摘要:

AbstractIn order to study the morphological substrate of possible thalamic influence on the cells of origin and area of termination of the projection from the entorhinal cortex to the hippocampal formation, we examined the pathways, terminal distribution, and ultrastructure of the innervation of the hippocampal formation and parahippocampal region by the nucleus reuniens of the thalamus (NRT). We employed anterograde tracing withPhaseolus vulgaris‐leucoagglutinin (PHA‐L). Injections of PHA‐L in the NRT produce fiber and terminal labeling in the stratum lacunosum‐moleculare of field CA1 of the hippocampus, the molecular layer of the subiculum, layers I and III/IV of the dorsal subdivision of the lateral entorhinal area (DLEA), and layers I and III‐VI of the ventral lateral (VLEA) and medial (MEA) divisions of the entorhinal cortex. Terminal labeling is most dense in the stratum lacunosum‐moleculare of field CA1, the molecular layer of the ventral part of the subiculum, MEA, and layer I of the perirhinal cortex. In layer I of the caudal part of DLEA and in MEA, terminal labeling is present in clusters. Injections in the rostral half of the NRT produce the same distribution in the hippocampal region as those in the caudal half of the NRT, although the projections from the rostral half of the NRT are much stronger. A topographical organization is present in the projections from the head of the NRT, so that the dorsal part projects predominantly to dorsal parts of field CA1 and the subiculum and to lateral parts of the entorhinal cortex, whereas the ventral part projects in greatest volume to ventral parts of field CA1 and the subiculum and to medial parts of the entorhinal cortex.The distribution of the reuniens fibers coursing in the cingulate bundle was determined by comparing cases with and without transections of this bundle. The fibers carried by the cingulate bundle exclusively innervate field CA1 of the hippocampus, the dorsal part of the subiculum, and the presubiculum and parasubiculum. They participate in the innervation of the ventral part of the subiculum and MEA.Electron microscopy was used to visualize the axon terminals of PHA‐L‐labeled reuniens fibers. These terminals possess spherical synaptic vesicles and form asymmetric synaptic contacts with dendritic spines or with thin shafts of spinous dendrites. Following lesions of the cingulate bundle, large numbers of degenerating axon terminals are present in MEA. Scattered degenerating axon terminals are visible in the areas that in the light microscopic tracing/lesion experiments are depleted of PHA‐L‐labeled fibers, i.e., field CA1 of the hippocampus, the dorsal part of the subiculum, and MEA. Also, the molecular layer of the ventral part of the subiculum contains degenerating terminals.The results of the present study suggest that the NRT may simultaneously influence the parent cell bodies of the perforant pathway in the entorhinal cortex and the target neurons of this pathway in field CA1 and the subiculum of the hippocampal formation. The perforantpathway constitutes the major route along which cortical input is mediated to the hi

ISSN:0092-7317    

DOI:10.1002/cne.902960202

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe synaptic interactions between terminals of allocorticostriatal and thalamostriatal fibers and the cholinergic neurons in the nucleus accumbens were investigated using degeneration and dual labelling immunocytochemistry in Wistar rats. The presumptive cholinergic neurons were labelled with antibodies directed against choline acetyltransferase and the afferent fibers were labelled anterogradely withPhaseolus vulgaris‐leucoagglutinin.Fibers from the subiculum of the hippocampal formation and from the midline and intralaminar thalamus project densely into the medial nucleus accumbens where they overlap a relatively dense population of choline acetyltransferase‐immunoreactive neurons. Varicosities containingPhaseolus vulgaris‐leucoagglutinin juxtapose the immunoreactive neurons.To study the possibility that the cholinergic neurons could be the synaptic targets of these incoming fibers, the subiculum, the fornix, and the midline/intralaminar thalamus were lesioned in separate animals and brain sections were immunoprocessed for choline acetyltransferase and studied with the electron microscope. In addition, dual‐labelling electron microscopic immunocytochemistry was employed. In total, 164 synaptic terminals from the subiculum/hippocampus and 130 from the midline/intralaminar thalamus were examined; all formed asymmetrical synaptic specializations. No hippocampal endings were seen to contact the somata or primary dendrites of the choline acetyltransferase‐immunoreactive neurons; however, three were found in synaptic contact with distal, immunolabelled dendritic shafts. Most hippocampal terminals established contacts with unlabelled spines. Fifteen percent of the thalamic endings were found to synapse on the somata and the primary and distal dendrites of the choline acetyltransferase‐immunoreactive neurons. The remaining thalamic terminals established synaptic junctions with small unlabelled dendrites or spines. These findings have important implications not only for our understanding of the synaptic organization of the hippocampal and thalamic projections to the nucleus accumbens, but also for the contribution of the cholinergic neurons to the circuitry of t

