Journal of Comparative Neurology
1096-9861
0021-9967
Mỹ
Cơ quản chủ quản: WILEY , Wiley-Liss Inc.
Lĩnh vực:
Neuroscience (miscellaneous)
Các bài báo tiêu biểu
Autoradiographic and histological evidence of postnatal hippocampal neurogenesis in rats Abstract In the autoradiograms of young rats injected with thymidine‐H3 many of the granule cells of the dentate gyrus were found labeled. The number of labeled cells declined rapidly with increased age at the time of injection. Histological studies showed the presence in young rats of a large germinal matrix of mitotic cells in the ependymal and subependymal layers of the third and lateral ventricles. The areal extent and cell population of this germinal pool declined rapidly from birth on, with a transient rise with a peak at about 15 days. During this latter period the number of “undifferentiated” cells near the granular layer of the dentate gyrus showed a rapid rise with a subsequent decline. The decline in the number of “undifferentiated” cells was accompanied by a rise in the number of differentiated granule cells. Cell counts in homologous parts of the dentate gyrus indicated a six‐fold increase in the number of differentiated granule cells from birth to three months. We postulated that undifferentiated cells migrate postnatally from the forebrain ventricles to the hippocampus where they become differentiated. The possible functional significance of delayed hippocampal neurogenesis is discussed with reference to our finding of incorporation of testosterone‐H3 by cells of the hippocampus, implicating that they may function as receptors of gonadal hormones.
Tập 124 Số 3 - Trang 319-335 - 1965
Mode of cell migration to the superficial layers of fetal monkey neocortex Abstract Golgi and electronmicroscopic methods were used to define the shapes and intercellular relationships of cells migrating from their sites of origin near the ventricular surface across the intermediate zone to the superficial neocortical layers of the parietooccipital region in the brains of 75‐ to 97‐day monkey fetuses. After mitotic division in either ventricular or subventricular zones, the cells enter the intermediate zone and assume an elongated bipolar form oriented toward the cortical plate. The leading processes, 50 to 70 μ long, are irregular cytoplasmic cylinders containing prominent Golgi apparatus, mitochondria, microtubules, ribosomal rosettes, immature endoplasmic reticulum and occasional centrioles. They usually terminate in several attenuated expansions, the longest one oriented toward the cortical plate. The trailing processes are more slender, relatively uniform in caliber and display few organelles. Throughout the 3500 μ pathway across the intermediate zone the migrating cells are apposed to elongated, radially oriented, immature glial processes which span the full thickness of the cerebral wall. Most of the perikarya of these glial cells in the younger specimens lie in the ventricular or subventricular zones, but in older fetuses of this series many are found in the intermediate zone. The main characteristics of these fibers are: elongated cylindrical form contaiing numerous microtubules; electronlucent cytoplasmic matrix; short lamellate expansions protruding at right angles from the segment of the fiber which runs through the intermediate zone; and terminal endfeet joined at the pial surface to form a continuous sheet coated externally with basement membrane. It is suggested that glial radial fibers provide guidelines for cell migration through the complex mixture of closely packed cell processes and cell bodies that compose the developing cerebral wall. Strong surface affinity between radial fiber and migrating cell is suggested in regions where both follow precisely the same curving course from subventricular to intermediate zones and also in areas where large extracellular spaces separate other cells and processes but in which migrating cells and radial fibers remain closely paired nonetheless. Specific affinity between them is implied in the failure of migrating cells to follow any of the myriad differently‐oriented processes they encounter. Several generations of postmitotic cells appear to migrate along the same radial fiber, a developmental mechanism that would allow for the vertical cell columns of adult neocortex.
