Cannabinoids and opioids are widely consumed drugs of abuse that produce motor depression, in part via respective activation of the cannabinoid subtype 1 receptor (CB1R) and the -opioid receptor (OR), in the striatal circuitry originating in the caudate putamen nucleus (CPN). Thus, the CB1R and OR may show similar targeting in the CPN. To test this hypothesis, we examined the electron microscopic immunocytochemical labeling of CB1R and OR in CPN patches of rat brain. Of the CB1R-labeled profiles, 34% (588) were dendrites, presumably arising from spiny as well as aspiny-type somata, which also contained CB1R immunoreactivity. In dendrites, CB1R often was localized to nonsynaptic and synaptic plasma membranes, particularly near asymmetric excitatory-type junctions. Almost one-half of the CB1R-labeled dendrites contained OR immunoreactivity, whereas only 20% of all OR-labeled dendrites expressed CB1R. Axons and axon terminals as well as abundant glial processes also showed plasmalemmal CB1R and were mainly without OR immunoreactivity. Many CB1R-labeled axon terminals were small and without recognizable synaptic junctions, but a few also formed asymmetric, or more rarely symmetric, synapses. The CB1R-labeled glial processes were often perivascular or perisynaptic, surrounding asymmetric excitatory-type axospinous synapses. Our results show that in CPN patches CB1R and OR are targeted strategically to some of the same postsynaptic neurons, which may account for certain similarities in motor function. Furthermore, they also provide evidence that CB1R may play a major role in the modulation of presynaptic transmitter release and glial functions that are unaffected in large part by opioids active at OR in CPN.

Acute or chronic alterations in energy status alter the balance between excitatory and inhibitory synaptic transmission and associated synaptic plasticity to allow for the adaptation of energy metabolism to new homeostatic requirements. The impact of such changes on endocannabinoid and cannabinoid receptor type 1 (CB 1 )-mediated modulation of synaptic transmission and strength is not known, despite the fact that this signaling system is an important target for the development of new drugs against obesity. We investigated whether CB 1 -expressing excitatory vs. inhibitory inputs to orexin-A-containing neurons in the lateral hypothalamus are altered in obesity and how this modifies endocannabinoid control of these neurons. In lean mice, these inputs are mostly excitatory. By confocal and ultrastructural microscopic analyses, we observed that in leptin-knockout (ob/ob) obese mice, and in mice with diet-induced obesity, orexinergic neurons receive predominantly inhibitory CB 1 -expressing inputs and overexpress the biosynthetic enzyme for the endocannabinoid 2-arachidonoylglycerol, which retrogradely inhibits synaptic transmission at CB 1 -expressing axon terminals. Patchclamp recordings also showed increased CB 1 -sensitive inhibitory innervation of orexinergic neurons in ob/ob mice. These alterations are reversed by leptin administration, partly through activation of the mammalian target of rapamycin pathway in neuropeptide-Y-ergic neurons of the arcuate nucleus, and are accompanied by CB 1 -mediated enhancement of orexinergic innervation of target brain areas. We propose that enhanced inhibitory control of orexin-A neurons, and their CB 1 -mediated disinhibition, are a consequence of leptin signaling impairment in the arcuate nucleus. We also provide initial evidence of the participation of this phenomenon in hyperphagia and hormonal dysregulation in obesity.food intake | orexin-A/hypocretin 1 | high-fat diet | retrograde signaling M odulation of the activity of hypothalamic neurons is involved in the regulation of energy balance exerted by the adipose tissue-derived hormone leptin. In the arcuate nucleus (ARC), these neurons express either pro-opiomelanocortin (POMC) and cocaine and amphetamine-responsive transcript, or neuropeptide Y (NPY) and agouti-related peptide (AgRP). Orexigenic neurons containing the peptide hypocretin-1/orexin-A (hereafter referred to as OX) reside in the lateral hypothalamus (LH) and send projections throughout the brain (1). They have been implicated in a variety of functions, including wakefulness and energy homeostasis (2), behavioral responses to food reward (3, 4) and addictive drugs (5), and neuroendocrine and autonomic outflow (6-8).Short-term food deprivation results in decreased activity of POMC neurons and increased activity of NPY/AgRP neurons, thus facilitating food consumption (9). Such deprivation also causes enhancement of excitatory inputs to OX neurons. Reduction in leptin levels is responsible for these alterations, as they are reversed by administration of the hormo...

