Bicuculline and strychnine suppress the mesencephalic locomotor region-induced inhibition of group III muscle afferent input to the dorsal horn

• Published in: Neuroscience 2003-01, Vol.118 (3), p.779-788
• Main Authors: DEGTYARENKO, A. M, KAUFMAN, M. P
• Format: Article
• Language: English
• Subjects: Afferent Pathways - cytology; Afferent Pathways - physiology; Animals; Bicuculline - pharmacology; Biological and medical sciences; Cats; Central nervous system; Central neurotransmission. Neuromudulation. Pathways and receptors; Efferent Pathways - cytology; Efferent Pathways - physiology; Female; Fundamental and applied biological sciences. Psychology; GABA Antagonists - pharmacology; GABA-A Receptor Antagonists; gamma-Aminobutyric Acid - metabolism; Glycine - antagonists & inhibitors; Glycine - metabolism; Locomotion - drug effects; Locomotion - physiology; Male; Muscle, Skeletal - innervation; Muscle, Skeletal - physiology; Neural Inhibition - drug effects; Neural Inhibition - physiology; Pain - metabolism; Pain - physiopathology; Posterior Horn Cells - cytology; Posterior Horn Cells - drug effects; Posterior Horn Cells - metabolism; Receptors, GABA-A - metabolism; Receptors, Glycine - antagonists & inhibitors; Receptors, Glycine - metabolism; Reflex - drug effects; Reflex - physiology; Regional Blood Flow - drug effects; Regional Blood Flow - physiology; Spinal Nerve Roots - cytology; Spinal Nerve Roots - physiology; Strychnine - pharmacology; Synaptic Transmission - drug effects; Synaptic Transmission - physiology; Tegmentum Mesencephali - cytology; Tegmentum Mesencephali - physiology; Vasoconstriction - drug effects; Vasoconstriction - physiology; Vertebrates: nervous system and sense organs
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/S0306-4522(02)00999-5

We examined the effect of iontophoretic application of bicuculline methiodide and strychnine hydrochloride on the mesencephalic locomotor region (MLR)-induced inhibition of dorsal horn cells in paralyzed cats. The activity of 60 dorsal horn cells was recorded extracellularly in laminae I, II, V-VII of spinal segments L7-S1. Each of the cells was shown to receive group III muscle afferent input as demonstrated by their responses to electrical stimulation of the tibial nerve (mean latency and threshold of activation: 20.1+/-6.4 ms and 15.2+/-1.4 times motor threshold, respectively). Electrical stimulation of the MLR suppressed transmission in group III muscle afferent pathways to dorsal horn cells. Specifically the average number of impulses generated by the dorsal horn neurons in response to a single pulse applied to the tibial nerve was decreased by 78+/-2.8% (n=60) during the MLR stimulation. Iontophoretic application (10-50 nA) of bicuculline and strychnine (5-10 mM) suppressed the MLR-induced inhibition of transmission of group III afferent input to laminae I and II cells by 69+/-5% (n=10) and 29+/-7% (n=7), respectively. Likewise, bicuculline and strychnine suppressed the MLR-induced inhibition of transmission of group III afferent input to lamina V cells by 59+/-13% (n=14) and 39+/-11% (n=10), respectively. Our findings raise the possibility that GABA and glycine release onto dorsal horn neurons in the spinal cord may play an important role in the suppression by central motor command of thin fiber muscle afferent-reflex pathways.