The role of medial septum in the genesis of slow-wave sleep and the inhibition of rapid eye movement sleep has been established using neurotoxic lesion and chemical stimulation of the medial septum. Intracerebroventricular injection of endocannabinoids (anandamide) decreases wake and increases slow-wave and rapid eye movement sleep in rats. Central cannabinoid (CB1) receptors are localized in the rat medial septum; however, the role of cannabinoid receptors at the medial septum on the regulation of sleep-wakefulness in rats lacks evidence. In this study, we have examined the changes in sleep architecture of 21 male Wistar rats, divided into three groups. Initially, 6 rats were used for dose standardization. Subsequently, one group (n = 6) was microinjected with CB1 receptor agonist, R-(+)-WIN 55,212-2 mesylate salt, the second group (n = 6) received microinjection of CB1 receptor antagonist LY 320,135, and the third group (n = 5) was microinjected with the vehicle, DMSO at the medial septum using stereotaxy. The sleep-wake cycle was recorded using electroencephalogram, electro-oculogram, and electromyogram. Microinjection of CB1 receptor agonist at the medial septum decreased slow-wave sleep and increased total sleep time. The increase in total sleep time was due to an increased percentage of rapid eye movement sleep. After the third and fourth hour of CB1 receptor antagonist microinjection at the medial septum, slow-wave sleep decreased when compared to vehicle injection, while rapid eye movement sleep decreased compared to baseline. We conclude that the endocannabinoid system at the septal nucleus acts through CB1 receptors to increase rapid eye movement sleep in rats.

Central insulin resistance, the diminished cellular sensitivity to insulin in the brain, has been implicated in diabetes mellitus, Alzheimer's disease and other neurological disorders. However, whether and how central insulin resistance plays a role in the eye remains unclear. Here, we performed intracerebroventricular injection of S961, a potent and specific blocker of insulin receptor in adult Wistar rats to test if central insulin resistance leads to pathological changes in ocular structures. 80 mg of S961 was stereotaxically injected into the lateral ventricle of the experimental group twice at 7 days apart, whereas buffer solution was injected to the sham control group. Blood samples, intraocular pressure, trabecular meshwork morphology, ciliary body markers, retinal and optic nerve integrity, and whole genome expression patterns were then evaluated. While neither blood glucose nor serum insulin level was significantly altered in the experimental or control group, we found that injection of S961 but not buffer solution significantly increased intraocular pressure at 14 and 24 days after first injection, along with reduced porosity and aquaporin 4 expression in the trabecular meshwork, and increased tumor necrosis factor α and aquaporin 4 expression in the ciliary body. In the retina, cell density and insulin receptor expression decreased in the retinal ganglion cell layer upon S961 injection. Fundus photography revealed peripapillary atrophy with vascular dysregulation in the experimental group. These retinal changes were accompanied by upregulation of pro-inflammatory and pro-apoptotic genes, downregulation of anti-inflammatory, anti-apoptotic, and neurotrophic genes, as well as dysregulation of genes involved in insulin signaling. Optic nerve histology indicated microglial activation and changes in the expression of glial fibrillary acidic protein, tumor necrosis factor α, and aquaporin 4. Molecular pathway architecture of the retina revealed the three most significant pathways involved being inflammation/cell stress, insulin signaling, and extracellular matrix regulation relevant to neurodegeneration. There was also a multimodal crosstalk between insulin signaling derangement and inflammation-related genes. Taken together, our results indicate that blocking insulin receptor signaling in the central nervous system can lead to trabecular meshwork and ciliary body dysfunction, intraocular pressure elevation, as well as inflammation, glial activation, and apoptosis in the retina and optic nerve. Given that central insulin resistance may lead to neurodegenerative phenotype in the visual system, targeting insulin signaling may hold promise for vision disorders involving the retina and optic nerve.