RESUMEN
The present study examined the influence of physical activity vs. sedentary home cage conditions on baseline and opioid-driven high-fat feeding behaviors in two common strains of laboratory rats. Sprague-Dawley and Wistar rats were singly housed with either access to a voluntary running wheel (RUN) or locked-wheel (SED) for 5â¯weeks, before being stereotaxically implanted with bilateral cannulae targeting the nucleus accumbens. Following recovery, with RUN or SED conditions continuing the duration of the experiment, all rats were given 2â¯h daily access to a high-fat diet for 6 consecutive days to establish a stable baseline intake. Over the next 2â¯weeks, all subjects were administered the µ-opioid agonist D-Ala2, NMe-Phe4, Glyol5-enkephalin (DAMGO) (multiple dose range) or saline into the nucleus accumbens, immediately followed by 2â¯h access to a high-fat diet. Drug treatments were separated by at least 1â¯day and treatment order was counterbalanced. Baseline consumption of the high-fat diet during the 1-week baseline acclimation period did not differ between RUN and SED groups in either rat strain. Higher doses of DAMGO produced increased fat consumption in both strains of rats, yet no differences were observed between RUN vs. SED treated groups. However, SED treatment produced a greater locomotor response following intra-accumbens DAMGO administration, compared to the RUN condition, during the 2â¯h feeding session. The data suggest that the animals housed in sedentary versus voluntary wheel running conditions may differ in behavioral tolerance to the locomotor but not the orexigenic activating properties of intra-accumbens DAMGO treatment.
Asunto(s)
Analgésicos Opioides/farmacología , Encefalina Ala(2)-MeFe(4)-Gli(5)/farmacología , Conducta Alimentaria/fisiología , Actividad Motora/fisiología , Núcleo Accumbens/fisiología , Carrera/fisiología , Animales , Grasas de la Dieta/farmacología , Conducta Alimentaria/efectos de los fármacos , Masculino , Actividad Motora/efectos de los fármacos , Núcleo Accumbens/efectos de los fármacos , Ratas , Ratas Sprague-Dawley , Ratas Wistar , Receptores Opioides mu/agonistasRESUMEN
Previous research has demonstrated a dissociation of certain neural mediators that contribute to the increased consumption of a high-fat diet that follows intra-accumbens (Acb) administration of µ-opioid receptor agonists vs. 24-h food deprivation. These two models, both which induce rapid consumption of the diet, have been shown to involve a distributed corticolimbic circuitry, including the amygdala. Specifically, the central amygdala (CeA) has been shown to be involved in high-fat feeding within both opioid and food-deprivation driven models. The present experiments were conducted to examine the more specific role of CeA opioid transmission in mediating high-fat feeding driven by either intra-Acb administration of the µ-opioid agonist d-Ala2-NMe-Phe4-Glyol5-enkephalin (DAMGO) or 24-h home cage food deprivation. Injection of DAMGO into the Acb (0.25 µg/0.5 µl/side) increased consumption of the high-fat diet, but this feeding was unaffected by administration of opioid antagonist, naltrexone (5 µg/0.25 µl/side) administered into the CeA. In contrast, intra-CeA naltrexone administration attenuated high-fat intake driven by 24-h food deprivation, demonstrating a specific role for CeA opioid transmission in high-fat consumption. Intra-CeA naltrexone administration alone had no effect on baseline feeding levels within either feeding model. These findings suggest that CeA opioid transmission mediates consumption of a palatable high-fat diet driven by short-term negative-energy balance (24-h food deprivation), but not intra-Acb opioid receptor activation.