MK-801-induced sprouting by CGRP immunoreactive primary afferent fibers in the dorsal spinal cord of the rat

Recordings were made from 90 identified spinomesencephalic tract (SMT) cells in the lumbosacral spinal cord of cats anesthetized with alpha-chloralose and pentobarbital sodium. Recording sites were located in laminae I-VIII. Antidromic stimulation sites were located in different regions of the rostral and caudal midbrain including the periaqueductal gray, midbrain reticular formation, and the deep layers of the superior colliculus. Twelve SMT cells were antidromically activated from more than one midbrain level or from sites in the medial thalamus. The mean conduction velocity for the population of cells sampled was 45.2 +/- 21.4 m/s. Cells were categorized based on their responses to graded intensities of mechanical stimuli and the location of excitatory and/or inhibitory receptive fields. Four major categories of cells were encountered: wide dynamic range (WDR); high threshold (HT); deep/tap; and nonresponsive. WDR and HT cells had excitatory and/or inhibitory receptive fields restricted to the ipsilateral hindlimb or extending to other parts of the body including the tail, forelimbs, and face. Some cells had long afterdischarges following noxious stimulation, whereas others had high rates of background activity that was depressed by nonnoxious and noxious stimuli. Deep/tap cells received convergent input from muscle, joint, or visceral primary afferent fibers. The placement of mechanical lesions at different rostrocaudal levels of the cervical spinal cord provided information related to the spinal trajectory of SMT axons. Six axons were located contralateral to the recording electrode in the ventrolateral/medial or lateral funiculi while two were located in the ventrolateral funiculus of the ipsilateral spinal cord. Stimulation at sites used to antidromically activate SMT cells resulted in the inhibition of background and evoked responses for 22 of 25 cells tested. Inhibitory effects were observed on responses evoked by low/high intensity cutaneous stimuli and by the activation of joint or muscle primary afferent fibers. Based on the response and receptive-field properties of SMT cells it is suggested that the SMT may have an important role in somatosensory mechanisms, particularly those related to nociception.

Download Full-text

Postnatal development of the primary afferent fibers in the dorsal horn of the rat spinal cord

Neuroscience Research Supplements ◽

10.1016/0921-8696(88)90106-5 ◽

1988 ◽

Vol 7 ◽

pp. S46

Author(s):

Takashi Shiga ◽

Toshio Shirai

Keyword(s):

Spinal Cord ◽

Postnatal Development ◽

Dorsal Horn ◽

Rat Spinal Cord ◽

Primary Afferent ◽

Afferent Fibers ◽

Primary Afferent Fibers

Download Full-text

Plasticity of calcitonin gene related peptide neurotransmission in the spinal cord during peripheral inflammation

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y95-141 ◽

1995 ◽

Vol 73 (7) ◽

pp. 1007-1014 ◽

Cited By ~ 30

Author(s):

V. S. Seybold ◽

M. T. Galeazza ◽

M. G. Garry ◽

K. M. Hargreaves

Keyword(s):

Spinal Cord ◽

Calcitonin Gene Related Peptide ◽

Peripheral Inflammation ◽

Afferent Neurons ◽

Dorsal Spinal Cord ◽

Primary Afferent Neurons ◽

Primary Afferent ◽

Related Peptide ◽

Calcitonin Gene ◽

Dorsal Spinal

Injection of complete Freund's adjuvant (CFA; 75 μL) into the plantar surface of the hind paw of the rat results in a mild inflammation that lasts for several days and is accompanied by hyperalgesia. Multiple components of calcitonin gene related peptide (CGRP) neurotransmission in the spinal cord are altered during the course of this peripheral inflammation. The content of immunoreactive (i) CGRP in the dorsal horn of the spinal cord, where primary afferent neurons terminate, is significantly decreased within 2 days after injection of CFA but increases to a level greater than that of the control at 8 days. The early decrease in iCGRP in the spinal cord suggests that the release of CGRP from primary afferent neurons is increased during the period of maximal hyperalgesia that accompanies peripheral inflammation. Changes in the mRNA for CGRP suggest that the increase in spinal content of iCGRP is due to an increase in synthesis of the peptide as the level of mRNA for CGRP is increased from 2 to 8 days after injection of CFA. Despite the decrease in the content of iCGRP in the spinal cord, there is no apparent decrease in the amount of iCGRP that can be released from the dorsal spinal cord by capsaicin; in fact, capsaicin-evoked release is increased at 4 days. Measurements of the binding of 125I-labelled CGRP in the dorsal spinal cord indicate that high affinity binding sites for CGRP are downregulated at 4 days after injection of CFA. In total, these data support the hypothesis that the activity of CGRP-containing primary afferent neurons is increased during peripheral inflammation. CGRP released from primary afferent neurons in the spinal cord may contribute to cellular changes that accompany peripheral inflammation.Key words: calcitonin gene related peptide, dorsal root ganglion, hyperalgesia, inflammation, spinal cord.

Download Full-text