RESUMEN
RATIONALE: Evidence suggests that differential rearing influences the function of a receptor subtype critical for maintaining glutamate homeostasis. Maintaining homeostatic glutamatergic function may be an important protector against drug abuse. OBJECTIVE: This study sought to determine if differential rearing influences the function of a receptor critical for glutamate homeostasis, which could in turn affect rates of amphetamine self-administration. METHODS: Rats were assigned to enriched (EC), isolated (IC), or standard (SC) conditions. After rearing for 30 days, rats were trained to lever press for sucrose reinforcement before the implantation of indwelling jugular catheters. After reaching stable responding for amphetamine (0.03 or 0.1 mg/kg/infusion), rats were injected with five doses (0, 0.3, 1.0, 3.0, and 5.0 mg/kg) of the mGluR5 antagonist, 3-((2-methyl-1,3-thiazol-4-yl)ethynyl) pyridine hydrochloride (MTEP), 30 min before self-administration sessions. Following fixed-ratio (FR-1) testing, rats were administered identical doses of MTEP on a progressive-ratio (PR) reinforcement schedule. RESULTS: MTEP (3.0 mg/kg) attenuated FR-1 self-administration (0.03 mg/kg/infusion) in IC rats. MTEP also dose-dependently attenuated amphetamine self-administration (0.1 mg/kg/infusion) during FR-1 and PR sessions, with 5.0 mg/kg MTEP attenuating amphetamine self-administration in IC and SC rats and 3.0 mg/kg MTEP attenuating amphetamine self-administration in EC and SC rats. PR results also revealed that IC rats not treated with MTEP were more motivated to self-administer the higher dose of amphetamine. CONCLUSIONS: These results suggest that the mGlu5 receptor mediates differences in drug-taking behavior among differentially reared rats. Isolation also decreased sensitivity to MTEP, suggesting that environmental factors alter glutamate homeostasis which subsequently affects sensitivity and motivation to self-administer amphetamine.
Asunto(s)
Anfetamina/administración & dosificación , Ambiente , Motivación/efectos de los fármacos , Receptor del Glutamato Metabotropico 5/fisiología , Esquema de Refuerzo , Trastornos Relacionados con Anfetaminas/psicología , Animales , Relación Dosis-Respuesta a Droga , Masculino , Motivación/fisiología , Actividad Motora/efectos de los fármacos , Actividad Motora/fisiología , Ratas , Ratas Sprague-Dawley , Autoadministración , Sacarosa/administración & dosificaciónRESUMEN
Effects of chemical treatment of cotton byproduct (CBP) on apparent digestibility, mineral balance, urine volume and pH and in vitro digestibility were studied in three experiments with growing lambs and a rumen-fistulated steer. Apparent dry matter digestibility (DMD) and apparent organic matter digestibility (OMD) of total diets were increased (P < .01) by 35.4 and 35.7% in Exp. 1, and by 16.2 and 13.6% in Exp. 3. The CBP was treated wih 4% (4 kg sodium hydroxide/96 kg CBP dry matter) sodium hydroxide (NaOH) and fed at 70% of the total dietary intake. Treatment of CBP with nitric and sulfuric acid increased (P < .01) both DMD and OMD 25% (Exp. 1). In Exp. 2, NaOH treatment decreased (P < .05) organic matter, cellulose and lignin content of CBP and increased (P < .05) ash content. In vitro digestibilities of dry matter, organic matter and cell walls were increased (P < .05) by NaOH treatment. Volume of urine excreted by lambs in Exp. 1 and 3 was increased (P < .05) 53% but urine pH was affected by NaOH treatment. Acid treatment, however, resulted in a decrease (P < .01) in urine pH (9.4 vs 5.3). Feeding NaOH-treated CBP at increasing percentages of the diet increased Na balance and decreased K, Cl and Mg balance. NaOH-treated CBP had no effect on Ca or P balance. These results indicate the NaOH treatment of cotton byproduct increases apparent digestibility and that consumption of the treated product may increase the animal's requirement of K, Cl and Mg. Furthermore, urine volume is increased but urine pH is not affected by NaOH treatment.