Neuroanatomical Distribution of Cannabinoid Receptor Gene Expression in the Brain of the Rough-Skinned Newt, <i>Taricha granulosa</i>

Abstract

Type I cannabinoid receptor (CB1) is a G-protein coupled receptor with a widespread distribution in the central nervous system in mammals. In a urodele amphibian, the rough-skinned newt (Taricha granulosa), recent evidence indicates that endogenous cannabinoids (endocannabinoids) mediate behavioral responses to acute stress and electrophysiological responses to corticosterone. To identify possible sites of action for endocannabinoids, in situ hybridization using a gene and species specific cRNA probe was used to label CB1 mRNA in brains of male T. granulosa. Labeling of CB1 mRNA in the telencephalon was observed in the olfactory bulb and all areas of the pallium, as well as the bed nucleus of the stria terminalis and nucleus amygdalae dorsolateralis. The labeling of CB1 mRNA was also found in regions of the preoptic area, thalamus, midbrain tegmentum and tectum, cerebellum, and the stratum griseum of the hindbrain. A notable difference in CB1 labeling between this amphibian and mammals is the abundance of labeling in areas associated with olfaction (anterior olfactory nuclei, nucleus amygdalae dorsolateralis, and lateral pallium), which hints that endocannabinoids might modulate responses to odors as well as pheromones. This widespread distribution of CB1 labeling, particularly in sensory and motor control centers, fits with prior results showing that endocannabinoids modulate sensorimotor processing and behavioral output in this species. The distribution of CB1 in the brain of T. granulosa was in many of the same sites previously observed in the brain of the anuran amphibian, Xenopus laevis, as well as those of different species of mammals, suggesting that endocannabinoid signaling pathways are conserved.

Endocannabinoids affect the reproductive functions in teleosts and amphibians

“…All data reported in fish and amphibian brains strongly point out the functional relevance of the endocannabinoids as local messengers in several neural circuits as reported after pharmacological (Soderström et al, 2000;Valenti et al, 2005;Hollis et al, 2006) and behavioural (Soderström et al, 2000) approaches. Our observations support the hypothesis that amphibian GnRH neurons might be tuned by the endocannabinoids through CB1 .…”

“…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.…”

“…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.…”

Localization of three types of arginine vasotocin receptors in the brain and pituitary of the newt Cynops pyrrhogaster

“…The anatomical nomenclature as given in Table 2 is based on the studies of Smeets (1992a, 1992b), Lowry et al (1997), Lewis et al (2005), and Hollis et al (2006).…”

“…3k, 5m) of the mesencephalon Table 2 Distribution and relative abundance of three types of AVT receptor mRNAs and immunoreactive cells in the brain and pituitary of the newt (++ intense signal, + moderate signal, -no immunoreactivity or no mRNA hybridization signal). Anatomical nomenclature is according to Smeets (1992a, 1992b), Lowry et al (1997), Lewis et al (2005), and Hollis et al (2006) Structures…”