ISSN:0092-7317    

DOI:10.1002/cne.902960203

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

年代:1990

数据来源: WILEY

摘要:

AbstractTransaction of non‐tectotectal fibers in the caudal one‐half of the commissure of the superior colliculus restores visual orienting to a cat previously rendered hemianopic by a large unilateral visual cortical lesion. Other observations related to this recovery phenomenon (i.e., the Sprague effect) have suggested that the caudal commissural fibers whose destruction produces the recovery (1) are contralateral afferents to the superior colliculus on the side of the cortical lesion, and (2) profoundly influence visuo‐motor processing in this superior colliculus. We performed anatomical and behavioral experiments to determine which of the more than 40 contralateral collicular afferents are directly involved in the Sprague effect.To guide subsequent behavioral studies, we performed a pilot anatomical experiment in which we injected WGA‐HRP unilaterally into one superior colliculus at identical retinotopic loci in each of a pair of cats. One cat was normal (control), and the other (experimental) had previously received a caudal transection of the collicular commissure. Quantitative comparison of the retrograde labeling in collicular afferents revealed that a number of mesencephalic regions contain neurons that project to the colliculus via the caudal collicular commissure. Additional collicular injections of WGA‐HRP demonstrated the exact location and distribution of collicular afferent neurons within these nuclei.In the behavioral experiments, we attempted to replicate the Sprague effect by destroying the neurons giving rise to the axons in the caudal collicular commissure. Ibotenic acid lesions of these neurons were performed in cats that were hemianopic following the removal of the contralateral visual cortex. Small lesions of a “critical zone” in the rostro‐lateral substantia nigra pars reticulata and possibly the overlying ventral zona incerta consistently produced a visual recovery whereas lesions, of the other collicular afferents did not. Paradoxically, large nigral lesions that also included the critical zone did not result in a recovery. A conceptual framework for these findings involving striato‐nigro‐tecto‐preoculomotor inte

ISSN:0092-7317    

DOI:10.1002/cne.902960204

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

年代:1990

数据来源: WILEY

摘要:

AbstractWe have used tritiated leucine to trace the input projection pattern of olfactory sensory neurons in crayfishes. The olfactory neurons are associated with cuticular sensilla on the external antennular filaments. Each sensillum, or aesthetasc, harbors the distal dendritic segments of about 175 bipolar sensory neurons, the cell bodies for which are grouped in a subcuticular ensemble or ganglion. About 150–175 individual ganglia may be found on each antennule in an adult crayfish. When an aesthetasc is exposed to tritated leucine, the tracer is taken up by the associated olfactory sensory neurons and is transported along the axons to their central terminations within the glomeruli of the ipsilateral olfactory lobe. We tested the possibility that the sensory neurons from specific aesthetascs project to specific glomeruli. By restricting access of the leucine to small groups of aesthetascs, we exposed less than 2% of the olfactory sensory neurons to the tracer. Nonetheless, all glomeruli were labeled following such treatment. We conclude that the sensory neurons are generally distributed to the olfactory glomeruli. If each neuron terminates in a single glomerulus, these data support a divergent pattern of sensory projection from individual ganglia to all regions of the olfactory lob

ISSN:0092-7317    

DOI:10.1002/cne.902960205

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe purpose of the present study is to provide evidence that chronic spinal denervation leads to an increase in numbers of synaptic terminals from a specific population of primary afferent fibers. Rats were unilaterally deafferented for 35 days (chronic denervation) by dorsal rhizotomies performed from T2 to T8 and T10 to L5, which isolates or spares the T9 root. The contralateral T9 root was spared by similar surgery 5 days (acute denervation) prior to sacrifice. The survival time on the chronic side presumably allows sprouting of T9 primary afferents to occur, whereas the time on the acute side does not. The terminals were labeled with calcitonin gene‐related peptide (CGRP), which is a compound that labels a specific population of primary afferent fibers and terminals, and stereological methods were used to determine the numbers of immunolabeled terminals in laminae I and IIo on the chronic and acute sides of the T9 spinal cord. The findings are that the chronic side had approximately twice as many terminals as the acute side. This difference is statistically significant. These findings are compatible with the hypothesis that chronic denervation leads to synaptogenesis from surviving primary afferent fiber

ISSN:0092-7317    

DOI:10.1002/cne.902960206

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

年代:1990

数据来源: WILEY

摘要:

AbstractCalpain is a calcium‐activated neutral protease that degrades a number of cytoskeletal proteins. It may participate in the maintenance of the cytoskeleton and in the rapid turnover of structural proteins associated with synaptic plasticity. Calpain may also be involved in the neurodegeneration that accompanies aging and age‐related diseases. To aid in the interpretation of disease‐related alterations in staining patterns, the present study examined calpain's normal distribution in the mammalian brain and spinal cord. A monoclonal antibody was employed with the avidin‐biotin‐peroxidase immunocytochemical technique on samples of rat tissue. Glia (astrocytes, microglia) and virtually all neurons were immunopositive, although neuronal processes exhibited varying staining patterns. The axonal staining pattern depended upon either the origin or destination of the process: those axons remaining within the brain (e.g., corpus callosum) were only lightly immunoreactive, whereas spinal cord and peripheral axons (trigeminal nerve) were more darkly labeled. The architecture of the dendritic tree determined the dendritic staining pattern: neurons with prominent apical and basal dendritic trees (e.g., pyramidal cells) were immunolabeled along their entire extent; labeling of multipolar cells (e.g., hilar cells of dentate gyrus) was limited to the proximal dendrites. The ubiquitous distribution of calpain argues against a primary role for the enzyme in the regional pattern of neuronal death seen in Alzheimer's disease. An alteration in the concentration, localization, or inhibition of the enzyme could, however, lead to the abnormal accumulations of cytoskeletal elements seen with th

ISSN:0092-7317    

DOI:10.1002/cne.902960207

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

年代:1990

数据来源: WILEY

摘要:

AbstractCollateral projections are an important feature of the organization of ascending projections from the spinal cord to the brain. Primate spinothalamic tract (STT) neurons with collaterals to the periaqueductal gray (PAG) were studied by means of a fluorescent double‐labeling method. Granular Blue and rhodamine‐labeled latex microspheres were placed in the ventral posterior lateral (VPL) nucleus of the thalamus and the periaqueductal gray, respectively. Single and double labeled neurons were studied in the upper cervical cord, cervical enlargement, thoracic cord, lumbar enlargement, and sacral segments.The laminar distribution of double labeled neurons was similar to that of spinomesencephalic tract (SMT) neurons. Most double labeled (STT‐SMT) neurons were located in contralateral laminae I, V, VII, and X. Relatively more lamina I STT‐SMT neurons were found in the cervical enlargement and more lamina V STT‐SMT neurons in the lumbar enlargement. The density of STT‐SMT neurons in the upper cervical segments and cervical enlargement was almost equal. The density of STT‐SMT neurons in the lumbar enlargement was 40% of that in the cervical enlargement. The thoracic and sacral segments had the lowest density of STT‐SMT neurons, about 10% of that in the cervical enlargement. STT‐SMT neurons constituted 14.7% of SMT neurons and 6% of STT neurons in the cervical enlargement and 15.3% of SMT neurons and 2.9% of STT neurons in the lumbar enlargement.The branch points of eight STT‐SMT axons were studied electrophysiologically. The average percentage of conduction time spent in the parent axon was more than 85% for an antidromic action potential from the VPL nucleus and 91% from the PAG. Branch points of STT‐SMT axons were calculated to be 9–13 mm caudal to the PAG, in the

ISSN:0092-7317    

DOI:10.1002/cne.902960208

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

年代:1990

数据来源: WILEY

摘要:

AbstractImmunohistochemical studies of ventral tegmental area (VTA) neurons indicate that individual cells can contain dopamine as well as the neuropeptide neurotransmitters cholecystokinin (CCK) and neurotensin (NT). We have defined the distribution of the cells expressing the mRNAs encoding these two dopamine cotransmitter peptides in each of the subnuclei of the ventral tegmental area, and quantitated the extent of expression of each gene by using in situ hybridization methods.These studies reveal significant differences in the patterns of expression of each of these two genes within various subdivisions of the VTA. The rostral linear nucleus contained numerous CCK positive cells, some of which appeared to express preproCCK‐mRNA at a very high level, but this nucleus contained relatively few NT‐expressing cells. The parabrachialis pigmentosus contained numerous NT and CCK positive cells. The paranigralis and interfascicularis nuclei displayed positive CCK cells but with expression at only modest levels. NT cells were very few in these nuclei. The caudal linear nuclei contained the highest number of NT‐expressing neurons and these cells expressed very high levels of NT mRNA.The selective distribution of these peptide genes within the VTA subnuclei may have specific consequences. Studies of the connectivity of neurons in the VTA show that the different subnuclei of this region project to several functionally and architectonically different regions of the cerebral cortex and subcortically to nuclei related to the limbic system. Results from our study show very prominent expression of CCK mRNAs in those subnuclei that project heavily to the prefrontal, other cortical areas, and the amygdaloid complex. The NT gene is expressed prominently in those subnuclei of VTA that project heavily to the entorhinal cortex and amygdaloid complex.These results provide support for a differential role for the NT‐expressing neurons than that of CCK‐expressing neurons of VTA in “reward” mechanisms and in drug‐seeking and motivational behavior. These observations could be applied to create working hypotheses and experimental paradigms to test the differential functional activity of the subdivisions of VTA and their potential roles in the pathogenesis and treatment of drug‐seeking behavior and other neuropsyc

