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.     

Afferent connections of the cat caudate nucleus studied by the retrograde axonal transport method

Sources of direct and indirect afferent connections of the caudate nucleus were investigated in cats by the retrograde axonal transport of horseradish peroxidase method. Different parts of the neocortex were shown to form different types of projections to the caudate nucleus; the sources of these projections have a laminar organization. Connections of the globus pallidus with the caudate nucleus, not previously described, were found. Among the sources of the thalamo-caudate projections, besides nuclei of the intralaminar complex, an important place is occupied by the ventral anterior and mediodorsal nuclei. After injection of horseradish peroxidase into the caudate nucleus, retrograde axonal transport of the enzyme was observed in the caudal direction, as far as cells of the locus coeruleus. ON the basis of these results a general scheme of afferent projections to the caudate nucleus is drawn up, including its connections with the spinal cord mediated by the thalamic nuclei and mesencephalic reticular formation.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 2, pp. 146–154, March–April, 1980.     

Tonotopic organization of the dorsocaudal zone of cortical area aii in the cat

The tonotopic organization of the dorsocaudal (DC) auditory cortex area AII was investigated during acute experiments on cats anesthetized with Nembutal. A capacity for selective response to presentation of auditory stimuli at a certain frequency was found in 93% of the neurons investigated. It was further observed that 75% of these cells were characterized by their fine tuning to one characteristic frequency (CF), the remaining 26% had several CF, and 7% reacted with a spike response to acoustic stimulation at all test frequencies and had no clearcut CF. A relationship was found between the location of a unit within the DC zone and its CF level. Neurons with the lowest CF were located in the upper position of the sylvian gyrus near the posterior ectosylvian sulcus. The CF of neurons rose progressively in step with increasing distance between the site of microelectrode recording and the low frequency focus of the DC zone travelling along the sylvian gyrus in a ventrorostral direction. Distance between low and high frequency foci of the DC zone measured 2.5–3.5 mm. Location of this zone in relation to the auditory cortex sulci varied considerably from one animal to another. Neurons with similar CF levels and arranged on this basis in vertical cortical columns could vary substantially in the dimensions of their receptive fields, sharpness of tunining to their own CF, and firing response pattern.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 2, pp. 220–227, March–April, 1988.     

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.     

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.     

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.     

Functional connections between the tegmentum mesencephali and supraoptico-hypophyseal hypothalamic neurosecretory system in albino rats

Bilateral electrolytic destruction of the paramedian zones of the caudal part of the tegmentum mesencephali caused an increase in the number of neurosecretory cells with low functional activity and the appearance of degenerating forms in the supraoptic nucleus of the hypothalamus (mainly in the medial part of the nucleus, adjacent to the optic chiasma); destruction of individual Herring's bodies was observed in the posterior lobe of the pituitary. The subnormal content of neurosecretory substance in all parts of the supraoptico-hypophyseal neurosecretory system was matched by a low plasma level of vasopressin-antidiuretic hormone. In animals with destructive lesions in the tegmentum mesencephali exposure to nociceptive stimulation activated mainly the neurosecretory cells in the lateral part of the supraoptic nucleus; the loss of neurosecretion from the posterior pituitary was partial; the plasma neurohormone level was much lower than in the control animals after nociceptive stimulation. It is postulated that changes in the response of the supraoptico-hypophyseal system to stress were probably the result of interruption of afferent pathways to the hypothalamus from the tegmentum mesencephali. The result of these experiments suggest that the paramedian zones of the tectum mesencephali exert a modulating influence on the function of this system during stress.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 2, pp. 157–164, March–April, 1977.     

Induced facilitation in the ventral tegmentum area on the latency of biting evoked by hypothalamic stimulation in the cat

The effects of VTA stimulation on the quiet biting attack evoked by hypothalamic activation in the cat, were studied. The reference value of the aggressive behaviour was the latency of the biting. Concurrent activation of both the hypothalamus and VTA determined a decrease of the biting latency, which depended on the parameters of VTA stimuli. The facilitatory effect of the dopaminergic mesolimbic system on the attack behaviour is emphasized.     

