A membrane phosphoprotein associated with neural development, axonal regeneration, phospholipid metabolism, and synaptic plasticity

The atomic structure of visual rhodopsin: How and when?

Strong arguments are presented by Hargrave suggesting that the crystallization of visual rhodopsin for high resolution analysis by X-ray crystallography or electron microscopy is feasible. However, the effort needed to achieve this goal will most likely exceed the resources of a single laboratory and a concerted approach to the research is necessary.

Molecular insights gained from covalently tethering cGMP to the ligand-binding sites of retinal rod cGMP-gated channels

A photoaffinity analog of cGMP has been used to biochemically identify a new ligand-binding subunit of the retinal rod cGMP-activated ion channel, as well as amino acids in contact with cGMP in the original subunit. Covalent tethering of this probe to channels in excised menbrane patches has revealed a functional heteogeneity in the ligand-binding sites that may arise from the two biochemically identified subunits.

Genetic and functional complexity of inherited retinal degeneration

Recent findings emphasize the complexity, both genetic and functional, of the manifold genes and mutations causing inherited retinal degeneration in humans. Knowledge of the genetic bases of these diseases can contribute to design of rational therapy, as well as elucidating the function of each gene product in normal visual processes.

Channel structure and divalent cation regulation of phototransduction

The identification of additional subunits of the cGMP-gated cation channel suggests exciting questions about their regulatory roles and about structure/functional relationships. How do the different subunits interact? How is the complex assembled into the plasma membrane? Divalent cations have been implicated in the regulation of adaptation. One often overlooked cation is magnesium. Could this ion play a role in phototransduction?

Structure of the cGMP-gated channel

The subunit structure of the cGMP-gated cation channel of rod photoreceptors is rapidly being defined, and in the process the mode of regulation by Ca2+-calmodulin unraveled. Intriguingly, early results suggest that additional subunits of unknown function are associated with the channel and remain to be identified.

Linking genotypes with phenotypes in human retinal degenerations: Implications for future research and treatment

Although undoubtedly it will be incomplete by the time it is published, the target article by Daiger et al. organizes mutations in genes that produce retinal degenerations in humans into categories of clinically relevant phenotypes. Such classifications should help us understand the link between altered photoreceptor cell proteins and subsequent cell death, and they may yield insight into methods for preventing consequent blindness.

Genetic and clinical heterogeneity in tapetal retinal dystrophies

Large scale DNA-mutation screening in patients with hereditary retinal diseases greatly enhances our knowledge about retinal function and diseases. Scientists, clinicians, patients, and families involved with retinal disorders may directly benefit from these developments. However, certain aspects of this expanding knowledge, such as the correlation between genotype and phenotype, may be much more complicated than we expect at present.

The determination of rhodopsin structure may require alternative approaches

The structure of rhodopsin is a subject of intense interest. Solving the structure by traditional methods has proved exceedingly challenging. It may therefore be useful to confront the problem by a combination of alternate techniques. These include FTIR (Fourier transform infrared spectroscopy) and AFM (atomic force microscopy) on the intact protein. Furthermore, additional insights may be gained through structural investigations of discrete rhodopsin domains.

Na-Ca + K exchanger and Ca2+ homeostasis in retinal rod outer segments: Inactivation of the Ca2+ efflux mode and possible involvement of intracellular Ca2+ stores in Ca2+ homeostasis

Inactivation of the Ca2+ extrusion mode of the retinal rod Na- Ca + K exchanger is suggested to be the mechanism that prevents lowering of cytosolic free Ca2+ to < 1 nM when rod cells are saturated for a prolonged time under bright light conditions. Under these conditions, Ca2+ fluxes across disk membranes can contribute significantly to Ca2+ homeostasis in rods.

Nuclear magnetic resonance studies on the structure and function of rhodopsin

Magic angle spinning (MAS) NMR methods provide a means of obtaining high resolution structural data on rhodopsin and its photoin termediates. Current work has focused on the structure of the retinal chromophore and its interactions with surrounding protein charges. The recent development of MAS NMR methods for measuring internuclear distances with a resolution of ∼0.2 will complement diffraction methods for addressing key mechanistic questions.

