Opioid Modulation of Differential Gene Expression and Neuronal Differentiation in the Ventricular-subventricular Zone...

The endogenous opioid system regulates diverse functions including pain, physiological processes and motivation. An earlier study had demonstrated increased cell proliferation in the neurogenic niche, that is, the ventricular-subventricular zone (V-SVZ) of adult male zebra finches (Taenopygia guttata) following administration of naloxone, a general opioid antagonist.

To explore gene expression changes underlying the increase in cell proliferation in the V-SVZ of these birds after blocking opioid receptors (ORs) with systemic injections of naloxone. To assess whether opioid antagonism influences neuronal differentiation in the V-SVZ adjacent to the song control nuclei HVC and Area X, both critical for song learning and production.

Whole transcriptome microarray analysis of the V-SVZ was performed following naloxone or vehicle administration. The analysis identified 26 differentially expressed transcripts (fold change [FC] ≥ 1.5), including upregulated genes associated with neuroblast migration, neuronal differentiation, synaptic plasticity, and chromatin remodelling. Quantification of bromodeoxyuridine (BrdU) and doublecortin (DCX) positive cells was performed to determine proliferation and neuronal differentiation in the V-SVZ adjacent to HVC and Area X.

Among differentially expressed transcripts, tgu-miR-124-201 (the precursor of miR-124-3p, a key regulator of neuronal differentiation), showed significant upregulation. Selected transcripts were validated by qRT-PCR, confirming their altered expression following naloxone treatment, compared to controls. Furthermore, we observed higher neuroblast density in the ventral V-SVZ adjacent to striatal song nucleus Area X, but not in the V-SVZ above the pallial song nucleus HVC, suggesting region-specific opioid modulation of neurogenesis.

Together, these results demonstrate that OR blockade may promote neurogenesis in adult songbirds and is accompanied by the upregulation of key transcripts, including miR-124-3p. Given the established role of miR-124 in promoting neuronal differentiation, its upregulation suggests that OR blockade may enhance neuronal differentiation via microRNA (miRNA)-mediated pathways. This finding provides the first evidence linking opioid modulation to miRNA-driven neurogenic processes in an adult avian brain.