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PubMed1988

Auditory pathways in the budgerigar. II. Intratelencephalic pathways.

The projections of two telencephalic areas in receipt of projections from the auditory relay nucleus of the thalamus (nucleus ovoidalis) were studied in the budgerigar (Melopsittacus undulatus) with autoradiographic methods. These nuclei are called field 'L' and neostriatum intermedium pars dorsolateralis (NIDL). The results show that neurons in both fields project laterally to a portion of the neostriatum intermedium pars ventrolateralis (NIVL) and rostrally to the rostromedial archistriatum. Horseradish peroxidase experiments confirm these projections and indicate that field 'L', NIDL and NIVL also receive projections from neurons in the hyperstriatum ventrale (HV). The projections of field 'L' and NIDL neurons to the rostromedial archistriatum may act as pathways subserving auditory feedback. Neurons in this portion of the archistriatum project to the contralateral field 'L', NIDL and NIVL. Furthermore, the medial archistriatal projection field of neurons within field 'L', NIDL and NIVL (i.e. rostromedial archistriatum) is located adjacent to a large archistriatal neuronal field projecting to the medulla, including the lateral reticular formation of the medulla. This large archistriatal field includes the nucleus archistriatalis robustus, the telencephalic nucleus identified as the source of projections to the lower motoneurons of the syrinx. Thus, projections from auditory telencephalic areas to the rostromedial archistriatum may serve functions related to processes associated with learning and vocal motor control.

Animals↗
PubMed2003

Cytoarchitecture of the avian optic tectum: neuronal substrate for cellular computation.

To analyse cellular computation in the vertebrate brain, a thorough knowledge of the underlying anatomy, physiology and connectivity of the neuronal substrate is essential. This review compiles data on one of the best known structures of the vertebrate brain, the optic tectum of birds. The functions of this structure are multifold, but can be attributed largely to orientation and the basic analysis of sensory data in a spatial context. In the tectum, a wealth of data on physiology and anatomy has been gathered over more than a century and provides an excellent background for computational studies. The analysis of the optic tectum is facilitated by several principles of organisation, including the retinotopic input and the highly laminated layout with separated input and output layers. Moreover, the molecular mechanisms guiding the development and connectivity have been analysed in detail. As the avian tectum and the mammalian superior colliculus are partly homologous, the cellular mechanisms unraveled in the tectum can also be transferred to the colliculus and thus contribute to the understanding of the vertebrate visual system in general.

Afferent Pathways↗
PubMed1986

Sound reception and synaptic transmission in goldfish hair cells.

Great advances in studies on the mechanisms of stimulus reception and transmission in hair cell organs have been made. With the use of intracellular recording, mechanisms related to transduction have been elucidated. The cochlea possesses mechanisms much more sophisticated than in other hair cell organs. In this review, the author attempted to explain these points, in relation to investigation on the goldfish sacculus (i.e. its inner ear).

Afferent Pathways↗
PubMed1984

Pain and analgesia: the outlook for more rational treatment.

Recent advances have been made in research on the physiology of pain, especially that focusing on the primary afferent nociceptor and endogenous analgesia systems. These advances have shed new light on the mechanisms of action of some long-used methods of managing pain, have led to the development of several methods, and have suggested new lines of investigation that may lead to more rational treatment of pain. The earlier that we can intervene in the pain-transmission pathways, the more likely we are to produce adequate and lasting control of pain. The peripheral nervous system is an important target for this therapeutic approach. The elucidation of the central neural pathways, which contain endogenous opioids and mediate the analgesia elicited by opiates, has raised the possibility of more rational use of this class of analgesics. The rationale for the use of current therapies needs to be reexamined in light of these new findings, and both current and new methods need to be tested in controlled trials.

Afferent Pathways↗
PubMed2000

Different subthreshold mechanisms underlie song selectivity in identified HVc neurons of the zebra finch.

