T. Wood

Operant conditioning and its applications in eqine pharmacology

Summary Studies of the effects of drugs on equine performance require access to sensitive methods of measuring subtle behavioral changes. Variable interval (VI) reinforcement scheduling is a specific type of operant conditioning that is sensitive to drug effects even when overt clinical signs of the drug have diminished. In our VI studies, horses were conditioned to break a light beam with a head-bobbing movement and this behavior was reinforced with a reward of clean oats (approximately 30 mg/reinforcement). Initial training procedures included acclimatization to the behavioral equipment and fixed-ratio reinforcement scheduling. To establish baseline rates of behavior the horses were converted to a variable interval (60 seconds) reinforcement schedule and were kept on this schedule for the remainder of the experiments. Daily sessions lasted 30 minutes and responding rates remained remarkably stable even after long periods of inactivity. Responses and reinforcement were recorded and dispensed by use of an electromechanical relay system wired to an electric eye, an automatic feeder and a programming and recording system. Recently, responding rates from horses administered detomidine, hordenine, xylazine and saline were monitored and compared to responding rates in horses from previous studies using acepromazine, cocaine, methylphenidate, phenylbutazone and reserpine. Rates of behavior in these operant-conditioned horses were remarkably stable over time and readily detected subclinical pharmacological effects of drug administrations.

The detection, pharmacokinetics and behavioral effects of diisopropylamine dichloroacetate (DADA) in the horse: A preliminary report

1. Drug administration studies using diisopropylamine dichloroacetate (DADA) and diisopropylamine (DIPA) were conducted in Thoroughbred and Standardbred horses to assess physiological effects and develop detection methods. 2. Four horses received 0.08 mg DADA/kg body wt and showed no changes in heart and respiratory rates or body temperature as measured over a 1-hr period after administration. A transient diuretic effect was found to occur in 2 mares dosed with 0.80 mg DADA/kg body wt. 3. A qualitative detection method using thin-layer chromatography was developed to detect DIPA, the major metabolite of DADA in equine urine. A quantitative detection method (lower limit of detection 0.5 micrograms/ml urine) for this metabolite was also developed using gas chromatography. 4. Neither DADA or the free base, DIPA, were detectable in equine blood samples using the above-mentioned methodologies.