Tập 145 Số 1 - Trang 61-83 - 1972
Distribution of androgen and estrogen receptor mRNA‐containing cells in the rat brain: An in situ hybridization study Abstract The distribution of cells that express mRNA encoding the androgen (AR) and estrogen (ER) receptors was examined in adult male and female rats by using in situ hybridization. Specific labeling appeared to be largely, if not entirely, localized to neurons. AR and ER mRNA‐containing neurons were widely distributed in the rat brain, with the greatest densities of cells in the hypothalamus, and in regions of the telencephalon that provide strong inputs to the hypothalamus. Thus large numbers of heavily labeled cells were found in the medial preoptic and ventromedial nuclei, each of which is thought to play a key role in mediating the hormonal control of copulatory behavior, as well as in the lateral septal nucleus, the medial and cortical nuclei of the amygdala, the amygdalohippocampal area, and the bed nucleus of the stria terminalis. Heavily labeled ER mRNA‐containing cells were found in regions known to be involved in the neural control of gonadotropin release, such as the anteroventral periventricular and the arcuate nuclei, but only a moderate density of labeling for AR mRNA was found over these nuclei. In addition, clearly labeled cells were found in regions with widespread connections throughout the brain, including the lateral hypothalamus, intralaminar thalamic nuclei, and deep layers of the cerebral cortex, suggesting that AR and ER may modulate a wide variety of neural functions. Each part of Ammon's horn contained AR mRNA‐containing cells, as did both parts of the subiculum, but ER mRNA appeared to be less abundant in the hippocampal formation. Moreover, AR and ER mRNA‐containing cells were also found in olfactory regions of the cortex and in both the main and accessory olfactory bulbs. AR and ER may modulate nonolfactory sensory information as well since labeled cells were found in regions involved in the central relay of somatosensory information, including the mesencephalic nucleus of the trigeminal nerve, the ventral thalamic nuclear group, and the dorsal horn of the spinal cord. Furthermore, heavily labeled AR mRNA‐containing cells were found in the vestibular nuclei, the cochlear nuclei, the medial geniculate nucleus, and the nucleus of the lateral lemniscus, which suggests that androgens may alter the central relay of vestibular and auditory information as well. However, of all the regions involved in sensory processing, the heaviest labeling for AR and ER mRNA was found in areas that relay visceral sensory information such as the nucleus of the solitary tract, the area postrema, and the subfornical organ. We did not detect ER mRNA in brainstem somatic motoneurons, but clearly labeled AR mRNA‐containing cells were found in motor nuclei associated with the fifth, seventh, tenth, and twelfth cranial nerves. Similarly, spinal motoneurons contained AR but not ER mRNA. Nor was ER mRNA detected in Purkinje cells of the cerebellum, the pontine gray, or inferior olive, all of which harbor AR mRNA, although the parvicellular part of the dentate (lateral cerebellar) nucleus had clearly labeled ER mRNA‐containing neurons. The density of labeling in other parts of the brainstem tended to be greatest in those regions that have the strongest connections with the hypothalamus like the midbrain periaqueductal gray, the peripeduncular nucleus, and the locus coeruleus. Although no absolute sexual dimorphisms in the distributions of AR and ER mRNA‐containing cells were found, more subtle quantitative differences between levels of AR and ER mRNA in certain regions of the male and female rat brain cannot be ruled out. In at least a few regions, there appeared to be differences in either the number of cells expressing each receptor mRNA. or in the relative density of labeling over certain cell groups. Whether or not both receptors are contained within individual neurons remains to be demon‐ strated; however. The remarkable overlap between the distributions of AR and ER mRNA containing neurons suggests that such coexpression is indeed possibility and that the two receptor systems may interact to differentially activate overlapping sets of genes in a variety of neural systems.
