Cerebellar mechanisms were explored underlying the effects of amphetamine (Amph) on the brain, by monitoring primarily the neurochemistry of the cerebellum. Adult mice received repeated intermittent injections of d-Amph, 5mg/kg or saline, twice daily for three days and once on day 4. As revealed by the biochemical analysis, the levels of GABA content were increased by 68-93% in the cerebellar vermis and hemisphere of mice at 4h after the first (acute) or the last (repeated) Amph injections, though the glutamate content was unaltered, compared to the respective saline-treated controls. By contrast, at 4h post-repeated Amph, in the vermis, the level of norepinephrine was approximate 38% lower than the corresponding control and 5-hydroxytryptamine (5-HT) resembled the control, whereas in the hemisphere, the norepinephrine content was similar to control and 5-HT 66% higher, implying cerebellar lobe-dependent changes. However, in both lobes, at 4h after the acute and repeated Amph exposures, changes of the transmitter content were correlated with reductions of 50-64% in the levels of the phosphorylated (p) MAP kinase (K) expression and 39-55% in the calbindin-D28k (CB) of the Purkinje cell somata, and increases of 289-556% in pCREB, 373-594% c-FOS, and 51-76% calretinin of the granular layer, as shown by immunohistochemical analysis. The up-regulated GABA content in the vermis and hemisphere may be associated with the decreased expression of Purkinje somatal CB and pMAPK, implicating a relation between the Ca(2+) of Purkinje cells and the level of GABA. Furthermore, the prominent increases of the granular layer pCREB, c-FOS and calretinin may influence the activity of Purkinje cells, which are known to be modulated by the granule cells. The data indicate that the Amph exposure selectively alters specific transmitters in the cerebellar lobes and modifies the cellular expression of distinct signaling proteins in the cerebellar layers.
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