Table 1.

Localization of cannabinoid receptors in dogs, cats and horses

Localization	Type of receptor	REFERENCES
Dog
Central nervous system	CB1: claustrum and neocortex, cerebellar cortex, midbrain, medulla oblongata, globus pallidus and substantia nigra, trigeminus, basal ganglia, cochlear nucleus, olfactory bulb and hippocampus.	Pirone et al. 2016 Freundt-Revilla et al. 2017 Silver 2019 Kostic et al. 2023 Chiocchetti et al. 2019
	CB1s decrease in dogs with idiopathic epilepsy and increase in dogs with structural epilepsy.
Peripheral nerve system	CB1: neurons, myelinating Schwann cells and dorsal root ganglia.
	CB2: neuron, Schwann cells, blood vessel smooth muscle cells, pericyte-like cells TRPV1: neuron, satellite glial cells
	GPR55: neuron, satellite glial cells
	PARRα: satellite glial cells, endothelial cells.
Immune Cells	CB1 and CB2: peripheral blood mononuclear cells, macrophages.	Brown et al. 2023 Silver 2019
	CB2: mast cells.
Skin	CB1 and CB2: basal e suprabasal epidermal cell layers, inner epithelial root sheaths cell of hair follicles, reserve cells of sebaceous glands, secretory and ductal cells of sweat glands.	Campora et al. 2012
	CB1 and CB2: perivascular cells with mast cell morphology, fibroblasts, and endothelial cells.
	CB2: basal e suprabasal cells of outer epithelial root sheaths of hair follicles and cells of arrector pili muscles.
	Stronger immunoreactivity in skin of dogs with atopic dermatitis.
	CB1, CB2, GPR55, TRPV1, TRPA1 and PPARα: basal and suprabasal keratinocytes.	Chiocchetti et al. 2022a
	Significant upregulation of CB2 and TRPA1 in samples from dogs with atopic dermatitis.
	CB2, GPR55, TRPV1 and TRPA1: inflammatory infiltrate of the skin of atopic dogs (mast cells, macrophages/dendritic cells, T lymphocytes).	Chiocchetti et al. 2022b
	GPR55: calprotectin immunoreactive neutrophils.
	CB1: hair follicles (bulb and suprabulbar region of both primary and secondary hair follicles).	Mercati et al. 2012
Gastrointestinal tract	CB1: enterochromaffin cells of pylorus, small and large intestine; some lamina propria and epithelial cells of small and large intestine.	Galiazzo et al. 2018
	CB2: endothelial and smooth muscle cells of mucosal and submucosal blood vessels, smooth muscle cells of the muscularis mucosae, mast cells of the lamina propria, unidentified immunocytes within intestinal lymphatic nodules, muscular layers of the intestine (small intestine > colon > pylorus), neurons and glial cells of intestinal submucosal plexus.
	GPR55: lamina propria (macrophages, plasma cells and mast cells) and epithelial cells, enterochromaffin cells, muscular layers.
	PPARα: lamina propria cells, epithelial cells, blood vessels, smooth muscle cells of the muscularis mucosae and tunica muscularis, glial cells of submucosal and myenteric plexus.
Hip and Stifle Joints	CB1, CB2 and GPR55: synoviocytes.	Zamith Cunha et al. 2023a
	CB2 and GPR55: macrophages, neutrophils and vascular cells.
Mast cell tumors	CB1 and CB2: highly expressed in low-grade mast cell tumors.	Rinaldi et al. 2022
Salivary gland	CB1: epithelial ductal cells.	Dall’Aglio et al. 2010
Embryo	CB1: epithelial immunoreactivity detected in several structures of central and peripheral nervous system, several nervous and non-nervous structures of sensory organs (inner ear structures, the developing eye and the olfactory epithelium), and thyroid.	Pirone et al. 2015
Cat
Skin	CB1 and CB2: epidermal layers and hair follicle sheaths, differentiated sebocytes and hair bulb matrical cells.	Miragliotta et al. 2018
	CB2: sweat glands.
	PPAR: basal keratinocytes of epidermis, outer epithelial root sheath and isolated dermal papillae.
	Overexpression in cats with dermatitis related to hypersensitivity, with the main distribution changes being suprabasal for CB1, dermal for CB2 and marked expression of PPAR-α in hyperplastic epidermis and perivascular infiltrate.
Oral mucosa	CB1: TRPA1: mucosal epithelium.	Polidoro et al. 2021
	CB2 and GPR55: subepithelial inflammatory cells.
	Upregulation in cats with chronic gingivostomatitis.
Gastrointestinal tract	CB1: gastric epithelial cells, intestinal enteroendocrine cells, goblet cells, lamina propria mast cells, and enteric neurons.	Stanzani et al. 2020.
	CB2: intestinal enteroendocrine cells, enterocytes, and macrophages.
	GPR55: intestinal enteroendocrine cells macrophages, immunocytes, and myenteric plexus neurons.
	PPARα: immunocytes, smooth muscle cells, and enteroglial cells.
	TRPA1: enteric neurons and intestinal goblet cells.
Arterial smooth muscle cells	CB1.	Gebremedhin et al. 1999
Ovary and oviduct	CB1: tertiary follicle granulosa cells, luteal cells, oviduct ciliated cells.	Pirone et al. 2017
Femoropatellar synovial membrane	CB1: in cats with synovitis.	Ruel et al. 2022
Horse
Metacarpophalangeal synovial membrane	CB1: synoviocytes.	Miagkoff et al. 2023; Zamith Cunha et al. 2023c
	CB2, TRPV1 and PPARα: synoviocytes, blood vessels and fibroblasts.
	GPR55: synoviocytes and endothelial cells.
	CB1 and CB2 overexpressed in presence of synovitis; CB1 decreased in horses with osteoarthritis.
Ileum	CB1: enterocytes, enteric neurons and enteric glial cells of the myenteric and submucosal plexus.	Galiazzo et al. 2021
	CB2: enterocytes, subclasses of immune cells in the lamina propria.
	PPARα: peripheral smooth muscle cells of the longitudinal muscular layer, neurons and glial cells.
	TRPA1: neurons of the myenteric and submucosal plexus and the nerve fibers.
Skin	CB1 and CB2: epidermis, dermal fibroblast-like cells, sebaceous glands, sweat glands.	Kupczyk et al. 2022;
	CB2: hair follicles, endothelial cells and their perivascular cells (pericytes, vascular smooth muscle).
Trigeminal ganglion	CB1, CB2, TRPV1, GPR55 and PARRγ.	Zamith Cunha et al. 2023b
Dorsal root ganglia	CB1, CB2, PPARα and γ, TRPV1, TRPA1, GPR3 and GPR55.	Chiocchetti et al. 2021 Galiazzo et al. 2022

CB1: cannabinoid receptor type 1; CB2: cannabinoid receptor type 2; GPR55 and GPR3: G protein-coupled receptor 55 and 3; PPAR: peroxisome proliferator-activated receptor; TRPV1: transient receptor potential vanilloid 1; TRPA1: transient receptors potential ankyrin 1