Tập 294 Số 1 - Trang 76-95 - 1990
An autoradiographic analysis of the differential ascending projections of the dorsal and median raphe nuclei in the rat Abstract The differential projections from the dorsal raphe and median raphe nuclei of the midbrain were autoradiographically traced in the rat brain after 3 H‐proline micro‐injections. Six ascending fiber tracts were identified, the dorsal raphe nucleus being the sole source of four tracts and sharing one with the median raphe nucleus. The tracts can be classified as those lying within the medial forebrain bundle (dorsal raphe forebrain tract and the median raphe forebrain tract) and those lying entirely outside (dorsal raphe arcuate tract, dorsal raphe periventricular tract, dorsal raphe cortical tract, and raphe medial tract). The dorsal raphe forebrain tract lies in the ventrolateral aspect of the medial forebrain bundle (MFB) and projects mainly to lateral forebrain areas (e.g., basal ganglion, amygdala, and the pyriform cortex). The median raphe forebrain tract lies in the ventromedial aspect of the MFB and projects to medial forebrain areas (e.g., cingulate cortex, medial septum, and hippocampus). The dorsal raphe cortical tract lies ventrolaterally to the medial longitudinal fasciculus and projects to the caudate‐putamen and the parieto‐temporal cortex. The dorsal raphe periventricular tract lies immediately below the midbrain aqueduct and projects rostrally to the periventricular region of the thalamus and hypothalamus. The dorsal raphe arcuate tract curves laterally from the dorsal raphe nucleus to reach the ventrolateral edge of the midbrain and projects to ventrolateral geniculate body nuclei and the hypothalamic suprachiasmatic nuclei. Finally, the raphe medial tract receives fibers from both the median and dorsal raphe nuclei and runs ventrally between the fasciculus retroflexus and projects to the interpeduncular nucleus and the midline mammillary body. Further studies were done to test whether the fiber tracts travelling in the MFB contained 5‐HT. Unilateral (left) injections of 5,7‐dihydroxytryptamine (5 μgm/400 nl) 18 days before midbrain raphe microinjections of 3 H‐proline produced a reduction in the grain concentrations in all the ascending fibers within the MFB. Furthermore, pharmacological and behavioural evidence was obtained to show that the 5‐HT system had been unilaterally damaged; these animals displayed preferential ipsilateral turning in a rotameter which was strongly reversed to contralateral turning after 5‐hydroxytryptophan administration. The results show that DR and MR nuclei have numerous ascending projections whose axons contain the transmitter 5‐HT. The results agree with the neuroanatomical distribution of the 5‐HT system previously determined biochemically, histochemically, and neurophysiologically. The midbrain serotonin system seems to be organized by a series of fiber pathways. The fast transport rate in these fibers was found to be about 108 mm/day.
Tập 179 Số 3 - Trang 641-667 - 1978
Differential expression of orexin receptors 1 and 2 in the rat brain Abstract Orexins (hypocretins) are neuropeptides synthesized in the central nervous system exclusively by neurons of the lateral hypothalamus. Orexin‐containing neurons have widespread projections and have been implicated in complex physiological functions including feeding behavior, sleep states, neuroendocrine function, and autonomic control. Two orexin receptors (OX1 R and OX2 R) have been identified, with distinct expression patterns throughout the brain, but a systematic examination of orexin receptor expression in the brain has not appeared. We used in situ hybridization histochemistry to examine the patterns of expression of mRNA for both orexin receptors throughout the brain. OX1 R mRNA was observed in many brain regions including the prefrontal and infralimbic cortex, hippocampus, paraventricular thalamic nucleus, ventromedial hypothalamic nucleus, dorsal raphe nucleus, and locus coeruleus. OX2 R mRNA was prominent in a complementary distribution including the cerebral cortex, septal nuclei, hippocampus, medial thalamic groups, raphe nuclei, and many hypothalamic nuclei including the tuberomammillary nucleus, dorsomedial nucleus, paraventricular nucleus, and ventral premammillary nucleus. The differential distribution of orexin receptors is consistent with the proposed multifaceted roles of orexin in regulating homeostasis and may explain the unique role of the OX2 R receptor in regulating sleep state stability. J. Comp. Neurol. 435:6–25, 2001. © 2001 Wiley‐Liss, Inc.