Differential expression of p140trk, p75NGFR and growth-associated phosphoprotein-43 genes in nucleus basalis magnocellularis, thalamus and adjacent cortex following neocortical infarction and nerve growth factor treatment

A loss of target-derived neurotrophic factors is hypothesized to be one of the major determinants of central nervous system neuronal degeneration. In order to obtain further insight into early neuronal responses to injury, lesion-induced alterations in the expression of high- and low-affinity nerve growth factor receptors, as well as growth-associated phosphoprotein-43 genes in nucleus basalis magnocellularis, thalamic and neocortical neurons were studied. For this purpose, unilateral cortical devascularization operations were conducted on adult rats. Animals received i.c.v. infusions of vehicle or nerve growth factor (12 micrograms/day) and were killed at one, three, seven and 15 days post-lesion. In situ hybridization studies using 35S-labelled oligonucleotide probes for p75NGFR, p140trk and growth-associated phosphoprotein-43 messenger RNAs reveals that these genes were differentially regulated following the lesion. In the nucleus basalis magnocellularis ipsilateral to the lesion, p140trk gene expression significantly decreased on days 3 and 7, while p75NGFR messenger RNA initially increased on day 3 and decreased on days 7 and 15 after lesion. GAP-43 messenger RNA levels were significantly increased in the nucleus basalis magnocellularis on post-lesion days 3 and 7. Moreover, in contrast to p75NGFR or 140trk, growth-associated phosphoprotein-43 messenger RNA levels were significantly increased in pyramidal neurons located in the remaining cortex adjacent to the cortical lesion at all time points. In the lateral and ventroposterior nuclei of the thalamus, growth-associated phosphoprotein-43 messenger RNA level was slightly increased on days 1 and 3 and was dramatically decreased, significantly below the levels in sham-operated controls, on post-lesion days 7 and 15. During nerve growth factor application, the level of p140trk messenger RNA in the lesioned nucleus basalis magnocellularis returned to values observed in the contralateral nucleus basalis magnocellularis while p75NGFR messenger RNA was increased above values noted in all animals not treated with nerve growth factor. Nerve growth factor treatment did not affect the expression of growth-associated phosphoprotein-43 messenger RNA in any of the areas studied. p140trk messenger RNA was not up-regulated during the time that nerve growth factor was applied, as observed for p75NGFR, but only eight days after interrupting nerve growth factor treatment. Three cell types, nucleus basalis magnocellularis, cortical pyramidal and thalamic neurons, were probably affected in different ways by the devascularization with respect to lesion extent. Consequently, the remaining number of synaptic contacts in each of these brain areas is most likely different which may lead to a differential regulation of growth-associated phosphoprotein-43 messenger RNA.(ABSTRACT TRUNCATED AT 400 WORDS)

Glutamate accumulation in the photoreceptor-presumed final common path of photoreceptor cell death

Genetic abnormalities of three factors related to the photoreceptor mechanism have been reported in both animal models and humans. Apoptotic mechanism has also been suggested as a final common pathway of photoreceptor cell death. Our findings of increased level of glutamate in photoreceptor cells in rds mice suggest that amino acid might mediate between these two pathological mechanisms.

Unique lipids and unique properties of retinal proteins

Amino-terminal heteroacylation has been identified in retinal proteins including recoverin and α subunit of G-protein, transducin. The tissue-specific modification seems to mediate not only a proteinmembrane interaction but also a specific protein-protein interaction. The mechanism generating the heterogeneity and its physiological role are still unclear, but an interesting idea for the latter postulates a fine regulation of the signal transduction pathway by distinct N-acyl groups.

Further insight into the structural and regulatory properties of the cGMP-gated channel

Recent studies from several different laboratories have provided further insight into structure-function relationships of cyclic nucleotide-gated channel and in particular the cCMPgated channel of rod photoreceptors. Site-directed mutagenesis and rod-olfactory chimeria constructs have defined important amino acids and peptide segments of the channel that are important in ion blockage, ligand specificity, and gating properties. Molecular cloning studies have indicated that cyclic nucleotide-gated channels consist of two subunits that are required to reproduce the properties of the native channels. Biochemical analysis of the cGMP-gated channel of rodcells have indicated that the 240 kDa protein that co-purifies with the 63 kDa channel subunit contains both the previously cloned second subunit of the channel and a glutamic acid-rich protein. The regulatory properties of the cGMP-gated channel from rod cells has also been studied in more detail. Studies indicate that the beta subunit of the cGMP-gated channel of rod cells contains the binding site for calmodulin. Interaction of calmodulin with the channel alters the apparent affinity of the channel for cGMP in all in vitro systems that have been studied. The significance of these recent studies are discussed in relation to the commentaries on the target article.

