The behavioral effects of chronic sugar and/or caffeine consumption in adult and adolescent rats

Caffeine is a psychostimulant frequently consumed by adults and children, often in combination with high levels of sugar. Chronic pretreatment with either substance can amplify both amphetamine and cocaine-induced hyperactivity in rodents. The present study sought to elucidate whether age at the time of exposure to sugar and/or caffeine alters sensitivity to an acute illicit psychostimulant (methamphetamine, [METH]) challenge in adulthood. Adult and adolescent (Postnatal Day 35 on first day of treatment) male Sprague–Dawley rats were treated for 26 days with water, caffeine (0.6 g/L), 10% sucrose or their combination. Locomotor behavior was measured on the first and last day of treatment. Following 9-days treatment free, animals were challenged with saline (1 ml/kg, i.p.) or METH (1 mg/kg, i.p.) and locomotor activity was measured. During the treatment period, adolescent rats maintained a higher caffeine (mg/kg) dose than their adult counterparts. Adding sugar to caffeine increased adolescent consumption and the highest caffeine dose consumed was measured in these animals. Drinking sugarsweetened caffeinated water or combination did not produce cross-sensitization to METH administration in either age group. Nevertheless, the finding that regular exposure through adolescence to caffeinated sugar-sweetened beverages could increase consumption of caffeine and sugar later in life is important, as there is a large body of evidence that has linked excess consumption of sugar-sweetened beverages to a broad range of other negative physical and mental health outcomes.