Cannabinoid receptor Type 1 densities reflect social organization in Microtus. Issue 5 (24th August 2020)

• Record Type: Journal Article
• Authors: Simmons, Trenton C.; Freeman, Sara M.; Lackey, Nicholas S.; Dreyer, Brooke K.; Manoli, Devanand S.; Bales, Karen L.
• Is Part Of: Journal of comparative neurology. Volume 529:Issue 5(2021)
• Page Start: 1004
• Page End: 1017
• Publication Date: 2020-08-24
• Subjects: CB1 -- CB2 -- endocannabinoids -- monogamy -- pair bonding -- social behavioral neural network; Comparative neurobiology -- Periodicals; Neurology -- Periodicals; 616
• DOI: 10.1002/cne.24996
• Languages: English
• ISSNs: 0021-9967

Abstract

Abstract: Across many species, endocannabinoids play an important role in regulating social play, reward, and anxiety. These processes are mediated through at least two distinct cannabinoid receptors (CB), CB1 and CB2. CB1 expression is found in appreciable densities across regions of the brain that integrate memory with socio‐spatial information; many of these regions have been directly linked to the neurobiology of pair bonding in monogamous species. Using receptor autoradiography, we provide the first distributional map of CB1 within the brains of closely related monogamous prairie voles and promiscuous meadow voles, and compare receptor densities across sexes and species in limbic regions. We observe CB1‐specific signal using [3H] CP‐55, 940 and [3H] SR141716A, though the latter exhibited a lower signal to noise ratio. We confirmed the presence of CB2 in prairie vole spleen tissue using [3H] CP‐55, 940. However, we found no evidence of CB2 in the brain using either [3H] CP‐55, 940 or [3H] A‐836, 339. The overall distribution of putative CB1 in the brain was similar across vole species and followed the pattern of CB1 expression observed in other species—high intensity binding within the telencephalon, moderate binding within the diencephalon, and mild binding within the mesencephalon and metencephalon (aside from the cerebellar cortex). However, we found profound differences in CB1 densities across species, with prairie voles having higher CB1 binding in regions implicated in social attachment and spatial memory (e.g., periaqueductal gray, hippocampus). These findings suggest that CB1 densities, but not distribution, correlate with the social systems of vole species. Abstract : Validation of [3H] CP‐55, 940 for autoradiography of endocannabinoid receptors in prairie vole brains. Three adjacent sections of brain tissue were incubated with [3H] CP‐55, 940 with or without an unlabeled receptor competitor. Coincubation of the radioligand with the CB2 blocker (HU308) had no discernible impact on binding in the hippocampus but increased binding in the prefrontal cortex relative to control. Coincubation of the radioligand with the CB1 blocker (AM251) significantly decreased signal in both regions.