ISSN:0092-7317    

DOI:10.1002/cne.902960209

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

年代:1990

数据来源: WILEY

摘要:

AbstractPrevious studies of the monocularly deprived (lid‐sutured) primate (Galago crassicaudatus) have shown that magnocellular (M) and parvocellular (P) lateral geniculate nucleus (LGN) cells that receive input from the deprived eye are smaller than counterparts that receive input from the nondeprived eye; deprived koniocellular (K) cells show wide variability in size, but they do not differ from their nondeprived counterparts (Casagrande and Joseph, '80)‐ Although deprivation results in cell‐size changes, the physiological properties of deprived LGN cells do not change from normal (that is, P cells have normal X‐like properties, M cells have normal Y‐like properties, and K cells have normal W‐like properties)Because of these findings, we were interested in determining how the morphology of retinogeniculate axon arbors is affected by deprivation. To this end, 104 horseradish‐peroxidase‐filled retinogeniculate arbors from galagos deprived from birth to maturity were completely reconstructed within the binocular segment of the LGN. These arbors were qualitatively and quantitatively compared with 56 arbors reconstructed from normal galagos as part of another study (Lachica and Casagrande, '88)Our main findings are as follows. Deprived M and P arbors are affected by deprivation in the same general manner: compared with normal arbors, they are altered in shape (rather than being round or columnar, respectively, both groups have terminals that are elongated parallel to laminar borders); they are smaller in area, and they have fewer boutons but innervate the LGN with a greater density of boutons. K arbors are affected by deprivation in the same manner, but less severely. Finally, our results show that nondeprived arbors are also affected by eyelid suture. Specifically, all nondeprived arbor groups are smaller in area than normal and possess more boutons/mm3. We interpret these changes in the morphology of deprived retinogeniculate axons to suggest that abnormal competitive interactions begin by affecting primarily immature LGN cells and their axons and that the retinogeniculate axons presynaptic to these cells experience secondary degenerative effects. Our results also show that similar manipulations of visual experience can result in changes that are not necessarily comparable across species such as ca

ISSN:0092-7317    

DOI:10.1002/cne.902960210

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe efferent and afferent pathways of the chick tangential nucleus were studied by using horseradish peroxidase (HRP: Sigma type VI) to label nerve cell bodies and fibers. Depositions of HRP into the tangential nucleus, as well as into the second cervical level of the spinal cord, show that the axons of tangential neurons on leaving the nucleus form an anteriorly coursing tract that passes through the ventrolateral vestibular nucleus without branching and then to the contralateral medial longitudinal fasciculus (MLF). Within the MLF, the tangential axons course posteriorly, forming collaterals that innervate the abducens nucleus, and then proceed to the cervical spinal cord. This pathway was demonstrated for the axons of the two main neurons, the principal and elongate cells, in 1‐day, 1‐week, and 7‐week‐old animals. In addition, we propose the existence of an unidentified, ipsilateral pathway to the spinal cord for the tangential axons, since HRP injections into one side of the spinal cord resulted in the bilateral labeling of tangential neurons. No labeled cells were found in the tangential nucleus following HRP depositions into the uvula, flocculus, pontine reticular formation, nucleus piriformis, nucleus jumeaux, vestibulocerebellar nucleus, retrotangential nucleus, or the dorsomedial part of the medial vestibular nucleus.The tangential nucleus receives afferents from the colossal vestibular fibers (spoon endings), small collaterals of fine vestibular ampullary fibers, flocculus, and high cervical levels of the spinal cord. From our small sample, it appears that the spinal cord fibers form most of the afferent terminals in the tangential nucleus in 1‐day, 1‐week, and 7‐wee

ISSN:0092-7317    

DOI:10.1002/cne.902960211

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

年代:1990

数据来源: WILEY