Essential role of the C148-C227 disulphide bridge in the human 5-HT2A homodimeric receptor.

The 5-HT2A receptor is a homodimeric G protein-coupled receptor implied in multiple diseases, including schizophrenia. Recently, its co-crystallisation with the antipsychotic drugs zotepine and risperidone has revealed the importance of its extracellular domains in its pharmacology. Previous studies have shown that the non-specific disruption of extracellular disulphide bridges in the 5-HT2A receptor decreases ligand binding and receptor activation. There is enough evidence to hypothesize that this decrease may be due to a reduction of the disulphide bridge that links transmembrane domain 3 (TM-3) and extracellular loop 2 (ECL-2) of the 5-HT2A receptor via cysteine 148 (C148) and C227. Thus, to study the influence of the C148-C227 disulphide bridge on 5-HT2A receptor pharmacology, we substituted C148 and C227 in the human 5-HT2A receptor (WT) with alanines, to obtain two single mutants (C148A and C227A) and a double mutant (C148A/C227A), and the resultant DNA constructs were used to generate four stable cell lines. These substitutions reduced the binding of the 5-HT2A receptor to [3H]lysergic acid diethylamide ([3H]LSD) and impeded the 5-HT2A receptor-mediated activation of phospholipase C (PLC). Furthermore, bioluminescence resonance energy transfer (BRET) and western blotting analysis revealed that these mutations did not alter the homodimeric nature of the 5-HT2A receptor. However, fluorescence microscopy showed that these mutations hindered receptor trafficking to the cell membrane. These results illustrate the importance of the disulphide bridge between TM-3 and ECL-2 in maintaining the correct 5-HT2A receptor conformation to allow ligand binding and migration of the homodimeric receptor to the cell membrane.

Oral self-administration of buprenorphine in the diet for analgesia in mice.

Postsurgical oral self-administration of analgesics in rodents is an interesting technique of providing analgesia, avoiding the negative effects of manipulation. Several strategies, using gelatin or nutella, have already been described. However, rodents require some habituation period to reach a good intake because of their neophobic behavior. The current study aimed to explore whether buprenorphine when mixed with an extruded diet offers a potential treatment option in the pain management of mice using a triple approach: by measuring the spontaneous intake in healthy animals; by using the hot-plate test; and finally by assessing the drug's ability to provide postoperative analgesia in a surgical intervention of moderate severity (intra-utero electroporation). Mice consumed during 20 hours, similar amounts of extruded diet alone, mixed with glucosaline, and mixed with buprenorphine (0.03 mg per pellet) or meloxicam (0.25 mg per pellet) both of which were diluted in glucosaline, showing that no neophobia was associated with these administrations. Relative increase from baseline latency (% maximal possible effect) in the hot-plate test at 20 h of administration was significantly higher for oral buprenorphine in diet 0.03 mg/pellet, and diet 0.15 mg/pellet, compared with placebo and no differences were found between those oral administrations and subcutaneous buprenorphine 0.1 mg/kg measured 3 h later. The treatment was also effective in attenuating the reductions in food consumption and body weight that occur after surgery. These data suggest that providing buprenorphine with the diet is a feasible and effective way of self-administration of analgesia in mice and does not cause neophobia and may easily contribute to the refinement of surgical procedures.