Localization of CB1 cannabinoid receptor mRNA in the brain of the chick (Gallus domesticus)

Abstract

The cannabinoid receptor one (CB1) is prevalent in the brains of many species. Receptor binding, in situ hybridization and immunohistochemical surveys have described the distribution of this receptor in a limited number of species. The current study used in situ hybridization to examine the expression of CB1 mRNA in the chick brain, a non-mammalian vertebrate. The results were compared to the observed patterns of expression for CB1 mRNA, protein, and agonist binding that have been reported for other avian species and mammals. Importantly, since CB1 receptors are typically located on neuronal terminals, comparison of the somatic mRNA expression with previously reported descriptions of the location of functional receptors, allows speculation about the circuits that make use of these receptors. The expression pattern for CB1 mRNA appears to be highly conserved across species in key areas such as the cerebellum and portions of the forebrain. For example, high levels of expression were observed in the avian amygdala and hippocampus, areas which express high levels of CB1 in mammals. The avian substantia nigra and ventral tegmental area, however, showed specific labeling. This finding is in stark contrast to the high levels of receptor binding or CB1 protein, but not CB1 mRNA in these areas of the mammalian brain. Moderate labeling was also seen throughout the hyperpallium and mesopallium. Throughout the brain, a number of regions that are known to be involved in visual processing displayed high levels of expression. For example, the tectum also had strong mRNA expression within layers 9-11 of the stratum griseum et fibrosum superficale and stratum album centrale.

The localization and physiological effects of cannabinoid receptor 1 in the brain stem auditory system of the chick

“…The pattern of expression observed with skull-intact sections matched that found in extracted-brain sections (Stincic and Hyson, 2008). For example, the cerebellum displayed strong labeling in the granular layer, the tectum showed the same laminar-restricted labeling, and the brainstem was relatively devoid of any CB1 expression.…”

“…CB1 expression in the chick brain appears to follow a pattern described in mammalian literature both in concentration and localization with few exceptions (Mailleux et al, 1992, Mailleux and Vanderhaeghen, 1992, Matsuda et al, 1993, Stincic and Hyson, 2008). Using ISH and IHC in a complementary fashion, CG cells were revealed to be the likely source of CB1 localized to the calyceal terminals synapsing with NM.…”

“…Our previous survey of CB1 distribution throughout the chick brain (Stincic and Hyson, 2008) revealed the robust expression of CB1 mRNA in the vestibular ganglion of the chick, but the CG was not preserved during the brain extraction procedure. The present study preserved the periphery during sectioning.…”

“…Our laboratory recently reported the distribution of the cannabinoid receptor 1 (CB1) mRNA throughout the brain of the chick (Stincic and Hyson, 2008). While little mRNA expression was found in NM or NL, the cnVIII ganglion (vestibular portion) displayed robust CB1 mRNA expression.…”

The evolution and comparative neurobiology of endocannabinoid signalling

“…In birds, CB 1 expression has been analysed in the brain of the chick Gallus gallus [93], the zebra finch Taeniopygia guttata [89] and the budgerigar Melopsittacus undulates [94], revealing some patterns of expression that are strikingly similar to findings in mammals [56,95]. For example, high levels of CB 1 expression are observed in the hippocampus and amygdala and, as in mammals, in the cerebellar cortex, the CB 1 gene is expressed in granule cells and the receptor protein is targeted to parallel fibres in the molecular layer.…”