Tập 435 Số 1 - Trang 6-25 - 2001
Topographical organization of the efferent projections of the medial prefrontal cortex in the rat: An anterograde tract‐tracing study with <i>Phaseolus vulgaris</i> leucoagglutinin Abstract The purpose of the present investigation was to examine the topographical organization of efferent projections from the cytoarchitectonic divisions of the mPFC (the medial precentral, dorsal anterior cingulate and prelimbic cortices). We also sought to determine whether the efferents from different regions within the prelimbic division were organized topographically. Anterograde transport of Phaseolus vulgaris leucoagglutinin was used to examined the efferent projections from restricted injection sites within the mPFC. Major targets of the prelimbic area were found to include prefrontal, cingulate, and perirhinal cortical structures, the dorsomedial and ventral striatum, basal forebrain nuclei, basolateral amygdala, lateral hypothalamus, mediodorsal, midline and intralaminar thalamic nuclei, periaqueductal gray region, ventral midbrain tegmentum, laterodorsal tegmental nucleus, and raphe nuclei. Previously unreported projections of the prelimbic region were also observed, including efferents to the anterior olfactory nucleus, the piriform cortex, and the pedunculopontine tegmental‐cuneiform region. A topographical organization governed the efferent projections from the prelimbic area, such that the position of terminal fields within target structures was determined by the rostrocaudal, dorsoventral, and mediolateral placement of the injection sites. Efferent projections from the medial precentral and dorsal anterior cingulate divisions (dorsomedial PFC) were organized in a similar topographical fashion and produced a pattern of anterograde labeling different from that seen with prelimbic injection sites. Target structures innervated primarily by the dorsomedial PFC included certain neocortical fields (the motor, somatosensory, and visual cortices), the dorsolateral striatum, superior colliculus, deep mesencephalic nucleus, and the pontine and medullary reticular formation. Previously unreported projections to the paraoculomotor central gray area and the mesencephalic trigeminal nucleus were observed following dorsomedial PFC injections. These results indicate that the efferent projections of the mPFC are topographically organized within and across the cytoarchitectonic divisions of the medial wall cortex. The significance of topographically organized and restricted projections of the rat mPFC is discussed in light of behavioral and physiological studies indicating functional heterogeneity of this region.
Tập 290 Số 2 - Trang 213-242 - 1989
An autoradiographic study of the organization of the efferet connections of the hippocampal formation in the rat Abstract The efferent connections of the hippocampal formation of the rat have been re‐examined autoradiographically following the injection of small quantities of 3 H‐amino acids (usually 3 H‐proline) into different parts of Ammon's horn and the adjoining structures. The findings indicate quite clearly that each component of the hippocampal formation has a distinctive pattern of efferent connections and that each component of the fornix system arises from a specific subdivision of the hippocampus or the adjoining cortical fields. Thus, the precommissural fornix has been found to originate solely in fields CA1‐3 of the hippocampus proper and from the subiculum; the projection to the anterior nuclear complex of the thalamus arises more posteriorly in the pre‐ and/or parasubiculum and the postsubicular area; the projection to the mammillary complex which comprises a major part of the descending columns of the fornix has its origin in the dorsal subiculum and the pre‐ and/or parasubiculum; and finally, the medial cortico‐hypothalamic tract arises from the ventral subiculum. The lateral septal nuclei (and the adjoining parts of the posterior septal complex) constitute the only subcortical projection field of the pyramidal cells in fields CA1‐3 of Ammon's horn. There is a rostral extension of the pre‐commissural fornix to the bed nucleus of the stria terminalis, the nucleus accumbens, the medial and posterior parts of the anterior olfactory nucleus, the taenia tecta, and the infralimbic area, which appears to arise from the temporal part of field CA, or the adjacent part of the ventral subiculum. The projection of Ammon's horn upon the lateral septal complex shows a high degree of topographic organization (such that different parts of fields CA1 and CA3 project in an ordered manner to different zones within the lateral septal nucleus). The septal projection of “CA2 ” and field CA3 is bilateral, while that of field CA1 is strictly unilateral. In addition to its subcortical projections, the hippocampus has been found to give rise to a surprisingly extensive series of intracortical association connections. For example, all parts of fields CA1 , CA2 and CA3 project to the subiculum, and at least some parts of these fields send fibers to the pre‐ and parasubiculum, and to the entorhinal, perirhinal, retrosplenial and cingulate areas. From the region of the preand parasubiculum there is a projection to the entorhinal cortex and the parasubiculum of both sides. That part of the postsubiculum (= dorsal part of the presubiculum) which we have examined has been found to project to the cingulate and retrosplenial areas ipsilaterally, and to the entorhinal cortex and parasubiculum bilaterally.
