Cannabinoid receptor CB1-like and glutamic acid decarboxylase-like immunoreactivities in the brain of Xenopus laevis

Abstract

Investigation of the cannabinoid system in a vertebrate group phylogenetically distant from mammals might improve understanding of its physiological role. Thus, in the present study, the distribution of the cannabinoid CB1 receptor has been investigated in the brain of Xenopus laevis (anuran amphibians) by immunohistochemistry, using both light and confocal laser-scanning microscopy. Immunostained neuronal perikarya and terminals were found in the olfactory bulb, dorsal and medial pallium, striatum, and amygdala. Varicosities and nerve terminals containing CB1-like immunoreactivity were also seen in the thalamus and hypothalamus. A number of stained cells were observed in the pars distalis of the pituitary gland. Positive nerve fibers were distributed throughout mesencephalic tegmentum, and in the cerebellum immunolabeling was observed in some Purkinje and possibly Golgi cells. The confocal microscopic analysis of CB1-like and glutamic acid decarboxylaselike immunoreactivities in both the medial pallium of the telencephalon and the olfactory bulbs showed a wide codistribution of the two markers. The present results indicate that distribution of CB1 is conserved in the course of phylogeny. Furthermore, the close relationship between CB1-like and glutamic acid decarboxylase-like immunolabelings point toward the existence of a functional link between cannabinergic and GABAergic innervations also in amphibian brain.

Endocannabinoids affect the reproductive functions in teleosts and amphibians

“…By using the double immunofluorescence technique on the same brain section, aided by confocal laser microscope, relationships between CB1 and other signalling molecules were analysed in Xenopus CNS. In particular CB1-LI-IR was found to co-exist with GABA immunolabelling in a number of periglomerular cells of the olfactory bulb (Cesa et al, 2001), with GABA-, SP-and μ opioid receptor-LI-IRs in the spinal cord (Salio et al, 2002). Moreover the CB1 receptors were detected in lactotrophs, gonadotrophs and thyrotrophs of the pituitary gland (Cesa et al, 2002).…”

“…Moreover, since the intense CB1 mRNA ISH staining found in Taricha amigdaloid complex (Hollis et al, 2006) well matched the strong CB1-LI-IR and mRNA expression in the corresponding nucleus of Xenopus (Cesa et al, 2001;Cottone et al, 2003), the cannabinergic modulation of fear, anxiety and stress responses was postulated.…”

“…The distribution of CB1 was investigated in the CNS of adults and embryos/larvae of Xenopus laevis (Cesa et al, 2001;Beatrice et al, 2006) and Rana esculenta ) and many similarities with mammalian CB1 distribution (Tsou et al, 1998) were shown. By using the double immunofluorescence technique on the same brain section, aided by confocal laser microscope, relationships between CB1 and other signalling molecules were analysed in Xenopus CNS.…”

“…On the basis of their neuroanatomical distribution (Cesa et al, 2001;Cottone et al, 2003;Hollis et al, 2006) and relationship with a number of other signalling molecules (Cesa et al, 2001;Salio et al, 2002;Guastalla et al, 2006) the amphibian CB1 cannabinoid receptors were mainly considered modulators in sensory and sensorimotor integrations, endocrine and behavioral outputs. Moreover, since the intense CB1 mRNA ISH staining found in Taricha amigdaloid complex (Hollis et al, 2006) well matched the strong CB1-LI-IR and mRNA expression in the corresponding nucleus of Xenopus (Cesa et al, 2001;Cottone et al, 2003), the cannabinergic modulation of fear, anxiety and stress responses was postulated.…”

The evolution and comparative neurobiology of endocannabinoid signalling

“…Complementing the use of in situ hybridization techniques by Hollis et al, for analysis of CB 1 mRNA expression in Taricha, Cesa et al have used immunocytochemical techniques to investigate the distribution of CB 1 in the brain of Xenopus leavis, revealing CB 1 -immunoreactive cells and/or fibres in the olfactory bulbs, dorsal and medial pallium, striatum, amygdala, thalamus, hypothalamus, mesencephalic tegmentum and cerebellum [87]. CB 1 -immunoreactivity is also present in the dorsal and central fields of the Xenopus spinal cord, regions that correspond to laminae I-IV and X of the mammalian spinal cord [88].…”