Endocannabinoids acting at the cannabinoid type 1 receptor (CB1R) are known to regulate attention, cognition and mood. Previous studies have shown that, in the rat medial prefrontal cortex (mPFC), CB1R agonists increase norepinephrine release, an effect that may be attributed, in part, to CB1Rs localized to noradrenergic axon terminals. The present study was aimed at further characterizing functional interactions between CB1R and adrenergic receptor (AR) systems in the mPFC using in-vitro intracellular electrophysiology and high-resolution neuroanatomical techniques. Whole-cell patch-clamp recordings of layer V/VI cortical pyramidal neurons in rats revealed that both acute and chronic treatment with the synthetic CB1R agonist WIN 55,212-2 blocked elevations in cortical pyramidal cell excitability and increases in input resistance evoked by the α2-adrenergic receptor (α2-AR) agonist clonidine, suggesting a desensitization of α2-ARs. These CB1R–α2-AR interactions were further shown to be both action potential- and gamma-aminobutyric acid-independent. To better define sites of cannabinoid–AR interactions, we localized α2A-ARs in a genetically modified mouse that expressed a hemoagglutinin (HA) tag downstream of the α2A-AR promoter. Light and electron microscopy indicated that HA-α2A-AR was distributed in axon terminals and somatodendritic processes especially in layer V of the mPFC. Triple-labeling immunocytochemistry revealed that α2A-AR and CB1R were localized to processes that contained dopamine-β-hydroxylase, a marker of norepinephrine. Furthermore, HA-α2A-AR was localized to processes that were directly apposed to CB1R. These findings suggest multiple sites of interaction between cortical cannabinoid–adrenergic systems that may contribute to understanding the effect of cannabinoids on executive functions and mood.

In the era of combined antiretroviral therapy (cART), human immunodeficiency virus type 1 (HIV-1) is considered a chronic disease that specifically targets the brain and causes HIV-1-associated neurocognitive disorders (HAND). Endocannabinoids (eCBs) elicit neuroprotective and anti-inflammatory actions in several central nervous system (CNS) disease models, but their effects in HAND remain unknown. HIV-1 does not infect neurons, but produces viral toxins, such as transactivator of transcription (Tat), that disrupt neuronal calcium equilibrium and give rise to synaptodendritic injuries and cell death, the former being highly correlated with HAND. Consequently, we tested whether the eCBs N-arachidonoyl ethanolamine (anandamide/AEA) and 2-arachidonoyl-glycerol (2-AG) offer neuroprotective actions in a neuronal culture model. Specifically, we examined the neuroprotective actions of these eCBs on Tat excitotoxicity in primary cultures of prefrontal cortex neurons (PFC), and whether cannabinoid receptors mediate this neuroprotection. Tat-induced excitotoxicity was reflected by increased intracellular calcium levels, synaptodendritic damage, neuronal excitability, and neuronal death. Further, upregulation of cannabinoid 1 receptor (CB1R) protein levels was noted in the presence of HIV-1 Tat. The direct application of AEA and 2-AG reduced excitotoxic levels of intracellular calcium and promoted neuronal survival following Tat exposure, which was prevented by the CB1R antagonist rimonabant, but not by the CB2R antagonist AM630. Overall, our findings indicate that eCBs protect PFC neurons from Tat excitotoxicity in vitro via a CB1R-related mechanism. Thus, the eCB system possesses promising targets for treatment of neurodegenerative disorders associated with HIV-1 infection.

Introduction: An escalating number of fatalities resulting from accidental opioid overdoses typically attributed to respiratory depression continue to define the opioid epidemic. Opioid respiratory depression results from a decrease in reflexive inspiration within the preBö tzinger complex in the brainstem. Objective: Cannabinoid receptor agonism is reported to enhance opioid analgesia, yet whether cannabinoids enhance or inhibit opioid-induced respiratory depression is unknown. Methods: Studies herein sought to define the roles of cannabinoid-1 receptor (CB1R) and cannabinoid-2 receptor (CB2R) on respiratory depression using selective agonists alone and in combination with morphine in male mice. Results: Using whole body plethysmography, the nonselective CB1R and CB2R agonist (D 9-tetrahydrocannabinol) and the CB1R synthetic cannabinoid, AM356, induced respiratory depression, whereas the well-published selective CB2 agonist, JWH 133, and the novel CB2 agonist (AM2301) did not. Moreover, a selective CB2R agonist (AM2301) significantly attenuated morphine sulfate-induced respiratory depression. Conclusion: Notably, findings suggest that attenuation of opioid-induced respiratory depression relies on CB2R activation, supporting selective CB2R agonism as an opioid adjunct therapy.