Baroreceptor reflex stimulation does not induce cytomegalovirus promoter-driven transgene expression in the ventrolateral medulla in vivo.

Adenoviruses are being employed to induce transgene expression in the central nervous system in vivo. In these studies, the cytomegalovirus (CMV) promoter is commonly employed to drive expression of the transgene because of its strong, constitutive activity in a wide range of cell types. However, using this promoter, expression in neurons is variable, with strongest expression being observed in non-neuronal cells. Indeed, even in vitro, CMV driven expression in neurons is variable. In cultured sympathetic ganglion cells it has been demonstrated that CMV-driven expression requires activation of cAMP-response element-binding protein (CREB) and that this can be induced by depolarization. In this study we tested whether depolarization might induce CMV-driven transgene expression, delivered by microinjection of an adenovirus, in the rostral ventrolateral medulla (RVLM) of rats. Prior to stimulation, transgene expression occurs in non-neuronal cells in the RVLM. Some neuronal expression was observed in neighbouring regions, in the nucleus ambiguus and in facial motor neurons. Within the RVLM, depolarization, induced by intraperitoneal administration of the ganglion blocking drug, pentolinium, did not lead to induction of transgene expression. This stimulus is known to induce expression of the immediate early gene c-fos. We conclude that either this experimental paradigm was not sufficient for activation of the CREB pathway or that possibly the virus does not gain access to the neurons of the RVLM. The adoption of specific promoters or viruses with higher neuronal transduction efficiency appears to be essential for the genetic modification of RVLM presympathetic neurons in vivo.