Korean J Physiol Pharmacol.  1998 Feb;2(1):9-19.

Sensory inputs to upper cervical spinal neurons projecting to midbrain in cats

• Kim JH
• Jeong HS
• Park JS
• Kim JK
• Park SH

Abstract

The present study was primarily carried out to characterize the properties of the spinomesencephalic tract (SMT) neurons that project from the upper cervical spinal segments to the midbrain. It was also investigated whether these neurons received convergent afferent inputs from other sources in addition to cervical inputs. Extracellular single unit recordings were made from neurons antidromically activated by stimulation of midbrain. Recording sites were located in lamina IapprxVIII of C1apprxC3 segments of spinal cord. Receptive field (RF) and response properties to mechanical stimulation were studied in 71 SMT neurons. Response profiles were classified into six groups: complex (Comp, n = 9), wide dynamic range (WDR, n = 16), low threshold (LT, n = 5), high threshold (HT, n = 6), deep/tap (Deep, n = 10), and nonresponsive (NR, n = 25). Distributions of stimulation and recording sites were not significantly different between SMT groups classified upon their locations and/or response profiles. Mean conduction velocity of SMT neurons was 16.7 +/- 1.28 m/sec. Conduction velocities of SMTs recorded in superficial dorsal horn (SDH, n = 15) were significantly slower than those of SMTs recorded in deep dorsal horn (DDH, n = 18), lateral reticulated area (LRA, n = 21), and intermediate zone and ventral horn (IZ/HV n = 15). Somatic RFs for SMTs in LRA and IZ/VH were significantly larger than those in SDH and DDH. Five SMT units (4 Comps and 1 HT) had inhibitory somatic RFs. About half (25/46) of SMT units have their RFs over trigeminal dermatome. Excitabilities of 5/12 cells and 9/13 cells were modulated by stimulation of ipsilateral phrenic nerve and vagus nerve, respectively. These results suggest that upper cervical SMT neurons are heterogenous in their function by showing a wide range of variety in location within the spinal gray matter, in response profile, and in convergent afferent input.

Keyword

Spinomesencephalic tract; Vagus nerve; Phrenic nerve

MeSH Terms

Animals
Cats*
Horns
Mesencephalon*
Neurons*
Phrenic Nerve
Spinal Cord
Vagus Nerve