This experiment was designed to elucidate the neurotransmitter systems
that mediate the discriminative stimulus effects of methamphetamine.
Four pigeons were trained to peck one key following saline injections
and a second key following methamphetamine injections (1.0 or 1.7 mg/k
g, IM). Substitution tests revealed drug-appropriate responding follow
ing administration of the psychomotor stimulants methamphetamine, amph
etamine and cocaine, the dopamine (DA) reuptake inhibitor bupropion, n
orepinephrine (NE) reuptake inhibitors imipramine and tomoxetine, and
the serotonin (5-HT) releaser fenfluramine. Saline-key responding occu
rred following administration of the D-1 agonist SKF-38393, the D-1 an
tagonist SCH-23390, the alpha(2) receptor agonist clonidine, the alpha
(1)-antagonist prazosin, a nonselective beta-antagonist propranolol an
d the selective 5-HT reuptake inhibitor fluoxetine. The D-2/D-3 agonis
t quinpirole produced drug-appropriate responding in two pigeons and p
artial substitution in the remaining two pigeons. The 5HT(1A) agonist
8-OH-DPAT produced drug-appropriate responding at higher doses (0.3-1.
0 mg/kg), whereas much lower doses (0.003-0.1 mg/kg) antagonized the m
ethamphetamine stimulus. The stimulus effects of methamphetamine were
attenuated by pretreatment with prazosin, SCH-23390 and eticlopride, w
hereas pretreatment with propranolol and the 5-HT3 antagonist, MDL 722
22, failed reliably to attenuate drug key responding. These results su
ggest that NE and DA reuptake inhibition and 5-HT release mediate the
discriminative stimulus effects of methamphetamine as do the 5-HT1A an
d DA D-1 and D-2 receptors.