Unsolved issues in S-modulin/recoverin study

S-Modulin is a frog homolog of recoverin. The function and the underlying mechanism of the action of these proteins are now understood in general. However, there remain some unsolved issues including; two distinct effects of S-modulin; Ca2+-dependent binding of S-modulin to membranes and a possible target protein; S-modulin-like proteins in other neurons. These issues are considered in this commentary.

Mechanisms of photoreceptor degenerations

The candidate gene approach has identified many causes of photoreceptor rod cell death in retinitis pigmentosa. Some mutations lead to increased cyclicGMP concentrations in rods. Rod photoreceptors are also particularly susceptible to some mutations in housekeeping genes. Although many more cases of macular degeneration than retinitis pigmentosa occur each year, there is much less known about both genetic and sporadic forms of this disease.

Reduced cytoplasmic calcium concentration may be both necessary and sufficient for photoreceptor light adaptation

Light adaptation is modulated almost exclusively by changes in intracellular Ca2+ concentration, and other Ca2+-independent mechanisms are likely to play only a minor role. Changes in Ca2+i may be not only necessary for light adaptation to take place but sufficient to cause it.

The genetic kaleidoscope of vision

Site-specific phenotypic effects of the 73 known alleles in the rhodopsin gene that cause retinal degeneration are difficult to interpret because most alleles are documented in only one case or one family, which means variation in effects could actually arise from interactions with other loci. However, sample sizes necessary to detect epistatic interaction may place an answer to this question beyond our grasp.

Evidence that the type I adenylyl cyclase may be important for neuroplasticity: Mutant mice deficient in the gene for type I adenylyl cyclase show altered behavior and LTP

The regulatory properties of the neurospecific, type I adenylyl cyclase and its distribution within brain have suggested that this enzyme may be important for neuroplasticity. To address this issue, the murine, Ca2+ -stimulated adenylyl cyclase (type I), was inactivated by targeted mutagenesis. Ca2+ -stimulated adenylyl cyclase activity was reduced 40% to 60% in the hippocampus, neocortex, and cerebellum. Long term potentiation in the CA1 region of the hippocampus from mutants was perturbed relative to controls. Both the initial slope and maxim um extent of changes in synaptic response were reduced. Although mutant mice learned to find a hidden platform normally in the Morris water task, they did not display a preference for the region where the platform had been when it was removed. The behavioral phenotype of these mice is very similar to that exhibited by mice which have been surgically lesioned in the hippocampus. These results indicate that disruption of the gene for the type I adenylyl cyclase produces changes in spatial memory and indicate that the cAMP signal transduction pathway may play an important role for synaptic plasticity.

Calcium/calmodulin-sensitive adenylyl cyclase as an example of a molecular associative integrator

Evidence suggests that the Ca2+/calmodulin-sensitive adenylyl cyclase may play a key role in neural plasticity and learning in Aplysia, Drosophila, and mammals. This dually-regulated enzyme has been proposed as a possible site of stimulus convergence during associative learning. This commentary discusses the evidence that is required to demonstrate that a protein in a second messenger cascade actually functions as a molecular site of associative integration. It also addresses the issue of how a dually-regulated protein could contribute to the temporal pairing requirements of classical conditioning: that relationship between stimuli display both temporal contiguity and predictability.

The key to rhodopsin function lies in the structure of its interface with transducin

Light activated rhodopsin functions by catalyzing the exchange of GTP for GDP on numerous copies of transducin. Peptide mapping has shown that at least six regions, three on rhodopsin and three on the transducin alpha subunit, are involved in the active interface between the two proteins. The most informative structural studies of rhodopsin should include focus on the transducin interaction.

