The morphology of spinocervical tract neurones revealed by intracellular injection of horseradish peroxidase (cat)

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199

SUMMARY1. The enzyme horseradish peroxidase (HRP) was injected into single axons that innervated hair follicle receptors to study the morphology of their collaterals in the dorsal horn of the cord. The axons were impaled near the dorsal root entrance zone in the lumbosacral spinal cord of anaesthetized cats and HRP injected by passing current through the intra-axonal micro-electrode. The morphology was revealed by subsequent histochemistry.2. Thirteen hair-follicle afferent fibres were stained including six that innervated tylotrichs (type T hair follicle afferent units) and one that innervated guard hairs (type G unit). The remaining six axons were not classified according to hair type, but, on the basis of their axonal conduction velocities, would have been either type G or T.3. Eleven axons could be traced back into the dorsal roots. Eight of these, upon entering the cord, turned and ran towards the brain. They did not divide into rostral and caudal branches. Three of the eleven did divide and gave rise to both rostral and caudal branches.4. Sixty-three collaterals were given off the thirteen stained axons. All well-filled collaterals had a strikingly similar morphology. They descended through laminae I-III of the dorsal horn into the deeper parts of lamina IV or into lamina V, before turning and ascending back into superficial lamina IV and lamina III where they branched profusely to give rise to their terminal arborizations. Terminal boutons, most commonly of the 'en passant' type, were numerous in lamina III, but were also seen in the dorsal part of lamina IV and in ventral lamina II. None were observed in

Section: Discussionmentioning

confidence: 99%

The morphology of hair follicle afferent fibre collaterals in the spinal cord of the cat

Brown¹,

Rose²,

Snow³

1977

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199

“…The absence of local axon collaterals in deep, lumbar, s.t.t. cells suggest that, like dorsal spinocerebellar tract cells (Randic, Miletic & Loewy, 1981), but unlike spinocervical tract cells (Brown, Rose & Snow, 1977 a) and post-synaptic dorsal column units Fyffe, 1981), these cells probably do not participate in neural circuits at the segmental level.…”

Section: Axonal Projectionsmentioning

confidence: 99%

The morphology of physiologically identified deep spinothalamic tract cells in the lumbar spinal cord of the cat

Meyers

Snow

1982

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1. The morphology of eleven physiologically identified, deep, spinothalmic tract (s.t.t.) cells in the seventh lumbar segment of the cat were studied after being intracellularly injected with horseradish peroxidase (HRP).2. Four of these cells, prepared for-combined light and electron microscopy, did not appear to be as well filled with HRP as the other cells which were prepared solely for the light microscope. In these four cells the axons were not stained and significantly fewer distal dendrites were stained.3. The axons of the other seven cells projected medially, crossed the mid line in the ventral white commissure and ascended in the contralateral ventral funiculus. No axon collaterals were found.4. The dendrites of eight cells could be divided into three groups. The first group projected laterally across lamina VII, usually passing through the ventrolateral portion of lamina VI before entering the lateral funiculus. The second group projected ventrally, ventromedially and ventrolaterally through the ventral parts of laminae VII and VIII and into the ipsilateral ventral funiculus. The third group projected towards the central canal, the ventral border of the dorsal columns and the dorsal parts of the ipsilateral ventral funiculus. This group usually branched profusely and projected into lamina X.5. Of the remaining three cells, one was located more deeply than any other cell, one was probably incompletely filled, and one was located more laterally. The first two cells had dendritic trees which bore strong similarities to the other eight cells described above.6. In all, 12-3-37-5 % of dendritic tips were found in the white matter ofthe ventral or lateral funiculi.7. Dendrites never entered the dorsal columns but they could often be traced to points very close to the dorsal columns before they turned abruptly and ran parallel to the grey-white border.8. These data are discussed in relation to the excitatory and inhibitory responses of s.t.t. cells to somatic stimuli and the axonal projections of physiologically identified primary afferents and spinal interneurones.

“…However, recent work has shown that the PSDC and SCT systems arise, at least in substantial part, from separate populations of neurones in the dorsal horn (Brown, Noble & Riddell, 1986). Furthermore, studies of the morphology (Brown, Rose & Snow, 1977;Brown & Fyffe, 1981; Enevoldson, 1982) and ultrastructure of neurones of the two systems have revealed important differences between them. PSDC neurones are contacted by boutons which may participate in axo-axonic contacts, triadic arrangements and glomerular complexes (Maxwell, Koerber & Bannatyne, 1985; (Bannatyne, Maxwell & Brown, 1987), suggesting that both their course and fine fibre inputs are subject to presynaptic modulatory influences.…”

Section: Introductionmentioning

confidence: 99%

Cutaneous excitatory and inhibitory input to neurones of the postsynaptic dorsal column system in the cat.

Noble

Riddell

1988

SUMMARY1. In chloralose-anaesthetized cats single-unit microelectrode recordings were made from axons in the dorsal columns, at the lumbar level, identified as belonging to the postsynaptic dorsal column (PSDC) system.2. Excitatory and inhibitory receptive field arrangements of a sample of seventyfive PSDC neurones were examined in detail using natural cutaneous stimuli.3. The sample was characterized by a high degree of convergent input: 80% of units were activated by both light tactile and noxious mechanical stimuli and more than half of those examined were excited by noxious radiant heat. In addition, threequarters of the units had inhibitory receptive fields on the ipsilateral limb.4. Twenty-three units (27 %) were influenced by input from areas of both hairy and glabrous skin covering the foot and distal limb. Neurones in this group had complex receptive fields, many of which occupied several discontinuous areas of skin. Background and evoked activity of these units could frequently be inhibited by light tactile and/or noxious stimuli. Their inhibitory receptive fields occupied small areas of skin overlapping or adjacent to excitatory fields.5. Fifty-two units (73 %) had receptive fields restricted to areas of hairy skin on the thigh and upper hindlimb. Half the units in this group had coextensive low-and high-threshold excitatory areas but about one-third had a concentric receptive field organization; a high-threshold excitatory component extending beyond, or around, a central low-threshold area. The discharge of these units could be inhibited only by light tactile stimuli. Their inhibitory receptive fields covered extensive areas of skin, sometimes completely surrounding the excitatory field.6. The complex receptive field arrangements observed for neurones of the postsynaptic dorsal column system are discussed in relation to previous observations on dorsal horn neurones of other ascending tracts.