Dequalinium chloride has been used primarily as antiseptic compounds, but recently has been investigated for its effects on specific targets, including muscarinic acetylcholine receptors. Here we investigated dequalinium chloride as an antagonist to α7 nicotinic acetylcholine receptors. The pharmacological properties of dequalinium were established using cell lines stably co-transfected with the calcium-permeable human α7 nicotinic acetylcholine receptors and its chaperone NACHO, calcium dye fluorescent measurements or a calcium-sensitive protein reporter, and patch clamp recording of ionic currents. Using calcium dye fluorescence plate reader measurements, we find dequalinium chloride is an antagonist of α7 nicotinic acetylcholine receptors with an IC50 of 672 nM in response to activation with 500 μM acetylcholine chloride and positive allosteric modulator PNU-120596. However, using a membrane-tethered GCAMP7s calcium reporter allowed detection of α7-mediated calcium flux in the absence of PNU-120596. Using this approach revealed an IC50 of 157 nM for dequalinium on 300 μM acetylcholine-evoked currents. Using patch clamp recordings with 300 μM acetylcholine chloride and 10 μM PNU-120596, we find lower concentrations are sufficient to block ionic currents, with IC50 of 120 nM for dequalinium chloride and 54 nM for the related UCL 1684 compound. In summary, we find that dequalinium chloride and UCL1684, which are generally used to block SK-type potassium channels, are also highly effective antagonists of α7 nicotinic acetylcholine receptors. This finding, in combination with previous studies of muscarinic acetylcholine receptors, clearly establishes dequalinium compounds within the class of general anti-cholinergic antagonists.

Intracellular calcium ([Ca(2+)]i) influx through N-methyl-d-aspartic acid (NMDA) receptors in cortical neurons is central to NMDA receptor-mediated excitotoxicity. Drugs that uncompetitively modulate NMDA receptor-mediated [Ca(2+)]i influx are potential leads for development to treat NMDA receptor-mediated neuronal damage since these drugs spare NMDA receptor normal functions. Ligands to alpha(2)-adrenoceptors and imidazoline I(2) receptors confer neuroprotection possibility through modulating NMDA receptor-mediated [Ca(2+)]i influx. Here, we investigated the characteristics of several ligands to alpha(2)-adrenoceptors and imidazoline I(2) receptor, in inhibiting NMDA receptor-mediated [Ca(2+)]i influx in cultured cortical neurons using a ratiometric calcium imaging technique. In contrast to MK801, which non-reversibly blocks NMDA receptor-mediated [Ca(2+)]i influx, imidazoline I(2) receptor antagonists, Idazoxan, and 2-(2-benzofuranyl)-2-imidazoline (2-BFI)-mediated inhibition of [Ca(2+)]i influx can be rapidly reversed when removed, in a manner similar to that of memantine, an uncompetitive antagonist to NMDA receptors. Interestingly, ligands to alpha(2)-adrenoceptors, including agmatine sulfate and yohimbine, and a ligand to the nicotinic receptor, levamisol, neither inhibited NMDA receptor-mediated [Ca(2+)]i influx, nor provided neuroprotection against glutamate toxicity, suggesting selective inhibition of NMDA receptor activities. The inhibition of NMDA receptor by Idazoxan and 2-BFI also led to the suppression of NMDA receptor-mediated calpain activity as a result of blocking NMDA receptor activity, rather than through direct inhibition of calpain activity. Collectively, these studies demonstrated that imidazoline I(2) receptor antagonists transiently and reversibly block NMDA receptor-mediated [Ca(2+)]i influx. These compounds are leads for further development as uncompetitive antagonists to NMDA receptor-mediated excitotoxicity.

