摘要:

AbstractGap junctions of the H1 horizontal cell of the turtle retina (Leeper, 1978) were studied in thin‐sectioned material and in freeze‐fracture replicas. Peri‐karyal gap junctions were extremely restricted, 0.02–0.07 μm2in area, whereas those of axon terminals were much larger, most being 0.1–1.0 μm2. Both varieties, however, had the usual seven‐layered appearance in thin sec‐tion and measured 15 ± 1 nm in overall width between cytoplasmic faces. Freeze‐fractured views of the perikaryal junctions revealed roughly circular patches of P‐face 9‐nm particles and E‐face pits. The axon terminal gap junctions were seen as large areas of P‐face particles and E‐face pits containing occasional islands of unsnecialized membrane. Particle densities varied from 1, 455to 2, 448 μm−2serial reconstruction was made or a portion of the axon terminal network in order to measure the surface areas of the axons con‐tained therein and the fraction occupied by gap junctions. These data demonstrated that the fractional area occupied by gap junctions was roughly in inverse proportion to the area of the axon region (tuberous core vs. terminal process). It is argued that this constitutes an impedance matching device to ensure adequate current flow through the axon processes. Assuming that each P‐face particle represents a connexon having a conductance of 10−10and given the P‐face particle density and gap junctional areas determined in this report, we calculated that the gap junction distribution is adequate to account for the spatial properties of the ho

ISSN:0092-7317    

DOI:10.1002/cne.902160402

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

年代:1983

数据来源: WILEY

摘要:

AbstractThe nervous systems of locusts(Schistocerca gregaria)and flightless grasshoppers(Barytettix psolus)are compared to evaluate modifications to neurons which are associated with flight loss.Locusts are well known for their powerful flight capability. Barytettix never fly. They lack hindwings, have immobile vestiges of forewings, and are devoid of skeletal specializations for wing movement. Their pterothoracic musculature is similar to that of locusts, except for the absence of those muscles that, in locusts, have the primary function of moving the wings.Individually identified leg motorneurons, the extensors of the tibia, were compared between locusts andBarytettixand were found to have very similar morphologies.Nerve roots which correspond to those suppyling wing muscles of locusts were stained by cobalt backfilling inBarytettixto test for presence of counterparts to wing muscle motorneurons.Cobalt backfills of metathoracic nerve 1 reveal the presence in Barytettix of neurons corresponding to locust dorsal longitudinal motorneurons‐neurons which persist in adultBarytettixin the complete absence of pe‐ripheral targets. These cells occupy characteristic positions within the CNS but their soma sizes are greatly reduced by comparison to their locust counterparts.Locust metathoracic ganglia bear large flight motorneurons on their ventral anterolateral margin. Viewed in toluidine blue‐stained wholemounts,Barytettixganglia show considerably smaller neuron somata in the corresponding region. In locusts, comparisons of the fast extensor tibiae (FETi) motorneuron soma profile areas with those of the largest anterior cell showed no significant difference between the two, while inBarytettix, the largest anterior cell is 51% smaller than the FETi.A counterpart to the locust wing hinge stretch receptor (SR) was revealed by backfilling metathoracic nerve 1 inBarytettix.Despite its lack of function as a wing movement detector, the central projection ofBarytettixSR differs from its locust counterpart only in reduced spread of specific central bra

ISSN:0092-7317    

DOI:10.1002/cne.902160403

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

年代:1983

数据来源: WILEY

摘要:

AbstractComparison of the nervous systems of a flightless grasshopper(Barytettix psolus), and locusts(Schistocerca)is extended to include two large interneurons, the descending contralateral movement detector (DCMD) and the tritocerebral commissure giant (TCG). These interneurons are thought to play a role in locu st flight. Both were visualized inBarytettixwith cobalt staining techniques.Most features of the two neurons are similar in both locusts and Barytettix. Yet, several differences were noted. In locusts, the dorsal DCMD branch in its metathoracic projection terminates in dorsolateral neuropile and synapses with flight motorneurons (Pearson and Goodman, 1979). InBarytettix, no branch terminates in the corresponding region. Of the animals examined, 52% lacked branches corresponding to locust dorsal branches. When present, they all had abnormal projections by comparison to their counterparts in locusts.The maintenance of the TCG inBarytettixwith so similar a form to that of locusts suggests that the role of the cell in behavior other than flight should be examined. The differences in DCMD projection suggest that a discrete set of output connections may have been modified inBarytettixby the alteration of a single first‐order axonal branc

ISSN:0092-7317    

DOI:10.1002/cne.902160404

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

年代:1983

数据来源: WILEY

摘要:

