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The responses of A5 region neurons, the phrenic nerve, and systemic blood pressure to short-term hypoxia were examined in rats under conditions of spontaneous respiration. Tonic and respiration-modulated neurons increasing their discharge activity during hypoxia were identified. This hypoxia-induced response was more pronounced in the neurons with baseline discharge rate of 0.1-4.5 Hz (electrical activity of neurons increased by 4-5 times) compared to neurons with the baseline activity of 5.4-49.6 Hz (discharge rate increased by 1.4-2.0 times). The latency and duration of activation of all types A5 neurons correlated with the parameters of activation of the phrenic nerve. During hypoxia, activation of A5 neurons corresponded to the period of blood pressure drop (one-third of the reaction time), but not to the period of plateau or recovery phase. Low-, middle, and high-frequency A5 neurons participated in the modulation of hypoxia-provoked respiratory and hypotensive responses. Modulation of the respiratory response by A5 neurons was observed during the entire period of phrenic nerve activation, while modulation of the hypotensive response occurred only during blood pressure decrease.

The nucleus pontis oralis' neurons were responsive to electrical stimulation of posterior hypothalamus. PS-on neurons showed an inhibitory response, and PS-off cells demonstrated an excitatory response. Neurons that discharged in association with phasic paradoxical sleep phenomena were found to have both the excitatory and the inhibitory responses. Evoked responses changed across sleep-waking cycle. The findings suggest that posterior hypothalamus is involved in the control of paradoxical sleep generation mechanisms located in the nucleus pontis oralis.

Neurons of cuneiform, subcuneiform, medial parabrachial, median raphe nuclei were studied. 26-47% units were found to send monosynaptic inputs to the raphe magnus nucleus, gigantocellular reticular and ventral reticular nuclei. 17-43% responded to stimulation of the inhibitory brain stem areas with excitatory-inhibitory reactions. Reciprocal distribution projections among inhibitory brain stem areas, were found.

Three subpopulations of Golgi-stained neurons of the brainstem reticular nuclei have been studied by the method of computer morphometry in 30-day old kittens. 23 parameter of the neuronal geometry were analyzed after uni-and bilateral lingual nerve section 5-7 days after birth. All of cells display statistically valid changes in some parameters, typically differing in every group: for reticular neurons--free distribution of dendrite endings in the dendritic field; for arborescent ones--the length of dendritic segments; for giant multipolar neurons--distribution of foci of maximal dendrite branching in the dendritic field. Unilateral lingual nerve section gives more pronounced quantitative deviations from the normal state, than bilateral one.

In the brain stem of 30-day-old kittens three types of Golgi-stained neurons are distinguished: sparsely branched reticular neurons, densely branched arborescent neurons and multipolar giant neurons (according to the classification by Leontovich). Implication of the new method of computer morphometry permits obtaining formalized characteristics of 23 parameters of the above types of neurons. An analysis of the quantitative characteristics of the studied neurons has revealed statistically significant differences in most parameters. This fact permits advancing a conclusion about morphological identity (stability) of each type of the neurons. Structural differences and similarities in reticular nuclei are discussed with respect to their functional features.

Formation of structures in the cochlear complex, olfactory bulb and cerebellum has been studied during postnatal development, with special reference to the development of granular cells in the structures mentioned. The granular cells have been demonstrated to be formed rather synchronously and according to a common plan By the time of birth, every structure has a layer of the granular cells formed which is cambial for most of the granular cells in the given structure. It has bene found out that in the cochlear complex, by the time of birth, there is an external layer of the granular cells which is analogous to the external cerebellar granular layer and is connected with it by a cellular cord. Morphological changes in the structure of the granular cells have been described in the process of their differentiation.

In the cochlear complex of white male rats the dorsal nucleus, the anterior ventral nucleus, the posterior ventral nucleus and the granular layer were studied histologically and morphometrically. While counting the number of different cells in all the above mentioned formations, by means of ocular grid (S.B. Stefanov, 1974) it was revealed that the granular neurons of the cochlear nuclei of the rats form 72--86 per cent of all the cells. The granular cells represent an independent type of neurons and these differ clearly from other neurons by the diameter of their nuclei and by the size of the pericarion. The granular cells form two cell types according to patterns of their nuclei, and these cell types are independent of each other within the limits of every cochlear complex. Percentage of different types of neurons in different parts of cochlear nuclei depends on the cell density. The distribution of the granular neurons is independent on that of large and middle size neurons.

Two cell types can be distinguished in granular cells of the chochlear complex of the rat by the form of their processes and the structure of the nuclear chromatin. It is shown cytophotometrically that the majority of the granular cells of the cochlear complex and in the cerebellar cortex are diploid. However, some cells contain DNA amount close to tetraploid. Some correlation between the size of the nucleus and its DNA amount was discovered both in the cerebellar cortex and in the cochlear complex.

The investigation of the reactions of the neurons of the cochlear nuclei in the bats Myotis oxygnathus to frequency-modulated stimuli showed that the neurons with one best frequency (20%) have phasic responses while those with one or two best frequencies--tonic responses in the case when frequency of the stimulus changes from high to low frequencies.

The nuclei of the human pons varolii have been studied in 4 fetuses at the age of 7-8 lunar months by Burt's method. Neuronal types with low, moderate, high and very high cholinacetyltranspherase (ChAT) activity have been revealed, with special reference to their part in 29 pontine cholinergic nuclei. Neurons with the highest ChAT activity are specific for the motor nuclei; sensitive nuclei include, as a rule, neurocytes with low ChAT activity. The part of cholinergic neurons in some pontine nuclei changes from 75 +/- 9% (locus ceruleus) up to 98.8 +/- 2.9% (superior salivary nucleus). Cholinergic function has been stated in the mesencephalic nucleus of the trigeminal nerve, the medial and superior vestibular nuclei, the tegmental ventral nucleus, the reticular parabrachial nucleus, the nucleus of the round fasciculus, the dorsal nucleus of the raphe, the central superior medial nucleus, the nucleus of the superior cerebellar peduncles.

The lamellar ultrastructure of the dorsal cochlear nucleus (DCN) was studied in frontal ultrathin wide sections of the nucleus which were placed on lead aprons and included all the nucleus layers. The electron-microscopic description of the different cell types and distribution of the axonal terminals are presented. Large branchy axonal terminals (6-8micron) with small spherical synaptic vesicles 40-50 nm in diameter, small terminals (1-3 micron) with spherical synaptic vesicles (45-60 nm) and thin unmyelinated axons prevail in the surface and middle layers of the neuropile as compared to the deep layer. The number of the myelinated axons and large oval terminals 4-6 micron in diameter with central distribution of mitochondria and neurofilaments as well as with spherical synaptic vesicles 50-60 nm in diameter increased from the middle layer to the deep one. The number of granular cells was larger in the surface and middle layers than in the deep one. The functional significance of each terminal type is discussed.