Ultrastructural quantitative analysis of glutamatergic and GABAergic synaptic terminals in the phrenic nucleus after spinal cord injury

Quantitative analysis of electron microscopic postembedding immunochemically stained material indicates that 48% of all terminals in the rat phrenic nucleus are glutamatergic and 33% are γ-aminobutyric acid (GABA) ergic. Three distinct types of glutamatergic terminals were observed in the rat phrenic nucleus: terminals characterized by large, loosely arranged spherical synaptic vesicles (SI) or small, compact spherical synaptic vesicles (Ss) and elongated terminals containing spherical synaptic vesicles with neurofilaments (NFs). All three types of glutamatergic terminals display asymmetrical synaptic membrane densities with postsynaptic dense bodies being present in some of the S-type terminals. The GABAergic immunoreactive terminals in the phrenic nucleus most closely resemble F-type terminals. They are characterized by flattened or pleomorphic synaptic vesicles and symmetric synaptic membrane densities. Among the 48% glutamatergic terminals, 27% are SI, 65% are Ss, and 8% are NFs, respectively. Significantly fewer glutamate, GABA, and unlabeled terminals per unit area are present in the phrenic nucleus 30 days after a C2 spinal cord hemisection as compared to nonhemisected controls. The average number of active zones per terminal, however, is greater in the hemisection group (1.45 ± 0.03) than in the control group (1.34 ± 0.03), with the active zones in the glutamate terminals mainly accounting for this difference. Moreover, the length of the active zones in the glutamate terminals was significantly longer in the hemisection group (0.37 ± 0.013 μm) as compared to the controls (0.24 ± 0.008 μm). In addition, the mean length of synaptic active zones in GABAergic terminals was also found to be longer in the hemisection group (0.36 ± 0.022 μm) as compared to controls (0.28 ± 0.014 μm). Finally, there is also a significantly higher ratio of synaptic active zones to the total number of glutamate-labeled terminals after injury (1.73 ± 0.08) as compared to controls (1.41 ± 0.04). The number of double/multiple synapses, the percentages of Sl, Ss, and NFs-type terminals, and the percentages of synaptic active zones contacting either distal dendrites or proximal dendrites/somata do not change significantly 30 days after injury. These results are important for a more complete understanding of the synaptic plasticity that occurs in the phrenic nucleus after spinal cord injury and to show how the plasticity may relate to the unmasking of latent bulbospinal respiratory connections which restore function to the hemidiaphragm paralyzed by an ipsilateral spinal cord hemisection. © 1996 Wiley-Liss, Inc.     

Genesis of neurons in the dorsal lateral geniculate nucleus of the cat

Neurons that will ultimately form the dorsal and ventral lateral geniculate nuclei, the medial interlaminar nucleus, the perigeniculate nucleus, and the nucleus reticularis of the cat undergo their final cell division beginning on, or slightly before, embryonic day 22 (E22) and ending on, or before, E32. Early in this period, neurogenesis proceeds for all of these geniculate nuclei, whereas only in the dorsal lateral geniculate nucleus does cell birth continue until E32. Distinct spatiotemporal gradients of cell birth are not obvious within any of the individual geniculate nuclei. For the dorsal lateral geniculate nucleus in particular, and for the other geniculate nuclei in general, neurons born early in this period exhibit a full range of adult soma sizes, including large and small neurons. Neurons born late in this period exhibit only small adult somas. The location and size of a neuron within the dorsal lateral geniculate nucleus provide clues to that cell's functional properties. On the basis of presently available information regarding the relationship between structure and function of neurons in the cat's dorsal lateral geniculate nucleus, the findings described here suggest that all functional classes of neurons in the dorsal lateral geniculate nucleus are born at the same time throughout most of this period.     

