Disruptive lysosomal-metabolic signaling and neurodevelopmental deficits that precede Purkinje cell loss in a mouse model of Niemann-Pick Type-C disease

Purkinje cell (PC) loss occurs at an early age in patients and animal models of Niemann-Pick Type C (NPC), a lysosomal storage disease caused by mutations in the Npc1 or Npc2 genes. Although degeneration of PCs occurs early in NPC, little is known about how NPC1 deficiency affects the postnatal development of PCs. Using the Npc1^nmf164 mouse model, we found that NPC1 deficiency significantly affected the postnatal development of PC dendrites and synapses. The developing dendrites of Npc1^nmf164 PCs were significantly deficient in mitochondria and lysosomes. Furthermore, anabolic (mTORC1) and catabolic (TFEB) signaling pathways were not only perturbed but simultaneously activated in NPC1-deficient PCs, suggesting a loss of metabolic balance. We also found that mice with conditional heterozygous deletion of the Phosphatase and Tensin Homolog Deleted on Chromosome 10 gene (Pten-cHet), an inhibitor of mTORC1, showed similar early dendritic alterations in PCs to those found in Npc1-deficient mice. However, in contrast to Npc1^nmf164 mice, Pten-cHet mice exhibited the overactivation of the mTORC1 pathway but with a strong inhibition of TFEB signaling, along with no dendritic mitochondrial reductions by the end of their postnatal development. Our data suggest that disruption of the lysosomal-metabolic signaling in PCs causes dendritic and synaptic developmental deficits that precede and promote their early degeneration in NPC.

Retinoic acid treatment recruits macrophages and increases axonal regeneration after optic nerve injury in the frog Rana pipiens

Retinoic acid (RA) plays major roles during nervous system development, and during regeneration of the adult nervous system. We have previously shown that components of the RA signaling pathway are upregulated after optic nerve injury, and that exogenous application of all-trans retinoic acid (ATRA) greatly increases the survival of axotomized retinal ganglion cells (RGCs). The objective of the present study is to investigate the effects of ATRA application on the macrophages in the optic nerve after injury, and to determine whether this affects axonal regeneration. The optic nerve was crushed and treated with PBS, ATRA and/or clodronate-loaded liposomes. Nerves were examined at one and two weeks after axotomy with light microscopy, immunocytochemistry and electron microscopy. ATRA application to the optic nerve caused transient increases in the number of macrophages and microglia one week after injury. The macrophages are consistently labeled with M2-type markers, and have considerable phagocytic activity. ATRA increased ultrastructural features of ongoing phagocytic activity in macrophages at one and two weeks. ATRA treatment also significantly increased the numbers of regenerating GAP-43-labeled axons. Clodronate liposome treatment depleted macrophage numbers by 80%, completely eliminated the ATRA-mediated increase in axonal regeneration, and clodronate treatment alone decreased axonal numbers by 30%. These results suggest that the success of axon regeneration is partially dependent on the presence of debris-phagocytosing macrophages, and that the increases in regeneration caused by ATRA are in part due to their increased numbers. Further studies will examine whether macrophage depletion affects RGC survival.

Increased interactions and engulfment of dendrites by microglia precede Purkinje cell degeneration in a mouse model of Niemann Pick Type-C

Niemann Pick Type-C disease (NPC) is an inherited lysosomal storage disease (LSD) caused by pathogenic variants in the Npc1 or Npc2 genes that lead to the accumulation of cholesterol and lipids in lysosomes. NPC1 deficiency causes neurodegeneration, dementia and early death. Cerebellar Purkinje cells (PCs) are particularly hypersensitive to NPC1 deficiency and degenerate earlier than other neurons in the brain. Activation of microglia is an important contributor to PCs degeneration in NPC. However, the mechanisms by which activated microglia promote PCs degeneration in NPC are not completely understood. Here, we are demonstrating that in the Npc1^nmf164 mouse cerebellum, microglia in the molecular layer (ML) are activated and contacting dendrites at early stages of NPC, when no loss of PCs is detected. During the progression of PCs degeneration in Npc1^nmf164 mice, accumulation of phagosomes and autofluorescent material in microglia at the ML coincided with the degeneration of dendrites and PCs. Feeding Npc1^nmf164 mice a western diet (WD) increased microglia activation and corresponded with a more extensive degeneration of dendrites but not PC somata. Together our data suggest that microglia contribute to the degeneration of PCs by interacting, engulfing and phagocytosing their dendrites while the cell somata are still present.

