PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Inferior Colliculi”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 325 records · Page 18Linked to original sources
PubMed1996

Distribution of descending projections from primary auditory neocortex to inferior colliculus mimics the topography of intracollicular projections.

To ascertain whether the auditory neocortex also innervates the central nucleus of the inferior colliculus (CNIC) and not only its dorsal (DCIC) and external (ECIC) cortices, the anterograde tracers Phaseolus vulgaris-leucoagglutinin (PHA-L) and biotinylated dextran (BD) were injected into the primary auditory neocortex of albino rats (Te1), and labeled corticocollicular fibers were studied via light and electron microscopy. Axons from discrete regions of Te1 form two rostrocaudally oriented laminar plexuses of terminal fibers in the ipsilateral inferior colliculus (IC) and one in the contralateral IC. The first ipsilateral plexus, located in the medial half of the IC, has a dorsomedial to ventrolateral orientation, parallel to the isofrequency planes of the IC; is continuous through the CNIC and DCIC; and extends into the rostral ECIC. The second plexus is located in the deep layers of the lateral ECIC. These two plexuses meet caudally and ventrally, at the border between the CNIC and the lateral ECIC. The plexus in the contralateral IC is less dense and shorter than the two ipsilateral plexuses and is symmetric to the medial plexus. The thickness of the three plexuses is correlated with the size of the injection site, and their mediolateral and dorsoventral positions change as the injection site in Te1 is displaced rostrocaudally, with more caudal injections resulting in more dorsolateral medial plexuses and more dorsomedial lateral plexuses. Furthermore, the ventromedial border of the IC receives nontopographic, convergent projections from wide regions of rostral portions of Te1. The distribution of these corticocollicular plexuses mimics the topography of previously described intracollicular fibers. Electron microscopy shows that, in all three subdivisions of the ipsilateral IC, corticocollicular fibers form small boutons with features generally associated with excitatory transmission; i.e., they contain round synaptic vesicles and form asymmetric synapses with thin dendritic shafts and spines. These results demonstrate that the auditory corticocollicular projections innervate more extensive regions of the IC than were previously observed. Although peripheral regions receive the densest projection, the entire IC appears to be the target of corticofugal input.

Animals↗
PubMed1996

Anatomy of the ventral nucleus of the lateral lemniscus in rats: a nucleus with a concentric laminar organization.

The lateral lemniscus contains relay nuclei of the auditory pathway in which the neurons have been grouped into dorsal and ventral (VNLL) nuclei. The data about the cytoarchitecture of the VNLL are controversial and no agreement exists concerning its tonotopical organization. In this paper, the cytoarchitecture of VNLL and the spatial distribution of its neurons projecting to the central nucleus of the inferior colliculus (CNIC) have been studied by using different tracers. Rats were iontophoretically injected in the CNIC and grouped in three sets. Group 1 rats received large injections of biotinylated dextran amine (BDA). Group 2 animals received restricted single injections of BDA in the low-, medium-, or high-frequency regions of the CNIC. Group 3 rats were double injected, with horseradish peroxidase placed in the high-frequency region of the CNIC, and with biocytin in the low-frequency one. The distribution of retrogradely labeled neurons in the ipsilateral VNLL was three-dimensionally reconstructed by use of a computer microscope. The analysis of labeled neurons and Nissl material suggests that the VNLL contains flat stellate neurons. Labeled flat stellate neurons and fibers are oriented in parallel and form fibrodendritic laminae. The projection from the VNLL to the CNIC is topographically organized: neurons in peripheral laminae project to dorsolateral, low-frequency regions of the CNIC, and those of central laminae project to ventromedial, high-frequency regions. Each VNLL lamina forms a continuous ventrodorsal structure which resembles a helicoid.

Animals↗
PubMed1996

Sources of GABAergic input to the inferior colliculus of the rat.