Genesis of morphologically identified neurons in the dorsal lateral geniculate nucleus of the cat

Neurons in the dorsal lateral geniculate nucleus of the cat can be grouped into five morphological classes based on a variety of structural characteristics. These same structural characteristics can serve as morphological signatures for the three physiological classes (X, Y, W) of neurons found in this nucleus. The purpose of this study was to determine if a relationship exists between the birthdate of neurons within the dorsal lateral geniculate nucleus and the adult morphology of those neurons. Seven cats, each of which had received a single injection of 3H-thymidine, were studied. A total of 2,138 Golgi-impregnated neurons were identified in the dorsal lateral geniculate nuclei of these seven cats; 1,517 of these neurons were successfully resectioned and recovered, of which 385 (25%) were found to contain the 3H label. Neurons from each of the five morphological classes were labeled in each of the six animals that received a 3H-thymidine injection between embryonic day 24 (E24) and E28. Class 3 and class 5 neurons were labeled in a cat injected with 3H-thymidine on E30. These findings demonstrate that the development of the morphological class of a neuron in the dorsal lateral geniculate nucleus is independent of the time of its final cell division. Further, given the relationship that exists in the cat's dorsal lateral geniculate nucleus between neuronal structure and function, the present findings suggest that the different physiological classes of cells found in this nucleus undergo their final cell divisions throughout most of the period of neurogenesis except that the functional role of neurons born late in this period may be more restricted.     

Doublecortin as a marker of adult neuroplasticity in the canary song control nucleus HVC

It is established that in songbirds the size of several brain song control nuclei varies seasonally, based on changes in cell size, dendritic branching and, in nucleus HVC, the incorporation of newborn neurons. In the developing and adult mammalian brain, the protein doublecortin (DCX) is expressed in postmitotic neurons and, as a part of the microtubule machinery, required for neuronal migration. We recently showed that in adult canaries, DCX-immunoreactive (ir) cells are present throughout the telencephalon, but the link between DCX and the active neurogenesis observed in songbirds remained uncertain. We demonstrate here that DCX labels recently born cells in the canary telencephalon and that, in parallel with changes in HVC volume, the number of DCX-ir cells is increased specifically in the HVC of testosterone-treated males compared with castrates, and in castrated testosterone-treated males paired with a female as compared with males paired with another male. The numbers of elongated DCX-ir cells (presumptive migrating neurons) and round multipolar DCX-ir cells (differentiating neurons) were also affected by the sex of the subjects and their photoperiodic condition (photosensitive vs photostimulated vs photorefractory). Thus, in canaries the endocrine state, as well as the social or photoperiodic condition independently of variation in steroid hormone action, affects the number of cells expressing a protein involved in neuronal migration specifically in brain areas that incorporate new neurons in the telencephalon. The DCX gene may be one of the targets by which testosterone and social stimuli induce seasonal changes in the volume of song nuclei.     

Reduced effects of monocular deprivation on a population of A-laminae neurons in the cat's dorsal lateral geniculate nucleus

The generation of nerve cells for the cat's dorsal lateral geniculate nucleus takes place between embryonic day (E) 22 and E32. Neurons generated before E28 exhibit a full range of soma sizes and morphological features, whereas neurons generated after E28 have only smaller somata and a more limited array of morphological features. We measured the effects of monocular deprivation on neurons in the cat's dorsal lateral geniculate nucleus that were generated at different times, with birthdates defined by injections of ³H-thymidine. Whereas populations of nerve cells generated before E28 exhibit changes in cell size that are, on average, typical of those seen in monocularly deprived cats, populations of nerve cells generated after E28 are, on average, less affected by visual deprivation.     

