Endocannabinoid Regulation of Acute and Protracted Nicotine Withdrawal: Effect of FAAH Inhibition

Evidence shows that the endocannabinoid system modulates the addictive properties of nicotine. In the present study, we hypothesized that spontaneous withdrawal resulting from removal of chronically implanted transdermal nicotine patches is regulated by the endocannabinoid system. A 7-day nicotine dependence procedure (5.2 mg/rat/day) elicited occurrence of reliable nicotine abstinence symptoms in Wistar rats. Somatic and affective withdrawal signs were observed at 16 and 34 hours following removal of nicotine patches, respectively. Further behavioral manifestations including decrease in locomotor activity and increased weight gain also occurred during withdrawal. Expression of spontaneous nicotine withdrawal was accompanied by fluctuation in levels of the endocannabinoid anandamide (AEA) in several brain structures including the amygdala, the hippocampus, the hypothalamus and the prefrontal cortex. Conversely, levels of 2-arachidonoyl-sn-glycerol were not significantly altered. Pharmacological inhibition of fatty acid amide hydrolase (FAAH), the enzyme responsible for the intracellular degradation of AEA, by URB597 (0.1 and 0.3 mg/kg, i.p.), reduced withdrawal-induced anxiety as assessed by the elevated plus maze test and the shock-probe defensive burying paradigm, but did not prevent the occurrence of somatic signs. Together, the results indicate that pharmacological strategies aimed at enhancing endocannabinoid signaling may offer therapeutic advantages to treat the negative affective state produced by nicotine withdrawal, which is critical for the maintenance of tobacco use

The allosteric modulation of the GABAB receptor: a medicinal chemistry perspective

Since its cloning, the GABAB receptor has progressively become a target for potential drugs to be used in the treatment of a wide range of pathological conditions such as spasticity, pain, drug addiction, epilepsy, anxiety, mood disorders. Baclofen, the only GABAB receptor agonist currently approved for the treatment of muscle rigidity and spasm associated with multiple sclerosis or spinal cord injury, suffers from a number of side effects which hamper its clinical use. As a result, there has been a strong impetus for the development of positive allosteric modulators that modulate the physiological mechanisms of GABAergic regulation and are expected to have a much lower side effect potential than orthosteric ligands. Herein, the major structural classes of GABAB allosteric modulators are described with an emphasis on structure–activity relationships (SAR) and synthesis of the main representatives of each class. Medicinal chemistry strategies to overcome issues related to allosteric modulators development are also discussed. © Springer International Publishing Switzerland 2016

Role of CB2 cannabinoid receptors in the rewarding, reinforcing, and physical effects of nicotine

This study was aimed to evaluate the involvement of CB2 cannabinoid receptors (CB2r) in the rewarding, reinforcing and motivational effects of nicotine. Conditioned place preference (CPP) and intravenous self-administration experiments were carried out in knockout mice lacking CB2r (CB2KO) and wild-type (WT) littermates treated with the CB2r antagonist AM630 (1 and 3 mg/kg). Gene expression analyses of tyrosine hydroxylase (TH) and α3- and α4-nicotinic acetylcholine receptor subunits (nAChRs) in the ventral tegmental area (VTA) and immunohistochemical studies to elucidate whether CB2r colocalized with α3- and α4-nAChRs in the nucleus accumbens and VTA were performed. Mecamylamine-precipitated withdrawal syndrome after chronic nicotine exposure was evaluated in CB2KO mice and WT mice treated with AM630 (1 and 3 mg/kg). CB2KO mice did not show nicotine-induced place conditioning and self-administered significantly less nicotine. In addition, AM630 was able to block (3 mg/kg) nicotine-induced CPP and reduce (1 and 3 mg/kg) nicotine self-administration. Under baseline conditions, TH, α3-nAChR, and α4-nAChR mRNA levels in the VTA of CB2KO mice were significantly lower compared with WT mice. Confocal microscopy images revealed that CB2r colocalized with α3- and α4-nAChRs. Somatic signs of nicotine withdrawal (rearings, groomings, scratches, teeth chattering, and body tremors) increased significantly in WT but were absent in CB2KO mice. Interestingly, the administration of AM630 blocked the nicotine withdrawal syndrome and failed to alter basal behavior in saline-treated WT mice. These results suggest that CB2r play a relevant role in the rewarding, reinforcing, and motivational effects of nicotine. Pharmacological manipulation of this receptor deserves further consideration as a potential new valuable target for the treatment of nicotine dependence.This study was supported by the following research grants: Ministerio de Ciencia e Innovación (SAF2011-23420 to Jorge Manzanares, SAF2009-10689 to Pere Berbel, and SAF2011-29864 to Rafael Maldonado); Ministerio de Economía y Competitividad, Dirección General de Investigación (PSI2011-24762) to José Miñarro; Generalidad Valenciana, Consejería de Educación (PROMETEO/2009/072) to José Miñarro; Gobierno Catalán (SGR2009-00131) to Rafael Maldonado; ICREA Academia-2008 to Rafael Maldonado; and Instituto de Salud ‘Carlos III’ (FIS), RETICS, Red de Trastornos Adictivos (RD06/0001/1004, RD12/0028/0019 to Jorge Manzanares; RD06/001/0016, RD12/0028/005 to José Miarro; RD06/001/001, RD12/0028/0023 to Rafael Maldonado