Primary structural modules of the dorsal nuclei of the thalamus and motor cortex in humans.

The aim of the present work was to study the primary structure of the modular organization of neurons in the dorsal nucleus of the thalamus (ventral anterior, ventral lateral, anterior ventral, anterior medial, anterior dorsal, medial, reticular) and motor cortex (fields 4 and 6) in humans by the Nissl, Kluver-Barrera, and Golgi silver nitrate impregnation methods. These studies showed that neurons in the dorsal nuclei of the thalamus and the motor cortex are organized as small groups and short chains fulfilling defined criteria. These neuronal complexes, forming individual structural units, were termed primary structural modules. Comparison of primary structural modules in the dorsal nuclei and motor cortex showed that the principles of organization were identical in both locations. Thus, the dorsal nuclei of the thalamus and motor cortex in humans show two principles of the organization of neurons into primary structural modules: the group and chain principles.

A common system of sparsely-branched projection (reticular) NADPH-diaphorase neurons in formations of densely-branched cells in the human forebrain.

Morphometric studies of human forebrain formations composed of densely branched cells - the entorhinal cortex, the basolateral amygdala, the nucleus accumbens, the striatum, and the dorsal thalamus - were performed using nine parameters, with statistical analysis of the resulting data; measurements addressed the major projection-type densely branched and sparsely branched reticular neurons (scattered reticular and marginal reticular cells of the dorsal thalamus) stained by the Golgi method and with NADPH-diaphorase. Scattered reticular cells in the various formations showed no differences in any of the nine measures, while there were significant differences (in 5-7 measures, apart from one comparison, where there were differences in two measures) in their major projection-type densely branched cells. Scattered reticular and main projection-type densely branched neurons in each formation differed in terms of 7-9 measures. In endbrain formations, scattered reticular neurons contained NADPH-diaphorase; in the dorsal thalamus, only intermediate marginal reticular neurons were NADPH-diaphorase-positive. Thus, these human formations contained a common system of ancient integrative NADPH-diaphorase-containing reticular cells. Our results, along with published data, show these to be projection-type cells with projections to layers V and VI of the neocortex, which suggests that they have modulatory influences on its descending systems.

Neuronal organization of the reticular nucleus of the thalamus in adult humans.

The neuronal composition of the thalamic reticular nucleus was studied in serial sections of the sagittal and frontal projections impregnated with silver nitrate by the Golgi method. The neuronal composition of the reticular nucleus of the human thalamus was wider than has previously been described in animals and humans. This nucleus, apart from two types of large, sparsely branched, long-dendrite, reticular, aspiny, neurons, i.e., types R1 and R2, contained cells with spines. Intermediate and small, sparsely-branched, short-dendrite neurons and densely-branched cells with spines were demonstrated. The principles of the organization of the reticular nucleus of the human thalamus are described.

NADPH-diaphorase-positive cells in the thalamic nuclei and internal capsule in humans.

The nuclei of the dorsal thalamus and reticular nucleus in humans were found to contain separated NADPH-diaphorase (NADPH-d)-positive neurons. Staining of NADPH-d-positive neurons and all their processes, along with previous studies of neurons in the nuclei of the dorsal thalamus based on the Golgi method, allowed the type of these cells to be identified as sparsely branched. The main, densely branched, efferent neurons did not contain NADPH-d. NADPH-d-positive neurons included reticular cells and cells of one of the types of short-axon interneurons. The internal capsule contained large numbers of NADPH-d-positive reticular neurons. NADPH-d-positive neurons were found in contact with vessels. Thus, NADPH-d-positive cells of the dorsal thalamus, reticular nucleus, and internal capsule were evolutionarily more ancient and less structurally complex cells.

A monosynaptic connection between identified snail neurons.

Electrophysiological and morphological studies of a monosynaptic connection are performed on specimens of the isolated CNS of the snail Achatina fulica, using the standard techniques of intracellular leading-off and neuron stimulation and intracellular pressure injection of cobalt chloride. The presence of a monosynaptic connection between two identified neurons is demonstrated both in the physiological experiment and by means of the intracellular dye.