Structural organization and connections of cell ensembles of the olfactory bulb of the cat brain

The cat cerebral olfactory tubercle (OT) includes into its composition certain cellular ensembles distinguished by means of morphological criteria. The ensembles consist of three cellular components: clusters of granular neurons (islands of Calleja), pyramid-like neurons of the layer II, situating along the periphery of the islands, and groupings made by polygonal and spindle-like neurons of the layer III. Morphometrical analysis of every of the three cellular complex components has been carried out. About 7-10 islands of Calleja are situated on the OT territory, which makes nearly 75% of the whole surface of the OT. Neuronal composition of the cellular ensembles has been studied by Golgi method. Varieties of long and short axonal neurons, included into the ensemble composition, have been characterized. Presence of projections of the macrocellular neurons of the layer III (a part of the third component of the ensemble) has been revealed in the posterior part of the lateral hypothalamus and in the field of Forel H1. Possible role of the cellular ensembles is discussed for ensuring various functions of the OT.     

Neurons of upper cervical segments responding to stimulation of the bulbar locomotor strip

Synaptic responses of single neurons to stimulation of the bulbar "locomotor strip" were recorded extracellularly from superior cervical segments in mesencephalic cats. With a strength of stimulation of about 30 µA these responses usually had a latent period of 2–7 msec and they arose in neurons located at a depth of between 2 and 4 mm from the dorsal surface (Rexed's laminae V–VIII). These neurons could not be excited antidromically by stimulation of the lumbar or lower cervical segments. However, antidromic responses could be evoked by stimulation of a region located 3–5 mm caudally to the site of recording. It is suggested that neurons of segments C2 and C3 excited by stimulation of the locomotor strip are components of a cell column along which activity spreads polysynaptically in the direction of spinal stepping generators.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 11, No. 3, pp. 245–253, May–June, 1979.     

Structural features of corticospinal connections in the cat

Structural features of connections between corticospinal fibers and neurons of the cervical and lumbar segments of the cat spinal cord were studied by the experimental degeneration method. It was shown by the Fink-Heimer method that the preterminals of these fibers are mainly located in the lateral part of Rexed's laminae V and VI (the lateral basilar region — LBR) and also, to some extent, in the medial basilar region (MBR). The diameters of the myelinated part of these fibers in LBR vary from 0.8 to 11µ. They form chiefly terminals of the F-type (with flattened synaptic vesicles), which undergo degeneration of the light type (lysis of the internal structures) or, less frequently, the dark type (increase in electron density), followed by phagocytosis by glial cells. No degenerating terminals are found in the glomerulus-like synaptic complexes, in axo-axonal synapses, or on dendrites with a dark matrix. Only a few degenerating axon terminals still remained 20 days or more after extirpation of the cortex. The relative number of terminals of different types was counted at this period. The number of axon terminals of F-type on the dendrites was reduced by 1.5 times, while the number on the soma remained relatively unchanged. The results confirm the earlier hypothesis that corticospinal fibers terminate on dendrites and their appendages in LBR as endings of the F-type. These neurons also receive many terminals from other intracerebral systems.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol.4, No.5, pp. 480–487, September–October, 1972.     

Responses of bulbar neurons to stimulation of locomotor and inhibitory sites in the cat brainstem

Bulbar locomotor and inhibitory sites were located in the pons of mesencephalic decerebellate cats. Rhythmic stimulation of locomotor sites through microelectrodes at the rate of 60 Hz elicited stepping movements in the forelimbs which were halted when the inhibitory sites were rhythmically stimulated. Neuronal response was elicited by single or paired stimulation of locomotor sites at the rate of 1.5 Hz or by applying a series of 2–4 stimuli spaced 2 msec apart to the inhibitory site. Medial neurons generated synaptic responses (postsynaptic potentials or action potentials) to stimulation of the inhibitory site twice as frequently as when the locomotor site was stimulated. Responses in lateral neurons, however, occurred twice as frequently to stimulation of the locomotor site, while IPSP were only observed half as often as EPSP in neurons of both groups. In neurons excited by stimulation of the locomotor site, stimulation of the inhibitory site did not normally produce IPSP. Possible mechanisms underlying the halt of locomotion occurring in response to stimulation of the inhibitory site are discussed.Information Transmission Institute, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 18, No. 4, pp. 525–533, July–August, 1986.     

