Asymmetrical changes in lumbar sympathetic nerve activity following stimulation of the sciatic nerve in rat

Korim, Willian Seiji, et al. "Asymmetrical changes in lumbar sympathetic nerve activity following stimulation of the sciatic nerve in rat." Brain research 1391 (2011): 60-70. The somatosympathetic reflex (SSR) can be observed as responses in post ganglionic sympathetic nerves after the stimulation of Type 2 and 3 sensory fibers. Before this study it was known that this reflex produced differential responses in ipsilateral and contralateral hindlimb blood flow (HFB) following activation of the sciatic nerve. However, how these changes were occurring was unknown, Pilowsky's laboratory hypothesized that changes in HBF was due to differential changes in lumbar sympathetic nerve activity (lSNA) and this was being driven by supraspinal structures (RVLM). To do this sciatic nerve stimulation was accomplished while both ipsilateral and contralateral lSNA was recorded under a variety of conditions (normal, cervical spinal transections, and injections of muscimol into the contralateral RVLM). Before the the cervical spinal transections and blockade of the RVLM it was observed that following sciatic nerve stimulation a differential response was observed at the level of the lSNA. Specifically, the ipsilateral recording showed inhibitory potentials corresponding to decreases in lSNA, while contralateral recordings showed sympathoexcitatory potentials corresponding to increased lSNA. This is consistent with previous literature showing increases in ipsilateral HBF and decreases in contralateral HBF following stimulation of type 2 and 3 sensory fibers. The second observation, was following cervical spinal transections both ipsilateral inhibitory and contralateral excitatory response were diminished. This suggests the reflex is controlled partially by a supraspinal structure. Pilowsky hypothesized that the RVLM was taking part in this reflex and initially did microinjections of muscimol into the contralateral RVLM. Following the microinjections all inhibitory and excitatory responses were abolished. To further investigate, microinjections of glutamate antagonist (kynurenic acid) were also injected into the RVLM and it was seen that only the sympathoexcitatory responses were abolished. In conclusion, the microinjections studies suggest that the RVLM plays a role in the sympathoexcitatory SSR by activating pre-ganglionic sympathetic nerves in which then activate the post-ganglionic sympathetic nerves (lSN) controlling blood flow at the level of the hindlimbs. However, the exact role the RVLM plays in sympathoinhibition is still not clear and needs further investigation. ~JI