110 years from the appearance of the first bacteriology treatise and other priorities of Victor Babe?

The mouse Engrailed-2 gene, En-2, appears to be involved in cerebellar pattern formation. Homozygous null mutants for En-2 have abnormal foliation patterns in the posterior half of the cerebellum and there are changes in Purkinje and granule cell gene expression in some posterior folia, possibly reflecting changes in cell identity. We have examined the distribution of spinocerebellar mossy fiber terminals in homozygous En-2hd null mutants to determine if En-2 is involved in regulating the pattern of afferent connectivity in the cerebellum. Spinocerebellar mossy fiber terminals were labeled following WGA-HRP injections in the lumbar region of 5 homozygous En-2hd mutants and 4 heterozygous controls. The distribution of spinocerebellar mossy fiber terminals was consistently altered in lobules VIII and IX of the En-2hd mutants. The principal changes were a reduction in the number of mossy fiber terminal fields in the dorsal aspect of lobule VIII and the dorsal midline field in lobule IX was fused into a single compartment. The results suggest that the deletion of En-2 expression does not transform lobule identity, at least with respect to afferent fiber positional information cues. However, the changes in foliation and afferent connectivity in the En-2 mutant support a broad role for the En-2 gene in cerebellar patterning.     

Compartmentation of the granular layer of the cerebellum

Numerous studies have demonstrated that the cerebellum is highly compartmentalized. In most cases, compartmentation involves the Purkinje cells and the molecular layer, but there is also substantial evidence that the granular layer is subdivided into a large number of highly reproducible modules. We first review the evidence for a modular granular layer. Compartmentation of the granular layer has been revealed both functionally and structurally. First, tactile receptive field mapping has revealed numerous discrete functional modules within the granular layer. The molecular correlates of the receptive fields may be the compartments revealed by histological staining of the cerebellum for several enzymes and antigens. The structural substrate of the receptive fields is the mossy fiber afferent projection map, and anterograde tracing of various mossy fiber projections shows afferent terminals in parasagittal bands within the granular layer that are topographically aligned with the Purkinje cell compartments. Based on this evidence we argue that the cerebellum consists of many hundreds of reproducible structural/functional modules, and that a modular organization is a prerequisite for the efficient parallel processing of information during motor control. The complex organization of the adult granular layer implies elaborate developmental mechanisms. In the second part of the review we consider five developmental models to generate the modular organization of the adult granular layer: 1) the external granular layer is heterogeneous, and its topography translates directly into a modular granular layer; 2) granular layer modules are clones, derived from single external granular layer precursors; 3) modules in the granular layers are a secondary epigenetic response to the compartmentation of the Purkinje cells; 4) modules are secondary to the compartmentation of the afferent terminal fields; 5) modules are sculpted by activity-dependent processes.     

NADPH-diaphorase localization in the CNS and peripheral tissues of the predatory sea-slug Pleurobranchaea californica

The distribution of putative nitric oxide synthase (NOS)-containing cells in the opisthobranch mollusc Pleurobranchaea californica was studied histochemically via NADPH-diaphorase (NADPH-d) reduction of Nitro Blue Tetrazolium (NTB). Whole mounts and cryostat sections were prepared from the central nervous system and peripheral organs, including the buccal muscles, esophagus, salivary glands, foot, mantle, and gills. NADPH-d-positive neurons were localized predominantly to the buccal and pedal ganglia as well as to distinct areas of the cerebropleural and visceral ganglia. A variety of identified neurons were positive for NADPH-diaphorase in various central ganglia, including the metacerebral cells of the cerebropleural ganglion, putative locomotor neurons of the pedal ganglia, and buccal motoneurons. Specific staining was observed only in somata of central neurons, whereas neuropil areas remained unstained. However, NADPH-d-reactive axons were dense in buccal ganglion nerves, whereas peripheral nerves and connectives of other ganglia had few or no NADPH-d positive terminals. In the periphery, NADPH-d activity was detected only in a few neurons of the rhinophore and tentacle ganglia. NADPH-d staining was marked in the salivary glands and gills, but there was no or very little staining in the esophagus, buccal mass, and foot. Histochemical stain production required the presence of both beta-NADPH and NBT; alpha-NADPH could not substitute for beta-NADPH. The inhibitor of NOS, 2,6-dichlorophenol-indophenol, at 10(-3) M, totally abolished NADPH-d-positive staining. The apparent high activity of central NADPH-d contrasts with much lower activity in the ganglia of the related gastropod Tritonia. These data suggest a role for nitric oxide as a signal molecule in the central nervous system of Pleurobranchaea.     

