Supersensitivity of the cholinergic muscarinic system in the rat's brain is induced by high concentrations of Cu+2

Transition metals have been described as regulators of receptor's function. here, we studied the effects of chronic administration of Cu2+ or the Cu2+ chelator penicillamine (PA) on the functional and binding properties of the muscarinic receptors (MR) on selected areas of rat's brain. Groups of 10 Sprague-Dawley rats were treated daily, for 45 days with either 1) 1 mg/Kg CuSO4 (Cu2+), 2) 100 mg/Kg PA, or 3) saline solution. Double T-maze and motility cages were used for behavioral testing and the binding assays were performed using [3H]-QNB or [3H]-N-MSCP as MR's ligands. Cu2+ brain levels were measured in the cerebral cortex by atomic absorption spectrophotometer. Results showed that PA treated rats displayed a significant decrease of locomotor's activity (LA) and rearing behavior (RB), but a significant increases in memory efficiency (ME). Cu2+ treated rats displayed diminished RB with no significant changes in LA. Cu2+ treated rats displayed higher MR's density (Bmax) in cortex (C), striatum (S), and hippocampus (H). An increase in Bmax was also observed in PA treated rats, but only in C and S. Finally, Cu2+ tissue concentration was significantly higher in C of both Cu2+ and with PA treated animals. In conclusion, 45 days of Cu2+ or PA treatment induced brain hypercuprosis, which was associated with MR binding supersensitivity; however, change in ME was only observed in PA treated rats suggesting that might be still another factor in these experiments besides Cu2+ (i.e., Zn2+ or PA itself) involved in memory modulation.

Unión P[3H]-QNB al receptor muscarínico humano en presencia de diferentes buffers / Union of P[3H]-QNB at muscarinic receptor human in presence of different buffers

Se estudio el perfil de unión de [3H]-Benzilato de Quinuclidinilo ([3H]-QNB) al receptor colinérgico muscarínico (RCM) de corteza frontal (CFH) e hipocampo humano (HPH) en presencia de diferentes buffers. Cuando las fracciones de CFH se prepararon y ensayaron en Buffers TRIS, FOSFATO o HEPES, la unión fue compatible con una discreta cooperatividad homotrópica positiva (coeficiente de Hill: 1.10-1.37). Cuando los ensayos de unión de [3H]-QNB al RCM de CFH se realizaron con buffers imidazol o citrato, la cinética resultó hiperbólica simple. El fenómeno de cooperatividad positiva se encontró en HPH mediante el uso de buffer fosfato, pero no con iris e imidazole. El uso de borato como buffer para preparar y ensayar las fracciones de CFH o HPH indujo una cinética compatible con cooperatividad homotrópica negativa o heterogeneidad, con 32-36 por ciento de sitios de alta afinidad y 64-68 por ciento de baja afinidad. El efecto inhibitorio de la fuerza iónica sobre la unión de [3H]-QNB fue similar en borato, imidazol, tris, herpes y citrato. A altas concentraciones, el efecto del buffer fosfato fue también inhibitorio, sin embargo, a bajas concentraciones, se observó un 10 por ciento de aumento en la unión. Estos resultados sugieren que la unión de [3H]-QNB al RCM humano es compleja y dependiente de las condiciones del medio.