We have studied the GABAergic projections to the inferior colliculus (IC) of the rat by combining the retrograde transport of horseradish peroxidase (HRP) and immunohistochemistry for gamma-amino butyric acid (GABA). Medium-sized (0.06-0.14 microliter) HRP injections were made in the ventral part of the central nucleus (CNIC), in the dorsal part of the CNIC, in the dorsal cortex (DCIC), and in the external cortex (ECIC) of the IC. Single HRP-labeled and double (HRP-GABA)-labeled neurons were systematically counted in all brainstem auditory nuclei. Our results revealed that the IC receives GABAergic afferent connections from ipsi- and contralateral brainstem auditory nuclei. Most of the contralateral GABAergic input originates in the IC and the dorsal nucleus of the lateral lemniscus (DNLL). The dorsal region of the IC (DCIC and dorsal part of the CNIC) receives connections mostly from its homonimous contralateral region, and the ventral region from the contralateral DNLL. The commissural GABAergic projections originate in a morphologically heterogeneous neuronal population that includes small to medium-sized round and fusiform neurons as well as large and giant neurons. Quantitatively, the ipsilateral ventral nucleus of the lateral lemniscus is the most important source of GABAergic input to the CNIC. In the superior olivary complex, a smaller number of neurons, which lie mainly in the periolivary nuclei, display double labeling. In the contralateral cochlear nuclei, only a few of the retrogradely labeled neurons were GABA immunoreactive. These findings give us more information about the role of GABA in the auditory system, indicating that inhibitory inputs from different ipsi- and contralateral, mono- and binaural auditory brainstem centers converge in the IC.

Animals↗
PubMed1996

Afferent connections to the dorsal nucleus of the lateral lemniscus of the mustache bat: evidence for two functional subdivisions.

The dorsal nucleus of the lateral lemniscus (DNLL) of the mustache bat, Pteronotus parnellii, was found to consist of two divisions. The neurons in each division were distinguished by their temporal discharge patterns evoked both by tone bursts and sinusoidal amplitude-modulated (SAM) signals. Neurons in the anterior one-third of the DNLL responded to tone bursts with an onset discharge pattern and only phase-locked to SAM signals with low modulation frequencies (< 300 Hz). Neurons in the posterior two-thirds of the DNLL responded to tone bursts with a sustained discharge pattern and phase-locked to SAM signals with much higher modulation frequencies (400-800 Hz). In addition, there was a different frequency representation in the two divisions. The frequency representation in the posterior division was from about 15 to 120 kHz, whereas in the anterior division it was only up to 62 kHz. The physiological differences were further supported by data from experiments that revealed the sources of afferent projections to the two DNLL divisions. Retrograde labeling showed that the afferent projections to the two divisions were from different neuronal populations. Input differences were of two types. Some nuclei projected to one or the other DNLL division, but not to both. For instance, the ventral nucleus of the lateral lemniscus projected predominately to the anterior DNLL and provided little or no inputs to the posterior DNLL, whereas the medial superior olive innervated the posterior but not the anterior DNLL. Other lower nuclei projected to both DNLL divisions. These include the contralateral cochlear nucleus, the ipsi- and contralateral lateral superior olives, the intermediate nucleus of the lateral lemniscus, and the contralateral DNLL. However, the projections to each division of the DNLL originate from different neuronal subpopulations in each lower nucleus. The functional implications of these findings are discussed in the context of the possible impacts that the two DNLL divisions exert on their postsynaptic targets in the inferior colliculus.

Acoustic Stimulation↗
PubMed1996

Features of the structural development of the inferior colliculus in relation to the onset of hearing in a marsupial: the northern quoll, Dasyurus hallucatus.

