Time of day influences stress hormone response to ketamine.

Over 50% of depressed patients show hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis. Conventional therapy takes weeks to months to improve symptoms. Ketamine has rapid onset antidepressant effects. Yet its action on HPA axis activity is poorly understood. Here, we measured the corticosterone (CORT) response to ketamine administered at different times of day in the Wistar-Kyoto (WKY) rat. In male rats, blood was collected every 10 min for 28 h using an automated blood sampling system. Ketamine (5/10/25 mg · kg) was infused through a subcutaneous cannula at two time points-during the active and inactive period. CORT levels in blood were measured in response to ketamine using a radioimmunoassay. WKY rats displayed robust circadian secretion of corticosterone and was not overly different to Sprague Dawley rats. Ketamine (all doses) significantly increased CORT response at both infusion times. However, a dose dependent effect and marked increase over baseline was observed when ketamine was administered during the inactive phase. Ketamine has a robust and rapid effect on HPA axis function. The timing of ketamine injection may prove crucial for glucocorticoid-mediated action in depression.

Multiple roles of GluN2D-containing NMDA receptors in short-term potentiation and long-term potentiation in mouse hippocampal slices.

The GluN2 subunits of N-methyl-d-aspartate receptors (NMDARs) are key drivers of synaptic plasticity in the brain, where the particular GluN2 composition endows the NMDAR complex with distinct pharmacological and physiological properties. Compared to GluN2A and GluN2B subunits, far less is known about the role of the GluN2D subunit in synaptic plasticity. In this study, we have used a GluN2C/2D selective competitive antagonist, UBP145, in combination with a GluN2D global knockout (GluN2D KO) mouse line to study the contribution of GluN2D-containing NMDARs to short-term potentiation (STP) and long-term potentiation (LTP) in the CA1 region of mouse hippocampal slices. We made several distinct observations: First, GluN2D KO mice have higher levels of LTP compared to wild-type (WT) mice, an effect that was occluded by blockade of GABA receptor-mediated inhibition or by using a strong LTP induction protocol. Second, UBP145 partially inhibited LTP in WT but not GluN2D KO mice. Third, UBP145 inhibited a component of STP, termed STP2, in WT but not GluN2D KO mice. Taken together, these findings suggest an involvement for GluN2D-containing NMDARs in both STP and LTP in mouse hippocampus.