摘要:

AbstractVentral photoreceptors of the horseshoe crab,Limulus polyphemus, have been important in the study of visual transduction, due to their large size and hardiness in vitro. This study shows that there are two classes of ventral photoreceptors that can be distinguished on the basis of differences in cellular and nuclear dimensions, soma and rhabdom morphology, and axon size. Large photoreceptors, which have been the subject of many physiological studies, have an extensive superficial rhabdom, a nuclear diameter of 20–24 μm, and measure 100–150 μm in length. In contrast, small photoreceptors measure 45–65 μm in length and have a nucleus 13–16 μm across. Small photoreceptors are found singly or in association with large photoreceptors. The rhabdom of isolated small photoreceptors is surrounded by a calyx originating from the soma, so that it appears to be located internally. The rhabdomeral lobe of small photoreceptors associated with large photoreceptors characteristically is divided into several segments, each of which invaginates the rhabdomeral lobe of the adjacent large photoreceptor. The entire external rhabdom of the associated small photoreceptor abuts the rhabdom of the large photoreceptor. Morphometric analysis of the ventral nerves shows that there are two size classes of photoreceptor axons, corresponding to the two classes of photoreceptors. The numbers of axons in each size class are nearly equal. Unlike the ventral eye, none of the other eyes ofLimulushave been reported to have more than one morphological class of photoreceptor. Functional differences between the two classes of ventral photoreceptors are suggested by experiments, reported in the accompanying paper (Herman (1991), J. Comp. Neurol.303:11–21), showing that the large photoreceptors exhibit light‐stimulated rhabdom turnover while the sm

ISSN:0092-7317    

DOI:10.1002/cne.903030102

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe role of light in turnover of photosensitive membranes was studied in isolated photoreceptors maintained in vitro. Ventral photoreceptors of the horseshoe crab,Limulus polyphemus, were used since they have been the subjects of many in vitro physiological studies. This study shows that the two classes of ventral photoreceptors, the large and small photoreceptors (Herman: companion paper), differ in their morphological response to light. The rhabdom of small photoreceptors is remarkable for its regularity, independent of lighting condition. The photosensitive microvilli of the rhabdom of small photoreceptors are narrow and almost always tightly packed in a hexagonal arrangement.In contrast, the morphology of the rhabdom of the large ventral photoreceptors is different in the dark and in the light, and the rhabdom undergoes turnover during lighting transitions. When fully dark‐adapted, the photosensitive microvilli of large photoreceptors are narrow and well organized, sometimes in a crystalline array. However, in the light‐adapted state, the microvilli are much thicker and very irregular. The transitions between the dark and light‐adapted states, examined at midday, are rapid. After 5 minutes light exposure, the microvilli are dilated at their bases and shed membranes are present in the cytoplasm. By 30 minutes after light onset, the appearance of the rhabdom of large photoreceptors is indistinguishable from fully light‐adapted cells. The transition to the dark‐adapted state is equally rapid. Even at 5 or 12 minutes after light offset, most microvilli are narrow and quite regular, and by 30 minutes, the rhabdom usually appears to be fully dark‐adapted. These experiments show that both the synthetic and degradative phases of rhabdom renewal take place in isolated photoreceptors. No efferent neural activity is required to initiate turnover; rather, changes in illumination alone are sufficient to generate rhabdom turnover in large ventral photorecepto

ISSN:0092-7317    

DOI:10.1002/cne.903030103

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe thalamostriatal projections to rat neostriatal grafts were studied by using the Phaseolus vulgaris‐leucoagglutinin (PHA‐L) axonal tracing technique. Two to 6 months after implantation of striatal primordia into adult neostriata, PHA‐L was injected into two different portions of the intralaminar nuclear complex of the thalamus.In the host neostriatum, labeled fibers from the parafascicular nucleus (PF) arborized in a large region in the neostriatum, but avoided small patchlike areas. Most of the fibers from PF had irregular curved trajectories with short side branches that formed boutons. Labeled fibers from the centromedial and paracentral nuclei (CeM‐PC) projected to a similarly large area within the neostriatum but did not show any nonuniformity. CeM‐PC axons had relatively straight trajectories and formed boutons en passant.Both sets of thalamostriatal projection fibers were found in the grafts. Some of the labeled fibers in the grafts formed dense, focal arborizations. Compared to the host neostriatum, the distribution of postsynaptic elements in the grafts was altered dramatically. In the host neostriatum, 89% of the terminals from PF terminated onto dendritic shafts; 93% of the CeM‐PC terminals contacted dendritic spines. However, only 47% of the PF terminals in the grafts contacted dendritic shafts; 53% of them terminated on dendritic spines. In grafts, 81% of the terminals from CeM‐PC region contacted dendritic spines; 19% of them made synapses on dendritic shafts.The shift of postsynaptic elements in the grafts suggests a loss of pathway specificity in the induction of dendritic spines on neostriatal neur

ISSN:0092-7317    

DOI:10.1002/cne.903030104

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

年代:1991

数据来源: WILEY

摘要:

AbstractAntisera against a variety of vertebrate and invertebrate neuropeptides were used to map cerebral neurosecretory cells in the sphinx mothManduca sexta.Intense immunoreactive staining of distinct populations of neurosecretory cells was obtained with antisera against locust adipokinetic hormone, bovine pancreatic polypeptide, FMRFamide, molluscan small cardioactive peptide (SCPB), leucine‐enkephalin, gastrin/cholecystokinin, and crustacean β‐pigment dispersing hormone (βPDH). Other antisera revealed moderate to weak staining. Each type of neurosecretory cell is immunoreactive with at least one of the antisera tested, and most of these neurons can be identified anatomically. The staining patterns provide additional information on the organization of cerebral neurosecretory cells inM. sexta.Based upon anatomical and immunocytochemical characteristics, 11 types of neurosecretory cells have been recognized in the brain, one type in the suboesophageal ganglion, and one in the corpus cardiacum. Extensive colocalization experiments show that many neurosecretory cells are immunoreactive with several different antisera. This raises the possibility that these cells may release mixtures of neuropeptides into the hemolymph, as has been demonstrated in certain other systems. The immunocytochemical data should be helpful in efforts to identify additional peptide neurohormones released from the brain of this and other in

ISSN:0092-7317    

DOI:10.1002/cne.903030105

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe activities of choline acetyltransferase and acetylcholinesterase were assayed in submicrogram samples from layers of red‐tailed hawk and road runner retina. Both enzyme activities were concentrated in and near the inner plexiform layer. Within the inner plexiform layers of both species, activities of each enzyme were concentrated in two bands, one in each half of this layer. Little choline acetyltransferase activity was found superficial to the middle third of the inner nuclear layer. The distributions of acetylcholinesterase activities corresponded well to those of choline acetyltransferase, except in the outer plexiform layer and the outer margin of the inner nuclear layer of the hawk. These distributions of enzyme activities indicate that populations of amacrine cells in the retinae of these species are cholinergic. In addition to these same cells and presumably cholinoceptive amacrine and ganglion cells, acetylcholinesterase activity in the hawk was associated with a population of horizontal cells that may be unrelated to synaptic cholinergic neurotransmission. Choline acetyltransferase activities associated with amacrine somata and processes were about four times greater in the hawk than in the road runner suggesting important differences in the density and function of cholinergic elements between species. Possible synaptic relationships in the inner plexiform layer consistent with the interspecies differences in enzyme activities are considere

ISSN:0092-7317    

DOI:10.1002/cne.903030106

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe fine structure of substance P (SP) and adenosine deaminase (ADA) immunoreactive structures in synaptic contacts localized to the superficial layers of the superior colliculus of the rat was investigated by means of immunoelectron microscopy. We also examined the possibility of retinal innervation of SP‐ and ADA‐ containing neurons by immunohistochemistry after degeneration of retinal terminals caused by enucleation.SP‐like immunoreactive presynaptic terminals of the stratum griseum superficial (SGS) formed both asymmetric and symmetric synaptic contacts, Presynaptic dendrite like structures were also observed. SP immunoreactive postsynaptic elements made contacts with terminals showing diverse features. ADA‐like immunoreactive structures were seen only as postsynaptic elements to different kinds of nonimmunoreactive terminals and were mostly localized in the ventral third of the SGS and the dorsalmost stratum opticum (SO).After enucleation, degenerating retinal terminals were found to form synaptic contacts with SP and ADA immunoreactive structures. The highest number of such degenerating terminals on ADA immunoreactive structures was observed 2 days after retinal denervation, very few being seen after 5 days. These degenerating terminals were restricted to the ventral SGS and dorsal SO. SP immunoreactive structures postsynaptic to degenerating retinal terminals were most numerous 5 days after enucleation and mainly localized in the dorsal SGS. Occasionally, SP immunoreactive dendrite like processes forming synapses with degenerating retinal terminals were simultaneously presynaptic to other nonimmunoreactive profiles, defining, therefore, serial synapses. The present results suggest that SP‐I and ADA‐I collicular neurons may be part of distinct channels carrying visual information to the lateral posterior and lateral geniculate nuclei of the thalamus, r

ISSN:0092-7317    

DOI:10.1002/cne.903030107

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe dendritic and axonal morphology of neurons in the inferior colliculus of the cat was investigated after intracellular injection of HRP, in vivo. All injected axons gave off local collaterals, and most showed a widespread distribution and lacked a specific orientation. In contrast, the dendrites of injected neurons were distinguished by their degree of orientation and the direction of the longest axis of orientation. Dendrites showed a high, moderate, or low degree of orientation. Most highly oriented cells had their longest axis in the rostrocaudal direction with fewer in the mediolateral direction. In the central nucleus, only the rostrocaudally oriented cells correspond to the disc‐shaped cells identified in Golgi preparations. Unlike most cells in our sample, the two cells that were disc‐shaped had axons that were parallel to the orientation of the dendritic tree. In the dorsal cortex, rostrocaudally oriented cells also were found, but they had unoriented axons. In both the central nucleus and dorsal cortex, cells with a mediolateral axis of orientation or no specific orientation correspond to stellate cells and had axons with widespread local collaterals.These results suggest that an extensive network of local axon collaterals may contribute to neural processing within the inferior colliculus. In the central nucleus, local axons may establish connections within or across the fibrodendritic laminae. In the dorsal cortex, the local and afferent axons may form a complex reticular network. Finally, some injected cells had axons terminating locally and also entering the brachium of the inferior colliculus. This suggests that cells in the inferior colliculus may function as both interneurons and projection neur

ISSN:0092-7317    

DOI:10.1002/cne.903030108

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

年代:1991

数据来源: WILEY

摘要:

AbstractVarious cutaneous and visceral stimuli alter the discharge rates of neurons in the hypothalamus. Changes in the activity of hypothalamic neurons are thought to play important roles in eliciting neuroendocrine, autonomic, and affective responses to somatosensory and visceral stimuli. Information from peripheral structures has been considered generally to reach the hypothalamus via multisynaptic ascending pathways. Recently, a direct projection from the spinal cord to the hypothalamus was demonstrated in rats. The goal of this study was to determine whether a similar projection exists in cats. Either wheat germ agglutinin conjugated to horseradish peroxidase, a mixture of this tracer and the B subunit of cholera toxin conjugated to horseradish peroxidase, or fast blue was injected into the hypothalamus of cats. Injections were centered in the hypothalamus in seven cats and did not spread to the thalamus, zona incerta or midbrain. After these injections, retrogradely labeled neurons were observed bilaterally in each of the 17 spinal segments that were examined. A total of approximately 400–500 labeled neurons was observed in alternate sections through these segments in the most effective cases. Roughly 70% of the labeled neurons were located contralaterally. Labeled neurons were found predominantly in the deep dorsal horn, the intermediate zone/ventral horn and in the area surrounding the central canal. A few were also noted in the superficial dorsal horn. The first and second sacral segments contained the largest numbers of retrogradely labeled neurons in the spinal cord.The number of spinohypothalamic tract neurons observed in this study in cats was roughly an order of magnitude smaller than that previously reported for rats. This finding suggested either that the spinohypothalamic tract is relatively small in cats or that our tracing techniques did not label many spinohypothalamic tract neurons in cats. To test the sensitivity of one of our tracing techniques, control injections of wheat germ agglutinin conjugated to horseradish peroxidase that filled the ventrobasal thalamus were made in two cats. In both cases, thousands of spinal cord neurons were labeled.In summary, our results indicate that a spinohypothalamic tract exists in cats. However, our findings also suggest that the total number of spinohypothalamic tract neurons in cats may be an order of magnitude smaller than it is in rat

ISSN:0092-7317    

DOI:10.1002/cne.903030109

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

年代:1991

数据来源: WILEY

摘要:

AbstractGalanin, a 29‐amino acid peptide, has been shown by immunocytochemistry to occur in most large acetylcholinergic neurons of the complex that includes the nucleus basalis of Meynert and the nucleus of the diagonal band of Broca in nonhuman primates. In contrast, several studies have reported that most large neurons of the human nucleus basalis of Meynert complex appear to lack galanin immunoreactivity. We investigated this apparent species‐difference by hybridization histochemistry for galanin messenger ribonucleic acid (mRNA) in humans and baboons. The results confirm previous immunocytochemical data; very few large neurons of the nucleus basalis of Meynert complex in humans contained detectable galanin messenger RNA, whereas most such cells in baboons were labeled by the oligodeoxynucleotide probe. The few labeled neurons in humans were primarily medial or ventral to the main body of the nucleus basalis of Meynert and corresponded in location to a minor population of relatively intensely labeled cells in baboons. These findings indicate that the indetectability of immunoreactive galanin in most cells of the nucleus basalis of Meynert complex in humans is due to a paucity or an absence of galanin messenger RNA and not to differences in posttranslational processing or transport of the peptide. Inasmuch as the probe labeled neurons in several other nuclei of both species, it is unlikely that differences in galanin messenger RNA sequences underlie the species‐related disparity in hybridization in the nucleus basalis of Meynert complex. The indetectability of galanin messenger RNA in most cells of the human nucleus basalis of Meynert complex indicates that the expression of the galanin gene is regulated by as yet unidentified influences that differ in human and nonhuman primates. The varying phenotypes of galanin in primates suggest potentially important species‐differences in the function of galanin in neurons of the nucleus basalis of Meynert

ISSN:0092-7317    

DOI:10.1002/cne.903030110

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

年代:1991

数据来源: WILEY

摘要:

AbstractPrevious reports indicate that the midbrain periaqueductal gray and the central nucleus of the amygdala are interconnected but the organization of these projections has not been characterized. We have analyzed this reciprocal circuitry using anterograde and retrograde tracing methods and image analysis. Our findings reveal that innervation of periaqueductal gray from the central nucleus of the amygdala is extensive and discretely organized along the rostrocaudal axis of periaqueductal gray. In addition, the reciprocal projection from periaqueductal gray to the central nucleus of the amygdala is more extensive and more highly organized than previously suggested.Multiple or single discrete injections of wheatgerm agglutinin‐horseradish peroxidase into several rostrocaudal levels of periaqueductal gray retrogradely labeled a substantial population of neurons, predominantly located in the medial division of the central nucleus of the amygdala. Tracer injections into the central nucleus revealed a high degree of spatial organization in the projection from this nucleus to periaqueductal gray. Two discrete longitudinally directed columns in dorsomedial and lateral/ventrolateral periaqueductal gray are heavily targeted by central amygdalar inputs throughout the rostral one‐half to two‐thirds of periaqueductal gray. Beginning at the level of dorsal raphe and continuing caudally, inputs from the central nucleus terminate more uniformly throughout the ventral half of periaqueductal gray.In addition, a substantial population of periaqueductal gray neurons were retrogradely labeled from the central nucleus of the amygdala; these were heterogeneously distributed along the rostrocaudal axis of periaqueductal gray, and included both raphe and non‐raphe neurons. Thus, the present study demonstrates that periaqueductal gray receives heavy, highly organized projections from the central nucleus of the amygdala and in turn, has reciprocal connections with the central nucleus.Previous studies have demonstrated that longitudinally organized columns of output neurons located in dorsomedial and lateral/ventrolateral periaqueductal gray project to the ventral medulla. Thus, there may be considerable overlap between the two longitudinally organized terminal input columns from the central nucleus of the amygdala and the two longitudinal columns of descending projection neurons from periaqueductal gray to the ventral medulla. The central nucleus of the amygdala has been implicated in a variety of emotional/cognitive functions ranging from fear and orienting responses, defensive and aversive reactions, associative conditioning, cardiovascular regulation, and antinociception. Many of these same functions are strongly represented in the periaqueductal gray. It is noteworthy that the present results demonstrate that lateral periaqueductal gray, a preeminent central trigger site for behavioral and autonomic components of the defense/aversion response, is heavily targeted by inputs from the central nucleus of the amygdala at all levels of periaqueductal gray. Thus, the central nucleus of the amygdala to periaqueductal gray projection may be involved in the neural integration of behavioral, antinociceptive and autonomic responses with emotional state. In addition, the present demonstration of extensive reciprocal connections between the central nucleus of the amygdala and periaqueductal gray represents a route via which functional activity represented in periaqueductal gray may gain access to a forebrain structure long implicated m the integration of the cognitive and autonomic components of emotional behavior. Thus, the periaqueductal gray to central nucleus of the amygdala projection may provide a relatively direct linkage between critical species‐preserving behavioral reactions and a forebrain structure capable of influencing multiple nodal points in the descending autonom

ISSN:0092-7317    

DOI:10.1002/cne.903030111

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

年代:1991

数据来源: WILEY