The time course of synaptogenesis and the arrival and myelination of afferent connections were studied in the developing inferior colliculus (IC) of a marsupial, the Northern Quoll, and related to the onset of hearing and patency of peripheral auditory structures in that species. The quoll is born after 3 weeks of intrauterine growth and completes its development in a pouch for a further 80 days before weaning. Synaptic terminals in the IC at 9 days after arrival in the pouch were extremely rare and were associated with very low vesicle numbers. The number of synapses increased smoothly during pouch life, whereas the number of neurons with nucleoli fell over the same time period. The ratio of synapses to cells steadily increased from day 9 to day 63, then rapidly accelerated to day 73; a similar high ratio was observed in adults. Retrograde labeling from the IC of fibers projected from the medullary auditory nuclei, first observed on day 36, became progressively denser during pouch life. Myelination of lateral lemniscal fibers was absent on day 45, extremely sparse on day 54, and clear on day 63. Myelin sheaths were not observed within the IC electron microscopically until day 73. Examination of the peripheral auditory system revealed that until about day 40 the middle ear was fluid-filled, and middle ear structures were spongy. Between days 51 and 63 the middle ear cleared, the eardrum became shiny, and the ear canal became patent. The structural development of the IC is therefore very mature at the time hearing begins (67 days), and the last major anatomical change preceding hearing appears to be the opening of the external ear canal.

Animals↗
PubMed1997

Alterations of GABAA receptor subunit mRNA levels in the aging Fischer 344 rat inferior colliculus.

The inhibitory neurotransmitter, gamma-aminobutyric acid (GABA) is critically involved in shaping neuronal responses to simple and complex acoustic stimuli in the central auditory structure, the inferior colliculus (IC). Studies in rat and human suggest that age-related changes in markers for GABA neurotransmission occur in the IC. In particular, these changes include findings indicative of an age-related increase in the efficacy/potency of GABA to inhibit ligand binding at the GABAA receptor picrotoxin site in the Fischer (F344) rat IC. Such changes in GABAA receptor modulation suggest the potential for an alteration in GABAA receptor subunit composition in the old rat IC. To test this idea, the present study used in situ hybridization to quantify age-related changes in GABAA receptor subunit mRNA levels in the three major subdivisions of the IC in the F344 rat: dorsal cortex (DCIC), external cortex (ECIC), and the central nucleus (CIC). In support of earlier findings of an age-related change in GABAA receptor modulation, the present study found: (1) GABAA receptor subunit mRNA levels were significantly altered in the IC of old rats, and (2) age-related changes in subunit levels appeared to be regionally selective and subunit specific. A highly significant increase in the level of the gamma 1 subunit mRNA was observed with little change in the levels of the alpha 1, beta 2, and gamma 2 subunit mRNAs. A nonstatistically significant increase in alpha 2 subunit mRNA was also observed. This observed increase in alpha 2 subunit mRNA could be important since previous expression studies have shown that the alpha 2 and gamma 1 subunits coassemble and are incorporated into GABAA receptors which appear to be more sensitive to GABA. If the observed changes in subunit mRNA levels with age correlate well with enhanced GABAA receptor function in the IC of old rats, this, in turn, may represent a compensatory mechanism in response to presynaptic GABAergic changes.

Aging↗
PubMed1997

Simultaneous anterograde labeling of axonal layers from lateral superior olive and dorsal cochlear nucleus in the inferior colliculus of cat.

