Morphological classes of spinothalamic lamina I neurons in the cat

Abstract

We examined the morphology and distribution of retrogradely labeled spinothalamic tract (STT) neurons in lamina I (the marginal zone) of the spinal dorsal horn after large injections of cholera toxin subunit B (CTb) or Fast Blue (FB) into the contralateral thalamus of cats. Based on the shape and orientation of the somata and proximal dendrites in horizontal sections, three distinct cell types were identified: (1) fusiform cells with small, spindle-shaped somata and bipolar, longitudinal dendritic arbors; (2) pyramidal cells with triangular somata and three main dendritic origins with primarily longitudinal arborizations; and (3) multipolar cells with larger, multiangular somata and four or more radiating dendritic arbors directed both longitudinally and mediolaterally. These three morphological types differed significantly in the number of primary dendrites and the size of the somata. Subclasses of multipolar cells were noted. Nearly all cells could be categorized into these three classes consistently in horizontal sections. A small number of cells with transitional shapes or with small, round somata were unclassified. The proportional distributions of these cell types were found to vary over the length of the spinal cord (from the third cervical through the coccygeal segments) in three cats. The overall proportions of cell types were 34% fusiform, 36% pyramidal, 25% multipolar, and 5% unclassified. The proportions of pyramidal and multipolar cells were strikingly higher within the C7-8 and L6-7 segments and lowest in the thoracic segments. In contrast, fusiform cells formed about 20% of the labeled lamina I STT population in the C7-8 and L6-7 segments but more than 60% in thoracic segments. Across all nine cats, the proportions were similar within the cervical (C5-8) and lumbosacral (L5-S1) enlargements, although considerable interanimal variability was noted. These distinct morphological types of lamina I STT cells with differential longitudinal distributions probably have different functional roles. They may correspond to the three main physiological classes of lamina I STT cells.

Dorsal horn neurons presynaptic to lamina I spinoparabrachial neurons revealed by transynaptic labeling

“…The three morphological types of LI neurons described in the rat and other species, fusiform, multipolar (including both the multipolar and flattened type of Lima and Coimbra, 1986), and pyramidal (Zhang et al, 1996;Zhang and Craig, 1997;Yu et al, 1999Yu et al, , 2005 Only the labeling of neurons filled in vivo through intracellular recordings can favorably be compared to the one obtained in the present study (Hylden et al, 1986;De Koninck et al, 1992;Light et al, 1993;Ma et al, 1996); however, recording neurons in vivo is particularly difficult and invasive, and has a very low yield.…”

A quantitative and morphological study of projection neurons in lamina I of the rat lumbar spinal cord

“…These drawings were used to analyse morphology. For each cell included in the sample, the morphology was assessed independently by two observers and cells were allocated to one of the following classes: fusiform, multipolar or pyramidal (Zhang et al ., 1996; Zhang & Craig, 1997). In cases of disagreement, the cells were examined by a third observer, and in these cases the cell was allocated to a group if two of the observers agreed.…”

Cytoarchitecture of the Spinal Cord

“…In general, two to five primary trunks are seen which expand mediolaterally parallel to the surface of the dorsal horn. This cell type is less frequently identified than the other three and could not be identified in the monkey (Zhang et al, 1996;Zhang and Craig, 1997). This cell type is less frequently identified than the other three and could not be identified in the monkey (Zhang et al, 1996;Zhang and Craig, 1997).…”

“…These target the thoracolumbar sympathetic nuclei including the intermediolateral nucleus, the intermediomedial nucleus and the intercalated nucleus (Foreman et al, 1988). However, other studies in cat and monkey do not support this (Hylden et al, 1986;Light et al, 1993;Zhang et al, 1996). However, other studies in cat and monkey do not support this (Hylden et al, 1986;Light et al, 1993;Zhang et al, 1996).…”