SOURCE OF BRAINSTEM RAPHE AND LOCUS COERULEUS NUCLEI INPUTS MODULATING SPINAL CORD INHIBITORY CROSS REFLEX CIRCUITRIES

Abstract

Previous studies on cross reflexes in mice demonstrated that stimulations of cutaneous afferents elicited inhibitory cross reflex. Furthermore, it was shown that the inhibitory cross reflex response is downregulated selectively in the vastus lateralis (VL) and tibialis anterior (TA) muscles during Locomotion. While it was proposed that supraspinal inputs might drive this modulation, the specific nuclei involved had not been identified. Literature on cats indicates that the administration of serotonin (5-HT) and noradrenaline (NE) in the spinal cord contributed to the suppression of short-latency spinal cross reflexes, suggesting their role in modulating the inhibitory cross reflex. Therefore, this current study investigates the influence of brainstem sources of 5-HT from medullary raphe and the NE from locus coeruleus (LC) on inhibitory cross reflex. Optogenetic and chemogenetic techniques were established to allow the manipulation of these brainstem centers. Combined with electromyography (EMG) and sural nerve stimulation, these two methods allowed us to examine brainstem centers effects on the inhibitory cross reflex. In summary, this project suggests that the LC modulates the inhibitory cross reflex during rest, but its effect during locomotion requires further investigation.