Effects of chronic delta-opioid receptor agonist on the excitability of hippocampal glutamate and brainstem monoamine neurons, anxiety, locomotion, and habituation in rats

BackgroundShort-term treatment with non-peptide agonists of delta-opioid receptors, such as agonist SNC80, induced behavioral effects in rodents, which could be modulated via changes in central neurotransmission. The present experiments aimed at testing the hypothesis that chronic treatment with SNC80 induces anxiolytic effects associated with changes in hippocampal glutamate and brainstem monoamine pathways.MethodsAdult male Wistar rats were used in experiments. Rats were treated with SNC80 (3 mg/kg/day) for fourteen days. Neuronal excitability was assessed using extracellular in vivo single-unit electrophysiology. The behavioral parameters were examined using the elevated plus maze and open field tests.ResultsChronic SNC80 treatment increased the excitability of hippocampal glutamate and ventral tegmental area dopamine neurons and had no effect on the firing activity of dorsal raphe nucleus serotonin cells. Chronic SNC80 treatment induced anxiolytic effects, which were, however, confounded by increased locomotor activity clearly confirmed in an open field test. The ability to cope with stressful situations and habituation processes in a novel environment was not influenced by chronic treatment with SNC80.ConclusionOur study suggests that the psychoactive effects of SNC80 might be explained by its ability to stimulate hippocampal glutamate and mesolimbic dopamine transmission.

Automated summary

Chronic treatment with the non-peptide agonist SNC80 increases excitability of hippocampal glutamate and ventral tegmental area dopamine neurons, leading to anxiolytic effects. However, it does not affect the ability to cope with stress or habituation processes in a novel environment.