Unit responses in the "locomotor strip" of the cat hindbrain to microstimulation

Synaptic responses of single units in the "locomotor strip" of the hindbrain were recorded extracellularly. Short-latency responses appeared in neurons of the rostral part of the strip to stimulation of the "locomotor region" of the mesencephalon. Neurons of the caudal part of the strip responded to microstimulation of its other regions, including rostral. If the distance between the neuron and point of stimulation was under 2–3 mm, short-latency (1.2–1.6 msec) responses could be observed. The thresholds and latent periods of the responses increased when the distance apart increased. Polysynaptic responses with a latent period of 3–4 msec could be potentiated by an increase in the frequency of stimulation up to 30–40 Hz. It is suggested that axons of the "locomotor strip" are oriented in the rostrocaudal direction for a distance of 2–3 mm and give off collaterals which run toward neighboring neurons. The strip may be an integrative center, "intercalated" between the rostral portions of the brain stem and spinal cord.Deceased.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 10, No. 5, pp. 510–518, September–October, 1978.     

Spatial organization of direct connections of the sensomotor cortex with the rhombencephalon and spinal cord in the cat

The distribution and ultrastructure of terminals of corticofugal fibers in the rhombencephalon and spinal cord of the cat were studied by light and electron microscopy at various times (4–6 days) of experimental degeneration after extensive or local (about 3 mm in diameter) destruction of the sensomotor cortex. Definite topographical organization of corticofugal projections in the nuclei of the dorsal columns and in the spinal cord was detected by the Fink — Heimer method. After local destruction of the lateral zones of the sensomotor cortex, maximal foci of degeneration were found in the nucleus of Burdach and the lateral basilar region of the cervical segments; after local destruction of the medial zones of the sensomotor cortex maximal foci of degeneration of corticofugal fibers were observed in Goll's nucleus and the lateral basilar region of the lumbar segments. The results show that even an extremely localized area of the cat sensomotor cortex forms two separate systems of descending corticospinal fibers. The first projects into the dorsolateral and dorsomedial parts of the intermediate zone, chiefly contralaterally, whereas the second projects bilaterally into both dorsolateral and ventromedial parts of the intermediate zone. The possible physiological significance of this duality of projections is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 2, pp. 126–133, March–April, 1976.     

Caudate-cortical connections in the cat brain

By means of optical and electron microscopic methods, the cortical fields from the ipsilateral hemisphere was analysed in the cat after electrocoagulation of the dorsal part in the nucleus caudatus (NC). Degenerating axonal preterminals and terminals were detected in the preparations impregnated after Nauta--Gygax and Wiitanen's methods and in electronograms. To exclude degeneration of cortical and projective thalamic fibrillae from the great number of regenerated conductors, additional operations were performed on the same cats--thalamic and ventral NC nuclei were damaged and coagulative electrode was inserted into the dorsal NC a month before the last operation.     

Associative connections of the cat parietal cortex

Interneuronal connections of area 7 of the cat parietal cortex with projection areas of the visual, auditory, and somatosensory cortex were analyzed by orthograde degeneration and retrograde transport of horseradish peroxidase methods. By combined investigation the cortico-cortical sources of afferentation of parietal area 7 could be precisely identified and concentration sites of neurons sending their axons into this area identified, and the morphological characteristics of these neurons could also be determined.A. A. Ukhtomskii Physiological Institute, A. A. Zhdanov Leningrad State University. Donetsk Medical Institute. Translated from Neirofiziologiya, Vol. 12, No. 1, pp. 13–17, January–February, 1980.     

Morphological study of the origin of spinal locomotor strip fibers

The origin of spinal locomotor strip fibers was investigated in cats by applying electrical stimulation and the retrograde axonal horseradish peroxidase transport technique. It was found to be mainly composed of corticospinal tract fibers. Moderate numbers of reticulospinal tract and trigeminal spinal tract fibers were also observed. Descending projections from brain stem catecholaminergic neuronal groups do not pass through the test sites of the dorsolateral funiculus, nor, apparently, do they go to make up the spinal locomotor strip. Specificity of the brain stem and spinal locomotor region is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 3, pp. 327–335, May–June, 1989.     

