A correlative HRP, Golgi, and EM study of the intrinsic organization of the feline dorsal column nuclei

Abstract

The retrograde transport of horseradish peroxidase (HRP), Golgi impregnations, and electron microscopic (EM) observations have been employed to investigate the intrinsic organization of one cytoarchitectonic subdivision of the feline dorsal column nuclei (DCN): the "clusters" region. Previous studies have demonstrated that neurons arranged i n typical cell clusters in the dorsal two-thirds of the feline DCN project to the ventrobasal complex (VB) of the thalamus. Following injections of HRP in the VB of adult cats, over 9WX of the neurons in this region contain detectable reaction product. These thalamic projecting neurons tTPNj a r e typically round, range from 20 to 35 ,urn in diameter, and have round nuclei and abundant cytoplasm.In Golgi preparations, TPN are identified by their characteristic arrangement in the cell clusters. Observations of their cytological characteristics in gold-toned preparations in both 1-pm-thick sections, and in thin sections at the EM level, supplement the data from HRP material. The dendrites of TPN in the clusters region characteristically converge in hhe perikarya-free center of each cluster, and appendages originate from both proximal and distal portions of the major dendrites of the,se neurons. These appendages vary in morphology from shortstalked, occasionally multi-lobed, bulbous thorns to long-stalked processes terminating in a single or multilobed swelling. Other appendages often display beaded swellings along their length (moniliform appendages).Neurons in the clusters region unlabelled by HRP injected in the VB have cytological characteristics quite distinct from those of TPN in the same region.Typically located at the periphery of the cell clusters, unlabelled neurons have fusiform perikai-ya, range in diameter from 8 to 12 p m along their short axis, and have highly indented nuclei and sparse cytoplasm. Tn Golgi preparations, small fusiform neurons located at the periphery of cell clusters typically have two major dendritic trunks originating from opposite poles of their perikarya.Observations in 1-pm-thick plastic sections of re-embedded Golgi-impregnated neurons of this t.ype support their identifications as neurons which are unlabelled after HRP injection in VB. Dendritic appendages are present also on this type of neuron, although they do not appear to be as frequent as i n the case of the TPN. Although the axon of the small, fusiform neurons have not been impregnated beyond the initial segment in the present Golgi material, thus precluding the classification of this type of neuron as a Golgi type I1 neuron, a combination of the HRP and Golgi observations suggest that these neurons are distinct from TPN, and are possibly interneurons.

Quantitative stereological evaluation of the gracile and cuneate nuclei and their projection neurons in the rat

“…This number may even prove to be too low, insofar as the number of HRP-labeled neuronal profiles may easily be underestimated in semithin sections, as has been noted by others (Rustioni et al, 1984). Similar discrepancies in the proportion of projection neurons vs. interneurons are present in studies of the cat; whereas the numbers of thalamic-projecting neurons have been found to range between 70% and 92% in the cluster region of Cu (Ellis and Rustioni, 1981;Rustioni et al, 1984), up to 25% of the Cu neurons were reported to express GABA (Heino and Westman, 1991).…”

“…The volume of the DCN was also determined by the Cavalieri method. The cat is the only other species for which similar quantitative studies have been carried out (Blomqvist et al, 1978;Blomqvist, 1980;Ellis and Rustioni, 1981;Rustioni et al, 1984;Wiberg and Blomqvist, 1984;Heino and Westman, 1991;Avendañ o and Dykes, 1996b), and these were helpful in evaluating our results in the rat. The precision of the estimates for each rat was evaluated, and the contribution of the methodological "noise" to the observed interindividual variability was determined.…”

“…These nuclei contain several morphological types of projection neurons and interneurons (Ramon y Cajal, 1909;Valverde, 1966;Gulley, 1973;Ellis and Rustioni, 1981;Barbaresi et al, 1986), which express a variety of immunocytochemical markers (Heino and Westman, 1991;Broman, 1994;Popratiloff et al, 1996;Magnusson et al, 1996;Avendañ o and Dykes, 1996a;Paxinos et al, 1999;Wang et al, 2000). Also, it is customary to subdivide Cu into three major architectonic subdivisions, rostral (CuR), middle (CuM), and caudal (CuC), which were further subdivided in the cat (Cheema et al, 1983).…”

Processing Afferent Proprioceptive Information at the Main Cuneate Nucleus of Anesthetized Cats

“…The great majority of the mvCN proprioceptive neurons project through the medial lemniscus (ML) (Rosén, 1969b;Rosén and Sjölund, 1973;Cheek et al, 1975;Ellis and Rustioni, 1981;Rowinski et al, 1985;Pubols et al, 1989;Mackie et al, 1998), whereas only a minor proportion of the rvCN proprioceptive cells do (Kuypers and Tuerk, 1964;Blum et al, 1975;Cheek et al, 1975). Transmission through the ML decreases before and during movement (Ghez and Lenzi, 1971;Ghez and Pisa, 1972;Coulter, 1974;Chapman et al, 1988), suggesting prethalamic modulation, but the underlying mechanisms influencing proprioceptive ascending transmission at the main cuneate nucleus are largely unknown.…”

Functional and Anatomical Features of the Dorsal Column Nuclei in Mammals and Lower Animals

“…However, the neuronal connections of afferent, efferent, and intranuclear fibers may vary greatly at different rostrocaudal levels [36]. Based on anatomical and physiological studies in several mammalian species such as monkey [45] and cat [27,46,47], the DCN have been divided into three regions: caudal, middle and rostral.…”