Optic nerve injury upregulates retinoic acid signaling in the adult frog visual system

Retinoic acid (RA) is important during development, in neuronal plasticity, and also in peripheral nervous system regeneration. Here we use the frog visual system as a model to investigate the changes in RA signaling that take place after axonal injury to the central nervous system. Immunocytochemistry was used to localize different components of RA signaling within sections of the retina and optic tectum, namely, the synthetic enzyme retinaldehyde dehydrogenase (RALDH), the RA binding proteins CRABPI and II, the retinoic acid receptors RARα, β and γ, and finally the catabolic enzyme CYP26A1. The levels of these proteins were quantified in extracts of retina and tectum using Western blotting. Animals were studied at 1 week, 3 weeks and 6 weeks after optic nerve transection. At the latter time point the RGC axons were re-entering the optic tectum. All the components of RA signaling were present at low to moderate levels in retinas and tecta of control, unoperated animals. In retina, soon after optic nerve injury there was a large increase in RALDH, some increase in the CRABPs, and a large increase in RGC RARβ and (expression. These increases continued as the RGC axons were regenerating, with the addition of later RARα expression at 6 weeks. At no stage did CYP26A1 expression significantly change. In the tectum the levels of RALDH increased after axotomy and during regrowth of axons (3 weeks), then decreased at 6 weeks, at which time the levels of CYP26A1 increased. Axotomy did not cause an immediate increase in tectal RAR levels but RARα and RARβ increased after 3 weeks and RARγ only after 6 weeks. These results are consistent with RA signaling playing an important role in the survival and regeneration of frog RGCs.

Ciliary neurotrophic factor and fibroblast growth factor increase the speed and number of regenerating axons after optic nerve injury in adult Rana pipiens

Neurotrophins such as ciliary neurotrophic factor (CNTF) and brain-derived neurotrophic factor (BDNF) and growth factors such as fibroblast growth factor (FGF-2) play important roles in neuronal survival and in axonal outgrowth during development. However, whether they can modulate regeneration after optic nerve injury in the adult animal is less clear. The present study investigates the effects of application of these neurotrophic factors on the speed, number, and distribution of regenerating axons in the frog Rana pipiens after optic nerve crush. Optic nerves were crushed and the factors, or phosphate-buffered saline, were applied to the stump or intraocularly. The nerves were examined at different times after axotomy, using anterograde labeling with biotin dextran amine and antibody against growth-associated protein 43. We measured the length, number, and distribution of axons projecting beyond the lesion site. Untreated regenerating axons show an increase in elongation rate over 3 weeks. CNTF more than doubles this rate, FGF-2 increases it, and BDNF has little effect. In contrast, the numbers of regenerating axons that have reached 200 μm at 2 weeks were more than doubled by FGF-2, increased by CNTF, and barely affected by BDNF. The regenerating axons were preferentially distributed in the periphery of the nerve; although the numbers of axons were increased by neurotrophic factor application, this overall distribution was substantially unaffected.

Glial cells in peripheral nerves of the cockroach, Periplaneta americana

The ultrastructural organization and the junctional complexes of peripheral nerves have been investigated in the cockroach Periplaneta americana. Nerve 5 is surrounded by a layer of connective tissue, the neural lamella, beneath which is a layer of perineurial glial cells wrapping the axons. Adjacent perineurial cells are joined to one another by septate, gap and tight junctions. Septate and gap junctions were observed in freeze-fracture replicas of main trunk nerve 5. Septate junctions were found as rows of PF particles mainly in perineurial cell membranes. Gap junctions exhibited EF macular aggregates in perineurial and subperineurial glial cells. During incubations in vivo with extracellularly applied ionic lanthanum, the lanthanum did not penetrate beyond the perineurium. Where nerve 5 branches and contacts the muscle, lanthanum penetrated freely between the muscle fibres and the nerve branches. In small peripheral branches where the axons are surrounded by single a glial layer, lanthanum is unable to penetrate to the axolemma.

Up-regulation of brain-derived neurotrophic factor by application of fibroblast growth factor-2 to the cut optic nerve is important for long-term survival of retinal ganglion cells

Application of basic fibroblast growth factor (FGF-2) to the optic nerve after axotomy promotes the survival of retinal ganglion cells (RGCs) in the frog Rana pipiens and results in a rapid up-regulation of brain-derived neurotrophic factor (BDNF) and TrkB synthesis by the RGCs. Here we investigate whether this up-regulation is maintained over the long term and whether it is required for FGF-2's survival effect. At 6 weeks after axotomy and FGF-2 treatment, we found more RGCs immunopositive for BDNF protein and higher intensity of BDNF and TrkB immunostaining, accompanied by increases in BDNF and TrkB mRNA in RGCs. Application of fluorescently labeled siRNA targeted against BDNF to the cut RGC axons showed that it was transported to the cell bodies. Axonal siRNA treatment eliminated the increases in BDNF immunostaining and mRNA that were induced by FGF-2 and had no effect on TrkB mRNA. This reduction in BDNF synthesis by siRNA greatly reduced the long-term survival effect of FGF-2 on RGCs. This, taken together with previous results, suggests that, although FGF-2 may initially activate survival pathways via ERK signaling, its main long-term survival effects are mediated via its up-regulation of BDNF synthesis by the RGCs.

