Monoaminergic neurotransmission contributes to cannabinoid-induced activation of the hypothalamic-pituitary-adrenal axis

Administration of high doses of cannabinoid CB1 receptor agonists activates the hypothalamic-pituitary-adrenal (HPA) axis; however, the mechanism by which this occurs has not been well characterized. Both monoaminergic and glutamatergic neurotransmission are known to activate the HPA axis and cannabinoids have been found to modify levels of these neurotransmitters. Employing pharmacological antagonists to specific serotonergic, noradrenergic and glutamatergic receptor subtypes, we examined whether activation of these receptors is involved in the ability of a high dose of a cannabinoid CB1 receptor agonist to activate the HPA axis. We characterized a robust induction of corticosterone secretion following administration of a 100 µg/kg dose of HU-210, a potent cannabinoid CB1 receptor agonist. Pre-treatment with antagonists to the serotonergic type 1A (5-HT1A; WAY100635; 0.5 mg/kg) and 5-HT2A/2C (ketanserin; 1 mg/kg) receptors significantly attenuated the HU-210-induced increase in corticosterone secretion. Similarly, the increase in corticosterone secretion following HU-210 administration was significantly reduced by pre-treatment with antagonists to the α1-adrenoceptor (prazosin; 1 mg/kg) and β-adrenoceptor (propanolol; 2.5 mg/kg). However, pre-treatment with antagonists to the NMDA (MK-801; 0.1 mg/kg) and AMPA/Kainate (DNQX; 10 mg/kg) receptors did not modify activation of adrenocortical secretion evoked by HU-210. These data suggest that acute administration of exogenous cannabinoid ligands activates the HPA axis indirectly through an increase in serotonergic and noradrenergic neurotransmission.