Tập 172 Số 1 - Trang 49-84 - 1977
Somatosensory cortical map changes following digit amputation in adult monkeys Abstract The cortical representations of the hand in area 3b in adult owl monkeys were defined with use of microelectrode mapping techniques 2–8 months after surgical amputation of digit 3, or of both digits 2 and 3. Digital nerves were tied to prevent their regeneration within the amputation stump. Successive maps were derived in several monkeys to determine the nature of changes in map organization in the same individuals over time. In all monkeys studied, the representations of adjacent digits and palmar surfaces expanded topographically to occupy most or all of the cortical territories formerly representing the amputated digit(s). With the expansion of the representations of these surrounding skin surfaces (1) there were severalfold increases in their magnification and (2) roughly corresponding decreases in receptive field areas. Thus, with increases in magnification, surrounding skin surfaces were represented in correspondingly finer grain, implying that the rule relating receptive field overlap to separation in distance across the cortex (see Sur et al., '80) was dynamically maintained as receptive fields progressively decreased in size. These studies also revealed that: (1) the discontinuities between the representations of the digits underwent significant translocations (usually by hundreds of microns) after amputation, and sharp new discontinuous boundaries formed where usually separated, expanded digital representations (e.g., of digits 1 and 4) approached each other in the reorganizing map, implying that these map discontinuities are normally dynamically maintained. (2) Changes in receptive field sizes with expansion of representations of surrounding skin surfaces into the deprived cortical zone had a spatial distribution and time course similar to changes in sensory acuity on the stumps of human amputees. This suggests that experience‐dependent map changes result in changes in sensory capabilities. (3) The major topographic changes were limited to a cortical zone 500–700 μm on either side of the initial boundaries of the representation of the amputated digits. More distant regions did not appear to reorganize (i.e., were not occupied by inputs from surrounding skin surfaces) even many months after amputation. (4) The representations of some skin surfaces moved in entirety to locations within the former territories of representation of amputated digits in every monkey studied. In man, no mislocation errors or perceptual distortions result from stimulation of surfaces surrounding a digital amputation. This constitutes further evidence that any given skin surface can be represented by many alternative functional maps at different times of life in these cortical fields (Merzenich et al., '83b). These studies further demonstrate that basic features of somatosensory cortical maps (receptive field sizes, cortical sites of representation of given skin surfaces, representational discontinuities, and probably submodality column boundaries) are dynamically maintained. They suggest that cortical skin surface maps are alterable by experience in adults, and that experience‐dependent map changes reflect and possibly account for concomitant changes in tactual abilities. Finally, these results bear implications for mechanisms underlying these cortical map dynamics.