Local injection of kainic acid causes widespread degeneration of NADPH-d neurons and induction of NADPH-d in neurons, endothelial cells and reactive astrocytes

Nitric oxide (NO), a diffusible gas, is a messenger molecule that mediates vascular dilatation and neural transmission. The enzyme nitric oxide synthase (NOS) present in neurons is activated by Ca2+ influx associated with activation of glutamate receptors. Cultured cortical neurons containing NOS are selectively vulnerable to injury by kainic acid (KA). However, the relationship between NOS neurons and excitotoxicity under in vivo conditions is not entirely clear. In the present study, we examined the time course and spatial distribution of changes in NOS neurons caused by an intracortical microinjection of KA in adult rats. NADPH-diaphorase (NADPH-d) histochemistry was used as a marker for NOS and the neuronal changes were correlated with changes in glial cells and endothelial cells. We demonstrated a rapid loss of NADPH-d neurons in the lesion center and degeneration of NADPH-d neurons and nerve terminals throughout ipsilateral cortex and hippocampus; the striatal neurons appeared to be unaffected. Subsequent to cortical neuronal degeneration, new NADPH-d activity appeared in proliferative reactive astrocytes and in endothelial cells at lesion periphery, and in neuronal groups at lesion periphery, in ipsilateral entorhinal cortex and bilateral hippocampus. These findings indicate that neurons expressing NADPH-d in cerebral cortex and hippocampus are selectively vulnerable to KA toxicity in vivo. The subsequent induction of NOS in neural and non-neural cells may be regarded as an adaptive response to the kainate-induced brain lesion.     

Histochemical demonstration of neuronal nitric oxide synthase during development of mouse respiratory tract

Several studies, including histochemical ones, have indicated that nitric oxide (NO) of endothelial origin may be related to the pulmonary vasodilation that occurs at birth. Since no histologic studies have been done of the possible parallel perinatal increase in production of neuronal NO synthase (nNOS) by pulmonary nerve plexuses, we investigated the distribution of nNOS in fetal, neonatal, and adult mouse lung. Lungs from mice aged 13 d gestation to 6 d after birth and lungs of adults were studied through histochemistry for nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) activity and immunocytochemistry. Both techniques gave almost similar results in relation to time of appearance, distribution, and frequency of neural structures positive for NADPH-d and NOS. NADPH-d staining was also applied to whole mounts of developing and adult tracheae. Staining was found from gestational days 13 to 15 onward in a small portion of the neuronal population. In all stages studied, NADPH-d/NOS staining was found in neuron cell bodies in the hilar region and bronchiolar wall, as well as in neuronal processes. Labeled terminal nerve fibers with varicosities were more frequent in pulmonary blood vessels than in airways. In tracheae, similar NADPH-d/NOS-positive nerve plexuses were found. The presence of nNOS in fetal and neonatal mouse respiratory tract suggests that neurally derived NO must play a role in developing lung physiology. However, because no perinatal increase in the number or intensity of staining of nNOS-positive nerve structures was seen, no apparent relation between neural NO and vasodilation can be established at birth.     

