摘要:

AbstractThe auditory fields in the cortex of the guinea pig were investigated with microelectrode mapping techniques. Pure tones of varying frequencies and amplitudes were used as acoustic stimuli. Mainly, multiunit activity was recorded.A large tonotopic area is found in the anterior half of the auditory cortex. This area is named the anterior field (field A). Frequency tuning curves of multiunits in field A are generally narrow. Responses to tone stimuli are strong, and latencies are short. Low best frequencies are represented rostrally, high best frequencies caudally. The tonotopy is continuous and quite regular. Field A is narrow dorsally and becomes gradually broader ventrally. Correspondingly, the isofrequency lines slightly diverge from dorsal to ventral.Caudal to the first field, there is a second, smaller tonotopic area. It lies in the dorsal half of the posterior auditory cortex and is therefore named the dorsocaudal field (field DC). The frequency specificity of the cell clusters in this area is as strong as in field A, but the tonotopy is discontinuous: In the dorsal half of field DC, high best frequencies (16‐32 kHz) are represented rostrally; the low frequencies (0.5‐2.8 kHz) are represented immediately caudal to the high frequencies, while the intermediate frequencies are missing. Ventrally in field DC, the frequency representation is more complete. Except for this discontinuous map, we did not notice any differences between fields A and DC. A third tonotopic field was found rostral to field A. This field extends over a surface of less than 1 mm2and was named the small field (field S). It contains a complete representation of the frequency range; high best frequencies are located rostrally, low frequencies caudally. The response latencies are slightly longer in field S than in fields A or DC, and the tuning curves are broader.A broad strip of nontonotopic cortex (auditory belt) surrounds fields A and DC caudally. We subdivided this area into the dorsocaudal and the ventrocaudal belt region. In both areas, tuning curves are often broad, and response latencies are longer than in the tonotopic cortex. In the dorsocaudal belt, most multiunits react with a phasic on‐response to pure tones; in the ventrocaudal belt, tonic responses occur more frequently. Another nontonotopic region is located in the anterior auditory cortex, rostral to the tonotopic fields, and was therefore named the rostral belt. Tuning curves in this area are broad, latencies are short, and reponse thresholds are often high.In the discussion, the guinea pig is compared with other mammalian species. Species‐specific features in the organization of the tonotopic cortex of the guinea pig are r

ISSN:0092-7317    

DOI:10.1002/cne.902820402

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractWe investigated the projection from the medial geniculate body (MG) to the tonotopic fields (the anterior field A, the dorsocaudal field DC, the small field S) and to the nontonotopic ventrocaudal belt in the auditory cortex of the guinea pig. The auditory fields were first delimited in electrophysiological experiments with microelectrode mapping techniques. Then, small quantities of horseradish peroxidase (HRP) and/or fluorescent retrograde tracers were injected into the sites of interest, and the thalamus was checked for labeled cells.The anterior field A receives its main thalamic input from the ventral nucleus of the MG (MGv). The projection is topographically organized. Roughly, the caudal part of the MGv innervates the rostral part of field A and vice versa. After injection of tracer into low or medium best‐frequency sites in A, we also found a topographic gradient along the isofrequency contours: the dorsal (ventral) part of a cortical isofrequency strip receives afferents from the rostral (caudal) portions of the corresponding thalamic isofrequency band. However, it is not so obvious whether such a gradient exists also in the high‐frequency part of the projection. A second, weaker projection to field A originates in a magnocellular nucleus that is situated caudomedially in the MG and was therefore named the caudomedial nucleus.The dorsocaudal field DC receives input from the same nuclei as the anterior field, but the location of the labeled cells in the MGv is different. This was demonstrated by injection of different tracers into sites with like best frequencies in fields A and DC, respectively. After injection of HRP into the 1‐2‐kHz isofrequency strip in field A and injection of Nuclear Yellow (NY) into the 1‐2‐kHz site in field DC, the labeled cells in the MGv form one continuous array that runs from caudal to rostral over the whole extent of the MGv. The anterior part of this array consists of NY‐labeled cells; i.e., it projects to field DC. The caudal part is formed by HRP‐labeled cells; i.e., it innervates field A. These findings indicate that there is only one continuous tonotopic map in the MGv. This map is split when projected onto the cortex so that two adjacent tonotopic fields (A and DC) result. The cortical maps are rotated relative to the thalamic map in that rostral portions of the MGv project to caudal parts of the tonotopic cortex and vice versa.The small field S receives its main thalamic input from a region situated in the rostral half of the MG medial to the ventral nucleus (the rostromedial MG). After injection of tracer into the ventrocaudal belt, labeled cells were found dorsal, lateral, and ventral to the MGv. These cells form a continuous band that surrounds the MGv like a shell. A second population of labeled neurons was found in the caudomedial nucleus of the MG.Similarities and differences between the auditory thalamocortical systems in the guinea pig and other mammalian specie