AbstractUltrastructural characteristics and distribution of nigral and pallidal axon terminals on thalamic neurons were studied after injections of tritiated leucine into substantia nigra and entopeduncular nucleus respectively.Adult cats received 0.1–0.2‐μl injections of 2, 3, 4, 5,3H‐leucine in a concentration 60 μCi/μl and were allowed to survive for 4–5 days. The brain tissue was processed for electron (EM) and light microscopic (LM) autoradiography. EM samples were obtained from the ventral medial and ventral anterior thalamic nuclei. Ultrastructural features of labelled nigral and pallidal boutons were analyzed both qualitatively and quantitatively.Ultrastructural characteristics of nigral and pallidal boutons appeared similar. Their length along postsynaptic membrane ranged from 0.8 to 10 μm, with average length of apposition around 2 μm. Both types of bouton contained small clear vesicles of extremely variable shape and formed symmetrical type contacts. Mean diameter of synaptic vesicles profiles (n = 500) was 32.5 nm and 33.3 nm in nigral and pallidal terminal respectively, and mean vesicle profile areas were 846 nm2in nigral terminals and 878m2in pallidal. Both parameters showed normal distribution in percentage distribution histograms. The mean ratios of longest and shortest diameters was 1.6 for synaptic vesicles in both types of boutons.Thus, no significant differences in morphological parameters of nigral and pallidal axon terminals were discovered except that pallidal afferents often formed “en passant”‐type synapses while nigral did not. However, this feature alone is not sufficient for distinction between the two types of termi‐nals in unlabelled tissue.Analysis of distribution of synaptic sites showed that only pallidal bou‐tons formed axosomatic synapses on thalamocortical projection neurons (TCPN), which comprised 21% of total number of pallidal terminals studied. On primary dendritic trunks of TCPN the proportion of nigral boutons was larger (28.8%) as compared to pallidal (19%). The percentage of both types of bouton contacting secondary TCPN dendrites was similar (36% pallidal, 30.6% nigral), while the proportion of nigral terminals on tertiary TCPN den‐drites was larger (23.6% versus 13%). Both afferents revealed a tendency to synapse preferentially at the branching points of TCPN dendrites with sev‐eral boutons often found along the perimeter of the branching site. Small but equal proportions (8%) of both types of axon terminal were found to synapse on vesicle‐containing dendrites of local circuit neurons. Nigral boutons were also found in complex synaptic arrangements in glomeruli.It is concluded that the organizations of pallidal and nigral afferent in‐puts in the thalamus are rather similar. Both occupy strategic positions which would allow them to exert strong influence

ISSN:0092-7317    

DOI:10.1002/cne.902160405

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

年代:1983

数据来源: WILEY

摘要:

AbstractThe projections from the ventral tegmental area of Tsai (VTA) to the frontal cortex (FC), lateral septum (LS), nucleus accumbens (Acc), caudateputamen (CPu), and lateral habenula (LH) were investigated in the rat by means of the double retrograde fluorescent tracer technique.True blue and fast blue were used in combination with nuclear yellow as retrograde tracers. After combined injections placed into two different terminal fields, many singly and some doubly labeled neurons were seen in the midbrain. In all cases the labeled cells were observed in the ipsilateral VTA, while after injections placed into the LS and Acc some fluorescent neurons were also seen in the contralateral VTA. The patterns of distribution of the labeled neurons showed a topographic organization of the VTA efferent pathways. However, some degree of overlapping was evident in the distribution of cells retrogradely labeled from different terminal fields. The number of the doubly labeled neurons varied according to the sites of combined injections, but in each experiment it never exceeded 10% of the total number of labeled perikarya. Doubly labeled neurons were particularly numerous after combined injections placed into the FC, LS, or LH; on the contrary, very few doubly labeled cells were observed after combined injections placed into the CPu and LS or LH.The organization of the ascending VTA projections suggests that they are probably integrated into different anatomical sets.

ISSN:0092-7317    

DOI:10.1002/cne.902160406

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

年代:1983

数据来源: WILEY

摘要:

AbstractTo test the differentiation of visual interneurons that had their targets removed before axogenesis, we ablated neuronal precursors in brains of first instar fly larvae by using a laser microsurgery unit. We describe ablations that resulted in the elimination of the third neuropil region (the lobula complex) of the optic lobes. Neural differentiation in the more peripheral second and first neuropil regions (the medulla and the lamina) was thus studied in the absence of the lobula complex.It was found that the medulla neuropil differentiated with normal columnar and layered organization. The neuropil, however, folded along its central surface. The only connection between the medulla and more central neuropil (the midbrain) was via a bundle of axons (the Cuccati bundle) present also in the normal optic lobes. Some types of neurons that normally connect the medulla and the lobula complex could be identified. These appeared to end in a disorganized neuropil mass in the center of the folded medulla.The differentiation of the lamina neuropil also appeared normal in flies with the lobula complex eliminated and the medulla folded. Also, in optic lobes where the medulla was severely disorganized and/or reduced due to laser ablations, the lamina neuropil appeared more or less normal.The results suggest that lamina and medulla nerve cells can differentiate and develop normal neuropil patterns in absence of their appropriate targets.