Changes in nNOS and NADPH diaphorase in frog retina and tectum after axotomy and FGF-2 application

We have shown previously that application of fibroblast growth factor-2 (FGF-2) to the cut optic nerve of the frog, Rana pipiens, augments the survival of retinal ganglion cells (RGCs). In this study, we examine the effects of axotomy and FGF-2 treatment upon the distribution of nitric oxide synthase (NOS) and NADPH diaphorase (NADPH-d) activity in the frog retina and tectum. We find that NOS and NADPH-d are largely absent from RGCs but present in amacrine neurons and in retinorecipient tectal layers. Axotomy alone has little effect on NOS expression or diaphorase activity, apart from slightly increasing the levels of expression in a subpopulation of amacrine cells that arborize in the On sublamina of the inner plexiform layer. FGF-2 application to the optic nerve down-regulates NOS expression and activity in the retina and up-regulates it in the tectum, particularly in retinorecipient layers. Electron microscopy of the optic nerve and neurofilament immunostaining of the tectum suggests that FGF-2 treatment increases the number of regenerating retinal axons arriving at the tectum. The effects in the retina and tectum are probably indirect, that in the retina being due to retrograde signaling from RGCs to amacrine neurons, and that in the tectum being due to re-induction of NOS expression in tectal neurons by the arrival of regenerating axons. At this stage, it appears unlikely that these changes in NOS play a role in the FGF-2's survival effect on RGCs.

Fibroblast growth factor 2 applied to the optic nerve after axotomy up-regulates BDNF and TrkB in ganglion cells by activating the ERK and PKA signaling pathways

Application of basic fibroblast growth factor (FGF-2) to the optic nerve after axotomy promotes the survival of retinal ganglion cells (RGCs) in the frog, Rana pipiens. Here we investigate the effects of FGF-2 treatment upon the synthesis of brain-derived neurotrophic factor (BDNF) and its receptor, tyrosine receptor kinase B (TrkB). Axotomy alone increased the amounts of BDNF and TrkB mRNA in RGCs after 1 week and 48 h, respectively; FGF-2 treatment to the nerve accelerated and increased this up-regulation of both. FGF-2 also increased the amounts of phosphorylated cAMP response element binding protein (pCREB) in the retina. Blocking extracellular-regulated kinase (ERK) activation with PD98059 or U0126 prevented the FGF-2-induced up-regulation of BDNF transcription but had no effect on TrkB. However, blocking protein kinase A (PKA) with H89 or Rp-8-Cl-cAMPS reduced the up-regulation of both BDNF and TrkB, and reduced pCREB. In addition, H89 inhibited ERK activation, indicating cross-talk between the pathways. Finally, axonal application of blocking antibody against the FGF receptor 1 (FGFR1) prevented the FGF-2-induced up-regulation of BDNF and TrkB. Our results suggest that FGF-2 acts on RGCs via FGFR1, activating the ERK pathway and CREB to increase BDNF synthesis, and PKA and CREB to increase TrkB synthesis.

Fibroblast growth factor 2 applied to the optic nerve after axotomy increases Bcl-2 and decreases Bax in ganglion cells by activating the extracellular signal-regulated kinase signaling pathway

We have shown that application of basic fibroblast growth factor (FGF-2) to axotomized optic nerve promotes the survival of frog retinal ganglion cells (RGCs). In the present study we used western blotting and immunocytochemistry to investigate the effects of this FGF-2 treatment upon the activation of the extracellular signal-regulated kinase (ERK) pathway, the amounts and distribution of Bcl-2 family proteins, and the activation of caspase-3. Axotomy alone temporarily increased ERK activation; FGF-2 treatment to the nerve prolonged this activation. This effect was blocked by U0126, a selective ERK kinase (MEK) inhibitor. Axotomy caused a decrease in Bcl-2 and a small increase in Bcl-x(L). FGF-2 treatment caused an ERK-dependent increase in Bcl-2 and an ERK-independent increase in Bcl-x(L). The pro-apoptotic Bax was increased by axotomy; FGF-2 treatment greatly decreased Bax levels, an effect that was inhibited by U0126. Axotomy induced the cleavage of caspase-3; FGF-2 treatment blocked this effect in an ERK-dependent manner. Finally, intraocular application of the MEK inhibitor caused a large reduction in the survival-promoting effect that FGF-2 application to the nerve stump had on RGCs. Our results suggest that FGF-2 acts, at least in part, via the ERK pathway to prevent apoptosis of axotomized RGCs not only by increasing amounts of anti-apoptotic proteins, but also by a striking reduction in the levels of apoptotic effectors themselves.