The laminar organization of the central nucleus of inferior colliculus includes layers of axons that may be important in shaping the responses of neurons. Depending on their source, some layered axons are afferents that are superimposed and terminate on the same postsynaptic neurons, while other layered afferents, such as those from the ipsilateral and contralateral lateral superior olive, terminate side-by-side. The specific pattern of convergence may dictate which populations of axons are presynaptic to layered disc-shaped neurons in the central nucleus. We compared the distribution of afferent axons from the dorsal cochlear nucleus and the lateral superior olive to the contralateral inferior colliculus in the cat. Injection sites in cochlear nucleus and superior olive were physiologically characterized by extracellular recordings of single and multiple units in response to monaural and binaural acoustic stimulation. Two separate injections were made in each case, and both injection sites contained units with overlapping best frequencies. Biotinylated dextran, fluorescent dextran, 3H-leucine, and wheat germ agglutinin conjugated to horseradish peroxidase were used as anterograde tracers. The present results show that layered axons from the dorsal cochlear nucleus and lateral superior olive are superimposed in part of the contralateral central nucleus. Both projections were arranged in rostro-caudally oriented axonal layers that converged in the ventral part of the central nucleus. However, in the dorsal part of the central nucleus, the same layer of axons from the dorsal cochlear nucleus did not terminate with afferents from the lateral superior olive. Within the overlapping layers in the ventral central nucleus, the overlap of axons from the dorsal cochlear nucleus and the lateral superior olive was uniform except for small patches that were usually smaller than the dendritic fields of disc-shaped neurons. These data suggest that the layers may create specific functional zones in the central nucleus of the inferior colliculus. One zone may contain neurons with binaural responses that combine the properties of the inputs from the contralateral lateral superior olive and the dorsal cochlear nucleus. A second zone may contain inputs from the cochlear nucleus but lack those of the lateral superior olive.

Afferent Pathways↗
PubMed1997

Age-related changes in calbindin D-28k and calretinin immunoreactivity in the inferior colliculus of CBA/CaJ and C57Bl/6 mice.

This study examines calbindin D-28k and calretinin immunoreactivity in the inferior colliculus (IC) of young and old mice of two strains. The CBA/CaJ mouse maintains good hearing until very late in life, whereas the C57Bl/6 strain exhibits severe sensorineural hearing loss at an early age. Young and old mice of both strains were selected with matching auditory brainstem response audiograms and gap detection thresholds. Brain sections were reacted with anti-calbindin D-28k (CB) and anti-calretinin (CR). Staining patterns were characterized and cell counts performed. CB immunoreactivity was high only in the nucleus of the commissure (NCO); counts revealed a 22.3% decrease in the number of CB+ cells in old CBA mice and a 25.1% decrease in old C57 mice. Calretinin immunoreactivity was high in the pericentral regions of the IC, but the central nucleus was devoid of CR+ cells. The dorsal cortex, lateral nucleus, and NCO showed increases of 42.3, 49.0, and 61%, respectively, in the number of CR+ cells, but only in the old CBA mice. No significant change was observed in the old C57 mice. Whereas decreases in CB immunoreactivity are common with age, this study is the first to report an age-related increase in CR immunoreactivity in the auditory system. The increase in CR+ cells is a possible compensatory adaptation to the decrease in CB+ cells. That the number of CR+ cells remains constant with age in C57 mice suggests this compensation may depend upon stimulus-driven activity, but this requires further study.

Acoustic Stimulation↗
PubMed1998

Brainstem inputs to the ferret medial geniculate nucleus and the effect of early deafferentation on novel retinal projections to the auditory thalamus.

Following specific neonatal brain lesions in rodents and ferrets, retinal axons have been induced to innervate the medial geniculate nucleus (MGN). Previous studies have suggested that reduction of normal retinal targets along with deafferentation of the MGN are two concurrent factors required for the induction of novel retino-MGN projections. We have examined, in ferrets, the relative influence of these two factors on the extent of the novel retinal projection. We first characterized the inputs to the normal MGN, and the most effective combination of neonatal lesions to deafferent this nucleus, by injecting retrograde tracers into the MGN of normal and neonatally operated adult ferrets, respectively. In a second group of experiments, newborn ferrets received different combinations of lesions of normal retinal targets and MGN afferents. The resulting extent of retino-MGN projections was estimated for each case at adulthood, by using intraocular injections of anterograde tracers. We found that the extent of retino-MGN projections correlates well with the extent of MGN deafferentation, but not with extent of removal of normal retinal targets. Indeed, the presence of at least some normal retinal targets seems necessary for the formation of retino-MGN connections. The diameters of retino-MGN axons suggest that more than one type of retinal ganglion cells innervate the MGN under a lesion paradigm that spares the visual cortex and lateral geniculate nucleus. We also found that, after extensive deafferentation of MGN, other axonal systems in addition to retinal axons project ectopically to the MGN. These data are consistent with the idea that ectopic retino-MGN projections develop by sprouting of axon collaterals in response to signals arising from the deafferented nucleus, and that these axons compete with other sets of axons for terminal space in the MGN.