ISSN:0092-7317    

DOI:10.1002/cne.902160407

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

年代:1983

数据来源: WILEY

摘要:

AbstractCerebellopontine axonal boutons in the neuropil of the basilar pontine nuclei (BPN) were marked for ultrastructural identification by producing unilateral electrolytic lesions of the superior cerebellar peduncle (SCP) as it exited from the cerebellum and before its decussation in the caudal midbrain. Three varieties of degenerating boutons were distinguished on the basis of size, type of degeneration, and postsynaptic locus. A relatively large variety of bouton (2.5–6.0 μm) that exhibited filamentous degeneration throughout the range of survival times employed (1–14 days) was the most frequently observed type of degenerating Cerebellopontine bouton. Such boutons formed synaptic contacts with several small, dendritic, spinelike profiles as well as the shafts of intermediate or proximal dendrites. A second, far less numerous and somewhat smaller type of bouton (1.5–4.5 μm) was distinguished by the fact that it exhibited advanced dark degenerative changes after a 2‐day survival period, formed multiple spine contacts (but not shafts), and was no longer apparent in the neuropil after a postlesion survival time of 6 days. The third variety of degenerating bouton was small (0.8–2.0 μm), exhibited dark degeneration with a 2–6‐day survival period, contacted primarily shafts of small‐diameter dendrites, and was observed more frequently than the larger dark boutons but less often than the large filamentous boutons. All three types of degenerating boutons contained round, clear, synaptic vesicles and formed only asymmetric synaptic active sites. It is suggested that the three types of degenerating axon terminals arise from at least three varieties of neurons in the deep cerebellar nuclei. Further it is suggested that such boutons originate from cerebellar efferent axons which distribute in collateral fashion to the thalamus, red nucleus, and/or

ISSN:0092-7317    

DOI:10.1002/cne.902160408

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

年代:1983

数据来源: WILEY

摘要:

AbstractThe cerebellar cortex of the pigeon receiving direct vestibular afferents was delineated by anterograde transport of [3H]‐amino acids injected the vestibular nerve. Labelled mossy fiber rosettes in the granular layer were concentrated in lobule X (nodulus) and to a lesser extent, in the ventral portion of lobule IXd (uvula and paraflocculus). A few solitary labelled rosettes were also found in more dorsal portions of lobule IX, as well as in the anterior lobe between lobule II and IV. The lingularernainedunlabelled. Dis‐crete injections of [3H]‐leucine into the cristae of each of the three semicircu‐lar canals or the utricular macula yielded a similar distribution of fewer labelled rosettes. A few primary mossy fiber terminals labelled after cochlear injections are attributed to afferents from the lagenar macula. Since effective diffusion of label from the injection site was excluded by controls, it is concluded that projection of individual canal and macula nerves to the ves‐tibulocerebellar cortex is not topographically separated. It is proposed that this extensive convergence of various afferents is required by the cerebellum to compute precise and directionally specific control signals during head rotation in all conceivab

ISSN:0092-7317    

DOI:10.1002/cne.902160409

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

年代:1983

数据来源: WILEY

摘要:

AbstractThe tobacco hornworm moth,Munducasexta, shows extensive degeneration of abdominal neurons after the adult moth emerges (ecloses) from the old pupal skin. Death of interneurons begins about 2 hours before eclosion and continues through the next 30 hours. Motorneuron degeneration starts slightly later, commencing at about 8 hours after eclosion. Analysis of the death of identified motorneurons showed that there was a precise spatial and temporal program of neuronal death. Particular cells invariably either continued to live or died and, among the latter, the time of death varied from cell to cell but for a given cell was constant. This program of cell death was somewhat flexible in that the fates of certain cells could be adaptively modified by behaviors that might naturally occur in the life of the insect.

ISSN:0092-7317    

DOI:10.1002/cne.902160410

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

年代:1983

数据来源: WILEY

摘要:

AbstractThe distribution of immunoreactive substance P (sP)‐containing structures in the newt brain and spinal cord was explored with an indirect im‐munofluorescence method. Five sP‐positive elements were detected: perikarya, dots, fibers, pericellular appositions, and pipe‐shaped structures. Perikarya were seen at the levels of the spinal ganglia, spinal cord, raphe nucleus, interpeduncular nucleus, mesencephalon, preoptic area, infundibulum, dorsocaudal part of the ventral hypothalamus, habenula, and corpus striatum. Pericellular terminals were observed in periventricular areas, known to be rich in catecholaminergic cells; pipe‐shaped structures were ob‐served from the corpus striatum to diencephalon, and in mesencephalon. The olfactory nerve and nuclei were devoid of sP‐positive elements. Six sP‐immunofluorescent pathways were detected. One of them is composed of axons with huge varicosities and extends from the lateral spinal cord area to the mesencephalon. This pathway has not been described as yet in other animals and could be pecul

ISSN:0092-7317    

DOI:10.1002/cne.902160411

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

年代:1983

数据来源: WILEY