Spinal cord layer I neurons with axon collaterals that generate local arbors

Morphology and synaptic connections of ultrafine primary axons in lamina I of the spinal dorsal horn: candidates for the terminal axonal arbors of primary neurons with unmyelinated (C) axons

“…There is also considerable evidence documenting that the nociceptive and thermal inputs which are transmitted by these unmyelinated primary axons are conveyed to lamina I neurons (Christensen and Perl, 1970;Price and Mayer, 1975;Price et al, 1976Price et al, , 1978Price et al, , 1979Dostrovsky and Hellon, 1978;J. M. Chung et al, 1979;Light et al, 1979;Bennett et al, 1981). One of the most important current questions concerning lamina I neurons relates to the routes by which they might receive these inputs.…”

“…22) are two kinds of P axonal endings which form axoaxonic synapses on the ultrafine primary endings and axodendritic synapses on the S spine heads. These could arise from recurrent axon collaterals of lamina I neurons (Bennett et al, 1981) or from axons of neurons in the deeper layers of the dorsal horn. However, they are not thought to arise from the descending axons of serotonergic neurons in the brain stem (Ruda and Gobel, 1980;Ruda et al, 1981).…”

“…Most lamina I neurons receive nociceptive inputs from primary neurons with small caliber axons which conduct in the C and A6 ranges (Christensen and Perl, 1970;Kumazawa and Perl, 1978;Light et al, 1979;Bennett et , 1981). Some also receive innocuous inputs (Bennett et al, 1981; see Price and Dubner, 1977 for review). One of the most important current questions relating to the neural circuitry of the dorsal horn concerns the manner in which different kinds of primary afferent inputs reach lamina I neurons.…”

“…Golgi and intracellular horseradish peroxidase (HRP) studies have shown that lamina I neurons may send an occasional dendrite into the overlying white matter (Ramon y Cajal, 1911;Gobel, 1978) and that a rare lamina I neuron may send a dendrite into deeper layers of the dorsal horn (Ramon y Cajal, 1911;Beal, 1979;Light et al, 1979;Bennett et al, 1981). However, most lamina I neurons have their flattened dendritic arbors confined within lamina I (Gobel, 1978).…”

Structural characterization of marginal (lamina I) spinal cord neurons in the cat: A golgi study

“…In spite of the large amount of neuroanatomical information concerning lamina I neurons in the rat, the few studies aimed at functionally characterizing intracelularly stained lamina I neurons were performed in the cat and monkey, species lacking a thorough classification of this neuronal population (Cervero et al, 1976;Price et al, 1978Price et al, , 1979Light et al, 1979;Bennett et al, 1981;Molony et al, 1981;Miletic et al, 1984;Hylden et al, 1986;Han et al, 1998). A comprehensive view of the role of the lamina I neuronal population in nociception prompts, therefore, a systematic evaluation of its anatomical and electrophysiological features in various species using similar methodological approaches.…”