Rats display both fructose-conditioned flavor preference (CFP) and quinine conditioned flavor avoidance (CFA). Dopamine (D1 and D2), muscarinic and nicotinic, but not NMDA or opioid receptor antagonists reduced fructose-CFP expression. Dopamine D1, dopamine D2, muscarinic or NMDA, but not opioid or nicotinic receptor antagonists reduced fructose-CFP acquisition. Dopamine D1, NMDA, nicotinic or opioid, but not dopamine D2 or muscarinic receptor antagonists enhanced quinine-CFA acquisition. Baclofen (BAC), a GABAB receptor agonist, alternately enhances or reduces feeding under specific conditions. The present study examined whether systemic BAC administration mediated fructose-CFP expression and acquisition or quinine-CFA acquisition. Fructose-CFP expression studies trained rats with one flavor (CS+) in 8% fructose and 0.2% saccharin and a second (CS-) flavor in 0.2% saccharin, followed by vehicle (VEH) and BAC (0.5-5 mg/kg) preceding 2-bottle (CS+, CS-) 0.2% saccharin choice tests. Fructose-CFP acquisition studies administered VEH or BAC (3 or 5 mg/kg) prior to CS+ and CS- training sessions followed by six 2-bottle (CS+, CS-) 0.2% saccharin choice tests. Quinine-CFA acquisition studies administered VEH or BAC (3 or 5 mg/kg) prior to CS- (8% fructose+0.2% saccharin) and CS+ (fructose+saccharin+0.030% quinine) training sessions followed by six 2-bottle (CS-, CS+) fructose+saccharin choice tests. BAC (3 mg/kg) minimally (66%) reduced fructose-CFP expression. BAC failed to alter fructose-CFP acquisition. Quinine-CFA acquisition was enhanced by the 5 mg/kg BAC dose (15-25%) relative to VEH (34-48%). These data implicate GABAB receptor signaling in acquisition of quinine avoidance with minimal or no effects upon fructose preferences.

Nicotine has been shown to have neuroprotective and neurotrophic actions in the central nervous system. To elucidate the peripheral neurotrophic effects of nicotine, we determined whether nicotine affected the reinnervation of mesenteric perivascular nerves following a topical phenol treatment. A topical phenol treatment was applied to the superior mesenteric artery proximal to the abdominal aorta in Wistar rats. We examined the immunohistochemistry of the distal small arteries 7 days after the treatment. The topical phenol treatment markedly reduced the density of tyrosine hydroxylase (TH)-LI and calcitonin gene-related peptide (CGRP)-LI fibers in these arteries. The administration of nicotine at a dose of 3 mg/kg/day (1.5 mg/kg/injection, twice a day), but not once a day or its continuous infusion using a mini-pump significantly increased the density of TH-LI nerves without affecting CGRP-LI nerves. A pretreatment with nicotinic acetylcholine receptor antagonists hexamethonium, mecamylamine, and methyllycaconitine, but not dextrometorphan, canceled the TH-LI nerve reinnervation induced by nicotine. Nicotine significantly increased NGF levels in the superior cervical ganglia (SCG) and mesenteric arteries, but not in the dorsal root ganglia, and also up-regulated the expression of NGF receptors (TrkA) in the SCG, which were canceled by hexamethonium. These results suggested that nicotine exhibited neurotrophic effects that facilitated the reinnervation of adrenergic TH-LI nerves by activating α7 nicotinic acetylcholine receptor and NGF in the SCG.

Hemorrhagic cystitis is one of the most important complications of cyclophosphamide, a drug widely used in cancer chemotherapy and bone marrow transplantation. 5-HT3 antagonists are anti-emetic agents and have been shown to have notable anti-inflammatory and antioxidant properties. This study was designed to investigate the possible protective effects of tropisetron against cyclophosphamide-induced hemorrhagic cystitis in rats. Hemorrhagic cystitis was induced in female rats by cyclophosphamide (270 mg/kg). Tropisetron (2.5, 5 and 7.5 mg/kg), granisetron (2.5 and 5 mg/kg), and ondansetron (5 mg/kg) were injected 15 min before, 4 and 8 h after cyclophosphamide. To evaluate the role of alpha7 nicotinic acetylcholine receptor (α7nAChR), its antagonist, methyllycaconitine (5 mg/kg) was administered 30 min before tropisetron. After 24 h, animals were killed under anesthesia. Macroscopic and histological changes were evaluated. Malondialdehyde (MDA), glutathione (GSH) and Evans blue were measured spectrophotometrically. Furthermore, the protein levels of p38 mitogen-activated protein kinases (P38 MAPK), p-P38, signal transducer and activator of transcription 3 (STAT3), p-STAT3 and Poly (ADP-ribose) polymerase (PARP) were determined using Western blot. Cyclophosphamide administration significantly induced histopathological damages and increased MDA, p-p38/p38, p-STAT3/STAT3, and PARP levels compared with the saline group. Tropisetron treatment diminished histopathological injuries as well as MDA level, and STAT3 activity compared to cyclophosphamide treated rats. Co-administration of methyllycaconitine with tropisetron, partially or completely reversed the protective effects of tropisetron. Our results showed that prophylactic administration of tropisetron markedly ameliorated the cyclophosphamide-induced bladder hemorrhage and inflammation in rats. These effects of tropisetron were α7nAChR dependent.