Morphometric characteristics of synaptic apparatus in the dorsal nucleus of the medial geniculate body of the cat

Abstract

The synaptic apparatus in the dorsal nucleus of the medial geniculate body, MGB(d), of the cat was examined using electron microscopy. Within 2166 µm2 of studied sections obtained from five regions of MGB(d) tissue, 455 presynaptic terminal (PST) profiles were found, which corresponds, on average, to (210.0±28.4) · 103 PST per 1 mm2 of section surface. In accordance with their ultrastructural pattern (dimension of PST profile, shape of synaptic vesicles, SV, pattern of their arrangement within the terminal, and type of synaptic contact, SC), PST were classified into five main groups:RL, RS, F, P, andUT. The relative amount of PST of these groups constituted 8.1% (RL group), 50.5% (RS), 26.0% (F), 9.2% (P), and 6.2% (UT). According to the dimension of profile, number of SV, and pattern of their arrangement within the terminal,RS-PST were additionally divided into four subgroups:RS1, RS2, RS3, andRS4, whileF-PST were divided into three subgroups:F1, F2, andF3. Thus, MGB(d) possesses five various forms of PST with round SV and asymmetric SC, three PST forms with flattened SV and symmetric SC, one with a mixture of flattened and round SV and symmetric SC, and one with round SV and symmetric SC. It can be supposed that the MGB(d) neurons are supplied with afferent inputs from numerous different sources.