Cadherin-8 protein expression in gray matter structures and nerve fibers of the neonatal and adult mouse brain

The topological distribution of mouse cadherin-8 protein in the neonatal and adult mouse brain was studied immunohistochemically using a rabbit antiserum. Cadherin-8 expression was restricted to several areas in neonatal brains constituting particular neural circuits, i.e. the limbic system, the basal ganglia-thalamocortical circuit, and the cerebellum and related nuclei. In addition, the nerve fibers linking some of the cadherin-8-positive areas, i.e. the habenulo-interpeduncular tract, decussation of the dorsal tegmentum, the medial longitudinal fasciculus, transverse pontine fibers, the brachium conjunctivum and the inferior cerebellar peduncle were cadherin-8 positive, as were the spinal tract of the trigeminal nerve, oculomotor nerve, facial nerve and trigeminal nerve. Cadherin-8 expression also showed a patch-like distribution in the intermediate gray layer of the superior colliculus, resembling acetylcholinesterase-rich patches in allocation. Segmentally organized cadherin-8-positive areas were found in the neonatal cerebellar Purkinje cell layer. Some nuclei and fibers in the brainstem and cerebellum, expressing cadherin-8 at neonatal stages, were also stained in the adult mouse brain. These findings suggest that cadherin-8 is involved in the formation of particular neural circuits by connecting areas expressing this molecule with positive nerve fibers, and indicate its possible implication in subdivisional organization in the superior colliculus and cerebellum.     

Colocalization of nitric oxide synthase and some neurotransmitters in the intramural ganglia of the guinea pig urinary bladder

The distribution of nitrergic neurons was investigated by using nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry and nitric oxide synthase (NOS) immunohistochemistry in wholemount preparations of the urinary bladder in guinea pigs. Both NADPH-d+ and NOS+ neurons were located predominantly in the bladder base. Double staining showed that 70.9% of the NADPH-d+ neurons coexpressed NOS. Acetylcholinesterase histochemistry revealed that a majority of the intramural neurons were reactive, and about half of them (51.4%) were double labelled for NOS. Tyrosine hydroxylase-positive neurons were also distributed mainly in the bladder base but in a neuronal population that was separate from the preponderant NADPH-d+ neurons. Vasoactive intestinal polypeptide immunoreactivity was also detected in the some of intramural ganglion cells, in which 21.3% of them coexpressed NADPH-d. Calcitonin gene-related peptide and substance P immunoreactivities were confined to nerve fibers, often in close association with NADPH-d+ cells or extended along the blood vessels. These results have demonstrated the colocalization of NADPH-d and NOS in the majority of intramural ganglion cells. Many of the nitrergic neurons are apparently cholinergic, indicating that they are parasympathetic postganglionic neurons, and this underscores NO as the major neuromodulator in the parasympathetic nerves in the bladder walls. The localization of vasoactive intestinal polypeptide in nitrergic neurons suggests that the peptide may complement NO for regulation of micturition reflex. The close relationship of NADPH-d-reactive intramural neurons with calcitonin gene-related peptide and substance P fibers, most probably derived from dorsal root ganglion cells, suggests that NO released from the local neurons may exert its influence on the sensory neural pathways in the urinary bladder.     

Synchronization of golgi and granule cell firing in a detailed network model of the cerebellar granule cell layer