Increase in alpha-CGRP and GAP-43 in aged motoneurons: a study of peptides, growth factors, and ChAT mRNA in the lumbar spinal cord of senescent rats with symptoms of hindlimb incapacities

Sprague-Dawley rats develop progressive motor dysfunctions during the third year of life. We use this as a model to examine possible neuronal mechanism(s) that may cause motor impairments occuring during aging. In this study we have used indirect immunofluorescence histochemistry (IF) and in situ hybridization histochemistry (ISH) to study quantitatively and qualitatively the staining pattern and mRNA expression of calcitonin gene-related peptide (alpha-CGRP), growth-associated protein 43 (GAP-43), and acidic fibroblast growth factor (aFGF) in spinal lumbar motoneurons of young adult (2-3 months) and aged (30 months) Sprague-Dawley rats. In addition, mRNAs encoding choline acetyltransferase (ChAT), beta-CGRP, and cholecystokinin (CCK) were analyzed. All aged rats used in this study disclosed symptoms of hindlimb incapacity, ranging from mild weight-bearing insufficiency to paralysis of the hind limbs. The symptoms were confined to the musculature of the hindlimb and hip regions. Only a small number (approximately 15%) of the large motoneurons that innervate the hindlimb muscles were lost in those aged rats that had clinical symptoms of hindlimb motor incapacities. The remaining motoneurons expressed ChAT mRNA at levels similar to those of young adult rats. The vast majority of these motoneurons showed increased mRNA levels for alpha-CGRP and GAP-43. Aged motoneurons contained more CGRP like immunoreactivity (LI), but the number of immunoreactive neurons was smaller than in adult rats. GAP-43-LI could be detected in motoneurons in aged, but not in adult, rats. GAP-43-LI was always colocalized with CGRP-LI in aged motoneurons. Studies of individual aged rats revealed that the increase of GAP-43 mRNA-positive cell bodies occurred in cases with the most severe clinical symptoms, whereas the increase in alpha-CGRP was even evident in rats with mild symptoms. No alterations in content of aFGF-LI or aFGF mRNA could be detected in the aged rat, and the content of CCK and beta-CGRP mRNAs was also normal. The usefulness of this rat model for studies of neuromuscular aging and possible functional roles for GAP-43 and CGRP in plastic and regenerative processes during aging are discussed.

TGF-beta s and cAMP regulate GAP-43 expression in Schwann cells and reveal the association of this protein with the trans-Golgi network

We have shown previously that growth-associated protein 43 (GAP-43) is expressed by rat Schwann cells and is restricted to non-myelin-forming Schwann cells in vivo. Here we examined the regulation of GAP-43 using agents that are known to control Schwann cell differentiation in vitro. GAP-43 protein and mRNA levels are decreased by forskolin and other agents that elevate intracellular cAMP (and promote expression of the myelinating Schwann cell phenotype). We also found that expression of GAP-43 protein but not mRNA is down-regulated by transforming growth factor betas (TGF-beta s). Moreover, TGF-beta treatment of Schwann cells results in cell clumping, process retraction and disappearance of GAP-43 from the plasma membrane, revealing that GAP-43 is associated with the Golgi apparatus. This association was confirmed by partial overlap of GAP-43 with the trans-Golgi network marker (23c) and the disruption of the Golgi with brefeldin A or monensin leading to altered GAP-43 distribution. Golgi-associated GAP-43 appeared to have the same molecular weight as the plasma membrane-associated GAP-43. Thus these results show that GAP-43 expression in Schwann cells is subject to regulation by both extracellular and intracellular signalling molecules and that Schwann cell GAP-43 is often associated with the Golgi apparatus.

Characterization of a novel protein regulated during the critical period for song learning in the zebra finch

A male zebra finch learns a song by listening to a tutor, but song learning is normally restricted to a critical period in juvenile development. Here we identify an RNA whose expression in the song control circuit is altered during this critical period. The RNA encodes a soluble presynaptic protein that forms a predicted amphipathic alpha helix typical of the lipid-binding domain in apolipoproteins. We show this protein, which we call synelfin, to be the homolog of the human non-A beta component (and its precursor) recently purified from Alzheimer's disease amyloid. We suggest this highly conserved protein may serve a novel function critical to the regulation of vertebrate neural plasticity.

