Dynamic properties of neurons in cortical area MT in alert and anaesthetized macaque monkeys.

In order to see the world with high spatial acuity, an animal must sample the visual image with many detectors that restrict their analyses to extremely small regions of space. The visual cortex must then integrate the information from these localized receptive fields to obtain a more global picture of the surrounding environment. We studied this process in single neurons within the middle temporal visual area (MT) of macaques using stimuli that produced conflicting local and global information about stimulus motion. Neuronal responses in alert animals initially reflected predominantly the ambiguous local motion features, but gradually converged to an unambiguous global representation. When the same animals were anaesthetized, the integration of local motion signals was markedly impaired even though neuronal responses remained vigorous and directional tuning characteristics were intact. Our results suggest that anaesthesia preferentially affects the visual processing responsible for integrating local signals into a global visual representation.

Specificity of projections from wide-field and local motion-processing regions within the middle temporal visual area of the owl monkey.

The middle temporal visual area (MT) of the owl monkey is anatomically organized with respect to both preferred direction of motion and different types of center-surround interaction. The latter organization consists of clusters of neurons whose receptive fields have antagonistic surrounds that render them unresponsive to wide-field motion (local motion columns) interdigitated with groups of neurons whose receptive fields have additive surrounds and thus respond best to wide-field motion (wide-field motion columns). To learn whether the information in these regions remained segregated further along the visual pathways, we made injections of retrograde tracers into two visual areas to which MT projects [the medial superior temporal area (MST) and fundus of the superior temporal sulcus (FST)] and then labeled the wide-field and local organization using 2-deoxyglucose. In complementary experiments, we injected anterograde tracers into regions of MT that we had mapped using microelectrode recordings. Injections into both dorsal FST and ventral MST labeled clusters of cell bodies in MT that were concentrated within wide-field motion columns, whereas injections into dorsal MST labeled neurons predominantly within local motion columns. Results from the anterograde tracer experiments corroborated these findings. The high degree of specificity in the connections reinforces a model of functional organization for wide-field versus local motion processing within MT. Our data support the previously reported division of FST into separate dorsal and ventral areas, and they also suggest that MST of the owl monkey is, like MST of the macaque, functionally organized with respect to local versus wide-field motion processing.

Segmental diversification of an identified leech neuron correlates with the segmental domain in which it expresses Lox2, a member of the Hox gene family.

The cellular colocalization of LOX2 protein and small cardioactive peptide (SCP)-like immunoreactivity was studied in the nerve cord of the glossiphoniid leech Helobdella triserialis. Of the six neurons that express SCP in the midbody segments 7 to 17, only one, the MPS neuron, expresses LOX2 protein. The medial paired SCP (MPS) neurons are segmentally repeated and can be divided into three contiguous segmental domains according to cell body size and the timing and level of SCP expression. MPS neurons located in the anterior and middle segmental domains express LOX2 protein. In the middle domain, large MPS neurons begin to accumulate SCP shortly after the end of embryonic development, whereas in the anterior domain the MPS neurons are smaller and begin to express SCP at a later stage. In the posterior domain the MPS neurons exhibit a third phenotype -- they have large cell bodies, express low levels of SCP starting from the midjuvenile stage, and do not show detectable LOX2 expression. Lineage tracer injections showed that the MPS neurons arise from a stereotyped cell lineage and are descended from the O teloblast stem cell. In midbody ganglia 2 to 6 and 18 to 21, there are lineally homologous neurons that do not express either LOX2 protein or SCP. Thus, the boundaries of LOX2 expression coincide precisely with two of the segmental boundaries of MPS differentiation, suggesting that expression of LOX2 at the level of this single identified neuron governs some, but not all, aspects of the neuron's segmental diversification.

[Cellular and fibrillar organization of the locomotor regions of the brain stem in cats]. / Kletochnaia i volokonnaia organizatsiia lokomotornykh oblastei stvola mozga koshki.

