Voluntary oral dosing for precise experimental compound delivery in adult rats

Preclinical drug studies routinely administer experimental compounds to animal models with the goal of minimizing potential adverse events from the procedure. In this study, we assessed the ability to train adult male Long Evans rats to accept daily voluntarily syringe feedings of l-3,4-dihydroxyphenylalanine (L-DOPA) compared to intraperitoneal (IP) injections. Rats were trained to become familiar with the syringe and then fed a training solution that did not contain the experimental compound. If the rat was compliant during the training phase, the dilution of training solution was continuously decreased and replaced with the experimental solution. Voluntary oral dosing compliance was recorded and quantified throughout the study. To assess drug activity within the drug-targeted tissues, the striatum and retina were collected and analyzed for L-DOPA, dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) levels by high performance liquid chromatography (HPLC). Drug delivery efficiency by oral dosing was directly compared to IP injection by collecting plasma and analyzing L-DOPA levels with HPLC. Adult male rats had high compliance for voluntary oral dosing. HPLC showed that oral administration of the compound at the same dose as IP injection yielded significantly lower plasma levels, and that higher oral L-DOPA doses yield higher plasma L-DOPA content. This study describes detailed methodology to train adult rats to syringe feed experimental compounds and provides important preclinical research on drug dosing and drug delivery to the striatum and retina.