Cannabinoid type 1 receptor-containing axons innervate NPY/AgRP neurons in the mouse arcuate nucleus

Abstract

ObjectivesPhytocannabinoids, such as THC and endocannabinoids, are well known to promote feeding behavior and to control energy metabolism through cannabinoid type 1 receptors (CB1R). However, the underlying mechanisms are not fully understood. Generally, cannabinoid-conducted retrograde dis-inhibition of hunger-promoting neurons has been suggested to promote food intake, but so far it has not been demonstrated due to technical limitations.MethodsWe applied immunohistochemical labeling of CB1R for light microscopy and electron microscopy combined with three-dimensional reconstruction from serial sections in CB1R-expressing and CB1R-null mice, which served as a negative control. Hunger-promoting neurons expressing Agouti-related protein and neuropeptide Y (AgRP/NPY) in the hypothalamic arcuate nucleus were identified in NPY-GFP and NPY-hrGFP mice.ResultsUsing three-dimensional reconstruction from serial sections we demonstrated numerous discontinuous segments of anti-CB1R labeling in the synaptic boutons and axonal shafts in the arcuate nucleus. We observed CB1R in the symmetric, presumed GABAergic, synaptic boutons innervating AgRP/NPY neurons. We also detected CB1R-containing axons producing symmetric and asymmetric synapses onto AgRP/NPY-negative neurons. Furthermore, we identified CB1R in close apposition to the endocannabinoid (2-arachidonoylglycerol)-synthesizing enzyme diacylglycerol lipase-alpha at AgRP/NPY neurons.ConclusionsOur immunohistochemical and ultrastructural study demonstrates the morphological substrate for cannabinoid-conducted feeding behavior via retrograde dis-inhibition of hunger-promoting AgRP/NPY neurons.

Neuroprotective and Neuromodulatory Effects Induced by Cannabidiol and Cannabigerol in Rat Hypo-E22 cells and Isolated Hypothalamus

“…In contrast, the inhibition of the expression of the NPY gene registered after the treatment, although being consistent with the anorexigenic effects ascribed to CBD [6], appears to be discrepant with the orexigenic role of CBG [16,17]. This result is, however, in agreement with the expression of the CB1 receptor on synaptic endings innervating both NPY and POMC first order neurons in the hypothalamus [29,31]. Interestingly, the anorexigenic effects induced by bisphenol A in mice were followed by the concomitant reduction and stimulation of CB1 and cocaine and amphetamine-regulating transcript (CART) peptide gene expression, respectively; thus, further highlighting the importance of hypothalamic arcuate nucleus first order neurons as key targets of the anti-obesity effects of CB1-modulating compounds [32].…”

Cannabinoid Type 1 Receptor is Undetectable in Rodent and Primate Cerebral Neural Stem Cells but Participates in Radial Neuronal Migration

“…IHC labeling was performed as previously described [ 37 , 49 , 50 ]. Briefly, coronal 80-m-thick slices from the embryo cerebral cortex were cut by a vibratome.…”

Endocannabinoids in Body Weight Control

“…However, the activity of ARC neurons can be disrupted by cannabinoids and induce a feeding response in a state of satiety with concomitant paradox activity of POMC neurons [ 48 ]. Furthermore, presynaptic terminals on AgRP/NPY-neurons (but not the postsynaptic cells themselves) show CB1-expression, suggesting a retrograde control of AgRP activity through eCBs [ 69 ].…”