Effect of Chronic DL-Amphetamine Exposure on Brain Volume, Anxiogenic, Locomotor, and Social Behaviors in Male SD Rats

Abstract

Research examining the long-term effects of drugs such as Adderall^TM, a mixed DL-amphetamine, as a first-line treatment strategy for those diagnosed with attention deficit hyperactivity disorder (ADHD), is very much lacking. In order to address this, the present study sought to examine possible behavioral and neuroanatomical effects of chronic oral exposure to DL-amphetamine administered at a relatively low dose to the developing male Sprague Dawley rat. Animals were administered a mixture of chocolate drink and DL-amphetamine at a dose of 1.6 mg/kg for 36 days, beginning at PD 24 and ending at PD 60. Anxiety, a potential side effect of stimulant treatment, was assessed using three paradigms: The open field test (OF), the social interaction test (SI), and the elevated plus maze (EPM). The OF and SI were conducted using repeated testing over the course of five weeks. Testing occurred immediately after drug administration on a given day. The EPM was used only once on the penultimate day of treatment, before the drug was administered. Following drug treatment on PD 60, brain-to-body weight ratios were obtained. Results indicated that there were no group differences in brain-to-body weight ratios nor were differences in locomotor and social behaviors observed. However, rats treated with DL-amphetamine did show an anxiogenic response in the EPM. This was represented as a significant reduction in open arm entries. Overall our findings suggest that while chronic drug treatment fails to alter multiple measures of behavior, or reliable changes in brain volume, such treatment may impact a behavioral index of anxiety. Future research should seek to examine the implications of this heightened anxiogenic response in animals treated chronically with oral, low-dose DL-amphetamine.