Neurotrophin-3 and TrkC in the frog visual system: changes after axotomy

Neurotrophins are potent regulators of the survival of different neuronal populations in the CNS. Little is known of the immunodistribution of neurotrophin-3 (NT-3) and tyrosine kinase C (TrkC) receptor in the frog visual system, which can successfully regenerate and recover vision after injury. In this study we show that both NT-3 and TrkC are present in the frog retina and tectum, and that their distribution changes after optic nerve transection. Both NT-3 and TrkC are present in the ganglion cell layer, inner nuclear layer, nerve fiber layer and outer plexiform layer, and in Müller cells of control retinas. Quantification of identified RGCs shows that there are only small changes in the proportion, or intensity, of NT-3 immunostained cells surviving after axotomy and regeneration. Müller cell staining, however, is increased. TrkC staining in the retina does not change after axotomy. In the tectum, NT-3 immunoreactivity is present in the retinorecipient layer 9, and in radial processes of neurons and ependymoglia. TrkC is present in ependymoglia and in tectal neurons. After axotomy or colchicine treatment fewer NT-3-immunoreactive processes are present in layer 9 and there is decreased staining of tectal neurons. These data are consistent with the hypothesis that NT-3 is synthesized in the retina and anterogradely transported to the tectum. TrkC immunostaining, on the other hand, increases in tectal cells after optic nerve transection, suggesting that it may be regulated by the supply of NT-3 from the retina.

FGF-2 modulates expression and distribution of GAP-43 in frog retinal ganglion cells after optic nerve injury

Basic fibroblast growth factor (bFGF or FGF-2) has been implicated as a trophic factor that promotes survival and neurite outgrowth of neurons. We found previously that application of FGF-2 to the proximal stump of the injured axon increases retinal ganglion cell (RGC) survival. We determine here the effect of FGF-2 on expression of the axonal growth-associated phosphoprotein (GAP)-43 in retinal ganglion cells and tectum of Rana pipiens during regeneration of the optic nerve. In control retinas, GAP-43 protein was found in the optic fiber layer and in optic nerve; mRNA levels were low. After axotomy, mRNA levels increased sevenfold and GAP-43 protein was significantly increased. GAP-43 was localized in retinal axons and in a subset of RGC cell bodies and dendrites. This upregulation of GAP-43 was sustained through the period in which retinal axons reconnect with their target in the tectum. FGF-2 application to the injured nerve, but not to the eyeball, increased GAP-43 mRNA in the retina but decreased GAP-43 protein levels and decreased the number of immunopositive cell bodies. In the tectum, no treatment affected GAP-43 mRNA but FGF-2 application to the axotomized optic nerve increased GAP-43 protein in regenerating retinal projections. We conclude that FGF-2 upregulates the synthesis and alters the distribution of the axonal growth-promoting protein GAP-43, suggesting that it may enhance axonal regrowth.

Changes in brain-derived neurotrophic factor and trkB receptor in the adult Rana pipiens retina and optic tectum after optic nerve injury

In this study we used immunocytochemistry to investigate the distribution of brain-derived neurotrophic factor (BDNF) and its receptor tyrosine kinase (trkB) in retina and optic tectum of the frog Rana pipiens during regeneration after axotomy. We also measured changes in BDNF mRNA in retina and tectum. Retrograde labeling was used to identify retinal ganglion cells (RGCs) prior to quantification of the BDNF immunoreactivity. In control animals, BDNF was found in the majority of RGCs and displaced amacrine cells and in some cells in the inner nuclear layer (INL). After axotomy, BDNF immunoreactivity was reduced in RGCs but increased in the INL. BDNF mRNA levels in the retina remained high before and after axotomy. Three months after axotomy, after reconnection to the target, the staining intensity of many of the surviving RGCs had partially recovered. In the control tectum, BDNF staining was present in ependymoglial cells and in neurons throughout layers 4, 6, 8, and 9. After axotomy, BDNF staining in tectal neurons became more intense, even though mRNA synthesis was transiently down-regulated. In control retinas, trkB receptor immunostaining was present in most RGCs; no significant changes were observed after axotomy. In control tectum, trkB was detected only in ependymoglial cells. After axotomy, many neuronal cell bodies were transiently labeled. Our data are consistent with the hypothesis that a considerable fraction of the BDNF normally present in RGCs is acquired from their targets in the tectum. However, there are also intraretinal sources of BDNF that could contribute to the survival of RGCs.

