Pax6 Controls Progenitor Cell Identity and Neuronal Fate in Response to Graded Shh Signaling

Nociception from skeletal muscle in relation to clinical muscle pain.

Contents: Vestibular Nerve and Labyrinthine Disorders.- Central Vestibular Disorders.- Positional Vertigo.- Vascular Vertigo.- Traumatic Vertigo.- Familial Vertigo and Vertigo in Childhood.- Drugs and Vertigo.- Non-Vestibular Vertigo Syndromes.- Psychogenic Vertigo.- Physiological Vertigo.- Subject Index.

Vertigo: Its Multisensory Syndromes

Because of the likely involvement of central convergence of afferent inputs in mechanisms underlying referred pain, the activity of single neurones was recorded in the cat's trigeminal (V) subnucleus caudalis (medullary dorsal horn) to test for the presence and extent of convergent inputs to the neurones. In chloralose-anaesthetized or decerebrate unanaesthetized cats, electrical stimuli were applied to afferents supplying facial skin, oral mucosa, canine and premolar tooth pulp, laryngeal mucosa, cervical skin and muscle, and jaw and tongue muscles, and tactile and noxious mechanical and thermal stimuli were applied to skin and mucosa. Considerable proportions of caudalis neurones which could be functionally classified on the basis of their cutaneous receptive field properties as low-threshold mechanoreceptive (LTM), wide-dynamic-range (WDR), or nociceptive-specific (NS) neurones, could be excited by electrical stimulation of several of these afferent inputs. Extensive convergence of afferent inputs, including inputs from skin or mucosal areas outside the neuronal oral-facial receptive field delineated by natural stimuli, was a particular feature of the units classified as cutaneous nociceptive neurones (i.e., WDR and NS). On the basis of antidromic activation, 15% of these WDR and NS neurones were shown to have a direct projection to the contralateral thalamus. The findings question the use of terminology and classifications of somatosensory neurones based only on the cutaneous receptive field properties of the neurones since distinctions between the different neuronal populations become less obvious when properties other than those related to cutaneous afferent inputs are taken into account. Moreover, the observations of extensive convergence of different types of afferents, which was especially apparent in cutaneous nociceptive neurones, also suggest a role for these neurones in mediating deep pain and in spread and referral of pain.

Convergence of cutaneous, tooth pulp, visceral, neck and muscle afferents onto nociceptive and non-nociceptive neurones in trigeminal subnucleus caudalis (medullary dorsal horn) and its implications for referred pain.

Research on descending motor pathways to caudal brainstem and spinal cord in the spinal motor system is reviewed. Particular attention is given to somatic and autonomic motoneurons in the spinal cord and brainstem, local projections to motoneurons, bulbospinal interneurons projecting to motoneurons, descending pathways of somatic motor control systems, and descending pathways involved in limbic motor control systems.

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Descending motor pathways and the spinal motor system: limbic and non-limbic components

Transganglionic transport of HRP has been used to trace the pathways and termination sites of cutaneous and muscle afferent axons entering from the C2 and C3 dorsal rami. The muscle afferent projection in the spinal cord is restricted and (apart from the ventral horn) largely confined to the intermediate gray matter. There is a muscle afferent projection to the ventrolateral main cuneate nucleus and a complex pattern of projection through the extent of the external cuneate nucleus. In contrast, the cutaneous spinal projection is abundant with extensive filling of axons in the tract of Lissauer and many termination sites in the lateral substantia gelatinosa. Axons enter the lateral gray matter of the cervical spinal cord from the dorsal columns and the dorsolateral funiculus and terminate in the lateral one-third of the dorsal horn as far rostral as the spinomedullary junction. Axons of the tract of Lissauer form a complex web around the dorsal horn and many penetrate rostrally to the region of the spinomedullary junction, where they terminate among clusters of interstitial cells on and close to the dorsal medullary surface. Cutaneous afferent axons from the dorsal columns turn into the main cuneate nucleus and enter a dense mass of HRP-reaction product which occupies the most ventrolateral part of the nucleus for its entire length.

Projections from C2 and C3 nerves supplying muscles and skin of the cat neck: A study using transganglionic transport of horseradish peroxidase

Retrograde transport of HRP has been used to examine the distribution of motoneurons supplying the dorsal neck muscles biventer cervicis, and complexus in the cat. Retrogradely filled cells were present in the expected sites in lamina IX of the ventral horn, but were not confined to that area. Retrogradely labelled cells were also found more dorsally in the ventral horn and in the white matter medial to the ventral horn. Other filled cells were found in the commissural nuclei and in laminae VII and VIII contralateral to the nerve being dipped. Cells in the ipsilateral lamina IX ranged in size from 15 to 70 microns. Cells lying outside this region were smaller with the majority having mean equivalent diameters, of 40 microns or less.

Contralateral, midline, and commissural motoneurons of neck muscles: A retrograde HRP study in the cat

A combination of fluorescent retrograde tracers and horseradish peroxidase (HRP) was used to compare the spinal distributions of motoneurons supplying shoulder muscles with attachments to the skull and cervical spinal cord that suggest a significant role in head movement. Two muscles, the rhomboideus and the levator scapulae, were innervated by multiple segmental nerve bundles that entered the muscles at different rostrocaudal locations. Motoneurons that were labelled retrogradely from rhomboideus nerve bundles formed a single, long column in the ventral horn from C4 to C6, lateral to previously studied motor nuclei supplying deep neck muscles. When different tracers were used to differentiate motoneurons supplying specific nerve bundles, discrete subnuclei could be identified that were organized in a rostrocaudal sequence corresponding to the rostrocaudal order of the nerve bundles. Levator scapulae motoneurons formed a second elongate column immediately lateral to the rhomboideus motor nucleus. Three other muscles, the trapezius, sternomastoideus, and cleidomastoideus, were supplied by cranial nerve XI. Labelled motoneurons from these muscles formed a single column from the spinomedullary junction to middle C6. Within this column, the three motor nuclei supplying the sternomastoideus, cleidomastoideus, and trapezius were laminated mediolaterally. Sternomastoideus and cleidomastoideus motoneurons were confined to upper cervical segments, whereas trapezius motoneurons were found from C1 to C6. In C1 and C6, the motoneuron column was located centrally in the gray matter, but, between C2 and C5, the column lay on the lateral wall of the ventral horn in a position dorsolateral to motor nuclei supplying the rhomboideus and the deeper neck muscles. The findings in this study suggest that descending and propriospinal systems responsible for coordinating head movement may have to descend as far caudally as C6 if they are to project onto muscles controlling the mobility of the lower neck. J. Comp. Neurol. 377:298–312, 1997. © 1997 Wiley-Liss, Inc.

J. Keane

Papers

Projections from C2 and C3 nerves supplying muscles and skin of the cat neck: A study using transganglionic transport of horseradish peroxidase

Contralateral, midline, and commissural motoneurons of neck muscles: A retrograde HRP study in the cat

Distribution of motoneurons supplying feline neck muscles taking origin from the shoulder girdle