Ultrastructural studies on catecholaminergic terminals and GABAergic neurons in nucleus tractus solitarius of the rat medulla oblongata

Synaptogenesis of catecholamine (CA) boutons in the nucleus tractus solitarius (NTS) was compared between spontaneously hypertensive (SHR) rats and Wistar-Kyoto (WKY) rats at different ages. On the average, there were about 32 CA varicosities per 2200 μm² area of the NTS in both SHR and WKY rats as revealed by glyoxylic acid fluorescence microscopic (FM) morphometric study. The FM analysis indicated that there were no significant changes in the CA varicosity density between SHR and WKY rats.The CA boutons were labeled with 5-hydroxydopamine and appeared to contain small granular vesicles at the electron microscopic (EM) level. A total of 1402 CA boutons were studied in a 540, 000 μm² area of the NTS. The number of CA boutons involved in synaptic contacts vs the number of total CA boutons was used to obtain synaptic frequency which was taken as an index for synaptogenesis. A reduction of approximately 18% and 14% of synaptogenesis of CA boutons was observed in the NTS of SHR rats at 4 weeks (prehypertensive stage) and 12 weeks (early hypertensive stage) of age respectively, as compared to age-matched WKY rats. No significant difference of synaptogenesis of CA neurons was found between SHR and WKY rats at 16 weeks of age, a stage in which hypertension is well established and maintained in SHR rats. These results suggest that CA neurons with fewer synaptic contacts in the NTS may play a more important role in the initiation than in the maintenance of hypertension in the SHR rats.In addition to CA terminals, there were numerous GABAergic cell bodies in the NTS which were identified by immunocytochemistry using antibodies to the GABA synthesizing enzyme,l-glutamate decar☐ylase (GAD). GABAergic dendrites with GAD-positive reaction were often seen to receive several GAD-negative synapses at EM random profiles. In the text, a viewpoint is thus discussed that emphasizes that a synaptic abnormality of CA terminals with fewer synaptic contacts affecting GABAergic neurons may participate in the pathogenesis of hypertension. However, it remains to be determined as to whether or not there is a direct contact between CA boutons and GABAergic dendrites.     

Delineation of a brain nucleus: comparisons of cytochemical, hodological, and cytoarchitectural views of the song control nucleus HVc of the adult canary

The present investigation used stable area-specific, neuronal properties instead of Nissl stain to delineate the boundaries of the nucleus hyperstriatalis caudal c (HVc) in the telencephalon of the adult male canary. Immunocytochemical procedures combined with retrograde tracing labeled a large population of perennial long-projecting neurons that contain estrogen receptors in the canary HVc. The HVc area defined by the distribution of these neurons was congruent with the HVc area defined in Nissl-stained sections during the breeding period. The HVc area defined in Nissl-stained preparations showed an extensive seasonal change in size, confirming previous results (Nottebohm: Science, 214:1368-1370, '81). In contrast, the HVc area defined by the distribution of the estrogen receptor containing long-projection neurons showed little or no seasonal change in size. Because these neurons are permanent, the HVc seems to be of rather constant size year round. The internal morphology of the HVc, however, undergoes seasonal alterations, which are reflected in changes in size of the HVc area distinguishable in Nissl-stained sections. The combination of cytoarchitectural criteria of Nissl-stained preparations with area-specific cytochemical and hodological markers to delineate the boundaries of a brain nucleus might give new insights in the partitioning and neuronal plasticity of brain areas.     

Plasticity of catecholaminergic terminals in rat paraventicular hypothalamic nucleus after 6-Hydroxydopamine lesion: an emphasis on bouton sizes and synaptic frequency

