A method for the identification of pseudorabies virus protein and angiotensin AT_1A receptor mRNA expression in the same CNS neurons

Neurotropic viruses have been used over the last 10 years to map the distribution of chains of synaptically connected neurons in the CNS. The peptide content of infected neurons has been determined in a number of cases immunohistochemically. However, it has been unclear whether specific mRNA can be assessed in virus-infected neurons. We have established a technique which enables the identification of viral protein and mRNA in the same neuron. In the present study pseudorabies virus retrogradely transported from the kidney was localised using immunohistochemistry and mRNA for the angiotensin II AT_1A receptor was detected by hybridisation histochemistry. Virus protein was visualised using an immunohistochemical procedure with diaminobenzidine as the chromogen and the same sections were exposed to radioactively labelled (³⁵S) riboprobes, hybridising the angiotensin II AT_1A receptor. The combination of these two approaches resulted in the identification of neurons shown to project polysynaptically to the kidney and express AT_1A mRNA. These data provide neuroanatomical support for previous physiological observations that ablation of the lamina terminalis and administration of losartan, the AT₁ receptor antagonist, blocks the inhibition of renal sympathetic nerve activity following centrally injected Ang II in rats and sheep [5].