Changes in RNA content in neurons of the superior olivary complex during monaural and binaural stimulation

The character of binaural competitive connections at the level of the superior olive was investigated cytospectrophotometrically in cats. As a result of monaural stimulation for 2 h or binaural stimulation for 1.5 h by rhythmic noise signal the RNA content in the neurons of the ipsilateral and contralateral medial and lateral nuclei increased significantly. The volume of functioning neurons in the nuclei studied either increased or remained the same as in the control. The increase in the RNA content in neurons of both the ipsilateral and contralateral medial and lateral nuclei suggests a uniform distribution of binaurally converging connections on the neurons of these nuclei. The results also suggest that the accumulation of cytoplasmic RNA takes place in response not only to excitation, but also to inhibition.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 10, No. 1, pp. 67–74, January–February, 1978.     

Effects of binaural decorrelation on neural and behavioral processing of interaural level differences in the barn owl (Tyto alba)

The effect of binaural decorrelation on the processing of interaural level difference cues in the barn owl (Tyto alba) was examined behaviorally and electrophysiologically. The electrophysiology experiment measured the effect of variations in binaural correlation on the first stage of interaural level difference encoding in the central nervous system. The responses of single neurons in the posterior part of the ventral nucleus of the lateral lemniscus were recorded to stimulation with binaurally correlated and binaurally uncorrelated noise. No significant differences in interaural level difference sensitivity were found between conditions. Neurons in the posterior part of the ventral nucleus of the lateral lemniscus encode the interaural level difference of binaurally correlated and binaurally uncorrelated noise with equal accuracy and precision. This nucleus therefore supplies higher auditory centers with an undegraded interaural level difference signal for sound stimuli that lack a coherent interaural time difference. The behavioral experiment measured auditory saccades in response to interaural level differences presented in binaurally correlated and binaurally uncorrelated noise. The precision and accuracy of sound localization based on interaural level difference was reduced but not eliminated for binaurally uncorrelated signals. The observation that barn owls continue to vary auditory saccades with the interaural level difference of binaurally uncorrelated stimuli suggests that neurons that drive head saccades can be activated by incomplete auditory spatial information.     

Post-tetanic modification of the efficacy of excitatory transmission in neuronal networks with interhemispheric connections

The modifiable reciprocal transcallosal monosynaptic excitatory connections were for the first time detected in vivo experiments in rat motor cortex using multiunit recording and crosscorrelation analysis, It was shown that high-frequency microstimulation (MCS) of a small group of cortical cells of one hemisphere produces long-term changes in the efficacy of transcallosal excitatory connections, and also ipsilateral connections in both hemispheres. The posttetanic changes appear as long-term potentiation (LTP) and long-term depression (LTD). The bursting neurons were found to have more favorable conditions for the induction of LTP of most converging inputs (in contrast to cells with other discharge patterns). Both LTP and LTD could be simultaneously induced in synapses formed by axon collaterals of a callosal cell on several neurons. LTP and LTD could be simultaneously obtained at diverse synapses of the same cell. The number of spontaneously active callosal neurons as well as the number and efficacy of transcallosal connections increased after the MCS, whereas the number and efficacy of ipsilateral connections decreased. Basing on these data we assume that the ipsilateral inhibition is more effective than the transcallosal inhibition. MCS results in the modification of the pattern of initially existing connections between numerous neurons of an ensemble including cells of both hemispheres.     

Changes in the innervational connections of the urinary bladder upon experimental stimulation of the hypothalamus]

The innervation of the urinary bladder was studied in 40 rabbits, 5 of which were control and in 35 animals the posterior and anterior nuclei of the hypothalamus were stimulated by electric current through bipolar electrodes. The efferent innervation connections in whose terminal plexuses there occurred absorption of catecholamines were shown histochemically and neurohistologically to be involved in the pathological process. Reactive and degenerative changes were found to take place in receptory nerve terminations, and first of all in free ones. Then the bodies of pseudounipolar neurons of spinal ganglia were changed. Changes were also found in the connections of sensory neurons with the cells of Goll's and Burdach's nuclei.     