Age Factors↗
PubMed1999

Topographic organization of the dorsal nucleus of the lateral lemniscus in the cat.

The dorsal nucleus of the lateral lemniscus (DNLL) is an auditory structure of the brainstem. It plays an important role in binaural processing and sound localization and it provides the inferior colliculus with an inhibitory projection. The DNLL is a highly conserved auditory structure across mammals, but differences among species in its detailed organization have been reported. The main goal of this study was to analyze the topographic organization of the cat DNLL. Single, small iontophoretic injections of biotinylated dextran amine were made at different loci in the central nucleus of the inferior colliculus (CNIC). The distribution of the labeled structures in the ipsi- and contralateral DNLL was computer reconstructed in three dimensions. In individual sections, a band of labeling is seen in the DNLL on both sides. These two labeled bands occupy symmetric locations and are made of retrogradely labeled neurons with flattened dendritic arbors oriented parallel to each other. Moreover, the ipsilateral labeled band contains labeled terminal fibers parallel to the labeled dendrites. With three-dimensional reconstructions, it becomes evident that the labeled band seen in each individual DNLL section represents a slice through a rostrocaudally oriented lamina. The shape, size, orientation, and location of this lamina change as the injection site is shifted along the tonotopic axis of the CNIC. An injection in the low-frequency region of the CNIC, produces a lamina that resembles a flattened tube located in the dorsolateral corner of the DNLL. An injection in the high-frequency region of the CNIC, by contrast, results in a lamina that is an elongated sheet located at the ventromedial surface of the DNLL. The laminae of the DNLL might constitute the structural basis for its tonotopical organization. Previous studies (Merchan MA, et al. 1994. J Comp Neurol 342:259-278) in conjunction with our current results suggest that the laminar organization in the DNLL might be common among mammals.

Animals↗
PubMed1999

Descending auditory pathways: projections from the inferior colliculus contact superior olivary cells that project bilaterally to the cochlear nuclei.

Multiple retrograde and anterograde tracers were used to characterize a pathway that extends from the inferior colliculus to both the left and right cochlear nuclei via a synaptic relay in the superior olivary complex. Different fluorescent tracers were injected into the left and right cochlear nuclei to identify cells in the superior olivary complex that project bilaterally. Double-labeled cells were present in almost all periolivary nuclei; the majority were located in the ventral nucleus of the trapezoid body and the anteroventral periolivary nucleus. Because these two nuclei are targets of descending projections from the inferior colliculus, triple-labeling experiments were performed to determine whether collicular axons contact the periolivary cells that project to the cochlear nuclei. The results demonstrate that descending axons from the inferior colliculus contact periolivary cells that project to the cochlear nuclei, including periolivary cells that project bilaterally. This pathway could provide an opportunity for higher levels of the auditory system to influence activity bilaterally in the cochlear nuclei and thus to modulate the initial processing of acoustic information by the brain.

Animals↗
PubMed1999

Inputs to combination-sensitive neurons of the inferior colliculus.

