The dorsal nucleus of the lateral leminiscus in the cat: Neuronal types and their distributions

Abstract

The normal population of neurons and their distributions within the dorsal nucleus of the lateral lemniscus were studied in both Nissl-stained celloidin and frozen sections and in Golgi impregnations from brains of mature cats. According to axial measurements of somata in Nissl-stained material, neurons of the dorsal nucleus of the lateral leminscus (DNLL) were classified by width:length ratio (r) into round (0.80 ≤ r ≤ 1.0), ovoid (0.65 < r < 0.80), or elongate (r ≤ 0.65) types. These same neurons could also be classed by average diameter (D_m) as large (D_m ≥ 22), medium (12.0 ≤ D_m < 22.0), or small (D_m < 12.0). A combination of data on ratios (shape) and average diameters (size) provided the following possible categories of Nissl-stained, DNLL neurons: large round (LR), large ovoid (LO), large elongate (LE), medium round (MR), medium ovoid (MO), medium elongate (ME), small round (SR), small ovoid (SO), and small elongate (SE). Very few small cells were found, however. Quantitative studies of the distributions of cell types within the whole DNLL showed (1) most medium-sized and most LE cells in the caudal third of the DNLL and (2) most LO and LR cells dorsally located in the rostral third of the DNLL. There were progressively more large and more round types along the caudal-to-rostral axis. In Golgi impregnations of the DNLL, all medium and large cell types, but no small cell types (defined in the Nissl study) were found. Golgi material showed (1) subdivisions of the LO class into vertical (LOV) and horizontal (LOH) types, and (2) radiate (MRR) and oriented (MRO) subclasses of MR neurons according to dendritic arbor and cytology, orientation within the DNLL, and axonal morphology. Examples from all classes of large cells (particularly, LE cells) could have ventrally directed axons. These ventrally directed axons might be efferents to the cochlear nueleus, known from our previous work. A strong horizontal orientation of most DNLL cell somata and dendrites, shown in both our Nissl and Golgi material, is discussed in relation to known inputs to the DNLL. Correlations of our morphological findings with limited electrophysiological data on the DNLL are also discussed.