Glucocorticoid effects on serotonergic and noradrenergic facilitation of spinal monosynaptic transmission

The ability of an intensive glucocorticoid regimen (i.e., triamcinolone diacetate, 8 mg/kg i.m./7 days) to modify the lumbar spinal monosynaptic reflex response to serotonergic and noradrenergic agents has been examined in unanesthetized acute spinal (C-1 sectioned) cats. Triamcinolone pretreatment enhances the 2N facilitatory actions of amitriptyline (AMIT), 5 mg/kg i.v., when given after D, L-5-hydroxytryptophan (5-HTP), 50 mg/kg i.v., as compared to untreated control preparations. Subsequent administration of methysergide, a serotonin receptor blocking drug, in a dose of 1 mg/kg i.v. promptly and completely reverses the monosynaptic response increase by AMIT in untreated animals, but not in the glucocorticoid treated ones. In contrast, the monosynaptic facilitation normally produced in untreated preparations by methoxamine (MX), 1 mg/kg i.v., a centrally active noradrenergic agonist, is prevented as a result of triamcinolone dosing. These results demonstrate a glucocorticoid effect on spinal biogenic amine function such that serotonergic monosynaptic reflex activation is enhanced while noradrenergic reflex stimulation is depressed. Furthermore, they suggest that the elevations in plasma cortisol in certain cases of psychiatric depression may contribute to alterations in central biogenic amine synaptic activity.