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.     

Incremental mutual information: a new method for characterizing the strength and dynamics of connections in neuronal circuits

Understanding the computations performed by neuronal circuits requires characterizing the strength and dynamics of the connections between individual neurons. This characterization is typically achieved by measuring the correlation in the activity of two neurons. We have developed a new measure for studying connectivity in neuronal circuits based on information theory, the incremental mutual information (IMI). By conditioning out the temporal dependencies in the responses of individual neurons before measuring the dependency between them, IMI improves on standard correlation-based measures in several important ways: 1) it has the potential to disambiguate statistical dependencies that reflect the connection between neurons from those caused by other sources (e.g. shared inputs or intrinsic cellular or network mechanisms) provided that the dependencies have appropriate timescales, 2) for the study of early sensory systems, it does not require responses to repeated trials of identical stimulation, and 3) it does not assume that the connection between neurons is linear. We describe the theory and implementation of IMI in detail and demonstrate its utility on experimental recordings from the primate visual system.     

Movements generated by intraspinal microstimulation in the intermediate gray matter of the anesthetized, decerebrate, and spinal cat

The intermediate laminae of the lumbosacral spinal cord are suggested to contain a small number of specialized neuronal circuits that form the basic elements of movement construction ("movement primitives"). Our aim was to study the properties and state dependence of these hypothesized circuits in comparison with movements elicited by direct nerve or muscle stimulation. Microwires for intraspinal microstimulation (ISMS) were implanted in intermediate laminae throughout the lumbosacral enlargement. Movement vectors evoked by ISMS were compared with those evoked by stimulation through muscle and nerve electrodes in cats that were anesthetized, then decerebrated, and finally spinalized. Similar movements could be evoked under anesthesia by ISMS and nerve and muscle stimulation, and these covered the full work space of the limb. ISMS-evoked movements were associated with the actions of nearby motoneuron pools. However, after decerebration and spinalization, ISMS-evoked movements were dominated by flexion, with few extensor movements. This indicates that the outputs of neuronal networks in the intermediate laminae depend significantly on descending input and on the state of the spinal cord. Frequently, the outputs also depended on stimulus intensity. These experiments suggest that interneuronal circuits in the intermediate and ventral regions of the spinal cord overlap and their function may be to process reflex and descending activity in a flexible manner for the activation of nearby motoneuron pools.     

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.     

Efferent connections of the centrum medianum of the cat thalamus revealed by autoradiography

Efferent connections of the centrum medianum and parafascicular nucleus of the thalamus (CM-Pf complex) in cats were studied by the method of anterograde axonal transport of tritiated amino acids followed by autoradiography. Projections from CM-Pf ascend to nuclei of the ventral group and nonspecific nuclei of the thalamus, preoptic, dorsal, lateral, and posterior areas of the hypothalamus, and also into the subthalamic region. Descending pathways are formed only by neurons of the caudomedial part of CM-Pf. They project into the pretectal region, superior colliculus, reticular formation, locus coeruleus, region of the ramus communicans, and substantia grisea centralis of the mesencephalon and pons, and also into the nuclei raphe, magnocellular reticular area, and inferior olivary nucleus of the medulla. In agreement with previous observations it was found that the caudomedial part of CM-Pf does not send direct projections into the cortex and striatum.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 16, No. 2, pp. 224–230, March–April, 1984.     

Afferent connections to the abducent nucleus in the cat.

The afferent connections to the abducent nucleus in the cat were studied by means of retrograde transport of WGA-HRP after implantations of the tracer in crystalline form. Retrogradely labelled cells were found bilaterally in the medial and descending vestibular nuclei, mainly in their ventral and medial portions, in the rostral part of the ipsilateral gigantocellular reticular nucleus, in the medial part of the contralateral caudal pontine reticular nucleus and bilaterally in the oculomotor nucleus, mainly in its dorsolateral division. Some labelled cells were also found bilaterally in the mesencephalic reticular formation, the periaqueductal grey and the nucleus of the trapezoid body.