Alterations of BDNF and NT-3 genes expression in the nucleus paragigantocellularis during morphine dependency and withdrawal.

Locus coeruleus (LC) plays a key role in opioid dependence and withdrawal. Chronic morphine administration induces neurochemical adaptations in the noradrenergic system. The nature of signal responsible for opiate-induced adaptations of noradrenergic neurons in LC is not well defined. Neurotrophins-signaling pathways such as brain derived neurotrophic factor (BDNF) and Neurotrophin-3 (NT-3) play a key role for regulating the noradrenergic response of LC neurons to opiates. The nucleus paragigantocellularis (PGi) is one of the two major afferents to LC. The present study was designed to evaluate the expression of BDNF and NT-3 in the context of opiate dependence and withdrawal in PGi. Such data are important because they could reveal the role of PGi as an additional source of BDNF and NT-3 in the neurochemical plasticity of LC neurons. Opiate dependence was induced by a progressive intraperitoneal treatment of morphine. In morphine dependent group PGi nucleus was extracted for gene expression assay 6h after the last injection of morphine. In spontaneous withdrawal, rats received the same chronic treatment as morphine group. PGi was extracted for gene expression assay 24, 48 and 72 h after the last injection of morphine. PGi nucleus was assayed for the expression of BDNF and NT-3 using semi-quantitative RT-PCR normalized to beta-actin gene expression. Results showed that chronic administration of morphine significantly increased BDNF and NT-3 gene expression in PGi. In spontaneous withdrawal, BDNF/NT-3 genes expression were high in comparison to control group. It seems that BDNF/NT-3 -signaling pathway originating from PGi is essential for opiate-induced adaptations of the LC neurons.