Measuring the CP violating phase gamma using B+/- --> pi(+/-)pi(+)pi(-) and B+/- --> K+/-pi(+)pi(-) decays

A new and simple procedure to measure the angle gamma from B+/--->pi(+/-)pi(+)pi(-) and B+/--->K+/-pi(+)pi(-) decays using SU(3) symmetry is presented. It is based on a full Dalitz plot analysis of these decays. All diagrams, including strong and electroweak penguins, are considered in the procedure. The method is also free from final state interaction problems. The theoretical error in the extraction of gamma within the method should be of the order of 10(0) or even less. Taking into account the B-meson production in the first generation of B factories and recent measurements from CLEO, this method could bring the best measurement of gamma in the next years.

Basic fibroblast growth factor applied to the optic nerve after injury increases long-term cell survival in the frog retina

The neuroprotective effects of basic fibroblast growth factor (bFGF) on the long-term survival of axotomized retinal ganglion cells (RGCs) were studied in the frog Rana pipiens. Cell loss was quantified in different regions of the ganglion cell layer using Nissl staining and tetramethylrhodamine dextran amine backfilling. All regions of the retina showed a significant decrease (32-66%) in RGC numbers between 4 and 16 weeks after axotomy. Some cells showed morphological and biochemical signs of apoptosis. A single application of bFGF to the optic nerve stump at the time of axotomy protected many of the cells 6 weeks after the injury, but this effect was lost by 12 weeks. A second application of bFGF, 6 weeks after the injury, rescued many RGCs at 12 weeks. In contrast, single or double injections of bFGF into the eyeball had no effect on RGC survival. Axotomized RGCs were significantly enlarged and elongated after axotomy, and these morphological changes were increased by bFGF treatment. In the normal retina and optic nerve, immunocytochemical staining showed bFGF-like immunoreactivity (-LI) in the pigment epithelial layer, in the outer segments of photoreceptors, and in occasional RGCs. Strong bFGF-LI was present in Müller cells and in optic nerve astrocytes and oligodendrocytes. FGF receptor-LI was present in photoreceptors, outer plexiform layer, retinal ganglion cell axons, and Müller cells. FGF receptor-LI was also observed in optic nerve glia.

Ultrastructural studies of dorsal root axons regenerating through adult frog optic and sciatic nerves

Optic nerves of adult fish and amphibia can successfully regenerate, in part because their glial cells, unlike those of mammals, provide an environment permissive to regrowth. We altered the environment of regenerating dorsal root axons in the frog, Rana pipiens, by grafting segments of optic nerve to test the permissiveness of CNS glial cells to other sensory neurons. We compared these preparations to grafts of segments of sciatic nerve. After allowing various times for survival, light and electron microscopy were used to evaluate the grafts. An agglomeration of astrocytes, tightly joined by desmosomes, initially formed in the center of the optic nerve grafts. Around this grew regenerating dorsal root axons, accompanied by Schwann cells. At early stages, some axons formed dilated terminal structures, which were not seen in peripheral nerve grafts. The appearance of blood vessels within the graft and the dispersion of cells allowed larger numbers of axons to grow through the graft. By eight weeks, 48% of dorsal root sensory axons had grown through optic nerve grafts, compared to 84% for sciatic nerve. These results suggest that astrocytes from optic nerve are not inhibitory to, and provide a suitable substrate for, regrowing sensory neurons.

Somatostatin-like immunoreactive cells in the ground squirrel retina

Immunocytochemical techniques were employed to locate somatostatin (SS)-containing cells in the retina of the 13-lined ground squirrel (Spermophilus tridecemlineatus). In normal retinas immunostain was limited to neuronal processes, yet distinctly labeled somata were detected in retinas of animals pretreated with colchicine. Labeled cell bodies were located in the outermost and innermost portions of the inner nuclear layer (INL) and in the ganglion cell layer (GCL). The largest population of SS-like immunoreactive neurons was found in the innermost INL. These cells were identified as small and medium sized amacrine cells whose soma diameters ranged from 4 to 14 microns. A smaller population of immunoreactive cells was observed in the outermost region of the INL. These cells, presumptive horizontal cells, were found mainly in peripheral regions of the retina. Immunoreactive cells in the GCL were of two types: displaced amacrines, and retinal ganglion cells. SS-positive axons in the optic fiber layer suggest that some of the immunoreactive GCL neurons were ganglion cells, and it is our opinion that these cells belong to a class of associational ganglion cells previously identified in other species.