Lateral septal projections onto tubero-infundibular neurons in the hypothalamus of the guinea pig

Efferent projections of the lateral septal nucleus (LS) to the preoptic area and the hypothalamus were identified in 20 female guinea pigs after iontophoretic injection of the anterograde axonal tracer Fluoro-Ruby. Tubero-infundibular (TI) neurons of the preoptic area and the hypothalamus were retrogradely labeled after intracardiac injection of Granular Blue or Fluoro-Gold. Magnocellular neurons of the supraoptic and paraventricular nuclei were also labeled. The double labeling procedure allowed an estimation of the extent of the direct relationship between LS efferents and TI neurons. Contacts between lateral septal fibers and TI cell bodies were mainly observed at the light-microscopical level in the preoptic area. A group of labeled fibers coursing along the third ventricle established sparse connections with hypothalamic periventricular TI neurons. A few appositions was observed in the infundibular (arcuate) nucleus, suggestive of a monosynaptic regulation of TI neurons by a septo-arcuate tract. Close association with labeled magnocellular neurons was also noted at the edge of the supraoptic and paraventricular nuclei. The sparse but direct connections between LS and TI neurons may be involved in the neuroendocrine functions of the LS.     

Quantitative aspects in the analysis of the synaptic architecture of thalamic sensory relay nuclei

Special orientations of dendritic trees of projective (relay) neurons were observed in the thalamic nuclei; and it was found to be different in the various nuclei. It can be explained by the size, course, site of the fibre bundles which enter and/or transgress the nuclei. The orientation of dendritic tree and the size of the branching area of dendrites (specific active dendritic space) were analysed by computer. The quantitative data of neuronal elements in some thalamic nuclei gave the opportunity to consider the possible degree of divergence and convergence of sensory fibres regarding their connections with the projective neurons.     

Horseradish peroxidase-labeled cells as sources of the spinoreticular and spinothalamic systems of the brain]

The cells of spinoreticular and spinothalamic fibrous systems of the cat brain were studied by the method of axone transmission of horse-radish peroxidase (HP). A dense accumulation of HP-labeled neurons establishing direct relations with the reticular formation and thalamus was seen in the upper segments of the spinal cord. In the lower segments these zones were confined to the medial part of the ventral horn and the intermediate zone of the gray matter. The neurons established direct connections with contralateral nuclei of the reticular formation as well as with the thalamus ipsi- and contralateral nuclei. Possible pathways of transmitting somatic and pain sensitivity are discussed.     

Developmental study of rat vestibular neuronal circuits during a spaceflight of 17 days

The aim of this study was to investigate the potential plasticity of the vestibular system, in structural and biochemical terms, at the level of the gravity receptors (the sensory hair cells), the primary neurons relaying the sensory signals (the vestibular ganglion neurons) and their projections into the vestibular nuclei. We studied the biochemical differentiation of the sensory cells and of the vestibular ganglion by investigating which calcium-binding proteins were present. We studied the development of peripheral synaptic connections of the efferent system by investigating the distribution of CGRP (calcitonin-gene related-peptide) and we also studied the cerebellar synaptic connections in the vestibular nuclei, as identified by the presence of calbindin. Putative changes were studied after a 17-day episode of microgravity (Neurolab STS-90), in developing rats between postnatal days 8 and 25. The extent to which these changes could be caused by alterations in gravity was determined by examining sensory and nervous structures not involved in gravity detection, the cochlea and the cochlear nuclei.     

Responses of neurons in the primary auditory cortex of the cat to the auditory motion stimuli with variable interaural delay

Unit responses in the primary auditory cortex of anesthetized cats to stationary and apparently moving stimuli resulted from a static and dynamically varying interaural delay (ITD) were recorded. The static stimuli consisted of binaurally presented tones and clicks. The dynamic stimuli were produced by in-phase and out-of-phase binaurally presented click trains with time-varying ITD. Sensitivity to ITDs was mostly seen in responses of the neurons with low characteristic frequency (below 2.8 kHz). All cells sampled with static stimuli responded to simulated motion. A motion effect could take the form of a difference in response magnitude depending on the direction of stimulus motion and a shift in the ITD-function opposite the direction of motion. The magnitude of motion effects was influenced by the position of motion trajectory relative to the ITD-function. The greatest motion effect was produced by motion crossing the ITD-function slopes.     

