Selective vulnerability in striosomes and in the nigrostriatal dopaminergic pathway after methamphetamine administration : early loss of TH in striosomes after methamphetamine

Abstract

Methamphetamine (METH), a commonly abused psychostimulant, causes dopamine neurotoxicity in humans, rodents, and nonhuman primates. This study examined the selective neuroanatomical pattern of dopaminergic neurotoxicity induced by METH in the mouse striatum. We examined the effect of METH on tyrosine hydroxylase (TH) and dopamine transporter (DAT) immunoreactivity in the different compartments of the striatum and in the nucleus accumbens. The levels of dopamine and its metabolites, 3,4-dihidroxyphenylacetic acid and homovanillic acid, as well as serotonin (5-HT) and its metabolite, 5-hydroxyindolacetic acid, were also quantified in the striatum. Mice were given three injections of METH (4 mg/kg, i.p.) at 3 h intervals and sacrificed 7 days later. This repeated METH injection induced a hyperthermic response and a decrease in striatal concentrations of dopamine and its metabolites without affecting 5-HT concentrations. In addition, the drug caused a reduction in TH- and DAT-immunoreactivity when compared to saline-treated animals. Interestingly, there was a significantly greater loss of TH- and DAT-immunoreactivity in striosomes than in the matrix. The predominant loss of dopaminergic terminals in the striosomes occurred along the rostrocaudal axis of the striatum. In contrast, METH did not decrease TH- or DAT-immunoreactivity in the nucleus accumbens. These results provide the first evidence that compartments of the mouse striatum, striosomes and matrix, and mesolimbic and nigrostriatal pathways have different vulnerability to METH. This pattern is similar to that observed with other neurotoxins such as MPTP, the most widely used model of Parkinson's disease, in early Huntington's disease and hypoxic/ischemic injury, suggesting that these conditions might share mechanisms of neurotoxicity.

Fig. 1

Effect of METH on mouse rectal temperature. Repeated METH administration (4 mg/kg, i.p., every 3 h, 3×) produced a decrease in rectal temperature of the animals after the first injection and an increase in the rectal temperature, peaking 30 min after the second and third injections. The arrows indicate the time of drug injection. Data represent mean ± S.E.M., n = 6 animals/group

Fig. 2

Effect of METH on TH-immunoreactivity in the striatum. Photomicrographs of striatal sections from mice treated with saline (a–c) or METH (d–f) stained for TH. Animals were killed 7 days after treatment. Note the TH-ir loss in the METH-treated mice along the rostrocaudal axis of the striatum. (g) Histograms of the proportional stained area of TH-ir. METH (4 mg/kg, i.p., every 3 h, 3×) produced a reduction in TH-immunoreactivity levels. Data represent mean ± S.E.M., n = 6 animals/group. * P < 0.001 vs. saline, one-way ANOVA. Bar 500 μm

Fig. 3

METH produces a decrease in DAT-immunoreactivity in the striatum. Photomicrographs of striatal sections from mice sacrificed 7 days after treatment with saline (a–c) or METH (d–f) stained for DAT. Note the DAT-ir loss in the METH-treated mice along the rostrocaudal axis of the striatum. (g) Histograms show the proportional stained area of DAT-immunoreactivity. METH (4 mg/kg, i.p., every 3 h, 3×) produced a reduction in DAT-immunoreactivity levels. Data represent mean ± S.E.M., n = 6 animals/group; * P < 0.001 vs. saline, one-way ANOVA. Bar 500 μm

Fig. 4

TH- and DAT-ir loss occurs predominantly in striosomes. Serially adjacent sections from a mouse treated with METH were stained for TH (a), MOR-1 (b), and DAT (c). Most patches of weak TH-ir matched patches of weak DAT-ir and both areas corresponded with striosomes identified by MOR-1 immunostaining. a′–c′ show an example of a striosome at higher magnification. Bar 500 μm (a–c) and 200 μm (a′–c′)

Fig. 5

Loss of TH-immunoreactivity is greater in striosomes than in the matrix compartment. Histograms represent the proportional stained area of TH-immunoreactivity in striosomes (stm) and matrix (mtx) in the medial, center, and lateral areas of the striatum. Striatal slices from mice treated with METH (three injections of 4 mg/kg i.p. at 3 h intervals) were compared with those from saline-treated animals. * P < 0.001 vs. saline; ^# P < 0.01 vs. matrix; ^& P < 0.05 vs. lateral matrix

Fig. 6

Effect of METH on the striatal content of DA, DOPAC, and HVA. Amine levels were measured by HPLC in homogenates from striata of mice treated with METH (4 mg/kg) or saline. Mice were sacrificed 7 days after drug administration. Data represent the mean ± SEM, n = 6 animals/group. * 0.001 compared with control animals

Fig. 7

The NAc does not exhibit METH-induced neurotoxicity. Photomicrographs of TH-immunoreactivity in the NAc of mice treated with saline (a) or METH (b). Animals were killed 7 days after treatment. c Histograms of the proportional stained area of TH-immunoreactivity. METH (4 mg/kg, i.p., every 3 h, 3×) produced no reduction in TH-immunoreactivity. Data represent mean ± S.E.M., P = 0.12; n = 6 animals/group. Bar 500 μm