Cellular and fibrillar organization of the hypothalamic (HLR) and mesencephalic (MLR) locomotor regions of the brain stem has been studied in cats by means of staining the nervous tissue after Nissl and Sokolyansky. Morphometric investigations of neurons in these regions has been performed in frontal and sagittal slices. Within the limits of the HLR ad MLR there are about 45,000 of neurons, which are organized as various nuclei, the MLR cells arranging in them more compactly in comparison to diffusely ++ scattering HLR neurons. Within the limits of the locomotor regions, together with the cells and powerful compact fasciculi of fibers in the tract passing, that is especially specific for MLR, there are also numerous diffusely ++ scattered fibers. A possible role of the neurons and the fibers passing in starting locomotion at activation of the locomotor areas of the brain stem is discussed.

[Descending neuronal projections to the lumbar segment of the spinal cord of cats]. / Niskhodiashchie neironnye proektsii na poiasnichnyi otdel spinnogo mozga koshki.

In the experiments, performed on cats by means of retrograde axonal horseradish peroxidase transport, localization of the sources of descending supra- and propriospinal projections to the area of the lumbar parts of the spinal cord, where the generator of locomotor movements is located. After local administration of horseradish peroxidase into the spinal cord, the greatest amount of the labelled neurons is observed in the ipsilateral reticular formation and in the Koelliker-Fuse nucleus. Comparison of the number of neurons, forming the descending projections from the I cervical up to the IV lumbar segments demonstrates an essential predominance of short propriospinal connections over the long, as well as over the supraspinal ones.

[The brain stem pathways of locomotion initiation]. / Stvolovye puti initsiatsii lokomotsii.

The data about structural organization, connections and different ways of activation of the brain stem locomotor regions are offered in the review. The specificity of the locomotor regions and pathways of their influence on the spinal locomotor generator is discussed, the role of the reticular formation is elucidated. It is suggested that side by side with the multilevel system of the locomotion initiation, which has an output on the spinal cord via medial reticular formation, nonspecific afferent activation of the brain stem is also very significant.

[The participation of the interstitial nucleus of Cajal in initiating locomotion in cats and rats]. / Uchastie interstitsial'nogo iadra Kakhalia v vyzove lokomotsii u koshek i krys.

Electrical stimulation of the interstitial nucleus of Cajal and adjacent structures elicited locomotion in cats and rats. The thresholds were 20-30 muA for decerebrate and 70-100 microA for intact narcotized animals.

[Afferent projections of the bulbar locomotor region located in the medial reticular formation of the brain stem]. / Afferentnye sviazi bul'barnoi lokomotornoi oblasti, raspolozhennoi v medial'noi retikuliarnoi formatsii stvola mozga.

Afferent projections to the functionally identified bulbar locomotor region which is situated in the medial reticular formation were studied in cats and rats by means of horse-radish peroxidase technique. Cells of origin of such projections were found not only in hypothalamic and mesencephalic locomotor regions but also in the interstitial nucleus of Cajal and adjacent structures and in the ventral part of the caudate nucleus.

[Morphologic analysis of the origin of spinal locomotor strip fibers in the cat]. / Morfologicheskii analiz proiskhozhdeniia volokon lokomotornoi poloski spinnogo mozga koshki.

The origin of spinal locomotor strip fibres was studied in cat by means of electrical stimulation combined with the horse-radish peroxidase transport technique. It was revealed that the cortico-spinal tract presumably formed the locomotor strip. Some reticulo-spinal and spinal trigeminal tracts fibres were also found. Descending catecholaminergic fibres did not pass through the investigated regions of the dorso-lateral funiculus; they were not, apparently, a part of the spinal locomotor strip. The specificity of locomotor regions of the brain stem and spinal cord is discussed.

[Structural organization and connections of the locomotor strip of the medulla oblongata of the cat]. / Issledovanie strukturnoi organizatsii i sviazei lokomotornoi poloski prodolgovatogo mozga koshki.