The granular layer of the cerebellum has a disproportionately large number of excitatory (granule cells) versus inhibitory neurons (Golgi cells). Its synaptic organization is also unique with a dense reciprocal innervation between granule and Golgi cells but without synaptic contacts among the neurons of either population. Physiological recordings of granule or Golgi cell activity are scarce, and our current thinking about the way the granular layer functions is based almost exclusively on theoretical considerations. We computed the steady-state activity of a large-scale model of the granular layer of the rat cerebellum. Within a few tens of milliseconds after the start of random mossy fiber input, the populations of Golgi and granule cells became entrained in a single synchronous oscillation, the basic frequency of which ranged from 10 to 40 Hz depending on the average rate of firing in the mossy fiber population. The long parallel fibers ensured, through alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-mediated synapses, a coherent excitation of Golgi cells, while the regular firing of each Golgi cell synchronized all granule cells within its axonal radius through transient activation of their gamma-aminobutyric acid-A (GABAA) receptor synapses. Individual granule cells often remained silent during a few successive oscillation cycles so that their average firing rates, which could be quite variable, reflected the average activities of their mossy fiber afferents. The synchronous, rhythmic firing pattern was robust over a broad range of biologically realistic parameter values and to parameter randomization. Three conditions, however, made the oscillations more transient and could desynchronize the entire network in the end: a very low mossy fiber activity, a very dominant excitation of Golgi cells through mossy fiber synapses (rather than through parallel fiber synapses), and a tonic activation of granule cell GABAA receptors (with an almost complete absence of synaptically induced inhibitory postsynaptic currents). These three conditions were associated with a reduction in the parallel fiber activity, and synchrony could be restored by increasing the mossy fiber firing rate. The model predicts that, under conditions of strong mossy fiber input to the cerebellum, Golgi cells do not only control the strength of parallel fiber activity but also the timing of the individual spikes. Provided that their parallel fiber synapses constitute an important source of excitation, Golgi cells fire rhythmically and synchronized with granule cells over large distances along the parallel fiber axis. According to the model, the granular layer of the cerebellum is desynchronized when the mossy fiber firing rate is low.     

Morphology and histochemistry of the rabbit pancreatic innervation

Stimulation of extrinsic nerves markedly alters pancreatic endocrine and exocrine secretion, yet little is known of the neurochemical organization and physiologic roles of specific neural pathways within the pancreas. Here we report histochemical staining for acetylcholinesterase (AChE), NADPH-diaphorase (NADPH-d), nitric oxide synthase (NOS), and several neuropeptides to identify the neurotransmitter content of rabbit pancreatic nerves. An extensive network of AChE-positive nerve fibers was found throughout the islets, acini, ducts, ganglia, and blood vessels. All pancreatic neurons were AChE positive, two thirds were NADPH-d positive, and many were NOS positive. Ganglia in the head/neck region were connected to the duodenal myenteric plexus by AChE- and NADPH-d-positive fibers, and NADPH-d-positive pancreatic neurons appeared to send processes toward both the duodenum and pancreas. Many pancreatic neurons were vasoactive intestinal peptide (VIP) positive, and VIP nerve terminals were abundant in ganglia, acini, islets, and ducts. Pituitary adenylate cyclase-activating peptide (PACAP-38)-positive fibers also were observed within acini and passing through ganglia. Substance P (SP)-, calcitonin gene-related peptide (CGRP)-, and dopamine beta-hydroxylase (DBH)-positive fibers were abundant along blood vessels and ducts, and varicose fibers were observed in pancreatic ganglia. Fine galanin-positive fibers were also occasionally observed running with blood vessels and through ganglia. Thus the rabbit pancreas receives a dense, diverse innervation by cholinergic, adrenergic, and peptidergic nerves and cholinergic pancreatic neurons, most also containing VIP or NOS or both, appear to innervate both endocrine and exocrine tissue, and may mediate local communication between the duodenum and pancreas.     

Disregulation of ocular morphogenesis by lens-specific expression of FGF-3/int-2 in transgenic mice

