[Neuronal organization of the CGLd of Cavia porcellus. A morphometric study of Nissl preparations with reference to identified neuron types].

A morphometric study has been made of the alpha-sector (Giolli and Creel 1973) of the guinea pig's dorsal lateral geniculate nucleus (dLGN) in Nissl preparations. Golgi-deimpregnation methods (FAIREN et al. 1977, Braak and Braak 1982) made it possible to identify the neuron types as geniculo-cortical relay neurons (GCR-neurons) and interneurons (I-neurons). Thus, density and somal sizes of GCR- and I-neurons and their topographical distribution patterns were determined. The density of the GCR-neurons (3 per measuring volume) is lower than in the albino rat (Wistar strain) (7 per measuring volume). The somal size varies over a wide range and is higher on average (16 hits) than for the albino rat (12 hits). As reported by Brauer and Remmler (person, comm.), the dendrites of GCR-neurons are relatively smooth. Their distal portions show only a small number of spine-like protrusions. Distinct grape-like appendages are visible in the branching zone. In one case an axon initial segment with three varicosities was observed. The number of I-neurons is considerably higher (36%) than in the albino rat (8%). The somata of I-neurons are of different size. More than 52% of the GCR-neurons are of the same size as the I-neurons. According to Brauer and Remmler (person. comm.), the two very long main dendrites were found to be little branched. The alpha-sector is apparently cytoarchitectonically homogeneous. Only after the use of statistical methods is it possible to distinguish between lateral, medial and caudal regions as in the albino rat (Werner et al. 1975), laboratory mouse (Werner et al. 1984a), and cotton rat (Werner et al., 1984b). These differ with regard to the density and somal size of the GCR-neurons and the density of the I-neurons. The densities of the GCR- and I-neurons are highest in the lateral region. In contrast with the albino rat, laboratory mouse, and cotton rat neurons of the guinea pig differ from those of the Wistar rat. The results suggest that the guinea pig's visual specialization differs at least from that of the albino rat.