ISSN:0092-7317    

DOI:10.1002/cne.902820403

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe demonstration of coexistence of a peptide or peptides in neurons that produce a small molecule neurotransmitter has become increasingly frequent. The calcitonin gene‐related peptide (CGRP) is known to be colocalized in the cholinergic neurons of both cranial and spinal motor nuclei. The present study demonstrates that all somatic motor cranial nerve nuclei contain CGRP‐and galaninlike immunoreactivity. The perikaryal content of both peptides is increased by colchicine pretreatment and by transecting axons arising from the perikarya, and both peptides are found in nerve fibers innervating striated musculature. CGRP‐ and galaninlike immunoreactivity appear to be present in different populations of neurons. In contrast to CGRP, galaninlike immunoreactivity was not detected in spinal motor neurons. These observations suggest that galanin and CGRP participate in the process of synaptic transmission at the neuromuscular junction of cranial motor ne

ISSN:0092-7317    

DOI:10.1002/cne.902820404

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractHorseradish peroxidase was injected into the oculomotor nucleus of the chick in order to locate and characterize the neurons projecting to this nucleus. In the rostral mesencephalon, 120‐180 neurons were labelled in the medial area of the ipsilateral nucleus campi Foreli; 190‐220 in the interstitial nucleus of Cajal (most of them contralateral); and smaller numbers bilaterally in the medial mesencephalic reticular formation, the nucleus of the basal optic root complex, and the central grey matter. More caudally, numerous neurons were labelled in the contralateral abducens nucleus and the vestibular complex and a few in the nucleus reticularis pontis caudalis. Labelled neurons appeared ipsilaterally in the caudal region of the nucleus vestibularis superior and in the rostral tip of the nucleus descendens just lateral to the tractus lamino‐olivaris. In the contralateral vestibular complex, a group of labelled cells observed in the dorsolateral area may be homologous to the mammalian cell group Y. At the level of the contralateral abducens nucleus, the most numerous group of cells (625‐700) projecting to the oculomotor nucleus formed a lateromedial fringe that affected the nucleus tangentialis, the rostral tip of the nucleus descendens and the ventrolateral region of the nucleus medialis. Only a few labelled neurons were seen in the contralateral nucleus vestibularis superior, the ipsilateral cell group A, and the ipsilateral nucleus vestibularis m

ISSN:0092-7317    

DOI:10.1002/cne.902820405

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe role of retinal afferents and their binocular interactions in the development of mammalian primary visual centers has been studied in the marsupial wallaby. Monocular and binocular enucleation was performed prior to any retinal innervation of the visual centers. After monocular enucleation retinal projections were traced by horseradish peroxidase histochemistry and compared with those in normal animals and those during development. The topography of retinal projections to the superior colliculus and the dorsal lateral geniculate nucleus after monocular enucleation was determined by making retinal lesions and tracing the remaining projections with horseradish peroxidase. The position and nature of the filling defects in terminal label were compared with controls with similarly placed lesions.The superior colliculus and dorsal lateral geniculate nucleus ipsilateral to the remaining eye were shrunken. Projections to the ipsilateral superior colliculus, ipsilateral accessory optic nuclei, and ipsilateral suprachiasmatic nucleus, although enlarged, never approached the density contralaterally, as was also the case during normal development. The expanded projection in the ipsilateral superior colliculus came primarily from temporal and ventral retina. In the dorsal lateral geniculate nucleus, terminal bands and cellular laminae, although not identical to normal, did develop. During normal development overlap of afferents from the two eyes occurs in the binocular region. The decrease in volume of the nucleus ipsilateral to the remaining eye after monocular enucleation suggests that the monocular region disappears in the absence of appropriate input and the binocular region survives. Contralaterally there was no decrease in volume, compatible with this idea. The topography of retinal projections supports this interpretation. It was normal contralaterally while ipsilaterally it was appropriate for the normal binocular region. There was an expansion of the projection along the lines of projection in what would normally be binocular regions of the nucleus, where retinal afferents failed to segregate in the absence of binocular competition.After binocular enucleation the α and β segments of the dorsal lateral geniculate nucleus were still recognizable but cell‐sparse zones were absent, as was the characteristic orientation of primary dendrites of geniculocortical cells.There are rigid developmental constraints operating on the innervation of territory by retinal afferents from the two eyes, and many features of the mature pattern arise without binocular interactions during developm

