2 but not 72 h after the last dose of those drugs. Potentiation was also found after the single dose of imipramine or amitriptyline. On the other hand, citalopram and mianserin, administered either acutely or repeatedly, did not affect the TRH-induced hyperthermia.

Central muscarinic cholinergic antagonists block wet-dog shakes produced by the TRH analog MK-771 in the rat

Thyrotropin-releasing hormone (TRH) is known to elicit wet-dog shakes in rats through a central mechanism of action. In the present study, the ability of muscarinic cholinergic antagonists to inhibit TRH-mediated wet-dog shakes was examined. The longer-acting TRH analog, MK-771, at doses of 1.0, 1.5 and 3.0 mg/kg elicited wet-dog shakes in a dose-dependent manner. The centrally-acting muscarinic cholinergic antagonists, atropine and scopolamine, at doses of 5 and 0.8 mg/kg, respectively, significantly reduced the ability of only the highest dose of MK-771 to elicit wet-dog shakes. When the peripherally-acting antagonists, methylscopolamine and methylatropine, were examined, they were not found to significantly reduce wet-dog shakes produced by MK-771 at doses of 5 and 0.8 mg/kg, respectively. The results of this study suggest that cholinergic antagonists inhibit MK-771-induced wet-dog shakes in a noncompetitive manner and support the view that TRH-mediated wet-dog shakes are modulated by central muscarinic cholinergic systems.