Behavioral tolerance to repeated apomorphine administration in parkinsonian monkeys

Four consecutive injections (s.c.) of apomorphine (Apo) were given to 5 parkinsonian monkeys after i.v. MPTP administration.

The minimal effective dose (MED) of Apo was defined as that capable of reducing motor disability by 50% or more for a minimum period of 30 min. Repeated apomorphine injections were given with an interval of 30 min after the motor effect of the previous injection had worn off or with a separation of 3 h between injections.

The doses used in different experiments were the MED (2.4 micrograms/kg), 4 MED and 8 MED. In every experiment the duration of motor benefit was longest with the first Apo injection.

There was a decay in the duration of the response elicited by consecutive Apo injections when given 30 min after the previous effect had waned. This was significant for the MED and 4 MED (ANOVA, P < 0.01). When Apo boluses were given with an interval of 3 h there was a significant reduction in the duration of the response elicited by the MED, 4 MED and 8 MED of apomorphine. For the MED the reduction in the duration of the motor response was significantly greater for injections given with a 30-min interval than 3-h interval.

These findings indicate that behavioral hyposensitivity to repeated Apo administration in parkinsonian monkeys occurs preferentially when near threshold doses are given with short intervals.

CITA DEL ARTÍCULO  J Neurol Sci.  1993 Jan;114(1):40-4.  doi: 10.1016/0022-510x(93)90046-2.