Songbirds learn and maintain their songs via auditory experience. Neurons in many telencephalic nuclei important to song production and development are song selective, firing more to forward auditory playback of the bird's own song (BOS) than to reverse BOS or conspecific songs. Elucidating circuits that generate these responses can localize where auditory experience influences vocalization, bridging cellular and systems analyses of song learning. Song-selective responses in many song nuclei, including the vocal premotor nucleus robustus archistriatalis (RA) and the basal ganglia homolog area X, are thought to originate in nucleus HVc (used as a proper name), which contains interneurons and relay cells that innervate either RA or area X. Previous studies indicated that only X-projecting neurons have auditory responses, leaving open the source of RA's auditory input and the degree to which song selectivity may be refined in HVc. Here, in vivo intracellular recordings from morphologically and electrophysiologically identified HVc neurons revealed that both relay cell types fire song-selectively. However, their firing arises via markedly different subthreshold processes, and only X-projecting neurons appear to be sites for auditory refinement. RA-projecting neurons exhibited purely depolarizing subthreshold responses that were highly song selective and that were excitatory. In contrast, subthreshold responses of X-projecting neurons included less-selective depolarizing and highly selective hyperpolarizing components. Within individual birds, these BOS-evoked hyperpolarizations closely matched interneuronal firing, suggesting that HVc interneurons make restricted inputs onto X-projecting neurons. Because of the two relay cell types' subthreshold differences, factors affecting their resting membrane potentials could enable them to transmit distinct song representations to their targets.

Acoustic Stimulation↗
PubMed2003

Anatomophysiology of the central auditory nervous system: basic concepts.

The purpose of this review is to provide an overview of the central auditory nervous system (CANS). Three main relay nuclei are located between the auditory nerve and the primary auditory cerebral cortex: 1- the cochlear nucleus, 2- the contralateral inferior colliculus and 3- the contralateral medial geniculate body. Some fibers of this main ascending pathway branch off to other nuclei such as the nuclei of the superior olivary complex and the nucleus of the lateral lemniscus. Fiber tracts connect the two sides of the ascending pathway at several levels, in such a manner that each ear projects heavier to the contralateral temporal cortex. As sensory information travels within the CANS, its processing occurs not only in a serial order but also in a parallel manner resulting a highly efficient and redundant system. Finally, this review put forth a model of central auditory processing that can serve as the basis for evaluating and addressing the needs of eventual revalidation.

Auditory Cortex↗
PubMed2004

Input/output properties of the lateral vestibular nucleus.

This article is a review of work in three species, squirrel monkey, cat, and rat studying the inputs and outputs from the lateral vestibular nucleus (LVN). Different electrophysiological shock paradigms were used to determine the synaptic inputs derived from thick to thin diameter vestibular nerve afferents. Angular and linear mechanical stimulations were used to activate and study the combined and individual contribution of inner ear organs and neck afferents. The spatio-temporal properties of LVN neurons in the decerebrated rat were studied in response to dynamic acceleration inputs using sinusoidal linear translation in the horizontal head plane. Outputs were evaluated using antidromic identification techniques and identified LVN neurons were intracellularly injected with biocytin and their morphology studied.

Action Potentials↗
PubMed2004

Coupling sensory inputs to the appropriate motor responses: new aspects of cerebellar function.

It is known that proprioceptive signals modify the spatial organization of the postural reflexes, thus leading to body stability. The neurophysiological basis of this phenomenon are at present unknown. The present report documents that, in decerebrate cat, body-to-head rotation in the horizontal plane modified the preferred response direction to labyrinthine stimulation of the forelimb extensor triceps brachii. Such direction resulted always perpendicular to the longitudinal body axis of the animal, whatever its relative position with respect to the head could be. The rotation of the preferred response direction of the triceps was greatly reduced by functional inactivation of the ipsilateral cerebellar vermis. On the other hand, following body-to-head displacement, the preferred response directions of the corresponding P-cells tended, on the average, to rotate in the same direction and by the same angle as the body. We propose that the neck input finely tunes parallel vestibular channels, endowed with different spatial and temporal properties, impinging upon P-cells, thus modifying their responses to animal tilt and, as a consequence, the spatial properties of VS reflexes. It is possible that, by a similar mechanism, the cerebellum may contribute to the changes in reference frame occurring in sensorimotor transformations of reflex and voluntary nature.

