Psychopharmacological evidences for the involvement of muscarinic and nicotinic cholinergic receptors on sweet substance-induced analgesia in Rattus norvegicus

In order to investigate the effects of sweet substance intake on pain modul ation, male albino Wistar rats weighing 180-200 g received either tap water or sucrose solutions (250 g/l) for 14 days as their only source of liquid. Each rat consumed an average of 15.6 g sucrose/day. Their tail withdrawal latencies in the tail-flick test (probably a spinal reflex) were measured i mmediately before and after this treatment. An analgesia index was calculat ed from the withdrawal latencies before and after treatment. The index (mea n +/- SEM, N = 8) for the groups receiving sucrose solution plus saline (Na Cl; 0.9%) for 14 days was 0.70 +/- 0.01. Atropine (1 and 2 mg/kg)-treated r ats (N = 8) after intake of sucrose exhibited an analgesia index of 0.39 +/ - 0.09 and 0.39 +/- 0.08, respectively, while mecamylamine (1 and 2 mg/kg)- treated rats (N = 10) after intake of sucrose had an index of -0.02 +/- 0.0 7 and 0.03 +/- 0.07, respectively. These results indicate that the effect o f sucrose intake on nociceptive thresholds is controlled by neurotransmissi on of acetylcholine and depends on the nicotinic cholinergic receptors for its major analgesic effect, although muscarinic receptors were also involve d in this antinociceptive process. (C) 2001 Elsevier Science Ireland Ltd. A ll rights reserved.