Tập 224 Số 4 - Trang 591-605 - 1984
Amygdaloid projections to subcortical structures within the basal forebrain and brainstem in the rat and cat Abstract The efferent fiber connections of the nuclei of the amygdaloid complex with subcortical structures in the basal telencephalon, hypothalamus, midbrain, and pons have been studied in the rat and cat, using the autoradiographic method for tracing axonal connections. The cortical and thalamic projections of these nuclei have been described in previous papers (Krettek and Price, ′77b,c). Although the subcortical connections of the amygdaloid nuclei are widespread within the basal forebrain and brain stem, the projections of each nucleus have been found to be well defined, and distinct from those of the other amygdaloid nuclei. The basolateral amygdaloid nucleus projects heavily to the lateral division of the bed nucleus of the stria terminalis (BNST), to the caudal part of the substantia innominata, and to the ventral part of the corpus striatum (nucleus accumbens and ventral putamen) and the olfactory tubercle; it projects more lightly to the lateral hypothalamus. The central nucleus also projects to the lateral division of the BNST and the lateral hypothalamus, but in addition it sends fibers to the lateral part of the substantia nigra and the marginal nucleus of the brachium conjunctivum. The basomedial nucleus has projections to the ventral striatum and olfactory tubercle which are similar to those of the basolateral nucleus, but it also projects to the core of the ventromedial hypothalamic nucleus and the premammillary nucleus, and to a central zone of the BNST which overlaps the medial and lateral divisions. The medial nucleus also projects to the core of the ventromedial nucleus and the premammillary nucleus, but sends fibers to the medial division of the BNST and does not project to the ventral striatum. The posterior cortical nucleus projects to the premammillary nucleus and to the medial division of the BNST, but a projection from this nucleus to the ventromedial nucleus has not been demonstrated. Projections to the “shell” of the ventromedial nucleus have been found only from the ventral part of the subiculum and from a structure at the junction of the amygdala and the hippocampal formation, which has been termed the amygdalo‐hippocampal area (AHA). The AHA also sends fibers to the medial part of the BNST and the premammillary nucleus. Virtually no subcortical projections outside the amygdala itself have been demonstrated from the lateral nucleus, or from the olfactory cortical areas around the amygdala (the anterior cortical nucleus, the periamygdaloid cortex, and the posterior prepiriform cortex). However, portions of the endopiriform nucleus deep to the prepiriform cortex project to the ventral putamen, and to the lateral hypothalamus.
Tập 178 Số 2 - Trang 225-253 - 1978
The cortical projections of the mediodorsal nucleus and adjacent thalamic nuclei in the rat Abstract The mediodorsal nucleus of the rat thalamus has been divided into medial, central and lateral segments on the basis of its structure and axonal connections, and these segments have been shown by experiments using the autoradiographic method of demonstrating axonal connections to project to seven distinct cortical areas covering most of the frontal pole of the hemisphere. The position and cytoarchitectonic characteristics of these areas are described. The medial segment of the nucleus projects to the prelimbic area (32) on the medial surface of the hemisphere, and to the dorsal agranular insular area, dorsal to the rhinal sulcus on the lateral surface. The lateral segment projects to the anterior cingulate area (area 24) and the medial precentral area on the dorsomedial shoulder of the hemisphere, while the central segment projects to the ventral agranular insular area in the dorsal bank of the rhinal sulcus, and to a lateral part of the orbital cortex further rostrally. (The term “orbital” is used to refer to the cortex on the ventral surface of the frontal pole of the hemisphere.) A ventral part of this orbital cortex also receives fibers from the mediodorsal nucleus, possibly its lateral segment, but the medial part of the orbital cortex, and the ventrolateral orbital area in the fundus of the rhinal sulcus receive projections from the paratenial nucleus and the submedial nucleus, respectively. All of these thalamocortical projections end in layer III, and in the outer part of layer I. The basal nucleus of the ventromedial complex (the thalamic taste relay) has been shown to have a similar laminar projection (layer I and layers III/IV) to the granular insular area immediately dorsal to, but not overlapping, the mediodorsal projection field. However, the principal nucleus of the ventromedial complex appears to project to layer I, and possibly layer VI, of the entire frontal pole of the hemisphere. The anteromedial nucleus does not appear to project to layer III of the projection field of the mediodorsal nucleus, although it may project to layers I and VI, especially in the anterior cingulate and medial precentral areas. A thalamoamygdaloid projection from the medial segment of the mediodorsal nucleus to the basolateral nucleus of the amygdala has also been demonstrated, which reciprocates an amygdalothalamic projection from the basolateral nucleus to the medial segment. The habenular nuclei also appear to project to the central nucleus of the amygdala. These results are discussed in relation to the delineation and subdivision of the prefrontal cortex in the rat, and to amygdalothalamic and amygdalocortical projections which are described in a subsequent paper (Krettek and Price, '77).
Tập 171 Số 2 - Trang 157-191 - 1977