Afferent Pathways↗
PubMed1991

Excitatory responses of the dorsal root discharge in L7 segment elicited by ascending and descending volleys in the cat.

Excitatory responses of the dorsal root discharge (DRD) which consist in short-lasting increase in its frequency have been recorded from the central cut ends of single dorsal root fibres of L7 dorsal root in spinal cats. They were evoked by stimulation of afferent nerves entering the cord below and above the level of recording of antidromic discharge and then ascending and descending to this level. Ascending volleys were provided by stimulation of caudal femoral posterior and pudendal nerves and descending volleys by stimulation of saphenous and quadriceps nerves. The excitatory responses of the DRD were elicited by stimulation of low threshold cutaneous afferents and group II and III muscle afferents while high threshold cutaneous and group I muscle afferents were ineffective. The excitatory responses of the DRD evoked by ascending volleys were larger than the effects elicited by descending volleys. The incidence of the excitatory effects to ascending volleys was significantly higher than to descending volleys. The size and incidence of the excitatory responses to ascending and descending volleys were, however, smaller than those of the effects elicited by stimulation entering the cord at the level of recording of antidromic discharge (i.e. in the posterior tibial nerve). It is suggested that the size and incidence of the excitatory responses of the DRD are related to the direction of spread and the level of entry of afferent volleys.

Action Potentials↗
PubMed1990

[The connections of the parietal cortex with the lateral suprasylvian gyrus (the Clare-Bishop field) and the auditory cortex in the cat].

It has been shown that a parietal projection to the Clare--Bishop area is moderate and organized in a topographic manner. Associative fibres of area 5 terminate in the anterior part of the Clare--Bishop area, which corresponds to the intermediate and anterior part of the posterior suprasylvian sulcus belt. Area 7 projects to the posterior part of the intermediate and posterior suprasylvian sulcus belt. Area 5 and 7 send a few fibres to the auditory cortex. Associative fibres of area 5 terminate in the middle ectosylvian and sylvian gyri: areas 22, 50. Area 7 is connected only with the superior extremity of the middle ectosylvian gyrus or of areas 22, 50.

Afferent Pathways↗
PubMed1990

The anatomy of the visceral and autonomic nervous systems.

The visceral nervous system has several levels of anatomical organization. Individual viscera, including the heart and the intestines, have neural tissue embedded in their walls that is capable, under some circumstances, of a truly autonomic self-regulation of that organ's activity. This self-regulation will not respond to all the varying needs of the organ control, particularly when external or internal changes affect the whole animal. The parasympathetic, sympathetic, and visceral afferent systems and their CNS connections are the next level of reflex neural organization. A greater degree of central regulation is managed at this level. The third level of visceral control is located in the brainstem and includes the hypothalamus, parts of the reticular formation, and cardiorespiratory centers in the medulla. These visceral upper neuron centers exert a high degree of control over the parasympathetic and sympathetic LMN centers of the brainstem and spinal cord. The reticulobulbar and reticulospinal pathways are the means by which the visceral upper motor neurons communicate with the LMN systems. The hypothalamus-hypophyseal system exerts control by releasing hormones to act on distant target organs. The highest level of organization of visceral function takes place in the limbic system. The limbic system is in a position to integrate sensory information originating from both within (interoceptive) and outside (exteroceptive) the animal. Associations are made at this level and with the help of cortical association areas, memory is integrated with these sensations. The limbic system is then able to influence the hypothalamic and medullary centers as well as the somatic motor centers to develop the appropriate responses for the preservation of the animal.

Afferent Pathways↗
PubMed1989

[Brain stem projections of afferent fibres form the salivary gland].

The sensory nerve fibres and terminals exist in the salivary gland. However, the projection sites of these sensory fibres have not been clarified. The present study was examined electrophysiologically the projection site of the afferent fibres in the brain stem in urethane-chloralose anesthetized cats. The sensory fibres from the sublingual and submandibular glands were passing through the trigeminal nerve. The afferent fibres projected to the caudal end of subnucleus interpolaris of trigeminal spinal tract nucleus, then send the secondary neurons to the lateral and medial of bulbar reticular formation and pontine reticular formation. The sensory afferents from the salivary gland would control the salivary secretion and other autonomic functions.

Afferent Pathways↗
PubMed1989

Synaptic ultrastructure of functionally and morphologically characterized neurons of the superficial spinal dorsal horn of cat.

Recordings of neuronal unitary discharges evoked by primary afferent input were made in the superficial part of the spinal cord's dorsal horn, the marginal zone and substantia gelatinosa (also known as laminae I and II), using fine micropipette electrodes filled with HRP. After physiological characterization with respect to primary afferent input, HRP was injected intracellularly iontophoretically into the recorded neuron. Following histochemical processing, the neurons so delineated were studied at the light and electron microscopic levels. No clear relationship between function and either general cellular configuration or synaptic ultrastructure appeared in these analyses, although the concentration of dendritic distribution could be related to the nature of primary afferent excitation. Nocireceptive cells had dendrites mostly branching and ending in lamina I and IIo, while the dendrites of innocuous mechanoreceptive cells arborized principally in lamina II and III. Glomerular synaptic complexes (large, complex arrays of axonic and dendritic profiles with synaptic interconnections) were found to contact a few neurons of both the nocireceptive and mechanoreceptive classes. All neurons received large numbers of simple axonic contacts (small axonic boutons with only 1 or 2 synaptic contacts with a single postsynaptic profile). A degree of specificity in the presynaptic articulations appeared to be reflected by the observations that (1) nocireceptive neurons were never found to receive synaptic contacts from boutons which resembled the known ultrastructure of peripheral innocuous mechanoreceptors, and (2) mechanoreceptive neurons were never seen to receive synaptic contacts from boutons which resembled the known ultrastructure of primary afferent nocireceptors. The axons of the labeled neurons of both nocireceptive and mechanoreceptive classes terminated in simple axonic synapses. All classes of neurons participated in dendrodendritic contacts; however, only some mechanoreceptive neurons had dendrites containing vesicles that were presynaptic to other profiles. No nocireceptive neurons, regardless of gross configuration, were found to have vesicles in their dendrites, but 3 nocireceptive neurons received synapses from presynaptic dendritic profiles.

Afferent Pathways↗
PubMed1985

[Control of visual exploration: anatomic and physiologic data].

The idea that saccadic eye movements necessary for visual space exploration could be under the control of the frontal eye field was based mainly upon Ferrier's early experiments of electrical stimulation of the cortex. More recent anatomical as well physiological data have demonstrated in monkeys that the sensori-motor processing needed to locate visual targets and to program an accurate eye movement to them is achieved in the superior colliculus, the frontal prearcurate and the posterior parietal cortices. Cells in those three structures have been identified by microelectrode studies that modify their response to a visual target before any eye movement when a saccade directed to this stimulus is to occur. Motivation to move the eyes towards the stimulus is under the control of the limbic cortex of the cingulate gyrus. Lesions to any of these structures lead to a neglect phenomenon characterized by the paucity of spontaneous saccades towards the half of space opposite to the lesion. In primates and in man neglect is observed only after cortical or thalamic lesions but not, or very transiently, after collicular lesion. The prearcuate frontal, the cingulate, and the posterior parietal cortices are interconnected via direct cortico-cortical fibres and also by a cortico-thalamo-cortical circuit, the thalamic relay of which is the medial pulvinar. The medial pulvinar is known to receive polymodal sensory informations from the intermediate layers of the superior colliculus. Thus a complete network involving cortical, thalamic and subthalamic structures is responsible for a very secure and redundant control of gaze.

Afferent Pathways↗