摘要:

AbstractThe distribution of acetylcholinesterase (AChE) was examined in the multilayered posterior part of the hippocampal region of the adult mouse (Mus musculus domesticus), namely, the entorhinal area, the parasubiculum, the presubiculum, and those parts of the retrosplenial cortex that extend into the posterior hippocampal region (area retrosplenialis 29d and 29e). A modification of the Koelle copper thiocholine method was employed for the histochemical demonstration of AChE. The AChE staining resulted in a distinctly stratified pattern, which has been compared in detail with the fields and layers defined by cyto‐ and fibro‐architecture. Most of the enzyme activity was located in the neuropil, but both moderately and intensely stained nerve cell bodies were observed too.In the entorhinal area two main subfields were identified, which have been designated pars medialis and pars lateralis. In pars medialis, the superficial two thirds of layer I, the interstices between the stellate cell bodies, in layer II, and layers IV and VI showed moderate to high content of AChE, whereas layer V and, especially, layer III were poor in enzyme activity. A particular feature was the occurrence of cone‐shaped, darkly stained areas within layer II and, occasionally, the deep part of layer I. The staining of pars lateralis differed in several respects from that of pars medialis, the most prominent feature being a less conspicuous stratification. In addition, intensely stained somata occurred more frequently than in pars medialis, although they still constituted only a very small minority of the total number of nerve cell bodies. In the parasubiculum, a clear cytoarchitectural subdivision into a posterolateral parasubiculum a and an anteromedial parasubiculum b was observed. These subfields showed, however, only minor differences in AChE staining, Thus, in both subfields, layers I and IV stained intensely, whereas layers II and III showed moderate to intense staining. Layers V and VI did not differ in appearance from the corresponding layers of the entorhinal area. The retrosplenial areas 29d and 29e appeared very light in the AChE pattern, area 29e being the better stained. The presubiculum was very rich in AChE, with layers I, III and IV being particularly intensely stained. The small nerve cell bodies of layer II were unstained, whereas the intervening neuropil was intensely stained.The distribution of AChE in the mouse was compared with that in the rat, guinea pig, and rabbit, described previously. The staining pattern is largely similar in all four species, but striking species‐specific differences do exist. Possible structural correlates of the AChE observed in the four cortical fields are discussed. In the mouse, septohippocampal afferents appear associated with most of the entorhinal and parasubiculum AChE, but only to a lesser degree to the AChE of area retrosplenialis 29e and the presubiculum. A possible role of some of the AChE observed in the hippocampal region in the hydrolysis of a number of neuropeptides, in particular substance P and enkephalin, is con

ISSN:0092-7317    

DOI:10.1002/cne.903030302

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe anatomical distribution of autonomic, particularly cardiovascular, responses originating in the insular cortex was examined by using systematic electrical microstimulation. The localization of these responses to cell bodies in the insular cortex was demonstrated by using microinjection of the excitatory amino acid, D, L‐homocysteic acid. The efferents from the cardiovascular responsive sites were traced by iontophoretic injection of the anterograde axonal tracer Phaseoleus vulgaris leucoagglutinin (PHA‐L).Two distinct patterns of cardiovascular response were elicited from the insular cortex: an increase in arterial pressure accompanied by tachycardia or a decrease in arterial pressure with bradycardia. The pressor responses were obtained by stimulation of the rostral half of the posterior insular cortex while depressor sites were located in the caudal part of the posterior insular area. Both types of site were primarily located in the dysgranular and agranular insular cortex. Gastric motility, changes originated from a separate but adjacent region immediately rostral to the cardiovascular responsive sites in the anterior insular cortex.Tracing of efferents with PHA‐L indicated a number of differences in connectivity between the pressor and depressor sites. Pressor sites had substantially more intense connections with other limbic regions including the infralimbic cortex, the amygdala, the bed nucleus of the stria terminalis and the medial dorsal and intralaminar nuclei of the thalamus. Alternatively, the depressor region of the insular cortex more heavily innervated sensory areas of the brain including layer I of the primary somatosensory cortex, a peripheral region of the sensory relay nuclei of the thalamus and the caudal spinal trigeminal nucleus. In addition, there were topographical differences in the projection to the lateral hypothalamic area, the primary site of autonomic outflow for these responses from the insular cortex. These differences in connectivity may provide the anatomic substrate for the specific cardiovascular responses and behaviors integrated in the insular c

ISSN:0092-7317    

DOI:10.1002/cne.903030303

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

年代:1991

数据来源: WILEY

摘要:

AbstractAstrocytes migrate into the cat retina from the optic nerve, beginning from embryonic day (E) 52. Once they have entered the retina they concentrate along major axon bundles and fail to enter regions of the retina with high densities of neurones, in particular the area centralis region of the ganglion cell layer. These nonuniformities appear as the astrocytes spread over the retina during development, and in this study we have examined factors that might control their spread. First we examined astrocytes in a retina in which the axon bundles had degenerated following an optic nerve lesion at birth. The area over which astrocytes had spread was normal, suggesting that their spread does not depend on the presence of intact axons. Second, we noted that, despite the degeneration of all ganglion cells following the nerve lesion, astrocytes still did not spread over the area centralis. Their spread is apparently not inhibited by concentrations of neurones. Third, we examined astrocytes in retinas of animals raised in an atmosphere containing 70–80% oxygen, which prevents the formation of retinal vessels. Again, the area over which the astrocytes had spread was normal, suggesting that their spread does not depend on the presence of patent blood vessels. These negative findings led us to compare the distribution of spindle cells (precursors of retinal vasculature) and astrocytes in the cat during development. The close correspondence in their topographical distribution and the earlier spread of the spindle cells lead us to suggest that spindle cells provide a basal lamina component that may guide the migration of astrocyte

ISSN:0092-7317    

DOI:10.1002/cne.903030304

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe retina provides a valuable opportunity to examine the interaction of astrocytes with neurones and vasculature, in adult tissue and in vivo. We have studied astrocytes in cat retina to delineate the interactions that determine their morphology and distribution. Their morphology varied with their interaction with surrounding cells, from a classic stellate shape to an elongated bipolar form associated with axon bundles. Evidence is presented that the distribution of astrocytes across the retina is determined by their morphology and by a previously unrecognised interaction between astrocytes, which we term ‘contact‐spacing’ in which astrocytes maintain contact with their neighbours through their processes, but keep their somas apart. Evidence is also presented that astrocytes are not influenced in their distribution by surrounding neurones, and the influence of developmental mechanisms is identified. These observations are summarised in a contact‐spacing model of astrocyte distribution, and four predictions of the model are tested. The concentration of astrocytes along axon bundles dispersed when the axons degenerate but not when vessels were prevented from forming. Further, when both axons and vessels were eliminated, the concentrations of astrocytes dispersed and they became stellate in form. Finally, in the retina of the rat, in which astrocytes show no affinity for axons, the distribution of astrocytes is essentially uniform. We suggest that the contact‐spacing interaction among astrocytes provides the anatomical basis of a functional glial network extending across the retina and throughout the central nervo

ISSN:0092-7317    

DOI:10.1002/cne.903030305

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

年代:1991

数据来源: WILEY

摘要:

AbstractA previously unrecognised structure in the cat retina is described. Seen in Golgi‐impregnated, wholemounted retinas, each such structure comprises processes radiating across the inner plexiform layer from a dense, vellate core. The processes are numerous, and largely unbranched, and give the impression of rays radiating from a point source; the structure is therefore termed a “sunburst.” Evidence is presented from Golgi‐impregnated retinas, and from retinas labelled with monoclonal antibodies to Müller cells, that the core of each sunburst is the inner process of a Müller cell. The sunbursts are numerous and overlap extensively, so that when neighbouring sunbursts are impregnated, they are seen to form a dense mat of processes extending across the IPL. It is suggested that each Müller cell forms a sunburst and that sunbursts form a major glial component of the neuropil of the inner plexi

ISSN:0092-7317    

DOI:10.1002/cne.903030306

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn the normal goldfish, neighboring retinal ganglion cells terminate in one small tectal locus to produce the precise retinotopy characteristic of this projection. This can be directly demonstrated by labeling neighboring ganglion cells with small “spot” injections of WGA‐HRP, which yield a single small patch of product at the retinotopically appropriate part of the tectum. When the optic nerve is crushed, label from these spot injections was previously found to be widely dispersed during the early phase of regeneration. With time, label subsequently condensed, typically into several discrete patches reminiscent of ocular dominance columns.In this study, we tested whether the formation of these patches required impulse activity by injecting tetrodotoxin (TTX) into the eye during regeneration. We found that impulse blockade completely inhibited the formation of discrete patches while permitting considerable condensation of the label. This implies that these patches are generated by activity but that some map “refinement” utilized cellular processes that are activity independent. This activity‐independent condensation progressed at a noticeably slower rate than the equivalent condensation seen with activity, thus suggesting that activity normally participates as a “helper factor,” even though it is not strictly required.Since the formation of discrete patches during regeneration provides a sensitive measure of activity‐dependent refinement, this was used to further address two controversial questions concerning the role of impulse activity. One is whether there is a chronologically defined critical period for activity‐dependent refinement. This was tested by blocking impulse activity for 2 to 4 months, much longer than the activity‐dependent refinement is thought to last, and then permitting activity to resume. We found that multiple patches were formed following this period of late activity, thus indicating that synaptic plasticity extends for several months beyond the supposed critical period.The other question was whether spontaneous retinal activity was sufficient for activity‐dependent ordering. To test this, fish were kept in constant darkness during optic nerve crush and labelled with retinal spot injections at various times during regeneration. Condensation of label with the final formation of multiple patches formed at about the same time as fish with normal visual experience. This implies that the amount and extent of correlation of spontaneous activity in retina is adequate for driving activi

ISSN:0092-7317    

DOI:10.1002/cne.903030307

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

年代:1991

数据来源: WILEY

摘要:

AbstractA population of cells has been found in the chick optic tract and chiasm exhibiting GABA‐like immunoreactivity (GABA+; Granda and Crossland, J. Comp. Neurol.287:455–469, '89). It is not known, however, whether the cells are neurons. We have studied the GABA+ cells by using morphological and immunocytochemical methods. We found that there are more than 500 cells in each tract. At the light microscopic level, the cells possess processes resembling dendrites and axons. At the electron microscopic level, the organelle content of the cells is similar to that of neurons. The cells are immunoreactive with antibodies to MAP2 and neuron specific enolase, two proteins characteristic of neurons. Taken together the findings indicate that the GABA+ cells of the chick optic tract are neurons, perhaps similar to the interstitial neurons found in the white matter of other vertebra

ISSN:0092-7317    

DOI:10.1002/cne.903030308

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe hippocampus is a neural substrate playing a key role in short‐term memory. In order to achieve a better understand‐ding of how the hippocampus functions in “learning and memory,” we conducted an intracellular horseradish peroxidase (HRP) study of the CA3 pyramidal neurons and the granule cells of the fascia dentata. The axon of the CA3 pyramidal neurons has two components, the longitudinal association system and the Schaffer collateral system. The latter component is organized in a lamellar fashion and follows the alvear fiber stream. An electron microscopic analysis of myelinated fibers suggested that most myelinated fibers in the hippocampus are organized parallel to the alvear fibers. The mossy fibers of the granule cells, however, do not follow the alvear fiber stream. We propose a new model of the organization of the intrinsic excitatory circuitry of the rat hippocampus in which the distinct lamellar organization of the pyramidal and granule cells creates a crossing neural

ISSN:0092-7317    

DOI:10.1002/cne.903030309

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe effects of testosterone on the volume and cytoarchitecture of the sexually dimorphic nucleus of the preoptic area (POM) were investigated in male and female Japanese quail. It was confirmed that castration decreases the POM volume in males and that, in gonadectomized birds of both sexes, testosterone increases this volume to values similar to those observed in intact sexually mature males. This suggests that the sex difference in POM volume results from a differential activation by T so that this brain morphological characteristic is not truly differentiated in the organizational sense. This conclusion was extended here by demonstrating that males exposed to a photoperiod simulating long days and that are known to have high plasma levels of testosterone have a larger POM than short‐day males that have inactive testes. Detailed morphometric studies of POM neurons revealed a structural heterogeneity within the nucleus. A population of large neurons (cross‐sectional area larger than 70–80 μm2) was well represented in the dorsolateral but was almost absent in the medial part of POM. This lateral population of neurons was sensitive to variations of testosterone levels in males but not in females. The cross‐sectional area, diameter, and perimeter of the dorsolateral neurons were significantly increased in males exposed to high testosterone levels (intact birds exposed to long days or castrated birds treated with the steroid). These changes were not observed in the medial part of the nucleus. Interestingly, the size of the dorsolateral neurons was not affected by testosterone treatments in females. These results suggest that the swelling of neurons in the lateral POM of males might be responsible for the increase in total volume of the nucleus, which is observed in physiological situations associated with a high testosteronemia. In addition, the sensitivity to testosterone of the dorsolateral neurons in the POM appears to be sexually differentiated. This differential response to testosterone might represent a truly dimorphic feature in the organizational sense and additional studies manipulating the early steroid environment should be performed to test this pos

ISSN:0092-7317    

DOI:10.1002/cne.903030310

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

年代:1991

数据来源: WILEY

摘要:

AbstractTo gain more insight into the dopaminergic system of amphibians and the evolution of catecholaminergic systems in vertebrates in general, the distribution of dopamine and tyrosine hydroxylase immunoreactivity was studied in the brains of the anuranRana ridibundaand the urodelePleurodeles waltlii.In both species, dopamine‐immunoreactive (DAi) cell bodies were observed in the olfactory bulb, the preoptic area, the suprachiasmatic nucleus, the nucleus of the periventricular organ and its accompanying cells, the nucleus of the posterior tubercle, the pretectal area, the midbrain tegmentum, around the solitary tract, in the ependymal and subependymal layers along the midline of the caudal rhombencephalon, and ventral to the central canal of the spinal cord. Tyrosine hydroxylase (TH) immunohistochemistry revealed a similar pattern, although some differences were noted. For example, with the TH antibodies, additional cell bodies were stained in the internal granular layer of the olfactory bulb and in the isthmal region, whereas the same antibodies failed to stain the liquor contacting cells in the nucleus of the periventricular organ.Both antisera revealed an almost identical distribution of fibers in the two amphibian species. Remarkable differences were observed in the forebrain. Whereas the nucleus accumbens inRanacontains the densest DAi plexus, inPleurodelesthe dopaminergic innervation of the striatum prevails. Moreover, cortical structures of the newt contain numerous DAi fibers, whereas the corresponding structures in the frog are devoid of immunoreactivity. The dopaminergic system in amphibians appears to share many features not only with other anamniotes but also with amniote

ISSN:0092-7317    

DOI:10.1002/cne.903030311

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

年代:1991

数据来源: WILEY