Megatherium, the stabber

The traditional point of view that fossil ground sloths (Xenarthra) were a relatively uniform, ecologically little diverse group has been recently challenged. Marine habits have been ascribed to Thalassocnus natans of the Pliocene of Peru. Also, a more diverse diet has been proposed by one of us (R.A.F.) for some Lujanian (late Pleistocene-early Holocene of South America genera of ground sloths. In this paper, an aspect of this latter hypothesis is tested, i.e. that Megatherium americanum had morphological features that are better explained by its having had carnivorous habits rather than by solely herbivorous ones. Specifically, the question of its forearms having been designed for optimizing speed rather than strength of extension is addressed. Such a trait might have been associated with a potentially aggressive use of the animal large claws, whereas a strong extension would be more proper for tearing branches out. On the other hand the high mechanical advantage of the biceps might have made it possible for the animal to have lifted and carried heavy weights. This in turn, suggests the possibility that the animal could have manipulated large prey (for instance, turning dorsally armoured preys or carcasses upside down to expose softer parts and cached large food pieces in a safer place. By this view, Megatherium americanum would be the largest land mammal hunter to have existed.

Astrocytes and regenerating axons at the proximal stump of the severed frog optic nerve

We have studied the growing tip of the severed frog optic nerve, a central nervous system pathway that successfully regenerates. Since reconnection with the distal stump was prevented, guidance of the growing axons along anterogradely degenerating axons and their debris was precluded. One week after nerve section, there was vigorous mononuclear macrophage activity at the cut end, which quickly subsided. Phagocytosis of the remaining debris of retrograde degeneration in the proximal stump was carried out by astrocytes. Regenerating axons appeared at the tip of the stump 3 weeks after the cut. They were preferentially located near the periphery of the stump, in close proximity to astrocytes of the glia limitans. Eight weeks after the cut, regenerating axons formed a region of outgrowth protruding from the tip of the proximal stump. They were always accompanied by astrocytes, and no myelin-producing oligodendrocytes were seen in the outgrowth.

Specificity of identified central synapses in the embryonic cockroach: appropriate connections form before the onset of spontaneous afferent activity

The mechanisms by which neurons recognize the appropriate postsynaptic cells remain largely unknown. A useful approach to this problem is to use a system with a few identifiable neurons that form highly specific synaptic connections. We studied the development of synapses between two identified cercal sensory afferents and two giant interneurons (GIs) in the embryonic cockroach Periplaneta americana. By 46% of embryonic development, the axons of the filiform hair sensory neurons have entered the terminal ganglionic neuropil and grow alongside the GI primary dendrites, although they do not form synapses. From 50% of development, the GI dendrites grow outward from the center of the neuropil to contact the presynaptic axons and their branches. The sensory neurons begin to spike at 52% of development, and, from 55% of development, these action potentials evoked excitatory postsynaptic potentials in the GIs. Synaptic contacts were first seen at this time. The pattern of synaptic connections was highly specific from the outset. G12 had strong input from the medial (M) afferent and had almost negligible input from the lateral (L) afferent, whereas G13 had input from both. This specificity was present before bursts of spontaneous activity began in the sensory neurons at 59% of development. G12 filopodia selectively formed synaptic contacts with the M axon rather than the L axon. The few contacts made by G12 with the L axon had a normal morphology but fewer presynaptic densities. Filopodial insertions were not involved in selective synapse formation. In this system, highly specific synaptic recognition appears to be activity independent.

Localization of the heptapeptide GFSKLYFamide in the sea cucumber Holothuria glaberrima (Echinodermata): a light and electron microscopic study

Two peptides, Gly-Phe-Ser-Lys-Leu-Tyr-Phe-NH2 (GFSKLYFamide) and Ser-Gly-Tyr-Ser-Val-Leu-Tyr-Phe-NH2 (SGYSVLYFamide), recently isolated from the sea cucumber Holothuria glaberrima [Díaz-Miranda et al. (1992) Biol. Bull. 182:241-247] represent the first neuropeptides isolated from holothurians. Using an antibody against GFSKLYFa, we describe here the localization and distribution pattern of GFSKLYFa-like immunoreactivity in H. glaberrima, where immunoreactive fibers form a prominent and extensive peptidergic nervous system component. Neuron-like cells and nerve fibers expressing GFSKLYFa-like immunoreactivity are found in the ectoneural and hyponeural divisions of the radial nerve cords as well as in the digestive, haemal, respiratory, and reproductive systems; in the tentacles; and in tube feet. Neuroendocrine-like cells are found in the mucosal layer of the intestine. Ultrastructure immunocytochemical analysis revealed that, in nerve cells and fibers in the serosal layer of the intestine, the immunoreactivity is concentrated in vesicles. The immunoreactive nerve fibers are found mainly within a dense nerve plexus overlying and in close contact with smooth muscle cells of the intestine. The exclusive expression of GFSKLYFa-like immunoreactivity in neuronal or neuroendocrine tissue together with the close apposition of some fibers to muscle cells suggests that GFSKLYFa acts as a neuromuscular transmitter or neuromodulator in H. glaberrima. The wide occurrence of GFSKLYFa-like immunoreactivity throughout the nervous system of the sea cucumber suggests that GFSKLYFa plays an important role in the control of multiple action systems, including digestion, respiration, circulation, reproduction, and locomotion.

