Effect of Intrahippocampal γ Aminobutyrate B Receptor on Pain Sensitivity during Estrous Cycle

Problem statement: There is a relationship between sexual hormones and pain sensitivity and also a role for hippocampal GABA_B receptor in nociception. Therefore, the aim of the present investigation was to evaluate the effect of intrahippocampal injection of GABA_B receptor agonist (baclofen) and GABA_B receptor antagonist (CGP35348) on pain sensitivity during the estrous cycle. Approach: Forty eight adult female rats were used. The animals were divided into four groups: (1) Control; (2) Sham; (3) Baclofen 4.25 or 8.54 μg rat^-1; (4) CGP35348 alone with doses 3 or 5 μg rat^-1 and (5) CGP35348 3 or 5 μg rat^-1 after 0.75 μL of baclofen 8.54 μg rat^-1. Data were analyzed by two ways ANOVA measuring. The level of significance was p<0.05. Results: Our data showed that baclofen significantly decreased pain sensitivity in all stages of the estrous cycle, but this analgesic effect was higher during estrus. CGP35348 significantly increased pain sensitivity in all stages of the estrous cycle at 5 μg rat^-1, but this hyperalgesic was least effective during the estrus stages of the estrous cycle. Administration of CGP35348 doses 3 or 5 μg rat^-1 after a high dose of baclofen significantly increased pain sensitivity; This hyperalgesic effect was greater than CGP35348 alone. Conclusion/Recommendations: According to our results, the GABAB receptor in the hippocampus can modulate pain sensitivity during the estrous cycle.