Nerve growth factor signal transduction mediated through the trk receptor has been implicated in neuronal growth, differentiation, and survival. In this study, we examined the effects of gestational exposure to the developmental neurotoxicant methylmercury (CH3Hg) on the ontogeny of trk-immunoreactivity (IR). Long-Evans dams were dosed on gestational days 6-15 (p.o.) with 0, 1, or 2 mg/kg CH3Hg dissolved in saline. Pups were sacrificed and perfused with buffered paraformaldehyde on postnatal days (PND) 1, 4, 10, 21 and 85. The brains were sectioned sagitally, Nissl-stained or stained immunohistochemically for trk receptors or glial fibrillary acidic protein (GFAP), and examined throughout the medial to lateral extent of the brain. The greatest density of IR in neural cell bodies was seen in the olfactory bulb, hippocampus, cerebral, and cerebellar cortex, striatum, septum, nucleus basalis, inferior colliculus, pons, and brain stem nuclei. trk IR was not limited to nerve cell bodies, with prominent axonal and dendritic staining in the brainstem, neocortex, hippocampus, cerebellum, and olfactory tract. The regional pattern of trk IR varied in an age-dependent manner. In controls, trk-like IR appeared to peak in most regions between PND4-10 and decreased dramatically after PND21. This age-related difference in trk IR was supported by western blot analysis of PND10 and adult neocortex. This reduced and more adult-like pattern of trk IR was apparent on PND21 with some persistent trk-like IR in the olfactory bulb, hippocampus, neocortex, cerebellum and basal forebrain. In contrast to the normal regional patterns of trk IR, CH3Hg produced a dose-related decrease in trk-like IR in the absence of overt maternal toxicity or neonatal toxicity. CH3Hg-induced decreases in trk-like IR were especially apparent during the early postnatal period when trk IR was the greatest. The effects of CH3Hg exposure were restricted regionally, with the largest decrease in trk-like IR apparent in cortical regions, basal forebrain nuclei, and brain stem nuclei. Subsequent to the effects of CH3Hg on cortical trk-like IR were alterations in the development of cortical laminae on PND10 and 21 of neocortex. These alterations were characterized by quantifiable decreases in cell density, cell size and the widths of the layers of posterior neocortex. Not all of the CH3Hg-induced effects were characterized by decreased trk-like IR. Robust increases in trk IR in glial cells in the corpus callosum and brain stem were observed coincident with increased GFAP IR in cells of similar morphology. The present results localize the cellular and regional ontogeny of trk and suggest that developmental exposure to CH3Hg alters the normal ontogeny of this trophic factor receptor which may be associated with the developmental neurotoxicity of this chemical.     

Subcellular fractionation on Percoll gradient of mossy fiber synaptosomes: morphological and biochemical characterization in control and degranulated rat hippocampus

A method for preparation of hippocampal mossy fiber synaptosomes directly from the postnuclear pellet is presented. This method represents an adaptation of that previously described for the isolation of synaptosomes by centrifugation through Percoll gradients directly from the supernatant fraction. We have characterized by electron microscopy two fractions, PII and PIII, enriched in mossy fiber synaptosomes; fraction PIII had 75% mossy fiber synaptosomes with well-preserved morphology (large size 3 microns, complex morphology, high synaptic vesicle density, multisynapses), whereas fraction PII contained 12%. These fractions were enriched in lactate dehydrogenase activity indicating that the integrity of synaptosomes was preserved. Compared with the other synaptosomal fractions, these fractions showed greater levels of dynorphin A (1-8) immunoreactivity and endogenous zinc, which are particularly concentrated in hippocampal mossy fiber terminals. Furthermore, we prepared synaptosomes from adult hippocampus after neonatal irradiation, which destroys the majority of granule cells and associated mossy fibers. The levels of dynorphin and zinc decreased by 88 and 70% in fraction PII and by 95 and 90%, respectively, in PIII. These results suggest that the rapid Percoll procedure is convenient for the purification of mossy fiber synaptosomes.     

