The retinohypothalamic tract (RHT) is made of projections of the retinal ganglion cells to the hypothalamus able to detect light by melanopsin, a photopigment particularly responsive to light in the short-wavelength (blue) spectrum. Leak and Moore (1997) described projections of RHT to the lateral hypothalamus (LH). Orexin- (OX), melanin concentrating hormone- (MCH) and non-OX and non-MCH GABA-producing neurons are located in the LH and are critical regulators of wakefulness and sleep. Our previous studies suggest that endocannabinoid signaling exerts a powerful modulation of OX-A neurons, which synthesize the endocannabinoid 2-AG and are innervated by glutamatergic and GABAergic inputs carrying CB1 receptors. Since cannabinoids generate a distorted sense of time and the endocannabinoid 2-acylglicerol (2-AG) shows a circadian variation in the brain, we studied the role of the endocannabinoid system in the modulation of wakefulness hypothesizing a light-mediated endocannabinoid synthesis and release in the LH via RHT. At this purpose, we initially identified the RHT projections to the LH by intravitreal injection of the anterograde tracer colera toxin subunit B (CTB) in adult C57BL/6J mice. Among LH neurons, we observed a majority of glutamatergic CB1+/CTB+ inputs onto OX-A neurons, as confirmed by CB1/OXA and CB1/DAGL-alpha double immunoelectronmicroscopy. The functional RHT light-mediated activation of LH neurons was tested by exposure of mice to a blue light-pulse (LP) in darkness at CT14 after 1 week in constant darkness in order to study Fos immunohistochemistry coupled to OX-A or MCH or GAD65 immunostaining (30‘LP) and to perform quantitative evaluation of the 2-AG level at 10‘, 15‘, 20‘ and 30‘of light pulse. Strong Fos induction was observed in OX-A neurons, indicating that synthesis and release of 2-AG could be induced by glutamatergic light-mediated activation of OX-A neurons. This was supported by a significant increase of endocannabinoid levels in the LH of mice up to 15‘ after light-pulse, with concurrent activation of the calcium indicator Fluo-4-dextran presynaptically to OX-A neurons. These data suggest a 2-AG-induced DSE (depolarization-induced suppression of excitation) of OX-A neurons by means of RHT/CB1+ projections.
Retinal projections to the lateral hypothalamus are involved in the light-mediated endocannabinoid synthesis: Orexin and 2-acylglicerol interaction in the light-entrainable rhythms / L., Cristino; R., Imperatore; A., Iovine; Ferrandino, Ida; M. A., Di Grazia; S., Petrosino; V., Di Marzo; M., Bentivoglio. - 41:(2011), pp. P.P: 602.02/SS19-P.P.: 602.02/SS19. (Intervento presentato al convegno 41st Annual Meeting of the Society-for-Neuroscience tenutosi a Washington, DC nel 12-16 Novembre 2011).
Retinal projections to the lateral hypothalamus are involved in the light-mediated endocannabinoid synthesis: Orexin and 2-acylglicerol interaction in the light-entrainable rhythms.
FERRANDINO, IDA;
2011
Abstract
The retinohypothalamic tract (RHT) is made of projections of the retinal ganglion cells to the hypothalamus able to detect light by melanopsin, a photopigment particularly responsive to light in the short-wavelength (blue) spectrum. Leak and Moore (1997) described projections of RHT to the lateral hypothalamus (LH). Orexin- (OX), melanin concentrating hormone- (MCH) and non-OX and non-MCH GABA-producing neurons are located in the LH and are critical regulators of wakefulness and sleep. Our previous studies suggest that endocannabinoid signaling exerts a powerful modulation of OX-A neurons, which synthesize the endocannabinoid 2-AG and are innervated by glutamatergic and GABAergic inputs carrying CB1 receptors. Since cannabinoids generate a distorted sense of time and the endocannabinoid 2-acylglicerol (2-AG) shows a circadian variation in the brain, we studied the role of the endocannabinoid system in the modulation of wakefulness hypothesizing a light-mediated endocannabinoid synthesis and release in the LH via RHT. At this purpose, we initially identified the RHT projections to the LH by intravitreal injection of the anterograde tracer colera toxin subunit B (CTB) in adult C57BL/6J mice. Among LH neurons, we observed a majority of glutamatergic CB1+/CTB+ inputs onto OX-A neurons, as confirmed by CB1/OXA and CB1/DAGL-alpha double immunoelectronmicroscopy. The functional RHT light-mediated activation of LH neurons was tested by exposure of mice to a blue light-pulse (LP) in darkness at CT14 after 1 week in constant darkness in order to study Fos immunohistochemistry coupled to OX-A or MCH or GAD65 immunostaining (30‘LP) and to perform quantitative evaluation of the 2-AG level at 10‘, 15‘, 20‘ and 30‘of light pulse. Strong Fos induction was observed in OX-A neurons, indicating that synthesis and release of 2-AG could be induced by glutamatergic light-mediated activation of OX-A neurons. This was supported by a significant increase of endocannabinoid levels in the LH of mice up to 15‘ after light-pulse, with concurrent activation of the calcium indicator Fluo-4-dextran presynaptically to OX-A neurons. These data suggest a 2-AG-induced DSE (depolarization-induced suppression of excitation) of OX-A neurons by means of RHT/CB1+ projections.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
