Distribution of Calretinin-Immunopositive Neurons in the Cat Lumbar Spinal Cord

A variety of neural networks in the central nervous system is determined by the heterogeneity of its constituent neuronal populations. Calcium-binding proteins can be used as markers of different neuronal morphotypes. One of the most common calcium-binding proteins in the nervous system is calretinin. In the present work, using an indirect immunohistochemical method, calretinin-immunopositive neuronal populations were labeled in lumbar segments of the cat ( Felis catus ) spinal cord. We identified nineteen morphotypes of neurons with strictly segmental and laminar distribution patterns, and attempted to compare putative functions of these neurons with the available literature data. Three morphotypes are located in lamina I, corresponding to neurons involved in nociceptive and temperature processing. Lamina II contains neurons of a single morphotype, on which nociceptive afferents converge. Laminae III–IV comprise three types of projection neurons transmitting information from peripheral mechanoreceptors and nociceptors to supraspinal structures. Laminae V–VI are characterized by functionally different neurons of five morphotypes: two types of interneurons localized to the Clarke’s column and analogous zone of the caudal lumbar segments, which collect proprioceptive information; one type of neurons located at the lateral border between the white and gray matter and responding to pain and tactile signals; and two types of irregularly distributed interneurons (projection or propriospinal neurons) that receive heterogeneous afferent signals from muscle spindles. In laminae VII–VIII, there are two types of sympathetic preganglionic neurons (in the intermediolateral and intercalated nuclei), Renshaw interneurons, and three types of multi-sized dispersedly distributed multipolar cells with unidentified functions. No calretinin-immunopositive neurons were found in lamina IX represented by motoneuron pools. In lamina X, sparse neurons reside around the central canal; their function is also obscure due to the paucity of morphological traits.