Catecholaminergic (CA) nerve terminals in the paraventicular hypothalamic nucleus (PVN) of adult rats were studied at 4, 21, 56 and 180 days after a single injection of 6-hydroxydopamine (6-OHDA) neurotoxin into the right lateral ventricle of the brain. We previously described and quantified the extent of CA terminal sprouting in the PVN after 6-OHDA lesions. For this communication we studied parameters, specifically the bouton sizes and the synaptic frequencies of CA terminals during the renewal process, and evaluated how changes of these parameters are ralated to axonal sprouting. The CA boutons were identifiable in the electron microscope by exhibiting small granular vesicle (SGVs) after central administration of 5-hydroxydopamine (5-OHDA) marker. The marked CA boutons were measured and further categorized according to whether or not they were associated with distinct synaptic specializations at various post-lesion stages. The average sizes of CA boutons were strikingly similar in their diameters (1.0 υm) for both control and experimental tissues. However, CA boutons larger than 2.1 υm were rare and seen more often in the experimental tissues with 6-OHDA lesion and were sustained up to 180 days after lesions. Catecholaminergic profiles with ultrastructural features of growth cones were also seen in the PVN following the 6-OHDA lesions, indicating that there is growth activity in the PVN after 6-OHDA lesion. There were 33% of CA boutons in the PVN from the control tissues that appeared to have contacts. Four days after lesions with a significant reduction of CA terminals, the synaptic frequency was seen on 31% of surviving CA terminals; this synaptic frequency (31%) is close to that observed before lesioning. Of the CA boutons, 42% possessed synaptic contacts at both 21 and 56 days postlesion. At these stages there is still limited regeneration of CA terminals. At 180 days afler lesions with a significant CA terminal restoration, the synaptic frequency of CA boutons had dropped to 36%, a value closer to the control level. The following conclusions can be drawn: (1) the synaptic frequency of CA terminals 4 days afler lesions resembles that of controls, suggesting that synaptic contacts found at this short survival period are those CA terminals escaped from 6-OHDA destruction, not from regenerating fibers; (2) a higher synaptic frequency was exhibited by CA terminals at 21 and 56 days after lesions; by 180 days after the lesion; a subsequent decrease of synaptic frequency was observed on CA terminals, indicating synaptic plasticity of CA terminals; and (3) CA stumps in the PNV are able to extend to establish their synaptic contacts at a frequency close to control levels by 180 days after 6-OHDA lesion, suggesting that regenerative fibers may be functional.     

Caspase-mediated death of newly formed neurons in the adult rat dentate gyrus following status epilepticus

A large proportion of cells that proliferate in the adult dentate gyrus under normal conditions or in response to brain insults exhibit only short-term survival. Here, we sought to determine which cell death pathways are involved in the degeneration of newly formed neurons in the rat dentate gyrus following 2 h of electrically induced status epilepticus. We investigated the role of three families of cysteine proteases, caspases, calpains, and cathepsins, which can all participate in apoptotic cell death. Status epilepticus increased the number of bromodeoxyuridine (BrdU)-positive proliferated cells in the subgranular zone of the dentate gyrus. At the time of maximum cell proliferation, immunohistochemical analyses revealed protein expression of active caspase-cleaved poly (ADP-ribose) polymerase (PARP) in approximately 66% of the BrdU-positive cells, while none of them expressed cathepsin B or the 150-kDa calpain-produced fodrin breakdown product. To evaluate the importance of cysteine proteases in regulating survival of the newly formed neurons, we administered intracerebroventricular infusions of a caspase inhibitor cocktail (zVAD-fmk, zDEVD-fmk and zLEHD-fmk) over a 2-week period, sufficient to allow for neuronal differentiation, starting 1 week after the epileptic insult. Increased numbers of cells double-labelled with BrdU and neuron-specific nuclear protein (NeuN) marker were detected in the subgranular zone and granule cell layer of the caspase inhibitor-treated rats. Our data indicate that caspase-mediated cell death pathways are active in progenitor cell progeny generated by status epilepticus and compromise survival during neuronal differentiation.     