Morphology and distribution of dopaminergic neurons in the ground squirrel retina

Tyrosine hydroxylase (TH), the rate limiting enzyme in the conversion of tyrosine to DOPA, is a reliable marker for catecholaminergic (dopaminergic) neurons. To investigate the distribution of dopamine in the retina of the thirteen-lined ground squirrel (Spermophilus tridecemlineatus), retinal sections and wholemounts were incubated with an antiserum directed against TH and then processed using the avidin-biotin immunohistochemical method. TH-like immunoreactivity was exhibited by amacrine and interplexiform-like cells in the innermost portion of the inner nuclear layer (INL) and by cells we presume to be displaced amacrines in the ganglion cell layer (GCL). Their somata were 12 to 20 microns in diameter, with the majority measuring approximately 18 microns. In transverse sections the processes of the three types of neurons were seen to extend into lamina 1 of the inner plexiform layer (IPL). In horizontal sections 2-3 primary dendrites were seen to ramify and the branches extended for considerable distances, with overlap between the dendritic fields of neighboring TH cells. A distance to the nearest neighbor analysis suggests the TH-neurons in the INL are distributed in a non-random fashion.

Changes in ultrastructure and voltage-dependent currents at the glia limitans of the frog optic nerve following retinal ablation

The surface of the frog optic nerve consists of astrocytic processes separated by narrow extracellular clefts underlying a pial sheath of loose connective tissue. Macroscopic voltage dependent currents can be recorded from this surface using the loose patch-clamp technique. In this study the changes in ultrastructure and voltage dependent Na currents have been studied for up to 1 year following removal of the retina. During the first 1-4 weeks, many of the myelinated and unmyelinated axons of the retinal ganglion cells degenerate, and the debris is phagocytosed by macrophages and glial cells. However, some morphologically intact axons remain even 12 weeks after surgery. Finally, after 16 weeks all the axons have disappeared, leaving a nerve consisting only of glial cells, some of which contain phagosomes. At 40-52 weeks after enucleation, the nerve persists, at 20-40% of the normal diameter, consisting mostly of normal looking astrocytes. The amplitude of the voltage dependent Na currents recorded from nerves during the first 1-4 weeks after enucleation, with the pial sheath intact, decreases by about 50%. After 8 weeks, the Na current recorded from the surface is about 30% of control. At 16-52 weeks after removal of the retina, when there are no intact axons, the Na current is reduced by 90%. If, however, the pial sheath is stripped away, the Na currents recorded from the glial surface are 40-50% of control during this same 16- to 52-week period, suggesting that in the all-glia nerve, the currents are shunted by the relatively thicker pial sheath.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopaminergic neurons in the cone-dominated ground squirrel retina: a light and electron microscopy study

Tyrosine hydroxylase (TH), the rate limiting enzyme in the conversion of tyrosine to DOPA, is a reliable marker for catecholaminergic (dopaminergic) neurons. To investigate the distribution of dopamine in the cone-dominated retina of the thirteen-lined ground squirrel (Spermophilus tridecemlineatus), retinal sections and wholemounts were incubated with an antiserum directed against TH and then processed using immunofluorescence and the avidin-biotin immunohistochemical method. TH-like immunoreactivity was exhibited by amacrine and interplexiform-like cells in the innermost portion of the inner nuclear layer (INL) and by cells we presume to be displaced amacrines in the ganglion cell layer (GCL). Their somata were 12 to 28 microns in diameter, with the majority measuring approximately 18 microns. In transverse sections the processes of the three types of neurons were seen to extend into lamina 1 of the inner plexiform layer (IPL). In horizontal sections 2-3 primary dendrites were seen to ramify and the branches extended for considerable distances, with overlap between the dendritic fields of neighboring TH-cells. A distance to the nearest neighbor analysis suggested the TH-neurons in the INL are distributed in a non-random fashion. The mean overall density of labeled amacrines is 15 cells/mm2, low when compared to the mean density reported in other species. EM results indicate that TH-labeled amacrines make synaptic contacts with unlabeled amacrines, although the possibility that they may contact ganglion cells can not be ruled out.