ISSN:0092-7317    

DOI:10.1002/cne.902820406

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe postnatal fate of the first‐generated neurons of the cat cerebral cortex was examined. These neurons can be identified uniquely by3H‐thymidine exposure during the week preceding the neurogenesis of cortical layer 6. Previous studies in which3H‐thymidine birthdating at embryonic day 27 (E27) was combined with immunohistochemistry have shown that these neurons are present in large numbers during fetal and early postnatal life within the subplate (future white matter), that they are immunoreactive for the neuron‐specific protein MAP2 and for the putative neurotransmitters GABA, NPY, SRIF, and CCK. Here, the same techniques were used to follow the postnatal location and disappearance of the early generated subplate neuron population.At birth (P0), subplate neurons showing immunoreactivity for GABA, NPY, SRIF, or CCK are present in large numbers and at high density within the white matter throughout the neocortex, and the entire population can be observed as a dense MAP2‐immunoreactive band situated beneath cortical layer 6. Between P0 and P401 (adulthood), the MAP2‐immunostained band disappears so that comparatively few MAP2‐immunoreactive neurons remain within the white matter. There is a corresponding decrease in the number and density of neurons stained with antibodies against neurotransmitters. In each instance, these neurons could be double‐labeled by the administration of3H‐thymidine at E27, indicating that they are the remnants of the early generated subplate neuron population. The major period of decrease occurs during the first 4 postnatal weeks, and adult values are attained by 5 months. Within the white matter of the lateral gyrus (visual cortex), the density of immunostained neurons decreases dramatically: MAP2, 82%, SRIF, 81%, and NPY, 96%. While SRIF‐immunoreactive neurons compose a nearly constant percentage of MAP2‐immunoreactive neurons in the white matter between P0 (22%) and P401 (23%), those immunoreactive for NPY decline from 18 to 4%. These changes occur during the same period in which there is less than a twofold increase in white matter area.These observations indicate that the interstitial neurons of the adult neocortical white matter are the oldest neurons of the cerebral cortex since most if not all are derived from the subplate neuron population. In addition, a quantitative analysis suggests that the postnatal decline in subplate neuron density cannot be accounted for solely through dilution by differential growth of the white matter and most likely reflects an absolute decrease in subplate neuron number. Thus, the adult interstitial neurons have survived a postnatal period during which many of their early generated cohorts have disappeared, pr

ISSN:0092-7317    

DOI:10.1002/cne.902820407

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractClinical and experimental evidence shows that prenatal exposure to ethanol causes craniofacial malformations, microcephaly, and abnormal development of the central nervous system. This study describes the effects of ethanol on the development of the principal sensory nucleus of the trigeminal nerve (PSN). The offspring of two groups of rats were examined. Pregnant females in one group were fed a liquid diet containing 6.7% (v/v) ethanol (Et) and rats in the other group were fed an isocaloric liquid control diet (Ct). Each pregnant rat was administered [3H]thymidine on one day during the period from gestational day (G) 10 to G22. After pups grew to 30 days of age, they were killed and their brains were processed by an autoradiographic procedure.Qualitatively, the PSN of Ct‐ and Et‐treated rats appeared similar; they were composed chiefly of small neurons and a few scattered large neurons. On the other hand, quantitative analyses revealed significant differences between both groups. Although the volume of the PSN of Et‐treated rats was not significantly different (‐3.2%) than that for Ct‐treated rats, the PSN of Et‐treated rats had significantly (P<0.01) fewer (30.0%) neurons than did the PSN of Ct‐treated rats. The number of the small neurons, but not of the large neurons, was affected most by the ethanol exposure. Prenatal exposure to ethanol also altered the generation of PSN neurons. Most neurons in the PSN of Ct‐treated rats were born between G12 and G15, the small neurons being generated before the large neurons. In Et‐treated rats, too, small neurons were born before the large neurons; however, the time frame of neuronogenesis was delayed as it occurred between G13 and G16.Thus, prenatal exposure to ethanol produces profound developmental abnormalities that lead to permanent alterations in the structure of the mature centr

