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At least 19 recordsLinked to original sources
PubMed1984

The human medial geniculate body.

The medial geniculate body in non-human species is divided into several parts, each with a different structure, physiological organization, and pattern of connections. Which parts of the human medial geniculate body and which types of neurons might be homologous to those of other species is unknown, and the object of the present study. The cytoarchitecture, fiber architecture, and neuronal organization of the adult human medial geniculate body were studied in Nissl, Golgi, and other preparations. Three divisions, comparable to those in other mammals, were described. The ventral division had a bimodal distribution of somatic sizes in Nissl material which, in Golgi impregnations, may correspond, respectively, to a larger neuron with bushy dendrites and a tufted branching pattern, and a smaller stellate cell with a radiating, spherical dendritic field. The large neurons formed clusters surrounded by a particular pattern of neuropil which, together, constituted fibro-dendritic laminae whose long axis was oriented medio-laterally in parallel sheets or rows. The dorsal division was dominated by small and medium-sized somata representing at least three populations of neurons in the Golgi preparations. The large stellate cell had a radiate dendritic field and a dichotomous branching pattern; an equally large neuron with an elongated, multiangular perikaryon and bushy dendritic arbors forming tufts also occurred. Blended among these larger neurons were many smaller cells with tiny, flask-shaped, round, or drumstick-like perikarya, limited dendritic fields and thin dendrites, and poorly developed stellate or bushy dendritic configurations. In the medial division, larger somata were more common than in the other medial geniculate divisions, but small cells were present in considerable numbers. The fiber architecture and the different kinds of neurons distinguished the three major divisions and the nuclei within them. Thus, the ventral nucleus had long fascicles of axons running parallel to the dendrites of bushy neurons, while the marginal and ovoid nuclei had a different organization. The dorsal division had a more diffuse, irregular arrangement of thinner axons interspersed among bundles of coarser fibers, whereas the medial division was traversed by many coarse preterminal axons passing laterally and dorsally from the brachium of the inferior colliculus; these imparted a striated pattern to the neuropil. Regional variation in cytoarchitecture and the fiber plexus defined several nuclei in each subdivision, except in the medial division, where the density of the staining made further subdivision impossible.(ABSTRACT TRUNCATED AT 400 WORDS)

Auditory Pathways↗
PubMedDate not supplied

Inhibitory processes in the medial geniculate body.

Inhibition in the medial geniculate body was studied with a double click technique. A conditioning click caused a marked inhibition of field potentials and unit discharges to a subsequent test click. Cyclic inhibition with a period of about 150 ms was seen in the medial geniculate body and the auditory cortex, but not in the inferior colliculus. The postsynaptic excitability was tested by recording from the killed ends of the thalamocortical fibres. A preceding click reduced the direct response to a test stimulus delivered to the medial geniculate body indicating the presence of postsynaptic inhibition. The excitability of the fibres from the inferior colliculus terminating in the medial geniculate body was tested with a modified Wall (1958) method. The results suggest the presence of a presynaptic inhibitory mechanism in the medial geniculate body. The techniques employed do not allow an estimation of the relative contribution of the two inhibitory mechanisms to the inhibition at the medial geniculate level.

Acoustic Stimulation↗
PubMed1998

Postnatal cytoarchitecture of the rat medial geniculate body.

The medial geniculate body (MGB) is a thalamic structure that provides vital information flow to the forebrain for complex acoustic processing. The development of cytoarchitectural features of the MGB was examined in rat to identify age-related patterns of growth in major geniculate compartments that have been described previously (Clerici and Coleman [1990] J. Comp. Neurol. 297:14-31; Clerici et al. [1990] J. Comp. Neurol. 297:32-54): the ventral (MGv), dorsal (MGd), and medial (MGm) divisions. Results show that, on the day of parturition, all major nuclei of each division are characterized, including the ovoid (OV) and ventral (LV) nuclei of MGv; the dorsal, deep dorsal (DD), caudodorsal, limitans, and suprageniculate nuclei of MGd; and the MGm. The MGv and MGd, which display comparable areas at birth, show rapid growth to postnatal day 7 (PND7), which then slows until PND11, around the time of ear canal opening; subsequently, MGv accelerates growth to reach larger adult size. From PND11 to PND16, thionin facilitates parcellation by extensive staining of dendritic processes of MGd, MGm, and lateral posterior nucleus neurons but not neurons of the MGv or the dorsal lateral geniculate nucleus. Golgi stains after birth reveal restricted dendritic arborizations in MGv cells and dichotomous branching patterns of MGd neurons. Somal size in MGB increases dramatically subsequent to afferent innervation and again following onset of auditory function. Somal growth occurs between all postnatal age groups tested for OV, LV, and DD nuclei, although LV segments related to high and low frequencies do not differ. Cell packing density predicts the expanse of major MGB divisions better than somal size. These results demonstrate the integrity and growth patterns of MGB nuclei and divisions from nascence and provide a substrate for subsequent study of anatomical and physiological development of the MGB.