Localization of GAD- and GABA-like immunoreactivity in ground squirrel retina: retrograde labeling demonstrates GAD-positive ganglion cells

Glutamic acid decarboxylase (GAD)- and gamma-aminobutyric acid (GABA)-like immunoreactivity was examined in the retina of the 13-lined ground squirrel (Spermophilus tridecemlineatus). Labeling was observed in the inner nuclear layer (INL), inner plexiform layer (IPL) and ganglion cell layer (GCL). The immunoreactive cell bodies in the inner third of the INL were 6-13 microns in diameter and, because of their size and location it was considered that these were amacrine cells. Labeling in the IPL was concentrated in 5 bands corresponding to laminae 1a, 1c, 2, 4 and 5. In the GCL a heterogeneous population of neurons exhibited GAD- and GABA-like immunoreactivity. The soma diameters of the GCL cells ranged from 5 to 17 microns. These may represent displaced amacrines and/or ganglion cells. To determine if any of the immunoreactive cells in the GCL were ganglion cells, double labeling experiments were performed using rhodamine latex microspheres ('beads') as retrograde neuronal tracers. Rhodamine beads were injected into the superior colliculus, and retinas with retrogradely labeled ganglion cells were subsequently incubated with the anti-GAD antiserum. These experiments revealed a small population of GAD-positive ganglion cells, setting a lower limit for the total number of GABAergic ganglion cells.

Positional information determines the anatomy and synaptic specificity of cockroach filiform hair afferents using independent mechanisms

Mutant first instar cockroaches (Periplaneta americana) with supernumerary filiform hair sensilla on their cerci were used to study the effects of cell body position on axonal morphology and synaptic connections. The wild-type cercus has two hairs, one lateral (L) and the other medial (M), each with an underlying sensory neuron. Silver-intensified cobalt fills show that the supernumerary lateral neuron (SIN) in the mutant has the same shape of arborization as L, and electrophysiological recording shows that it forms synaptic connections with the same subset of giant interneurons (GIs) as L in the terminal ganglion: GI3 and GI6. The supernumerary medial neuron (SuM) has the same axonal morphology as M and synapses with the same GIs as does M: ipsilateral GIs 1 and 2 and contralateral GIs 1, 2, 3, 5 and 6. In 0.1% of approximately 8000 animals screened, a supernumerary hair arose on the cercal midline (C hair). The C neuron sends its axon to the CNS in the same branch of the cercal nerve as the L and SIN, and has a similar arborization. However, the C neuron forms synapses with the same GIs as do M and SuM. Electron microscopy of horseradish peroxidase-injected neurons was used to confirm that the C afferent forms a monosynaptic connection to GI2. It was concluded that the position of the sensory neuron cell body does control its axonal morphology and synaptic connectivity, but that these characteristics are produced by independent mechanisms.

Changes in intercellular junctions during peripheral nerve regeneration in insects

Peripheral nerves of the adult cockroach have been cut and the changes in glial cells followed during the subsequent process of regeneration. After three to four weeks of regrowth, the severed tips of nerves were examined by freeze-fracture to assess the state of intercellular junctions between the perineurial sheath cells as well as the underlying glial cells. Both pleated septate and gap junctions were found in the immature state; their intramembranous particle (IMP) distribution was characteristic of junctions in the process of assembly, since the IMPs were irregularly and loosely arrayed in contrast with the parallel septate junctional IMP rows and gap junctional plaques found in the fully regenerated or control tissues. These junctional stages resembled those occurring in developing embryonic or metamorphosing insect tissues.

Ultrastructural changes in glial cells during regeneration of cockroach peripheral nerve

After peripheral nerve 5 in the cockroach Periplaneta americana was cut, changes occurring in the glial cells in the proximal stump were studied immediately after damage and during the process of nerve regeneration. During the first week haemocytes accumulated outside the nerve and morphologically similar granule-containing cells appeared inside the nerve. These cells were involved in phagocytic activity. Between the second and the fourth week, signs of regeneration were distinguishable; many small axonal sprouts were formed which were surrounded by glial processes, and the nerve stump increased in length. During this period the glial cells produced large amounts of extracellular material in which the bundles of axons and glia were embedded. The structural differences between glial and perineurial cells were lost during these stages of regeneration and there was no restriction to the penetration of the extracellular tracer lanthanum. After 8 weeks, reinnervation of the muscles had taken place, perineurial and glial cells were again distinguishable, and the perineurial cells were able to exclude lanthanum.

Radiological Impact of Airborne Effluents of Coal and Nuclear Plants

Radiation doses from airborne effluents of model coal-fired and nuclear power plants (1000 megawatts electric) are compared. Assuming a 1 percent ash release to the atmosphere (Environmental Protection Agency regulation) and 1 part per million of uranium and 2 parts per million of thorium in the coal (approximately the U.S. average), population doses from the coal plant are typically higher than those from pressurized-water or boiling-water reactors that meet government regulations. Higher radionuclide contents and ash releases are common and would result in increased doses from the coal plant. The study does not assess the impact of non-radiological pollutants or the total radiological impacts of a coal versus a nuclear economy.