Relation between psychiatric disorder and abnormal illness behaviour in patients undergoing operations for cervical discectomy

The role of nitric oxide (NO) in pathophysiology of urethral obstruction in male guinea pig was investigated by using nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry. In normal and sham-operated control animals, NADPH-d reactivity in the ventral horn motoneurons at L5-L6 and S1-S2 segments of spinal cord was barely detectable or virtually absent. In animals receiving urethral ligation and killed at 6 h after operation, NADPH-d reactivity in the ventral horn motoneurons was comparable to that of control animals. At 12 h, NADPH-d reactivity in the same cells began evident and was markedly enhanced in animals killed at 24 and 48 h. In order to verify whether the increased NADPH-d reactivity was linked to neuronal death, some sections of the lumbosacral spinal cord from urethral obstructed animals were stained in Nissl staining. There was no sign of cell death or atrophy of the ventral horn neurons. Present results suggest the plasticity of NADPH-d in ventral horn neurons which is readily upregulated by urethral ligation. The enhanced NADPH-d reactivity would imply increased nitric oxide synthase (NOS) activity and consequently generation of higher levels of NO in ventral horn neurons. Such alteration maybe involved in distension-induced urethral relaxation in the external urethral sphincter following urethral ligation.     

Genetic polymorphism of drug metabolizing enzymes: new mutations in CYP2D6 and CYP2A6 genes in Japanese]

The postnatal development of serotonin (5HT)-immunoreactive axons was studied in the visual cortex of the cerebrum in both normal and microcephalic rats during early postnatal and young adult stages. Severe microcephaly in rat offspring was induced by prenatal exposure to methylazoxymethanol acetate (MAM), an anti-mitotic agent, on day 15 of gestation. From postnatal day 1 (PND 1) to PND 5, fine and short 5HT fibers were irregularly dispersed throughout the occipital cortex in both the control and MAM-treated rats (MAM-rats). A conspicuous aggregation of dot-like 5HT terminals was found in controls, but not in MAM-rats, in a shallow layer of the dorsomedial region of the occipital cortical plate. On PND 7, such an aggregation of 5HT terminals was found in both groups. The density of the aggregation increased up to PND 9, but then decreased gradually, finally becoming unrecognizable at around PND 15 in both groups. MAM-rats, however, always showed hyperaggregation of 5HT terminals when compared with controls on the same PND. The density of 5HT fibers gradually increased, and finally made up a network-like formation at PND 28 in both groups, its pattern was essentially identical to the abnormal distribution of 5HT fibers during the later stage. As a result, the network-like formation of 5HT fibers in the MAM-rats at PND 28 was markedly twisted and somewhat hyperdense. In Nissl-stained preparations from PND 9 to 15, the 5HT terminal aggregation in the control rats was precisely confined to the newly forming layer IV of the visual cortex. In the MAM-rats, on the other hand, the aggregation of 5HT terminals was not associated with a specific cortical layer because of a disarranged cytoarchitecture of the microcephaly.     

A histochemical study of iron-positive cells in the developing rat brain

The establishment of normal iron levels in the neonatal brain is critical for normal neurological development. Studies have shown that both iron uptake and iron concentration in the brain are relatively high during neonatal development. This histochemical study was undertaken to determine the pattern of iron development at the cellular level in the rat forebrain. Iron-stained cells were observed as early as postnatal day (PND) 3, which was the earliest time point examined. At PND 3, there were four major foci of iron-containing cells: the subventricular zone and three areas within the subcortical white matter. These latter foci are associated with myelinogenic regions. The blood vessels were prominently stained for iron throughout the brain. At PND 7, as in PND 3, the majority of the iron-containing cells were in white matter. However, there were also patches of iron staining located specifically in the layer IV of the somatosensory cortex. These cortical patches were no longer visible by PND 14. At PND 14, numerous iron-stained cells were dispersed throughout white matter regions and the tanycytes aligning the third ventricle were prominently stained. The blood vessel staining was less prominent than at earlier time periods. By PND 28, the adult pattern of iron staining was emerging. Iron-stained cells were aligned in rows in white matter and had an apparent preference for a location near blood vessels. This clustering of iron-positive cells around blood vessels gave the white matter a "patchy" appearance. The pattern of development, cell distribution, and morphological appearance of the iron-stained cells are consistent with that reported for oligodendrocytes. That iron-positive cells in the neonate may be oligodendrocytes is consistent with the reports for iron staining in adult brains. The recent reports that oligodendrocytes are highly susceptible to oxidative damage would be consistent with the high iron levels found in these cells. These results indicate that oligodendrocytes play a major role in the development of iron homeostasis in the brain. The role of iron in oligodendrocytes may be associated with metabolic demands of myelinogenesis, including cholesterol and fatty acid synthesis. However, these cells may be a morphologically similar but functionally distinct subset of oligodendrocytes whose function is to regulate the availability of iron in the brain.     