Response of Neurons of The Inferior Colliculi of Cats To Changes in the Intensity of One of The Monaural Components of Binaurally Presented Stimuli

In spite of the large quantity of psychophysiological investigations of binaural hearing, a systematic study of its concrete mechanisms has only been begun comparatively recently (cf. review [1]). In particular, changes in neuron response under conditions of lateral differentiation brought about by varying the intensity of one of the monaural components of binaurally presented stimuli have been studied in detail only at the site of the superior olivary body (3, 4, 6) — the first section of the auditory system — where afferent fibers from the right and left cochlea converge (7, 9). Published data provide evidence that variations in the intensity of one of the monaural components of binaurally presented signals has an appreciable effect on the firing rate of single neurons of the inferior colli cuius (5, 8), which is situated directly behind the superior olivary body of the auditory system. in the present report, the types of response of neurons in the inferior colliculus to variations in the intensity of one of the monaural components of binaurally presented stimuli are systematically investigated.     

Auditory centre projection of the lower brainstem to the dorsal cochlear nucleus in the rabbit

Afferent projection to dCN from SOC and the periolivary regions was studied in the rabbit by retrograde transport of WGA-HRP. The projection originates primarily from the bilateral TrV and TrL with a very clear contralateral and ipsilateral predominance, respectively. A clear-cut topographical relationship was disclosed between location of neurons in these nuclei and projection sites in dCN. Thus, the medial region of dCN is target of projection arising from the medial regions of TrV and TrL, whereas the lateral region of dCN is supplied by projection from their lateral regions. Although participation in the projection of the ipsilateral TrV is smaller and the contralateral TrL is very weak, the pattern of these preferential connections is also apparent. Minute connections were traced from the other principal olivary nuclei, i.e. MSO, LSO and TrM, mainly from neurons located in their peripheral regions. In the periolivary region the cells of origin of the projection were found in VLPO and VMPO, and in lesser extent in DPO, DMPO, DLPO, RPO and CPO. The present results are discussed in comparison with those of earlier studies and with reference to other inputs to CN.     

The distribution of cholinergic neurons in the human central nervous system

Choline acetyltransferase (ChAT), the enzyme responsible for the biosynthesis of acetylcholine, is presently the most specific marker for identifying cholinergic neurons in the central and peripheral nervous systems. The present article reviews immunohistochemical and in situ hybridization studies on the distribution of neurons expressing ChAT in the human central nervous system. Neurons with both immunoreactivity and in situ hybridization signals of ChAT are observed in the basal forebrain (diagonal band of Broca and nucleus basalis of Meynert), striatum (caudate nucleus, putamen and nucleus accumbens), cerebral cortex, mesopontine tegmental nuclei (pedunculopontine tegmental nucleus, laterodorsal tegmental nucleus and parabigeminal nucleus), cranial motor nuclei and spinal motor neurons. The cerebral cortex displays regional and laminal differences in the distribution of neurons with ChAT. The medial septal nucleus and medial habenular nucleus contain immunoreactive neurons for ChAT, which are devoid of ChAT mRNA signals. This is probably because there is a small number of cholinergic neurons with a low level of ChAT gene expression in these nuclei of human. Possible connections and speculated functions of these neurons are briefly summarized.     

Connections between the anterior thalamic nuclei in turtles (data of the peroxidase method)

It turtles, Testudo horsfieldi (Gray) connections of anterior dorsomedial and dorsolateral thalamic nuclei have been investigated by means of horseradish peroxidase, injected ionophoretically. Retrogradely labelled neurons are predominantly revealed ipsilaterally in the cerebral structures belonging to the limbic system: in the forebrain--basal parts of the hemisphere, septum, adjoining nucleus, nuclei of the anterior and hippocampal commissures, hippocampal cortex, preoptic area; in the diencephalon--in the subthalamus (suprapeduncular nucleus), in some hypothalamic structures (para- and periventricular nuclei, posterior nucleus, lateral hypothalamic area, mamillary complex); in the brain stem--ventral tegmental area, superior nucleus of the suture. Less vast connections are with nonlimbic cerebral formations: projections to the striatum, afferents from the laminar nucleus of the acoustic torus, nuclei of the posterior commissure. Similarity and difference of the nuclei investigated in the turtles with the thalamic anterior nuclei in lizards, with the anterior and intralaminar nuclei in Mammalia are discussed. An idea is suggested on functional heterogeneity of the anterior nuclei in reptiles and on their role for ensuring limbic functions at the thalamic level.     

