Down-regulation of delta-opioid receptors in Na+/H+ exchanger 1 null mutant mouse brain with epilepsy.

Mice lacking Na+/H+ exchanger 1 (NHE1) show a unique epilepsy phenotype although the underlying mechanisms remain unclear. Since expression of delta-opioid receptor (DOR) may be involved in control of epileptic activity, we conducted immunohistochemistry and autoradiography to investigate whether DOR expression is dys-regulated in the brain of NHE1 null mouse. Immunohistochemistry showed a decline in DOR expression in hippocampus and cortex. Autoradiographic results confirmed that the density of DOR was decreased in most cortical and hippocampal regions such as striate and temporal cortex, hippocampal CA1 and CA3 regions (reduced by 27.7 +/- 6.4%, 29.4 +/- 5.1%, 40.7 +/- 4.4% and 20.6 +/- 5.7%, respectively, P < 0.05). These data demonstrate that NHE1 null mutation leads to a reduction of DOR expression in the cortical and hippocampal regions, which provides a new clue for the genesis of epilepsy.