Centrifugal and centripetal connections of the cat visual cortex

In experiments on curarized cats unit responses in the dorsal lateral geniculate body to stimulation of various zones in area 17 of the visual cortex were analyzed. Of all cells tested 69% were found to respond antidromically and 8% orthodromically; in 7.6% of cells IPSPs occurred either after an initial antidromic spike or without it. The velocities of conduction of excitation along the corticopetal fibers of the optic radiation varied from 28 to 4.3 m/sec, but the three commonest groups of fibers had conduction velocities of 28–19, 14–12, and 10–9.5 m/sec. A difference between latent periods of antidromic responses of the same neurons was found to stimulation of different zones of the visual cortex; this indicates that axons of geniculo-cortical fibers split into several branches which form contacts with several neurons in area 17 of the visual cortex. The degree and possible mechanisms of cortical influences on neurons of the lateral geniculate body are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 3, pp. 243–249, May–June, 1976.     

Anisotropic connections in the cat midbrain tegmentum

Single unit responses of the cat midbrain tectum to stimuli applied through a microelectrode 500µ rostrally to the recording electrode were recorded extracellularly. The mean latency of both direct and monosynaptic responses was 0.3 msec greater than that for local microstimulation. The responses were identified from their latent and refractory periods, the presence of summation, and the dependence of the firing index on sodium glutamate application to the recorded neuron. Thresholds of synaptic responses were measured during vertical displacement of the stimulating electrode. The experimental relationships can be approximated by parabolic functions. The results indicate that rostrocaudal projections in the midbrain tegmentum are arranged horizontally.     

Non-uniformity of extrinsic connections and columnar organization

Afferent columns (>200 μm in diameter) have been intensively investigated in the context of thalamocortical and intrinsic connections. Many extrinsic cortical connections also form columnar terminations, but less is known about their fine organization. Results from intracellular injections of neighboring neurons (in rats: Johnson et al., 2000) suggest that even neurons within a common domain may have non-stereotyped projection patterns, with only partial overlap of terminal arbors. The issue of non-stereotyped projections at the columnar level is further considered by analysis of V1 axons terminating in primate area MT/V5 (an early visual area), and of an axon from temporal cortex terminating in area 7b (a higher cortical area). Both these axons have multiple non-uniform arbors. The implication is that each arbor recruits different numbers and possibly different combinations of postsynaptic elements. While more data are needed concerning convergence of connectional systems, and the actual identity and numbers of postsynaptic targets, the distributed spatial and laminar patterns do not evoke a repetitive uniformity, but rather a columnar substructure and the combinatoric possibilities of the 3-dimensional cortical organization.     

Afferent connections of the cat lateral vestibular nucleus

Location within the brain of HP-labeled neurons (origins of projections to the lateral vestibular nucleus) was investigated by iontophoretic injection of this enzyme. Bilateral projections to the following midbrain structures were revealed: the field of Forel, interstitial nuclei of Cajal, oculomotor nerve nuclei, and the red nucleus — to all parts of the lateral vestibular nucleus. Bilateral projections were also shown from more caudally located structures, viz. the superior, medial and inferior (descending) vestibular nuclei, Y groups of the vestibular nuclear complex, facial nucleus and hypoglossi, nucleus prepositus nervi hypoglossi and caudal nuclei of the trigeminal tract; ipsilateral projections from crus IIa of lobulus ansiformus of the cerebellar hemisphere; contralateral projections from the bulbar lateral reticular nucleus and Deiter's nucleus. A tonic organization pattern of afferent inputs from a number of brainstem formations to the dorsal and ventral lateral vestibular nucleus is revealed and trajectories of HP-labeled fiber systems projecting to Deiter's nucleus described.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 20, No. 4, pp. 494–503, July–August, 1988.     

Development and functional organization of spinal locomotor circuits

The coordination and timing of muscle activities during rhythmic movements, like walking and swimming, are generated by intrinsic spinal motor circuits. Such locomotor networks are operational early in development and are found in all vertebrates. This review outlines and compares recent advances that have revealed the developmental and functional organization of these fundamental spinal motor networks in limbed and non-limbed animals. The comparison will highlight common principles and divergence in the organization of the spinal locomotor network structure in these different species as well as point to unresolved issues regarding the assembly and functioning of these networks.     

Efferent projections of mesencephalic locomotor neurons in the cat

Efferent neuronal projections of the mesencephalic locomotor region were investigated in cats using a horseradish peroxidase retrograde axonal transport technique. It was found that neurons located within the locomotor area form ascending and descending projections to many structures of the spinal cord and the brain but that short-axon connections running to the reticular formation of the midbrain and the medulla predominate. Small numbers of long-axon fibers may merge into the locomotor strips of the medulla and the spinal cord. The locomotor regions of the two halves of the midbrain are interlinked.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 1, pp. 117–125, January–February, 1986.