Maturational sequence of newly generated neurons in the dentate gyrus of the young adult rhesus monkey

The generation of new neurons in the hippocampal dentate gyrus of adult mammals has been characterized in rodents, but the details of this process have not been described in the primate. Eleven young adult rhesus monkeys were given an injection of the DNA synthesis phase marker bromodeoxyuridine (BrdU) and killed at varying survival intervals (2 hours to 98 days). The immature neuronal marker TUC-4 (TOAD/Ulip/CRMP-4) was used to define three stages of morphological maturation. Stage I neurons had small somata and lacked dendrites. Stage II neurons had larger somata and short dendrites. Stage III neurons were similar in size to mature granule cells and had branching dendrites that extended into the molecular layer. Examination of TUC-4-positive immature neurons colabeled with BrdU indicated that stage I neurons first appeared 2 days after BrdU injection, stage II neurons at 14 days, and stage III neurons at 35 days. Electron microscopy of TUC-4-labeled cells showed that stage I cells had ultrastructural features of immature neurons, whereas stage III neurons were similar to mature granule cells and formed synapses in the molecular layer. This suggests that stage III neurons could potentially integrate into the circuitry of the dentate gyrus. This study shows that the maturational sequence for new neurons in the adult monkey is similar to that of the adult rodent; however, maturation takes a minimum of 5 weeks in the monkey, which is substantially longer than what has been reported in rodents.     

An ultrastructural characterization of the newly generated cells in the adult monkey dentate gyrus

Recent studies of adult neurogenesis in the hippocampus have focused on the maturational sequence and on the identification of the neural stem cell in the adult brain. Ultrastructural verification of cell type and marker expression has become increasingly important in this research, yet no standards exist for the identification of adult generated cells in the hippocampus. In this study, six adult rhesus monkeys were used, four of which were given an injection of the DNA-synthesis phase marker bromodeoxyuridine (BrdU) and perfused 2 days, 3 weeks, or 6 weeks later. The ultrastructural features of BrdU labeled cells in the dentate gyrus were determined. The characteristics of the different types of BrdU labeled cells were then used to find similar, but unlabeled, immature cells in tissue routinely prepared for electron microscopy. This enabled optimal characterization of the ultrastructural features of the newly generated cells. The results demonstrate that immature neurons, immature astrocytes, and oligodendrocyte progenitor cells can be reliably distinguished by ultrastructural features, without immunohistochemical processing.     

Coordination of presynaptic and postsynaptic maturation in a zebra finch forebrain motor control nucleus during song learning

While some species of birds retain the ability to learn new songs as adults, many species can only learn during a restricted period when young. Previous studies have suggested that one potential mechanism of such a limited learning period, an alteration in the composition of postsynaptic NMDA receptors, does not competely block further song learning. Here, we examined whether presynaptic function could play a role in the regulation of learning capacity. We first showed that the participation of NMDA receptor NR2B subunits in synaptic currents in the robust nucleus of the arcopallium (RA), a critical location for integration of signals during song learning by young birds, decreases from young birds to adults. Using release-dependent block of postsynaptic NMDA receptors by an open-channel antagonist to assay presynaptic function, we showed that transmitter release at RA synapses from both HVC and the lateral magnocellular nucleus of the anterior nidopallium systematically decreases during the period of song learning, and in adults is about half that of juveniles. Further, activation of postsynaptic NMDA receptors could induce an acute depression of transmitter release, while lack of exposure to a normal learning environment could delay the developmental reduction in transmitter release. These results suggest that regulation of learning capacity may occur in part by coordination of presynaptic and postsynaptic function.     

Seasonal change in neuron size and spacing but not neuronal recruitment in a basal ganglia nucleus in the avian song control system

Neural plasticity in the song control system of seasonally breeding songbirds accompanies seasonal changes in singing behavior. The volume of Area X, a song control nucleus that forms a portion of the avian basal ganglia, is 75% larger in the spring than it is in the fall. The neuronal basis of the seasonal plasticity in Area X is largely unknown, however. We examined neuronal attributes of Area X in wild adult male song sparrows (Melospiza melodia) captured during the spring and the fall after being implanted for 30 days with osmotic pumps containing [3H]thymidine. We measured the volume of Area X from thionin-stained sections, and neuronal density and number, and average area of the soma from sections labeled with an antibody against Hu, a neuron-specific protein. We sampled two neuron classes: "small" neurons that were most likely striatal-like spiny neurons and "large" neurons, which most likely included pallidal-like projection neurons. We also analyzed seasonal patterns of neuronal recruitment to Area X. The average area of the soma and neuronal spacing for both neuronal classes were greater in breeding birds. There was no difference in total neuron number for both neuronal classes between seasons. The average area of the soma and density and number of newly recruited neurons did not vary across seasons. These results demonstrate that seasonal plasticity in Area X includes changes in neuron size and neuronal density, but not changes in the rate at which new neurons are recruited.     

Efficacy of doublecortin as a marker to analyse the absolute number and dendritic growth of newly generated neurons in the adult dentate gyrus

Doublecortin (DCX), a microtubule-associated phosphoprotein, has been recently utilized as a marker of newly born neurons in the adult dentate gyrus (DG). Nonetheless, it is unknown whether DCX exclusively labels newly formed neurons, as certain granule cells with the phenotype of differentiated neurons express DCX. We addressed the authenticity of DCX as a marker of new neurons in the adult DG by quantifying cells that are positive for 5'-bromodeoxyuridine (BrdU), DCX and both BrdU and DCX in hippocampal tissues of adult rats treated with daily injections of BrdU for 12 consecutive days. We provide new evidence that neurons visualized with DCX immunostaining in the adult rat DG are new neurons that are predominantly born during the 12 days before euthanasia. This is confirmed by the robust expression of BrdU in 90% of DCX-positive neurons in the DG of animals injected with BrdU for 12 days. Furthermore, DCX expression is specific to newly generated healthy neurons, as virtually all DCX-positive cells express early neuronal antigens but lack antigens specific to glia, undifferentiated cells or apoptotic cells. As DCX expression is also robust in the dendrites, DCX immunocytochemistry of thicker sections facilitates quantification of the dendritic growth in newly born neurons. Thus, both absolute number and dendritic growth of new neurons that are generated in the adult DG over a 12-day period can be quantified reliably with DCX immunostaining. This could be particularly useful for analysing changes in dentate neurogenesis in human hippocampal tissues as a function of ageing or neurodegenerative diseases.     

Long-term survival and cell death of newly generated neurons in the adult rat olfactory bulb

In the adult rat olfactory bulb, neurons are continually generated from progenitors that reside in the lateral ventricle wall. This study investigates long-term survival and cell death of newly generated cells within the adult olfactory bulb. After injecting rats at 2 months of age with 5-bromodeoxyuridine (BrdU), the newly generated cells were quantified over a period of 19 months. A peak of BrdU-positive cells was reached in the olfactory bulb 1 month after BrdU injection, when all new cells have finished migrating from the ventricle wall. Thereafter, a reduction of BrdU-positive cells to about 50% was observed and it was confirmed by dUTP-nick end-labelling (TUNEL) that progenitors and young neurons undergo programmed cell death. However, cells that survived the first 3 months after BrdU injection persisted for up to 19 months. The majority of the BrdU-positive cells that reach the olfactory bulb differentiate into granule cells, but a small fraction migrate further into the glomerular layer. These newborn cells differentiate more slowly into periglomerular interneurons, with a delay of more than 1 month when compared to the granule cells. The newly generated periglomerular neurons, among them a significant fraction of dopaminergic cells, showed a similar decline in number compared to the granule cell layer and long-term survival for the remaining new neurons of up to 19 months. Rather than replacing old neurons, this data suggests that adult olfactory bulb neurogenesis utilizes the overproduction and turnover of young neurons, which is reminiscent of the cellular dynamics observed during brain development.     

Flash evoked responses in a song control nucleus of the zebra finch (Taeniopygia guttata castanotis)

The song of the zebra finch is facilitated and altered by the presence of a female. Thus, visual information should affect the song system of the bird. Visually evoked potentials can be recorded from n. hyperstriatum ventrale pars caudale (HVc). The long latency of this potential and its variability indicate several processing steps between primary sensory areas of the telencephalon and HVC. Within HVc, under these experimental conditions no interaction between acoustic and visual input could be demonstrated. However, at the dorsal border and within the shelf below HVc, visual information seems to enhance acoustically evoked potentials.     

Migration of newly generated neurons upon ependymally derived radial guide cells in explant cultures of the adult songbird forebrain

The adult songbird forebrain undergoes neuronal production through-out adulthood, with the production of new neurons in discrete regions of the neostriatal ventricular zone. Upon mitogenesis, these new neurons migrate into the subjacent brain parenchyma along radially directed guide fibers. In long-term ventricular zone explant cultures, derived from the higher vocal center of the adult canary, newly migratory neurons were found to associate preferentially with a characteristic substrate cell type. These small, parvonuclear substrate cells formed tightly packed epithelioid sheets, in which ciliated ependymal cells were common, as recognized by both live observation and electron microscopy. A subpopulation of these cells was immunostained by monoclonal antibody 3A7, which preferentially stains the guide fiber network of the adult avian brain. These 3A7⁺ cells included ependymal cells and bipolar radial cells, as well as morphologically defined astrocytes. As they matured in vitro, the 3A7⁺ bipolar radial cells extended long, unbranching fibers, which ultimately traversed the culture substrate. Like ependymal cells, they supported neuronal migration. These cells were likely homologous to radial guide cells in vivo. Thus, neuronal migration in adult avian forebrain culture occurred upon guide cells of ependymal derivation. © 1993 Wiley-Liss, Inc.     

Expression of collapsin response mediator proteins 1, 2 and 5 is differentially regulated in newly generated and mature neurons of the adult olfactory system

Collapsin-response mediator proteins (CRMPs) are highly expressed in the developing brain where they take part in several aspects of neuronal differentiation. CRMPs are still present postnatally, but their function remains speculative in the adult brain. We studied the expression and localization of CRMP1, CRMP2 and CRMP5 in two areas of the nervous system with persistent neurogenesis in adult mice, the olfactory mucosa and the olfactory bulb. In the olfactory mucosa, we have established that CRMP expression is restricted to postmitotic cells of the olfactory neurons lineage. CRMP5 is coexpressed with growth associated protein of 43 kDa (GAP43) in immature olfactory neurons and is down-regulated in olfactory marker protein-positive mature neurons. In contrast, CRMP1 and CRMP2 persist at all stages of differentiation from immature GAP43-positive to fully mature olfactory neurons. In the olfactory bulb, CRMP1, CRMP2 and CRMP5 are abundant in neuronal progenitors of the subependymal layer and in differentiating interneurons. In both areas, the subcellular distribution of CRMP1 or CRMP2 is different in mature vs. immature neurons, suggesting that these proteins are sequentially involved in various cellular events during neuronal lifetime. The variations of CRMP expression following axotomy are consistent with their differential localization and functional involvement in immature vs. mature neurons of the olfactory system. Our data bring new insight to the putative functions of CRMPs within areas of the adult nervous system with permanent neurogenesis, some related to differentiation of newly generated neurons but others occurring in mature neurons with a limited lifespan.     

Ultrastructural evidence of direct synaptic contact of catecholamine terminals with oxytocin-containing neurons in the parvocellular portion of the rat hypothalamic paraventricular nucleus

Ultrastructural evidence of the direct interaction between catecholamine (CA) terminals and oxytocin (OX)-containing neurons in the parvocellular portion of the rat hypothalamic paraventricular nucleus was demonstrated using immunohistochemistry combined with false transmitter (5-hydroxydopamine, 5-OHDA) histochemistry. At the parvocellular portion, 5-OHDA labelled CA terminals make synaptic contact with proximal dendrites or somas of OX-positive cells, suggesting that the ascending CA system monosynaptically regulates the extrahypothalamic OX system.