Influence of peripheral nerve grafts on the expression of GAP-43 in regenerating retinal ganglion cells in adult hamsters

We have examined the ability of axotomized retinal ganglion cells in adult hamsters, to regenerate axons into a peripheral nerve graft attached to the optic nerve and the expression of GAP-43 by these neurons. We also examined the effect on these events of transplanting a segment of peripheral nerve to the vitreous body. The left optic nerves in three groups of hamsters were replaced with a long segment of peripheral nerve attached to the proximal stump of the optic nerve approximately 2 mm from the optic disc to induce regeneration of retinal ganglion cells into the peripheral nerve. An additional segment of peripheral nerve was transplanted into the vitreous of the left eye in the second group. The animals from the first and second groups were allowed to survive for 1-8 weeks and the number of regenerating retinal ganglion cells was determined by applying the retrograde tracer, Fluoro-Gold to the peripheral nerve graft and the expression of GAP-43 was studied by immunocytochemistry in the same retinas. As a control, a segment of optic nerve was transplanted into the vitreous body of the left eye in the third group of hamsters. These animals were allowed to survive for 4 weeks and the number of regenerating retinal ganglion cells was counted as in Groups 1 and 2. The percentages of the regenerating retinal ganglion cells which also expressed GAP-43 were very high at all time points in Group 1 (with no intravitreal peripheral nerve) and Group 2 (with intravitreal peripheral nerve) and at 4 weeks for the Group 3 (with intravitreal optic nerve) animals. In addition, the number of regenerating retinal ganglion cells, the number of retinal ganglion cells expressing GAP-43 and the number of regenerating retinal ganglion cells which also expressed GAP-43 were much higher in Group 2 than in Group 1 at all the time points and it was also much higher in Group 2 than in Group 3 at 4 weeks whereas there was no significant difference between the results from Groups 1 and 3 at 4 weeks. These data suggested that there was a close correlation between the number of the axotomized retinal ganglion cells regenerating axons into the peripheral nerve graft attached to the optic nerve and the expression of GAP-43.(ABSTRACT TRUNCATED AT 400 WORDS)

Inhibition of neuronal surface proteases decreases the requirement for GAP-43 in neurite outgrowth

Intracellular delivery of anti-GAP IgG inhibits the elaboration of neurites by NB2a/d1 cells. However, recent studies indicate that the extent of inhibition is minimized when cells were cultured on poly-L-lysine-coated or laminin-coated versus uncoated plates, suggesting that the role of GAP-43 in neuritogenesis may be specifically related to membrane adhesiveness. We therefore examined the influence of inhibition of thrombin, the neuronal surface protease that restricts neurite outgrowth, on GAP-43-dependent neurite outgrowth. Treatment of cells with the specific thrombin inhibitor hirudin in the presence of serum induced a similar percentage of neurite outgrowth as was observed following serum withdrawal. However, while neurite outgrowth induced by serum deprivation of cells was reduced following intracellular delivery of anti-GAP IgG, neurite outgrowth induced by hirudin treatment of cells was not. That inhibition of neuronal surface protease activity overcomes the inhibition of neurite outgrowth following intracellular delivery of anti-GAP IgG provides further evidence that the role that GAP-43 plays in neuritogenesis is related to membrane adhesiveness.

Inhibition of neurite outgrowth following intracellular delivery of anti-GAP-43 antibodies depends upon culture conditions and method of neurite induction

NB2/dl neuroblastoma cells acquire a neuronal phenotype in response to several differentiating agents, including dibutyryl cAMP (dbcAMP) and the withdrawal of serum. As shown previously, antibodies to the growth-associated protein, GAP-43, introduced intracellularly using a lipid carrier, blocked the differentiation induced by dbcAMP. Antibodies to GAP-43, at a low concentration, also blocked neurite outgrowth induced by serum withdrawal when cells were grown on a relatively unadhesive substrate. On more adhesive substrates such as poly-L-lysine and laminin, however, anti-GAP-43 antibodies had less of an effect on neurite outgrowth. Previous studies have shown that the increased adhesivity of laminin allows a small but significant population of neurites to grow from serum-deprived cells, even in the presence of the microtubule-depolymerizing drug, colchicine. The outgrowth of this population of neurites was blocked by antibodies to GAP-43. These results are in conformity with recent studies showing that the requirement for GAP-43 in neuritogenesis may be related to membrane adhesiveness, and may contribute to an understanding of some of the apparent discrepancies in the literature concerning the involvement of GAP-43 in neuronal differentiation.

