Differential alterations in the relations among GABAergic, catecholaminergic and calcium binding protein expression...

This study explores cellular responses of distinct layers of the main olfactory bulb (OB) to amphetamine (Amph), by examining the expression of glutamic acid decarboxylase67 (GAD67), calcium binding proteins (CaBP) and tyrosine hydroxylase (TH). Immunocytochemical analysis was performed on OB sections prepared from adult mice at 0.5 h or 4 h after receiving one intraperitoneal injection or multiple (2 doses/day, 7 doses in total) injections of saline or Amph, 5 mg/kg. In the glomerular layer, though the expression of TH and GAD67 was unaltered by the single Amph injection, at 0.5 h post-repeated Amph exposure the levels of TH-immunopositive somata and processes/punctates, and GAD67-somata/punctates were increased by 48-147%, compared with respective saline controls. By contrast, at 4 h post-repeated Amph GAD67 levels were lower than saline, and TH similar to saline. For the repetitively saline-injected groups, TH and GAD67 levels were higher at 4h than 0.5 h, suggesting an injection-associated stress response. Double staining revealed that at 0.5h post-repeated Amph exposure, the percentage of TH-soma number that expressed GAD67 was raised to 46%, compared with 30% of the corresponding saline, and thus implies an activation of dopaminergic neurons to become GABAergic. In the external plexiform layer, the numbers of CaBP, parvalbumin or calretinin-somata were increased at 0.5 h/4 h or 4 h post-acute Amph injection; double staining disclosed that at 4 h post-acute Amph, 66% or 47% of GAD67-somata contained parvalbumin or calretinin, being greater than 43% or 28% of the saline. In the granule somata, Amph probably inhibits expression of GAD67 by decreasing phosphorylation of CREB (pCREB). The up-regulation of CaBPs, GAD67 and TH at 0.5/4 h post-acute or 0.5 h post-repeated Amph could implicate protective roles and synaptic plasticity against Amph, whereas decreases of GAD67 and pCREB at 4 h post-repeated Amph may indicate toxicity of Amph.