Impact of impaired glucose metabolism on responses to a psychophysical stressor: modulation by ketamine

Effect of ketamine on the physiological responses to combined hypoglycemic and psychophysical stress

There is evidence that hypoglycemic stress can interact with other stressors, and that ketamine can mitigate the impact of these stressors on behavior and physiology. The current study in male Sprague-Dawley rats investigated whether pre-treatment with 0, 10, or 20 mg/kg ketamine could modulate the interaction between hypoglycemia induced by 0 or 300 mg/kg 2-deoxy-D-glucose (2-DG) and the psychophysical stress of forced swimming (FSS; 6 sessions, 10 min/session) on serum concentrations of corticosterone (CORT) and the pro-inflammatory cytokine, tumor necrosis factor (TNF)-α. It was found that 2-DG enhanced the CORT response to an initial session of FSS, and this effect dissipated after multiple sessions. More importantly, animals displayed significantly higher levels of CORT and lower levels of TNF-α in response to a drug-free test swim conducted 1 week after exposure to the combined stressors, and these responses were not observed in rats that were pre-treated with ketamine. Overall, these findings indicate that ketamine has the potential to reduce the negative impact of interacting stressors on the biological reactivity of the hypothalamic-pituitary-adrenal axis and the immune system.

Evidence of hypoglycemic anhedonia and modulation by bupropion in rats

BACKGROUND

Disorders characterized by dysfunction of glucose metabolism are often comorbid with depression. The current study investigated whether a hypoglycemic state caused by 2-deoxy-d-glucose (2-DG) can result in anhedonic behaviors responsive to stimulation of monoamine activity.

METHODS

In experiment 1, male Sprague-Dawley rats were tested for maintenance of intra-oral self-administration (IOSA) of a sweet solution after pre-treatment with 300 or 500 mg/kg 2-DG, a blocker of glucose metabolism. Experiment 2 determined whether exposure to an environment previously paired with the effects of 2-DG (0, 200 or 300 mg/kg) can influence IOSA, and whether 2-DG can modify taste reactivity to same sweet solution. Finally, experiment 3 examined whether 0 or 30 mg/kg bupropion, a monoamine-reuptake blocker, would attenuate the effect of 300 mg/kg 2-DG on IOSA and taste reactivity.

RESULTS

It was found that 2-DG produced a sustained decrease in IOSA when animals were tested drug-free. This decrease in IOSA did not appear linked to place conditioning or to alterations in taste reactivity, and it was partially normalized by pre-treatment with bupropion.

CONCLUSIONS

Taken together, these results in rats suggest that rapid hypoglycemia can induce an anhedonic state characterized by impaired consummatory responses to nutritional incentive stimuli and that can be alleviated by the antidepressant bupropion.