Methylphenidate cross-sensitization with amphetamine is dose dependent but not age dependent

Psychostimulants such as methylphenidate (MPD) and amphetamine (AMP) are often prescribed to young children and adolescents to treat behavioral disorders, or used to improve their intellectual performance in our competitive society. This is concerning as the temporal effects of how MPD exposure at a young age influences the response to MPD and AMP administration later in adulthood remains unclear. The objective of this study was to test whether MPD has the characteristics of substances that elicit behavioral symptoms of dependence and whether those effects are influenced by the initial age of MPD exposure. Three control and nine experimental groups of male rats were used. They were exposed to repetitive (chronic) 0.6, 2.5, or 10.0 mg/kg MPD in adolescence only, adulthood only, or adolescence and adulthood respectively. Then all groups were subsequently re-challenged with a single AMP dose in adulthood to test whether cross-sensitization between MPD and AMP was expressed, potentially as a result of prior MPD consumption. Exposure to 2.5 mg/kg and 10.0 mg/kg MPD in adolescence and adulthood or in adulthood alone led to cross-sensitization with AMP while exposure to 0.6 mg/ kg MPD in adolescence and adulthood or in adulthood alone did not lead to cross-sensitization with AMP. Thus, these results indicate that MPD cross-sensitization with AMP is dose dependent.