Nonuniformity in the linear network model of the oculomotor integrator produces approximately fractional-order dynamics and more realistic neuron behavior

The oculomotor integrator is a network that is composed of neurons in the medial vestibular nuclei and nuclei prepositus hypoglossi in the brainstem. Those neurons act approximately as fractional integrators of various orders, converting eye velocity commands into signals that are intermediate between velocity and position. The oculomotor integrator has been modeled as a network of linear neural elements, the time constants of which are lengthened by positive feedback through reciprocal inhibition. In this model, in which each neuron reciprocally inhibits its neighbors with the same Gaussian profile, all model neurons behave as identical, first-order, low-pass filters with dynamics that do not match the variable, approximately fractional-order dynamics of the neurons that compose the actual oculomotor integrator. Fractional-order integrators can be approximated by weighted sums of first-order, low-pass filters with diverse, broadly distributed time constants. Dynamic systems analysis reveals that the model integrator indeed has many broadly distributed time constants. However, only one time constant is expressed in the model due to the uniformity of its network connections. If the model network is made nonuniform by removing the reciprocal connections to and from a small number of neurons, then many more time constants are expressed. The dynamics of the neurons in the nonuniform network model are variable, approximately fractional-order, and resemble those of the neurons that compose the actual oculomotor integrator. Completely removing the connections to and from a neuron is equivalent to eliminating it, an operation done previously to demonstrate the robustness of the integrator network model. Ironically, the resulting nonuniform network model, previously supposed to represent a pathological integrator, may in fact represent a healthy integrator containing neurons with realistically variable, approximately fractional-order dynamics. Received: 8 August 1997 / Accepted in revised form: 18 June 1998     

Reactions of neurons of orbitofrontal cortex to stimulation of limbic system formations

The reactions of 164 neurons of the orbitofrontal cortex (OFC) to stimulation of the mediodorsal nucleus of the thalamus (MD), the amygdaloid complex, and various sections of the hypothalamus, were investigated in acute experiments on cats. Stimulation of the MD led to the development in OFC neurons of reactions with a short (sometimes less than 6 msec) and stable latent period. Similar reactions were observed upon stimulation of the lateral amygdaloid nuclei. Stimulation of the basal and central nuclei of the amygdala evoked synchronization of the discharges in OFC neurons. Stable responses of OFC neurons developed from nuclei of the hypothalamus only in the lateral region. Stimulation of the other nuclei of the hypothalamus was accompanied by irregular responses or synchronization of the discharges. In an analysis of the material obtained, the functional characteristics of the connections between the structures investigated and OFC neurons were examined.State Medical Institute, Kemerovo. Translated from Neirofiziologiya, Vol. 3, No. 5, pp. 484–490, September–October, 1971.     

The development of connections of the magnocellular hypothalamic nuclei with the posterior hypophyseal lobe in rat prenatal ontogeny]

The development of projections of the hypothalamic nuclei into the posterior lobe of the pituitary was studied on the fixed brain of rat fetuses from day 15 until day 19 of embryogenesis using retrograde staining with the fluorescent carbocyanine dye DiI. The formation of connections of the supraoptic and retrochiasmatic nuclei of the hypothalamus with the posterior lobe of the pituitary takes place during prenatal development on days 15 and 16-17, respectively, while only an insignificant number of the paraventricular nucleus neurons send their axons to the posterior lobe of the pituitary in rat fetuses. These facts suggest different temporal involvement of the above nuclei in formation of the hypothalamic-hypophysial neurosecretory system in rat fetuses.     

