Transmitter balances in the olfactory cortex: adaptations to early methamphetamine trauma and rearing environment

The olfactory cortex, comprising the anterior olfactory cortex (AOC) and the anterior piriform cortex (PirC), is a model system for the study of neural plasticity. We investigated the structural imbalances of different transmitter systems induced in this area by an early traumatisation (methamphetamine [MA] intoxication) and/or environmental deprivation (isolated rearing [IR]), with the working hypothesis that such alterations will not occur in an isolated fashion, but in mutual interaction. Indeed, acetylcholine fibre density is increased by IR in both hemispheres of the PirC (left: +22%, p<0.01, right: +21%, p<0.05) and the left hemisphere of the AOC (+13%, p<0.05), while an early MA intoxication increases it in afterwards enriched-reared animals in the PirC (+14%/+17%, p<0.05), but decreases it in the AOC (-18%/-22%, p<0.001). The serotonin fibre density is increased by IR in the right PirC of saline-treated (+13%, p<0.01), but not of MA-traumatised gerbils. GABA and dopamine in the AOC show an inverse correlation, with dopamine innervation density being increased by IR (+30%, p<0.001) and MA (+26%, p<0.01), and GABA neuropil density being reduced. Furthermore, switches in hemispheric laterality occur in the AOC. These results demonstrate the complex recursive interactions in structural cortical plasticity.