In the mustached bat, combination-sensitive neurons display integrative responses to combinations of acoustic elements in biosonar or social vocalizations. One type of combination-sensitive neuron responds to multiple harmonics of the frequency-modulated (FM) components in the sonar pulse and echo of the bat. These neurons, termed FM-FM neurons, are sensitive to the pulse-echo delay and may encode the distance of sonar targets. FM-FM neurons are common in high-frequency regions of the central nucleus of the inferior colliculus (ICC) and may be created there. If so, they must receive low-frequency inputs in addition to the expected high-frequency inputs. We placed single deposits of a tracer at FM-FM recording sites in the ICC and then analyzed retrograde labeling in the brainstem and midbrain. We were particularly interested in labeling patterns suggestive of low-frequency input to these FM-FM neurons. In most nuclei containing labeled cells, there was a single focus of labeling in regions thought to be responsive to high-frequency sounds. More complex labeling patterns were observed in three nuclei. In the anteroventral cochlear nucleus, labeling in the anterior and marginal cell divisions occurred in regions thought to respond to low-frequency sounds. This labeling comprised 6% of total brainstem labeled cells. Labeling in the intermediate nucleus of the lateral lemniscus and the magnocellular part of the ventral nucleus of the lateral lemniscus together comprised nearly 40% of all labeled cells. In both nuclei, multiple foci of labeling occurred. These different foci may represent groups of cells tuned to different frequency bands. Thus, one or more of these three nuclei may provide low-frequency input to high-frequency-sensitive cells in the ICC, creating FM-FM responses. We also examined whether ICC neurons responsive to lower frequencies project to high-frequency-sensitive ICC regions; only 0.15% of labeling originated from these lower frequency representations. If the spectral integration of FM-FM neurons is created at the level of the ICC, these results suggest that neurons of the anteroventral cochlear nucleus or monaural nuclei of the lateral lemniscus may provide the essential low-frequency input. In contrast, there is little evidence that the low-frequency representation of the ICC contributes to these integrative responses.

Acoustic Stimulation↗
PubMed1999

Development of calretinin immunoreactivity in the brainstem auditory nuclei of the barn owl (Tyto alba).

The early development of calretinin immunoreactivity (CR-IR) was described in the auditory nuclei of the brainstem of the barn owl. CR-IR was first observed in the auditory hindbrain at embryonic day (E17) and a day later (E18) in the inferior colliculus. In each of the auditory nuclei studied, CR-IR did not develop homogeneously, but began in the regions that map high best frequencies in the adult barn owl. In the hindbrain, CR-IR was first observed in the rostromedial regions of the cochlear nucleus magnocellularis and the nucleus laminaris, and in the dorsal regions of the nucleus angularis and in the nucleus of the lateral lemniscus. In the inferior colliculus, CR-IR began in the ventral region of the central core. The edge of these gradients moved along the future tonotopic axes during the development of all nuclei studied, until adult patterns of CR-IR were achieved about a week after hatching.

Animals↗
PubMed2000

Development of afferent patterns in the inferior colliculus of the rat: projection from the dorsal nucleus of the lateral lemniscus.

The inferior colliculus (IC) receives a variety of layered afferent projections. The purpose of the present study was to determine the development of the projection from the dorsal nucleus of the lateral lemniscus (DNLL) to the IC in rat prior to the onset of hearing (postnatal day 12/13). Lipophilic carbocyanine dye, DiI (1, 1'-dioctodecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate), was used to trace the crossed inhibitory projection of DNLL in a developmental series of rat embryos and pups between ages embryonic day 15 (E15) and postnatal day 12 (P12). Dye-coated pins were positioned in paraformaldehyde-fixed brains either unilaterally in DNLL (embryonic cases), or in the commissure of Probst where DNLL fibers cross the midline (postnatal cases). By E15, pioneer fibers have left DNLL and crossed the midline. A few fibers have nearly reached the contralateral IC by E19. At birth (E22 = P0), the projection has invaded ventromedial, high-frequency layers of the IC. The vast majority of DNLL axons parallel the presumptive IC layers by P4, and by P8 the projection has segregated into a pattern of bands (afferent dense) and interband (afferent sparse) spaces that encompasses the entire frequency axis of the IC. Adult-like patches, regions along afferent bands that exhibit the heaviest labeling, develop by P12. These results indicate that some mature projection patterns are in place prior to the onset of hearing. Such findings suggest that evoked activity may not be required for the initial organization of patterned projections in the ascending auditory pathway.

Animals↗
PubMed2000

Topographic projection from the optic tectum to the auditory space map in the inferior colliculus of the barn owl.