ISSN:0092-7317    

DOI:10.1002/cne.902820408

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe topographical distribution of cones and rods in the tree shrew retina was analysed quantitatively in whole‐mounted retinae and horizontal semithin sections stained with cresyl violet or toluidine blue. The outer nuclear layer consists of a single layer of photoreceptor nuclei with the rod nuclei slightly displaced towards the outer plexiform layer. This facilitated quantification of the photoreceptor populations. The density of cones ranges from 12,000/mm2in the peripheral retina to a maximum of 36,000/mm2in the inferior retina. Unlike ganglion cell density, the density of cones does not peak in the temporal retina. Rod density, between 500/mm2and 3,500/mm2, also peaks in the inferior retina, but not in the same region as cone density. Rods constitute from 1 to 14% of the photoreceptor population, depending on retinal location, and have a local minimum at the central area. Amongst the cones a regularly arrayed subpopulation of presumed blue‐sensitive cones is distinguished by its special staining properties. These cones constitute between 4 and 10% of the cone population depending on retinal location. A second, irregularly spaced, subpopulation of possibly pathological cones is also descri

ISSN:0092-7317    

DOI:10.1002/cne.902820409

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractWe distinguish two types of large multipolar cells designated sustained (Cs) and onset (Oc) choppers in the anterior posteroventral cochlear nucleus (A‐PVCN)/nerve root region on the basis of certain anatomical and physiological features. Csaxons head into the trapezoid body, while Ocaxons use the intermediate acoustic stria of Held. At the electron microscopic (EM) level, collateral terminals of Ocaxons contain pleomorphic vesicles; Csterminals contain small round vesicles. Csdendritic trees tend to be distributed in a stellate fashion while Ocdendritic trees tend to be elongated. At the EM level the sustained chopper somata are sparsely innervated while the proximal dendritic tree receives considerably more input. The Ocsomata are highly innervated and this heavy innervation continues out onto the proximal dendrites. Distally the dendritic innervation falls off considerably for both categories. Physiologically, members of the Ocpopulation have wider dynamic ranges at the characteristic frequency (CF), wider response areas that are typically not flanked by inhibitory sidebands, and responses to short tones that do not show the same form of regularity expressed by sustained choppers. Intracellularly the sustained choppers exhibit sustained depolarization to short tones for the duration of the stimulus with resultant regular spiking at a rate that is stimulus level dependent. The response to swept tone shows this same level‐dependent regularity. In response to tones, the Occells also show a sustained depolarization whose amplitude is stimulus‐level dependent but whose range is much greater and whose onset is initiated more abruptly. Although the onset component of the Ocspike output is reliably initiated by these levels of depolarization, regular firing to the sustained depolarization is not initiated at levels of depolarization that would surely generate regular firing in sustained choppers. This regularity is also absent in the swept tone response despite marked levels of excit

ISSN:0092-7317    

DOI:10.1002/cne.902820410

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe retrograde transport of the conjugate wheat germ agglutinin–horseradish peroxidase (WGA‐HRP) was used in the rat to identify the cell bodies of origin for all subcortical projections to the basilar pontine nuclei (BPN). A parapharyngeal surgical approach was used to allow the injection micropipette to enter the BPN from the ventral aspect of the brainstem and thus avoid any potential for false‐positive labeling due to transection and injury‐filling of axonal systems located dorsal to the basilar pontine gray.A surprisingly large number of BPN afferent cell groups were identified in the present study. Included were labeled somata in the lumbar spinal cord and a large variety of nuclei in the medulla, pons, and midbrain, as well as labeled cells in diencephalic and telencephalic nuclei such as the zona incerta, ventral lateral geniculate, hypothalamus, amygdala, nucleus basalis of Meynert, and the horizontal nucleus of the diagonal band of Broca.Quite a number of cell groups known to project directly to the cerebellum also exhibited labeled somata in the present study. To explore the possibility that such neurons were labeled because their axons were transected and injury‐filled as they coursed through the BPN injection site to enter the cerebellum via the brachium pontis, a series of rats received complete, bilateral lesions of the brachium pontis followed 30‐60 minutes later with multiple, diffuse injections of WGA‐HRP (12‐16 placements per animal) throughout the cerebellar cortex. In another series of animals, the massive cerebellar WGA‐HRP injections were not preceded by brachium pontis lesions. In the latter cases, each of the cell groups in question that were known to project directly to the cerebellum exhibited labeled somata. However, when the cerebellar HRP injections were preceded by brachium pontis lesions, each of the cell groups in question continued to exhibit labeled somata in numbers comparable to that observed in the nonlesion cases. This implies that such neurons project to the BPN and the cerebellar cortex and that the axons of these particular neurons do not project to the cerebellum via th

ISSN:0092-7317    

DOI:10.1002/cne.902820411

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY