Spinal cord, sensory transmission

SENSORY TRANSMISSION IN THE SPINAL CORD Morphology of the spinal cord dorsal horn... 

Ultrastructural studies showed S receptor immunoreactivity was presynaptically localized to sensory inputs to the spinal cord [48]. Dorsal rhizotomy caused a dramatic decrease in <5 receptor immunoreactivity in spinal cord and <5 receptors were also expressed in the peripheral ganglia which send inputs to the spinal cord. These findings support the notion that <5 receptors are presynaptic to sensory inputs and are involved in the presynaptic inhibition of the release of transmitters involved in mediating nociceptive transmission. 

Opioid agonists produce analgesia by binding to specific G protein-coupled receptors that are located in brain and spinal cord regions involved in the transmission and modulation of pain (Figure 31-1). Some effects may be mediated by opioid receptors on peripheral sensory nerve endings. 

Li, P., Wilding, T.J., Kim, S.J., Calejesan, A.A., Huettner, J.E., Zhuo, M. Kainate-receptor-mediated sensory synaptic transmission in mammalian spinal cord, Nature 1999, 397,161-164. 

Barazangi N, Role LW (2001) Nicotine-induced enhancement of glutamatergic and GABAergic synaptic transmission in the mouse amygdala. J Neurophysiol 86 463-74 Bardoni R, Torsney C, Tong C-K, Prandini M, MacDermott AB (2004) Presynaptic NMDA receptors modulate glutamate release from primary sensory neurons in rat spinal cord dorsal horn. J Neurosci 24 2774-81... 

Stage 1 (analgesia) is bronght about by a decrease in the activity of the dorsal horn of the spinal cord, which interferes with the sensory transmission in the spinothalamic tract. 

Nitric oxide synthase (NOS), the enzyme that generates nitric oxide (NO), is found in some neurons in the CNS. While NO plays a significant physiologic function in relaxation of vascular smooth muscle, a role for nitric oxide in synaptic transmission in the CNS has not been clearly established. Substance P is a neurotransmitter released from unmyelinated sensory neurons in the spinal cord involved in nociception. The answer is (D). 

In pain pathways, central sensitization involves enhanced efficiency of excitatory synaptic transmission pathways within the CNS, notably in the dorsal horn of the spinal cord at the synapse between the sensory nociceptor fibres and second-order relay neurones (Ji et al. 2003). It has been suggested that central sensitization in the cough reflex loop might also underlie hypertussive states (Bonham et al. 2004, 2006a, b), but to date, there are few data confirming this. 

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