Age Factors↗
PubMed2006

Unique combination of anatomy and physiology in cells of the rat paralaminar thalamic nuclei adjacent to the medial geniculate body.

The medial geniculate body (MGB) has three major subdivisions, ventral (MGV), dorsal (MGD), and medial (MGM). MGM is linked with paralaminar nuclei that are situated medial and ventral to MGV/MGD. Paralaminar nuclei have unique inputs and outputs compared with MGV and MGD and have been linked to circuitry underlying some important functional roles. We recorded intracellularly from cells in the paralaminar nuclei in vitro. We found that they possess an unusual combination of anatomical and physiological features compared with those reported for "standard" thalamic neurons seen in the MGV/MGD and elsewhere in the thalamus. Compared with MGV/MGD neurons, anatomically, 1) paralaminar cell dendrites can be long, branch sparingly, and encompass a much larger area; 2) their dendrites may be smooth but can have well defined spines; and 3) their axons can have collaterals that branch locally within the same or nearby paralaminar nuclei. When compared with MGV/MGD neurons, physiologically, 1) their spikes are larger in amplitude and can be shorter in duration; 2) their spikes can have dual afterhyperpolarizations with fast and slow components; and 3) they can have a reduction or complete absence of the low-threshold, voltage-sensitive calcium conductance that reduces or eliminates the voltage-dependent burst response. We also recorded from cells in the parafascicular nucleus, a nucleus of the posterior intralaminar nuclear group, because they have unusual anatomical features that are similar to those of some of our paralaminar cells. As with the labeled paralaminar cells, parafascicular cells had physiological features distinguishing them from typical thalamic neurons.

4-Aminopyridine↗
PubMed1999

Neural architecture of the rat medial geniculate body.

The rat medial geniculate body was subdivided using Nissl preparations to establish nuclear boundaries, with Golgi-Cox impregnations to identify projection and local circuit neurons, and in fiber stained material to delineate the fiber tracts and their distribution. Three divisions were recognized (ventral, dorsal and medial): the first two had subdivisions. The ventral division had lateral and medial parts. The main cell type had bushy tufted dendrites which, with the afferent axons, formed fibrodendritic laminae oriented from dorso-lateral to ventro-medial; such laminae were not as regular medially, in the ovoid nucleus. The dorsal division contained several nuclei (dorsal superficial, dorsal, deep dorsal, suprageniculate, and ventrolateral) and neurons with radiating or bushy dendrites; the nuclear subdivisions differed in the concentration of one cell type or another, and in packing density. A laminar organization was present only in the dorsal superficial nucleus. Medial division neurons were heterogeneous in size and shape, ranging from tiny cells to magnocellular neurons; the various cell types intermingled. so that no further subdivision could be made. This parcellation scheme was consistent with, and supported by, the findings from plastic embedded or fiber stained material. There were very few small neurons with locally ramifying axons and which could perform an intrinsic role like that of Golgi type II cells. Their rarity was consistent with the small number of such profiles in plastic embedded or Nissl material and the few GABAergic medial geniculate body neurons seen in prior immunocytochemical work. While similar neuronal types and nuclear subdivisions are recognized in the rat and cat, there may be major interspecific differences with regard to interneuronal organization in the auditory thalamus whose functional correlates are unknown.

Animals↗
PubMed2000

Comparison of the fine structure of cortical and collicular terminals in the rat medial geniculate body.