Localization of NADPH diaphorase in the thoracolumbar and sacrococcygeal spinal cord of the dog

The distribution of NADPH-d activity and NOS-immunoreactivity in the spinal cord of the dog was studied to evaluate the role of nitric oxide in lumbosacral afferent and spinal autonomic pathways. At all levels of the spinal cord examined, NADPH-d staining and NOS-immunoreactivity were present in neurons and fibers in the superficial dorsal horn, dorsal commissure and in neurons around the central canal. Sympathetic preganglionic neurons in the rostral lumbar segments identified by choline acetyl transferase (ChAT) immunoreactivity exhibited prominent NADPH-d and and NOS-immunoreactive staining; whereas the ChAT-immunoreactive parasympathetic preganglionic neurons in the sacral segments were not stained. The most prominent NADPH-d activity in the sacral segments occurred in fibers extending form Lissauer's tract through lamina I along the lateral edge of the dorsal horn to the region of the sacral parasympathetic nucleus. These fibers were prominent in the S1-S3 segments but not in adjacent segments (L5-L7 and Cx1 or in thoracolumbar segments. The NADPH-d fibers were not NOS-immunoreactive, but did overlap with a prominent fiber bundle containing vasoactive intestinal polypeptide immunoreactivity in the sacral spinal cord. These results indicate that nitric oxide may function as a transmitter in thoracolumbar sympathetic preganglionic neurons, but not in sacral parasympathetic preganglionic neurons. The functional significance of the NADPH-d positive, NOS-negative fiber bundle on the lateral edge of the sacral dorsal horn remains to be determined. However, based on anatomical studies in other species it seems reasonable to speculate that the fiber tract represents, in part, visceral afferent projections to the sacral parasympathetic nucleus.     

GABAergic cells are the major postsynaptic targets of mossy fibers in the rat hippocampus

Dentate granule cells communicate with their postsynaptic targets by three distinct terminal types. These include the large mossy terminals, filopodial extensions of the mossy terminals, and smaller en passant synaptic varicosities. We examined the postsynaptic targets of mossy fibers by combining in vivo intracellular labeling of granule cells, immunocytochemistry, and electron microscopy. Single granule cells formed large, complex "mossy" synapses on 11-15 CA3 pyramidal cells and 7-12 hilar mossy cells. In contrast, GABAergic interneurons, identified with immunostaining for substance P-receptor, parvalbumin, and mGluR1a-receptor, were selectively innervated by very thin (filopodial) extensions of the mossy terminals and by small en passant boutons in both the hilar and CA3 regions. These terminals formed single, often perforated, asymmetric synapses on the cell bodies, dendrites, and spines of GABAergic interneurons. The number of filopodial extensions and small terminals was 10 times larger than the number of mossy terminals. These findings show that in contrast to cortical pyramidal neurons, (1) granule cells developed distinct types of terminals to affect interneurons and pyramidal cells and (2) they innervated more inhibitory than excitatory cells. These findings may explain the physiological observations that increased activity of granule cells suppresses the overall excitability of the CA3 recurrent system and may form the structural basis of the target-dependent regulation of glutamate release in the mossy fiber system.     

