Motor Activity and Stereotypy. Fig. 2. Measures from a force-plate actometer showing how the behavioral effects of d-amphetamine sulfate at 2.5 mg/kg depends on time after treatment, amount of experience with the drug, and the route of administration. After experiencing a 4-h habituation session (black circles, panels a and b), in subsequent sessions eight male Sprague Dawley rats received injections (Inj) of amphetamine eleven times, 3-4 days apart. The first ten injections were given ip, and the 11th injection (green stars) was administered sc in the same volume and dose as the previous ip injections. Panel (a) shows distance traveled for successive 3-min periods in the 4-h recording session. In panel (b) are plotted, also in 3-min intervals, group mean focused stereotypy scores for the indicated treatment conditions. Panel (c) shows the group mean power spectra of the vertical force variations over 15-min periods for the same treatments. The distinctive spectral peaks near 10-hz in the red and green power spectra reflect the rhythm of the head movements of focused stereotypy.
Another important point is that a univariate (i.e., single-dependent-variable method such as distance traveled) approach to behavioral pharmacology with ► indirect-acting dopamine agonists can easily lead to erroneous interpretations of a drug's effects. For example, if one did not have a stereotypy score (Figure 2, panel b) and relied only on the distance traveled information (Figure 2, panel a), one may erroneously conclude that, between Injection 1 and Injection 10, ► tolerance (decrease in distance traveled) had occurred instead of sensitization.
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