Central circuits regulating the sympathetic outflow to lumbar muscles in spinally transected mice by retrograde transsynaptic transport.

Despite considerable interest in the mechanisms that control the hyperalgesia associated with muscle inflammation, the CNS descending pathways that coordinate autonomic circuits regulating lumbar muscles are not adequately understood. Here we used both pseudorabies virus (PRV)-614 retrograde transsynaptic tracing and spinally transected method in 33 C57BL/6J mice to map the polysynaptic pathways between lumbar muscle and CNS. Tissues were processed for dual-label immunocytochemical detection between PRV-614 and tryptophan hydroxylase (TPH) or tyrosine hydroxylase (TH)-expressing neurons in CNS. In intact mice, PRV-614 was transported to the intermediolateral column (IML) and ventral horn (VH) of spinal cord, with subsequent transport to many brain regions, including the medullary raphe nuclei, rostral ventrolateral medulla (RVLM), A5 cell group regions (A5), locus coeruleus (LC), the medullary and pontine reticular formation nucleus (MRN and PRN), paraventricular nucleus of the hypothalamus (PVN), and other central sites. However, PRV-614 in spinally transected mice produced retrograde infection of IML, with subsequent transport to main brain regions that have been shown to contribute to regulating sympathetic circuits, including RVLM, Lateral paragigantocellular reticular nucleus (LPGi), A5, LC, and PVN, whereas PRV-614 labeling in VH and MRN was eliminated in almost every case. In above five brain regions, dual-labeling immunocytochemistry showed coexpression of PRV-614/TPH and PRV-614/TH immunoreactive (IR) neurons involved in these regulatory circuits. Our results reveal a hierarchical organization of central autonomic circuits controlling the lumbar muscles, thus providing neuroanatomical substrates for the central catecholaminergic and serotonergic system to regulate the lumbar muscles.