The bulbar locomotor strip was studied by means of the horse-radish peroxidase technique. HRP microinjections were carried out under functional control of the evoked treadmill locomotion. The experiments have failed to reveal a special cellular column along the locomotor strip and the existence of such a strip as a separate structural formation is questioned. In fact the bulbar locomotor strip may conceal the spinal trigeminal tract and its nucleus. It is postulated that nonspecific afferent activation of the brainstem reticular formation plays a significant role in the locomotion initiation.

[New locomotor areas of the brain stem of the cat]. / Novye lokomotornye oblasti stvola mozga koshki.

New sites in the brainstem eliciting treadmill locomotion have been revealed in decerebrated cats by means of electrical stimulation. These sites--cochlear nuclei, ventral spinocerebellar tract and resciform body which includes dorsal spinocerebellar tract--are located outside the known locomotor regions. It is suggested that the nonspecific afferent activation of the brainstem reticular formation during electrical stimulation of the mentioned sensory tracts is sufficient for the initiation of the treadmill locomotion.

[Efferent projections of neurons of the mesencephalic locomotor region of the cat brain]. / Efferentnye proektsii neironov mezentsefalicheskoi lokomotornoi oblasti mozga koshki.

Efferent projections of mesencephalic locomotor region neurons were studied by means of horseradish peroxidase technique in cat. Ascending and descending projections of these neurons to different structures of the brain with predominant course to the brainstem reticular formation were traced. Some fibres passed through the bulbar and spinal locomotor strip. Mutual bilateral interconnections of the mesencephalic locomotor regions were observed.

[Locomotion in the cat induced by electric stimulation of midbrain structures]. / Lokomotsiia koshki, vyzvannaia élektricheskim razdrazheniem struktur srednego mozga.

Treadmill locomotion elicited by means of electrical stimulation of the central grey is shown in decerebrate cats. Thresholds were 20-200 microA. Stepping was also seen during 100 microA stimulation of the midline raphe nucleus.

[Afferent connections of the mesencephalic locomotor area of the cat brain]. / Afferentnye sviazi mesentsefalicheskoi lokomotornoi oblasti mozga koshki.

Afferent projections to the functionally identified mesencephalic locomotor region were studied in cat by means of the horse-radish peroxidase technique. Quantitative calculation of HRP-labelled neurons in the different brain structures after enzyme injections into mesencephalic locomotor region was made. Apart from the entopeduncular nucleus, different hypothalamic areas and substantia nigra, labelled neurons were found in ventral tegmental area, substantia grisea centralis, raphe and vestibular nuclei, nucleus of tractus solitarius and brainstem reticular formation. Neurons accumulating horse-radish peroxidase were found also in the brainstem sensory nuclei. This fact emphasized the structural heterogeneity of the mesencephalic locomotor region which includes neurons and passing fibers; both of them may be significant during locomotion elicited by the midbrain stimulation.

[Projections of neurons of the hypothalamic locomotor region to brain stem and spinal cord structures in the cat]. / Proektsii neironov gipotalamicheskoi lokomotornoi oblasti na struktury stvola i spinnogo mozga koshki.

Efferent projections of the hypothalamic locomotor region were studied by means of the horse-radish peroxidase technique. Labelled neurons in this region after HRP injections in different brain structures including lumbar spinal cord and other identified brainstem locomotor zones were found mainly ipsilaterally. The most considerable amount of labelled hypothalamic neurons was observed after HRP injections in the medial brainstem reticular formation and in the locus coeruleus area. The hypothalamic locomotor region also forms direct projections to the mesencephalic locomotor region and to the locomotor strip.

[Projection of forebrain structures of the cat to the hypothalamic locomotor area]. / Proektsii struktur perednego mozga koshki v gipotalamicheskuiu lokomotornuiu oblast'.

Descending projections of brain cortex and basal ganglia to the hypothalamic locomotor region were demonstrated in cat with horseradish peroxidase technique. Neurons projecting directly to the functionally identified locomotor region are dispersed in different gyri with predominance in areas 4 and 6 of the motor cortex. Such neurons are also located in entopeduncular nucleus. Massive cortico-and pallido-hypothalamic projections as a rule do not reach the most caudal hypothalamic divisions where the locomotor region is localized.