Neurons throughout the rat medial geniculate body, including the dorsal and ventral divisions, display a variety of responses to auditory stimuli. To investigate possible structural determinants of this variability, measurements of axon terminal profile area and postsynaptic dendrite diameter were made on inferior colliculus and corticothalamic terminal profiles in the medial geniculate body identified by anterograde tracer labeling following injections into the inferior colliculus or cortex. Over 90% of the synapses observed were axodendritic, with few axosomatic synapses. Small (<0.5 microm(2)) and large (>1.0 microm(2)) collicular profiles were found throughout the medial geniculate, but were smaller on average in the dorsal division (0.49+/-0.49 microm(2)) than in the ventral division (0.70+/-0.64 microm(2)). Almost all corticothalamic profiles were small and ended on small-caliber dendrites (0.57+/-0.25 microm diameter) throughout the medial geniculate. A few very large (>2.0 microm(2)) corticothalamic profiles were found in the dorsal division and in the marginal zone of the medial geniculate. GABA immunostaining demonstrated the presence of GABAergic profiles arising from cells in the inferior colliculus. These profiles were compared with GABAergic profiles not labeled with anterograde tracer, which were presumed to be unlabeled inferior colliculus profiles or thalamic reticular nucleus profiles. The distributions of dendritic diameters postsynaptic to collicular, cortical and unlabeled GABAergic profiles were compared with dendritic diameters of intracellularly labeled medial geniculate neurons from rat brain slices. Our results demonstrate a corticothalamic projection to medial geniculate body that is similar to other sensory corticothalamic projections. However, the heterogeneous distributions of excitatory inferior collicular terminal sizes and postsynaptic dendritic diameters, along with the presence of a GABAergic inferior collicular projection to dendrites in the medial geniculate body, suggest a colliculogeniculate projection that is more complex than the ascending projections to other sensory thalamic nuclei. These findings may be useful in understanding some of the differences in the response characteristics of medial geniculate neurons in vivo.

Animals↗
PubMed1998

Auditory illusions caused by a small lesion in the right medial geniculate body.

Although the medial geniculate body (MGB) is a well-known integration center for the central auditory pathways, auditory symptoms caused by MGB damage have not been described. We report the appearance of the auditory illusions of hyperacusis and palinacousis in a 49-year-old man without previous psychiatric or epileptic illness after a small hemorrhagic infarction located mainly in the right MGB.

Auditory Perception↗
PubMedDate not supplied

Participation of the lateral geniculate body in mechanisms of brain activation.

The significance of the lateral geniculate body for nonspecific activation of the brain was elucidated in experiments on cats. It was established that when the connections of the lateral geniculate body remain intact, its stimulation elicits the usual activation of the EEG, but at higher threshold values of the current (120-190 microA) than when the mesencephalic reticular formation of the medial center of the thalamus is stimulated (50-80 microA). If only direct connections with the cortex remain, however, and the others are disrupted, the threshold for activation increases to 220-400 microA. When the lateral geniculate body is coagulated, cortical activity occurs only in response to very bright light flashes (250-1000 1x). All of this indicates that, in addition to carrying out its principal function of processing and sending the basic flow of visual impulsation to higher optical centers, the lateral geniculate body may be the source of activating transmissions sent to the cortex. Nonspecific stimulation that develops in the cortex is subsequently regulated by the cortex itself; the cortex plays a leading role in these processes.

Animals↗
PubMedDate not supplied

[Electrophysiologic relations in the lateral geniculate body].

Responses were evoked in the lateral geniculate body (L.G.B.) of "encéphale isolé" cats by single-shock stimulation of either the geniculate body or the optic tract of the other side. Responses to optic tract stimulation were modified following excitability changes in the contralateral L.G.B. due to topical application of strychnine and KCl. Laminar stimulation and recording in different layers (A, A1, and B) suggested the existence of a certain homotopic organization of L.G.B. interconnections. The activity evoked in the L.G.B. was found to be abolished by electrocoagulation of the posterior commissure and intermediate gray matter. These results point to the presence of a transthalamic pathway which might mediate L.G.B. activity to the contralateral visual cortex.

Animals↗
PubMed1999

Differential projection patterns of superior and inferior collicular neurons onto posterior paralaminar nuclei of the thalamus surrounding the medial geniculate body in the rat.

The thalamic nuclei at the medial border of the medial geniculate body (i.e. the suprageniculate nucleus, the medial division of the medial geniculate nucleus, the posterior intralaminar nucleus and the peripeduncular nucleus) which relay sensory information to the amygdala are thought to receive convergent input from multiple sites. In order to delineate the organization of these multimodal thalamic nuclei, the locations of superior and inferior collicular neurons projecting to these nuclei were studied by means of retrograde transport methods. Small injections of the tracer Miniruby were made into single paralaminar thalamic nuclei. Injections of Miniruby into the suprageniculate nucleus labelled predominantly neurons in the stratum opticum of the superior colliculus, whereas injections into the medial division of the medial geniculate body, the posterior intralaminar nucleus and the peripeduncular nucleus labelled predominantly neurons in the deep layers of the superior colliculus. These injections also labelled neurons in the inferior colliculus. The majority of retrogradely labelled neurons were found in the external nucleus of the inferior colliculus and here predominantly in layer 2. Injections focused onto the medial division of the medial geniculate body additionally labelled magnocellular neurons in layer 3 of the external nucleus and a few neurons in the central nucleus. More ventrally located injections, focused onto the posterior intralaminar and peripeduncular nucleus, almost exclusively labelled neurons in layer 1 of the external nucleus and the dorsal part of the dorsal nucleus. After injections into the suprageniculate nucleus, only neurons in layer 2 were found. Neurons in the central nucleus of the inferior colliculus were only found after injections that involved the medial division of the medial geniculate body. The present results suggest that, despite a considerable degree of convergence in this thalamic region, each of these thalamic nuclei receives a unique pattern of projections from the superior and inferior colliculi. It appears that the thalamic nuclei may be concerned mainly, but not exclusively, with a single sensory modality, and give rise to parallel multimodal and unimodal pathways to the amygdala.

Animals↗
PubMed1978

[Analysis of the neuronal activity of the lateral geniculate body in cats].

Activity of the lateral geniculate body neurons was studied in immobilized cats. Four parameters of impulse activity of every neuron were determined by computer analysis: T1, minimal, T2, average interspike intervals of the spontaneous activity, T3, latent period, and T4, duration of the first cluster of poststimulation activity. Classification of neuronal groups was made according to these parameters. This classification was used as a basis for the construction of a scheme of neuronal interaction in the lateral geniculate body.

Animals↗
PubMed1979

[Electrophysiologic study of conduction of afferent impulses through the medial geniculate body].

In experiments carried out on cats immobilzed with d-tubocurarine 280 neurons located in pars principalis of the medial geniculate body and 408 auditory cortical neurons located in AI were studied extra- and intracellularly in response to stimulation of the brachium of the inferior colliculus and geniculocortical fibres. It was shown that the initial stage of the reaction observed in the medial geniculate body neurons response to stimulation of the brachium of the inferior colliculus continue for 13.0 ms. Excitation of 72% of neurons participating in the reaction occurs during the first 3 ms after stimulation. 84% of IPSPs arouse in the same period of time. It is found that some medial geniculate neurons have axons entering the inferior colliculus. Substantial part of fibres in the brachium of the inferior colliculus comes to the auditory cortex without synaptic switching in the medial geniculate body. 76% of medial geniculate neurons from the group excited monosynaptically are thalamocortical relay neurons and the rest are interneurons. 90% of relay neurons in the medial geniculate body are excited monosynaptically. Many medial geniculate neurons respond to stimulation of the brachium of the interior colliculus by EPSP-IPSP sequence or by primary IPSPs. About 20% of primary IPSPs develop monosynaptically. The maximal amount of IPSPs comes into being disynaptically with the participation of inhibitory interneuron located at the input to the medial geniculate body. The inhibition observed in this case is direct afferent one.

Action Potentials↗
PubMed1985

[Various ways of assessing the structure of trace reactions of neurons of the medial geniculate body].

Afterdischarges of the medial geniculate body units were recorded in anesthetized cats following different sound stimuli. With traditional PSTH-technique, a periodicity of afterdischarges was found in some neurons whereas others showed diffuse and prolonged changes of their activity. To estimate the diffuse afterdischarges a special method was used. The procedure of eliminating time shift in neuronal responses was employed followed by averaging the individual PSTHs. A consequent diminution of time dispersion of neuronal responses revealed a distinct time structure in the diffuse afterdischarges.

Animals↗
PubMed1983

The laminar organization of the lateral geniculate body and the striate cortex in the squirrel monkey (Saimiri sciureus).

The organization of the projection from the lateral geniculate body to the striate cortex in the squirrel monkey has been re-examined using the anterograde and retrograde transport of horseradish peroxidase (HRP) and wheat germ agglutinin conjugated to HRP. The results confirm earlier findings that the projections of the magnocellular and parvocellular layers of the lateral geniculate body terminate in separate sublaminae of layer IV of striate cortex; a more superficial projection of the parvocellular layers to a narrow strip at the base of layer III (IVA in Brodmann's terminology) has also been confirmed. In addition to these well characterized pathways, our results show that the projections of the lateral geniculate body terminate in more superficial levels of layer III and sparsely in layer I of striate cortex. The projections to the upper portion of layer III terminate in distinct patches which coincide precisely with patches of cytochrome oxidase activity previously identified in this zone. The projections to the patches originate primarily from small, pale-staining cells of the "intercalated layers" which surround the magnocellular layers of the lateral geniculate body. A comparison of the organization of the geniculo-cortical projections in the squirrel monkey with that of the cat, Galago, and Tupaia suggests that, despite marked species differences in the laminar organization of the lateral geniculate body and striate cortex, there are striking similarities in the pathway which terminates in the most superficial layers of striate cortex.

Afferent Pathways↗
PubMed1983

The effects of unilateral neonatal removal of visual cortex on transmitter parameters in the adult superior colliculus and lateral geniculate body.

High affinity glutamate uptake was reduced in the ipsilateral lateral geniculate body by 75% and in the ipsilateral superior colliculus by 50% one week after ablation of the visual cortex in the adult rat. Six days after neonatal removal of visual cortex, there were no effects on the high affinity glutamate uptake in these regions indicating that there were few functionally corticofugal fibres established at birth. Seventy-five days after unilateral neonatal ablation of visual cortex, the glutamate uptake in both ipsi- and contralateral superior colliculus was reduced 50% compared to unoperated controls. The glutamate uptake in the lateral geniculate body was reduced 55% ipsilateral to and 38% contralateral to the lesion. The neonatal lesion had therefore affected the development of glutamate nerve terminals bilaterally in these target regions. Destruction of the visual cortex on the unoperated side caused in these adults an additional bilateral decrease of the glutamate uptake in the superior colliculus, showing the presence of aberrant glutamatergic fibres crossing from the unoperated visual cortex. In the lateral geniculate body, a similar lesion was accompanied only by a reduction in glutamate uptake on the ipsilateral side. The neonatal ablation of visual cortex also induced small changes in glutamate decarboxylase and GABA uptake in superior colliculus 75 days after the operation.

Animals↗
PubMed1999

Response characteristics of neurons in the medial geniculate body of the little brown bat to simple and temporally-patterned sounds.

We examined the auditory response properties of neurons in the medial geniculate body of unanesthetized little brown bats (Myotis lucifugus). The units' selectivities to stimulus frequency, amplitude and duration were not significantly different from those of neurons in the inferior colliculus (Condon et al. 1994), which provides the primary excitatory input to the medial geniculate body, or in the auditory cortex (Condon et al. 1997) which receives primary input from the medial geniculate body. However, in response to trains of unmodulated tone pulses, the upper cutoff frequency for time-locked discharges (64 +/- 46.9 pulses per second or pps) and the mean number of spikes per pulse (19.2 +/- 12.2 pps), were intermediate to those for the inferior colliculus and auditory cortex. Further, in response to amplitude-modulated pulse trains, medial geniculate body units displayed a degree of response facilitation that was intermediate to that of the inferior colliculus and auditory cortex inferior colliculus: 1.32 +/- 0.33; medial geniculate body: 1.75 +/- 0.26; auditory cortex: 2.52 +/- 0.96, P < 0.01). These data suggest that the representation of isolated tone pulses is not significantly altered along the colliculothalamo-cortical axis, but that the fidelity of representation of temporally patterned signals progressively degrades along this axis. The degradation in response fidelity allows the system to better extract the salient feature in complex amplitude-modulated signals.

Acoustic Stimulation↗