The Protective Effects of Crocin on Input-Output Functions and Long-term Potentiation of Hippocampal CA1 Area in Rats Exposed to Chronic Social Isolated Stress

INTRODUCTION: The lack of social communication is associated with the primary risk of proper brain functions. It is reported that crocin helps relieve this problem. The present study examined the protective effect of two doses of crocin on Long-term potentiation (LTP) of hippocampal cornu ammonis 1 (CA1) area as a cellular mechanism in rats exposed to chronic social isolated stress. METHODS: Rats were assigned to the control, sham, isolation stress, and two stress groups (receiving 30 and 60 mg/kg crocin). Chronic isolation stress (CIS) was induced 6 h/d, and crocin was administrated for 21 days. The field excitatory postsynaptic potential (fEPSP) slope and amplitude were measured by input/output functions and LTP induction in the CA1 area of the hippocampus. Also, the corticosterone and glucose levels were assayed in the hippocampus and frontal cortex. RESULTS: The slope and amplitude of fEPSP severity were impaired in both input/output and LTP responses in the CIS group. Crocin at a dose of 30 and particularly 60 mg/kg improved input/output and LTP responses in the CIS group. Also, the corticosterone levels significantly increased in the frontal cortex and especially the hippocampus. In contrast, only a high dose of crocin decreased hippocampal corticosterone levels in the CIS condition. Finally, the glucose levels did not change in the hippocampus and frontal cortex in all experimental groups. CONCLUSION: The chronic isolation stress impaired neural excitability and Long-term plasticity in the CA1 area due to elevated corticosterone in the hippocampus and probably the frontal cortex. The low and high doses of crocin improved excitability and Long-term plasticity in the chronic isolation stress group by only decreasing corticosterone levels in the hippocampus, but not the frontal cortex. HIGHLIGHTS: Neuronal excitability and long-term plasticity of CA1 were impaired by chronic isolation stress. The memory was protected by low and particularly high doses of crocin in the chronic isolation stress condition. Crocin decreased the corticosterone levels in hippocampus, but not frontal cortex. PLAIN LANGUAGE SUMMARY: The lack of social communication (isolation stress) is associated with the primary risk of brain functions. On the other hand, crocin as one of effective components of saffron is helpful for improvement of memory. Therefore, the protective effect of two doses of crocin on cellular mechanism of memory in rats exposed to chronic social isolated stress was investigated in present study. Chronic isolation stress (CIS) was induced 6h/day, and crocin was administrated for a period of 21 days at two doses of 30 and 60 mg/kg. The electrophysiological and cellular mechanism of memory in the CA1 area of the hippocampus were investigated. Also, the corticosterone and glucose levels were assayed in the hippocampus and frontal cortex. It was concluded that the chronic isolation stress impaired neural excitability and long-term plasticity in the CA1 area due to elevated corticosterone in the hippocampus and probably the frontal cortex. The low and high doses of crocin improved excitability and long-term plasticity in the chronic isolation stress group by only decreasing corticosterone levels in the hippocampus, but not the frontal cortex. Also, the corticosterone levels significantly increased in the frontal cortex and especially the hippocampus. Also, the glucose levels did not change in the hippocampus and frontal cortex in all experimental groups.