has been found that a some ADHD people have a different receptor for thyroid hormone and to percent to 80 percent of all with this rare difference have ADHD. Additional studies link ADHD and three genes encoding receptors for the neurotransmitter dopamine. Research notes structural abnormalities. The anterior frontal part of the brain was on an average, found to be more than 5 percent smaller on the right side in ADHD boys; the right caudate and the globus pallidus were also smaller. These areas form the main neural circuit from which the cortex inhibits behavior (Leutwyler, 1996).
Gatley, Meehan, Chen, Pan, Schechter and Dewey (1996) studied pharmacological properties of Ritalin derivatives. Methylphenidate (Ritalin) binds to the dopamine transporter; its mechanism of action is believed to "involve increased synaptic dopamine subsequent to blockade of the dopamine transporter" (p. PL-345).
Rats fed ad libitum were used. After a stable baseline for dopamine was achieved, an injection of drug was made and extracellular dopamine and activity was monitored. Results demonstrated that p-methoxymethylphenidate and bromomethylphenidate share with methylphenidate, behavior typical of psychostimulant drugs, with a raise in striatal extracellular dopamine and stimulation of locomotor activity. It was also found that "methylphenidate has about twice the affinity for dopamine transporters as cocaine, and a different binding selectivity towards the other monoamine transporters" (p. PL-347). The authors stated that cocaine addicts given intravenous methylphenidate report that the "high" is similar to that of cocaine. It is therefore concluded that methylphenbidate can be an abusive drug when self-administered by intravenous injection; oral administration is expected to be less reinforcing (Gatley et al., 1996).
Leutwyler's article supports the text's conclusion that treatment with stimulant drugs for ADHD remains controversial....