Differential expression of VGLUT1, GAD65, GAD67, and MAP2 in the retina of hibernating Anatolian ground squirrel (Spermophilus xanthoprymnus).

The Anatolian ground squirrel (Spermophilus xanthoprymnus) offers a valuable model for investigating neuroadaptive processes in the retina during hibernation. This study aimed to assess the expression of vesicular glutamate transporter 1 (VGLUT1), glutamic acid decarboxylase (GAD) isoforms GAD65 and GAD67, and microtubule-associated protein 2 (MAP2) in the retina during pre-hibernation and hibernation states. Retinal tissues were analyzed using immunohistochemistry and densitometric quantification. VGLUT1 expression remained stable in the outer plexiform layer (OPL) but was significantly reduced in the inner plexiform layer (IPL) during hibernation, indicating a selective downregulation of excitatory transmission between bipolar and ganglion cells. GAD65 showed widespread distribution across retinal synaptic layers and optic fibers in pre-hibernation but declined markedly during hibernation, consistent with reduced activity-dependent GABAergic signaling. In contrast, GAD67 immunoreactivity increased in the inner nuclear layer, suggesting a shift toward sustained basal inhibitory tone that may support synaptic stability during metabolic suppression. MAP2 immunoreactivity increased in the inner nuclear layer (INL) and outer plexiform layer (OPL) but decreased in the photoreceptor layer (PRL) during hibernation. This shift in distribution suggests cytoskeletal reorganization in second-order neurons and reduced physiological activity in photoreceptor terminals under metabolic suppression. Together, the modulation of excitatory (VGLUT1), inhibitory (GAD65/67), and cytoskeletal (MAP2) markers suggest that the hibernating retina undergoes structural and functional adaptations aimed at preserving neural circuitry under metabolic suppression.