In the barn owl (Tyto alba), the external nucleus of the inferior colliculus (ICX) contains a map of auditory space that is calibrated by visual experience. The source of the visually based instructive signal to the ICX is unknown. Injections of biotinylated dextran amine and Fluoro-Gold in the ICX retrogradely labelled neurons in layers 8-15 of the ipsilateral optic tectum (OT) that could carry this instructive signal. This projection was point-to-point and in register with the feed-forward, auditory projection from the ICX to the OT. Most labelled neurons were in layers 10-11, and most were bipolar. Tripolar, multipolar, and unipolar neurons were also observed. Multipolar neurons had dendrites that were oriented parallel to the tectal laminae. In contrast, most labelled bipolar and tripolar neurons had dendrites oriented perpendicular to the tectal laminae, extending superficially into the retino-recipient laminae and deep into the auditory recipient laminae. Therefore, these neurons were positioned to receive both visual and auditory information from particular locations in space. Biocytin injected into the superficial layers of the OT labelled bouton-laden axons in the ICX. These axons were generally finer than, but had similar bouton densities as, feed-forward auditory fibers in the ICX, labelled by injections of biocytin into the central nucleus of the inferior colliculus (ICC). These data demonstrate a point-to-point projection from the OT to the ICX that could provide a spatial template for calibrating the auditory space map in the ICX.

Animals↗
PubMed1996

Distribution of mesencephalic trigeminal nucleus neurons in the reeler mutant mouse.

BACKGROUND: Reeler (gene symbol, rl) is an autosomal recessive mutation occurring in mice and characterized by the abnormal positioning of neurons in the central nervous system. In this mutant, however, the cytoarchitecture of the peripheral nervous system is normal, implying that the reeler genetic locus does not affect migration of neurons in the peripheral system. Mesencephalic trigeminal nucleus (Me5) neurons are unique in that they are derived from the neural crest like other neurons in the peripheral nervous system, but enter secondarily into the central nervous system. MATERIALS AND METHODS: Me5 neurons were labeled by injecting horseradish peroxidase or Fast Blue into the temporal muscle of normal and reeler mice to determine whether the migration of these neurons is affected by the reeler genetic locus. RESULTS AND CONCLUSIONS: Labeled Me5 neurons of the reeler mouse were more widely scattered in comparison with their normal counterparts, suggesting that the reeler genetic locus affects migration of neurons which originate in the neural crest and then migrate into the central nervous system.

Amidines↗
PubMed1999

PET study of the human foveal fixation system.

Positron emission tomography (PET) was used to investigate the functional anatomy of the foveal fixation system in 10 subjects scanned under three different conditions: at rest (REST), during the fixation of a central point (FIX), and while fixating the same foveal target during the presentation of peripheral visual distractors (DIS). Compared with the REST condition, both FIX and DIS tasks activated a common set of cortical areas. First, in addition to the involvement of the occipital visual cortex, both the frontal eye field (FEF) and the intraparietal sulcus (IPS) were bilaterally activated. Right frontal activation was also found in the dorsolateral prefrontal cortex, the inferior part of the precentral gyrus, and the inferior frontal gyrus. These results suggest that both FEF and IPS may constitute the main cortical regions subserving bilaterally the foveal fixation system in humans. The remaining right frontal activations may be considered as part of the anterior attentional network, supporting a role for the right frontal lobe in the allocation of the attentional mechanisms. Compared with the FIX condition, the DIS task also revealed the perceptual and cognitive processes related to the presence of peripheral visual distractors during foveal fixation. In addition to a bilateral activation of the V5/MT motion-sensitive area, a right FEF-IPS network was activated which may correspond to the engagement of the visuospatial attention. Finally, normalized regional cerebral blood flow (NrCBF) decreases were also observed during both DIS and FIX condition performance. Such NrCBF decreases were centered in the superior and middle temporal gyri, the prefrontal cortex, and the precuneus and the posterior retrosplenial part of the cingulate gyrus.

Adult↗