Early development of the motor and premotor circuitry of a sexually dimorphic vocal pathway in a teleost fish

The plainfin midshipman fish (Porichthys notatus) has a caudal hindbrain vocal motor circuit that has been proposed to share a common embryonic origin with the hindbrain vocal networks of other vertebrates. In midshipman, this vocal circuit includes three groups of neurons: sonic motor, pacemaker, and ventral medullary. Here, transneuronal transport of biocytin or neurobiotin was used to delineate the early ontogeny of the three hindbrain vocal nuclei and their pattern of connectivity. The organization of the vocal nuclei was studied in animals beginning soon after hatching until the nuclei have the adult phenotype at the time fish become free-swimming. There is a clear sequence of events whereby motoneurons establish their connections with the sonic muscle prior to establishing connections with premotor neurons; developmental milestones of the vocal pathway parallel those of the sonic muscle. The results also indicate that sexual differentiation of the vocal motor system in midshipman begins early in development, well before any evidence of sexual maturation. Embryonic males and females differ in the relationship between soma size and body length for the three hindbrain nuclei. Males are also more variable than females in body mass, volume of the sonic motor nucleus, and motoneuron cell size.     

Input of orexin/hypocretin neurons revealed by a genetically encoded tracer in mice

The finding of orexin/hypocretin deficiency in narcolepsy patients suggests that this hypothalamic neuropeptide plays a crucial role in regulating sleep/wakefulness states. However, very little is known about the synaptic input of orexin/hypocretin-producing neurons (orexin neurons). We applied a transgenic method to map upstream neuronal populations that have synaptic connections to orexin neurons and revealed that orexin neurons receive input from several brain areas. These include the amygdala, basal forebrain cholinergic neurons, GABAergic neurons in the preoptic area, and serotonergic neurons in the median/paramedian raphe nuclei. Monoamine-containing groups that are innervated by orexin neurons do not receive reciprocal connections, while cholinergic neurons in the basal forebrain have reciprocal connections, which might be important for consolidating wakefulness. Electrophysiological study showed that carbachol excites almost one-third of orexin neurons and inhibits a small population of orexin neurons. These neuroanatomical findings provide important insights into the neural pathways that regulate sleep/wakefulness states.     

Properties of monosynaptic connections between callosal neurons and specific thalamic nuclei

A comparative analysis of monosynaptic afferent and efferent connections of callosal neurons and target neurons of transcallosal fibers with neurons of the specific ipsilateral thalamic nuclei (ventral posterolateral, ventral posteromedial, ventral lateral, and anteroventral) was undertaken on the sensomotor cortex of unanesthetized rabbits, using an electrophysiological method. Differences were demonstrated between callosal neurons and target neurons of transcallosal fibers with respect to monosynaptic inputs from the thalamic nuclei and pathways proceeding toward these structures and (or) entering the pyramidal tract. Among target neurons, compared with callosal neurons, more cells had descending projections (54 and 14%, respectively). Monosynaptic action potentials arose in 22% of target neurons in response to stimulation of specific thalamic nuclei, whereas no such responses occurred in callosal neurons. Projections of target neurons into thalamic nuclei were shown to be formed both by independent fibers and by axon collaterals of the pyramidal tract. It is postulated that the distinctive properties thus discovered indicate significantly greater convergence of influence of thalamic relay neurons on the target neurons; this determines differences known to exist in characteristics of receptive fields and spontaneous and evoked activity of callosal neurons, on the one hand, and of neurons excited synaptically by transcallosal stimulation, on the other hand.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 3, pp. 305–314, May–June, 1985.     

Afferent brainstem projections to the hypothalmic locomotor region of the cat brain

The location of sources of direct projections to the hypothalamic locomotor region, electrical stimulation of which in the lightly anesthetized animal induced stepping along a moving treadmill, was studied by the retrograde axonal transport of horseradish peroxidase method in the cat brain stem. Different formations in the brain stem were shown to have direct connections with hypothalamic locomotor regions on both sides. Most sources of these afferent projections were located at sites of catecholamine- (nucl. reticularis lateralis, locus coeruleus, nucl. tractus solitarii) and serotonin-containing (nucl. raphe and substantia grisea centralis) neurons, parabrachial nuclei, and various sensory nuclei. Hypothalamic locomotor regions of both sides form bilateral connections.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 3, pp. 353–362, May–June, 1984.