Me. Gnegy et al., PHOSPHORYLATION OF NEUROMODULIN IN RAT STRIATUM AFTER ACUTE AND REPEATED, INTERMITTENT AMPHETAMINE, Molecular brain research, 20(4), 1993, pp. 289-298
Repeated, intermittent treatment of rats with amphetamine results in a
sensitization of locomotor and stereotyped behaviors that is accompan
ied by an enhancement in stimulus-induced dopamine release. Increased
phosphorylation of the neural specific calmodulin-binding protein, neu
romodulin (GAP-43, B-50, F1) has been demonstrated in other forms of s
ynaptic plasticity and plays a role in neurotransmitter release. To de
termine whether neuromodulin phosphorylation was altered during amphet
amine sensitization, the in vivo phosphorylated state of neuromodulin
was examined in rat striatum in a post hoc phosphorylation assay. Fema
le, Holtzman rats received saline or 2.5 mg/kg amphetamine twice weekl
y for 5 weeks. One week after the last dose of amphetamine, rats were
challenged with either 1 mg/kg or 2.5 mg/kg amphetamine or saline and
the rats were sacrificed 30 min later. Purified synaptic plasma membra
nes were prepared in the presence of EGTA and okadaic acid to inhibit
dephosphorylation, and were subsequently phosphorylated in the presenc
e of purified protein kinase C and [gamma-P-32]ATP. The protein kinase
C-mediated post hoc phosphorylation of neuromodulin was significantly
reduced in groups that received either acute or repeated amphetamine
suggesting that neuromodulin in those groups contained more endogenous
phosphate, The acute, challenge dose of amphetamine increased neuromo
dulin phosphorylation in the saline-treated controls but not in the re
peated amphetamine-pretreated group. Anti-neuromodulin immunoblots sho
wed no change in neuromodulin levels in any group. There was no signif
icant change in protein kinase C activity in any treatment group. To f
urther investigate the effect of acute amphetamine, the ability of amp
hetamine to alter neuromodulin phosphorylation in P-32(i)-preincubated
Percoll-purified rat striatal synaptosomes was examined. Amphetamine
(10 muM) significantly increased phosphorylation of a 53 kDa band that
migrated with authentic neuromodulin in the synaptosomes by 22% while
500 nM 12-O-tetradecanoylphorbol 13-acetate (TPA) increased neuromodu
lin phosphorylation by 45%. These data suggest that one injection of a
mphetamine can increase neuromodulin phosphorylation in rat striatum a
nd that this increase is maintained for at least 1 week following a re
peated, sensitizing regimen of amphetamine. Since sensitization can be
induced with one dose of amphetamine, it is possible that enhanced ne
uromodulin phosphorylation could contribute to neurochemical events le
ading to enhanced release of dopamine and/or behavioral sensitization.