In neurophysiological studies on learning and memory, L-glutamate receptors especially N-Methyl, D-Aspartate glutamate (NMDA) receptors have a major role in different aspect of the learning and memory. Two sites of mammalian brain that show high density of these receptors are CA1 region of hippocampus and Purkinje cell layer of cerebellum. Twenty four Sprague-Dawley rats were used in 4 groups: Control 1 (intact without learning); control 2 (intact with learning); experimental 1 (castration without learning) and experimental 2 (castration with learning). A shuttle box apparatus used for passive avoidance learning procedure. Immunohistochemical procedure was used for determination of NR1 subunit of NMDA receptor. Photoshop software was used for determination of color intensity. Data were analyzed by student t-test and one-way ANOVA, Tucky test as post-hoc test was used. The level of significant was considered p<0.05. Immunohistological finding of this experiment indicates that castration has a negative effect on density of NR1 subunit of NMDA receptors in two brain regions. Other finding of this study showed that passive avoidance learning significantly increased density of NR1 subunit of NMDA receptors in two brain regions. These results indicated that the sex hormone can modulate function and expression of the NR1 subunit of NMDA receptor in CA1 region of hippocampus and Purkinje cell layer of cerebellum.