L-Type calcium channels are required for one form of hippocampal mossy fiber LTP

The requirement of postsynaptic calcium influx via L-type channels for the induction of long-term potentiation (LTP) of mossy fiber input to CA3 pyramidal neurons was tested for two different patterns of stimulation. Two types of LTP-inducing stimuli were used based on the suggestion that one of them, brief high-frequency stimulation (B-HFS), induces LTP postsynaptically, whereas the other pattern, long high-frequency stimulation (L-HFS), induces mossy fiber LTP presynaptically. To test whether or not calcium influx into CA3 pyramidal neurons is necessary for LTP induced by either pattern of stimulation, nimodipine, a L-type calcium channel antagonist, was added during stimulation. In these experiments nimodipine blocked the induction of mossy fiber LTP when B-HFS was given [34 +/- 5% (mean +/- SE) increase in control versus 7 +/- 4% in nimodipine, P < 0.003]; in contrast, nimodipine did not block the induction of LTP with L-HFS (107 +/- 10% in control vs. 80 +/- 9% in nimodipine, P > 0.05). Administration of nimodipine after the induction of LTP had no effect on the expression of LTP. In addition, B- and L-HFS delivered directly to commissural/associational fibers in stratum radiatum failed to induce a N-methyl--aspartate-independent form of LTP, obviating the possibility that the presumed mossy fiber LTP resulted from potentiation of other synapses. Nimodipine had no effect on calcium transients recorded from mossy fiber presynaptic terminals evoked with the B-HFS paradigm but reduced postsynaptic calcium transients. Our results support the hypothesis that induction of mossy fiber LTP by B-HFS is mediated postsynaptically and requires entry of calcium through L-type channels into CA3 neurons.     

Tetracyclines and calcified tissues

Neuronal somata in the rat kidney are very often part of ganglionated plexus and contain nitric oxide synthase (NOS). Examining serial 100 microns slices of whole kidneys, we identified three subpopulations of neuronal somata by: (a) staining for NADPH-diaphorase (NADPH-d) histochemistry followed by the demonstration of dopamine beta-hydroxylase (DBH) by immunoperoxidase, and (b) staining for DBH by immunofluorescence followed by the demonstration of NADPH-d histochemical activity. The largest subpopulation of neuronal somata displayed both DBH immunoreactivity and NADPH-d histochemical activity. The second largest group of somata showed NADPH-d activity only. A small group of neuronal somata showed only DBH immunoreactivity. The presence of catecholaminergic characteristics in NOS-containing neuronal somata is unusual and raises the question as to their origin. Their heterogeneity suggests different functions for the different subpopulations.     

Target-specific expression of presynaptic mossy fiber plasticity

Mossy fiber synaptic transmission at hippocampal CA3 pyramidal cells and interneurons was compared in rat brain slices to determine whether mossy terminals are functionally equivalent. Tetanic stimulation of mossy fibers induced long-term potentiation in pyramidal neurons but was either without effect or it induced depression at synapses onto interneurons. Unlike transmission onto pyramidal neurons, transmission onto interneurons was not potentiated after adenosine 3',5'-monophosphate (cAMP) activation. Furthermore, metabotropic glutamate receptor depression of transmission onto interneurons did not involve cAMP-dependent pathways. Thus, synaptic terminals arising from a common afferent pathway do not function as a single compartment but are specialized, depending on their postsynaptic target.     

Idiotype usage by polyclonally activated B cells in experimental autoimmunity and infection

The effects of prenatal X-irradiation (0.3, 0.6, 1.2 or 1.8 Gy) on the hippocampal development were examined at six weeks of age in rats. The laminar structure of the hippocampus was deranged in the rats exposed to 0.6 Gy or more. Pyramidal cells in the CA-3 region were more susceptible than those in the CA-1 region. Aberrant mossy fiber terminals were observed in the stratum oriens of the CA-3 region (infrapyramidal mossy fibers) in rats exposed to 0.3 Gy or more.