Chronic rTMS induces subsensitivity of post-synaptic 5-HT_1A receptors in rat hypothalamus

Chronic administration of several antidepressants, notably the selective serotonin re-uptake inhibitors (SSRIs) induces sub-sensitivity of post-synaptic 5-HT_1A receptors in the hypothalamus. Chronic repetitive transcranial magnetic stimulation (rTMS) is a form of treatment for depression which is often compared to electroconvulsive shock therapy (ECT). rTMS was applied to rats either on a single occasion (acute) or daily for 8 d (chronic). Twenty-four hours after the last treatment, the rats were injected with saline or 8-OH-DPAT (50 μg/kg). The rats were killed 20 min later and trunk blood taken for measurement of corticosterone and ACTH levels. Chronic rTMS did not affect basal corticosterone or ACTH levels but significantly blunted the responses to 8-OH-DPAT, while acute rTMS had no effect on either basal or 8-OH-DPAT-stimulated responses. In common with several other antidepressant treatments, chronic rTMS reduces the sensitivity of post-synaptic 5-HT _1A receptors in the hypothalamus. This effect may be significant in relation to the therapeutic mechanism of rTMS.