Location and properties of dorsal horn neurons at origin of spinoreticular tract in lumbar enlargement of the rat

Abstract

1. Spinoreticular tract neurons at the rat lumbar cord level were identified by antidromic activation following stimulation at mainly pontine and mesencephalic levels. These units, which were found in the dorsal half of the cord, could be separated into two groups according to their spinal location, electrophysiological properties, and their central projections. 2. Units in the dorsolateral funiculus nucleus projected mainly to the cuneiformis area and adjacent structures with frequent bilateral projections. They had the slowest conduction velocities, sometimes in the unmyelinated range. Generally, they were driven only by stimulation of subcutaneous and/or deep structures. 3. Neurons located in the dorsal horn mainly projected contralaterally to pontine and mesencephalic levels. their conduction velocities and the electrophysiological properties were identical to those observed for the rat spinothalamic tract (22). Almost all (86%) had clear cutaneous sensitivity and generally large receptive fields: 40% responded to nonnoxious and noxious mechanical cutaneous stimuli and frequently to noxious radiant heat, 26% were exclusively excited by light tactile stimuli, and 20% required noxious cutaneous mechanical stimulation for activation. There was a good correlation between responses to natural and transcutaneous electrical stimulation: units driven by noxious mechanical stimuli received A-delta- and/or C-fiber inputs. The remaining units (14%) had more complex receptive fields associated with both excitatory and inhibitory inputs originating from a single peripheral area. 4. The functional heterogeneity of the rat spinoreticular tract is reminiscent of that demonstrated for the rat and monkey spinothalamic tracts. Similarly, the rat spinoreticular neurons are under the influence of descending inhibitory controls originating from the nucleus raphe magnus and bulbar reticular formation. 5. Responses of the rat spinoreticular tract neurons are consistent with the involvement of this pathway in the transmission of messages of both innocuous and noxious origins.

Multisegmental Aδ- and C-Fiber Input to Neurons in Lamina I and the Lateral Spinal Nucleus

“…Our data support the idea of involvement of LSN neurons in nociceptive processing (Olave and Maxwell, 2004). Converging inputs to LSN neurons can be from afferents innervating joints and deep tissue (Menétrey et al, 1980), muscles (Olave and Maxwell, 2004), and viscera (Sugiura et al, 1989).…”

“…However, little is known about the afferent inputs to the LSN. LSN neurons are not directly activated by cutaneous stimulation (Giesler et al, 1979;Menétrey et al, 1980) but respond to movement of joints and deep tissue (Menétrey et al, 1980). For this reason, the afferent input to the LSN is associated with C-fibers innervating muscles (Olave and Maxwell, 2004) and viscera (Sugiura et al, 1989).…”

Responses of thoracic spinothalamic neurons to intracardiac injection of bradykinin in the monkey.

“…Spinothalamic neurons were often found in clusters in this study. Clusters of spinoreticular and spinothalamic neurons have also been found by other investigators (Menetrey et al, 1980; G. Kevetter and W. D. Willis, personal communication). Although we made no attempt to verify this observation by anatomical techniques, the clusters extended approximately 200 jum in the rostral-caudal dimension, 100 jum mediolaterally, and 500 jum dorsoventrally.…”

Genotype-dependent responsivity to inflammatory pain: A role for TRPV1 in the periaqueductal grey

“…The LPAG receives input from the primary motor areas of the cortex (controlling hind limbs and forelimbs) (Newman et al, 1989), spinal cord and the spinal trigeminal nucleus (Keay et al, 1997;Keay and Bandler, 1992;Menétrey et al, 1980;Menétrey and De Pommery, 1991;Mouton et al, 2001Mouton et al, , 1997Mouton and Holstege, 1998;Vanderhorst et al, 1996;Wiberg et al, 1987, Yezierski, 1991Yezierski and Broton, 1991;Yezierski and Mendez, 1991). In turn, neurons project from the LPAG to the rostral and caudal regions of the ventromedial and ventrolateral medulla (Holstege, 1991;Holstege and Kuypers, 1982;Illing and Graybiel, 1986).…”