Colchicine induces the GAP-43 gene expression in rat hypothalamus

Injection of colchicine, a mitogen inhibitor, in the dorsal third ventricle induced the expression of the growth associated protein-43 (GAP-43) mRNA in some groups of cells of the adult rat brain. These mRNAs were detected by in situ hybridization histochemistry using an alkaline phosphatase labeled oligonucleotide probe. A substantial up-regulation of GAP-43 mRNA was noticed by the increase of both the number of positive cells and the intensity of the hybridization signal. These changes were observed in the hypothalamic nuclei located near the ventral third ventricle, namely the preoptic area, the supraoptic nucleus, the peri- and the paraventricular nuclei of the hypothalamus, the dorsal subnucleus of the ventromedial nucleus, the arcuate nucleus and the posterior part of the peri-mammillary region. Such abundant GAP-43 mRNA positive cells have not been observed in control adult rat hypothalamus. Since the positive cell number and shape initially suggested that these were neurons or astrocytes, double labeling in situ hybridization using both radioactive (for the detection of GFAP mRNA as a marker of astrocyte) and non-radioactive (for the detection of GAP-43 mRNA) probes was carried out. This demonstrated that these GAP-43 mRNA positive cells were not astrocytes. In addition enhanced GAP-43 mRNA expression was also found in some neuronal component, particularly in neurosecretory magnocells of the pareaventricular and the supraoptic nuclei. This up-regulation was further confirmed by the Northern blot analysis. About five fold increase in GAP-43 mRNA in the colchicine-treated hypothalamic tissue was shown.(ABSTRACT TRUNCATED AT 250 WORDS)

Cloning and promoter analysis of the human B-50/GAP-43 gene

We here report isolation of exon 1 and analysis of the human B-50 promoter. A human genomic lambda EMBL3 library was screened with a homologous PCR probe. Two independent clones were analyzed and partially sequenced: They contained up to 5 kb sequence upstream of the translation start site and approx 13 kb of intron 1 sequence. There was a high degree of homology between the rat and the human gene with 100% homology from -504 to -427, with respect to the translation start codon. However, relatively long GT and GA repeats as seen in the rat gene were absent. Various promoter-reporter constructs, containing 5.0 to 0.12 kb of the upstream region, were transfected into undifferentiated and neuroectodermally differentiated P19-EC. Two promoter activities were found. The minimal fragment with promoter activity still responsive to differentiation was the 0.22 kb construct, similar to rat promoter P2. We conclude that the human B-50 gene is expressed in a similar way to the rat B-50 gene, based on the presence of two transcripts, the high degree of homology between the rat and the human sequence, and the two promoter activities found in P19-EC cells.

Co-expression of GAP-43 with dopamine-beta-hydroxylase in adult rat spinal cord

Dual colour immunofluorescence was used to compare the distribution of dopamine-beta-hydroxylase (DBH) and GAP-43 in the spinal cord of the adult rat. GAP-43 immunostaining was observed in all spinal cord regions containing DBH immunoreactivity. DBH and GAP-43 double-labelled fibres and varicosities were present in the lateral and ventral funiculi of the white matter and in the ventral horn where they were most prominent around motoneurones. In the dorsal horn and around the central canal, GAP-43 immunoreactivity was too abundant to determine whether DBH immunoreactive fibres were double labelled. We conclude that the noradrenergic system is one of a small number of spinal cord systems that express high basal levels of GAP-43 in the adult.

Effects of decentralization on the levels of GAP-43 and p38 (synaptophysin) in sympathetic adrenergic neurons: a semi-quantitative study using immunofluorescence and confocal laser scanning microscopy

The distribution of GAP-43 in superior cervical ganglion (SCG) and iris were studied in normal animals and following decentralization using immunofluorescence and confocal laser scanning microscopy (CLSM). GAP-43-like immunoreactivity (LI) was compared with p38 (synaptophysin)-LI, and tyrosin hydroxylase (TH)-LI. In the control SCG, GAP-43-LI and p38-LI were mainly localized in nerve terminals around the principal neurons. The neuronal perikarya were negative for GAP-43, but positive for p38 in a perinuclear zone, as well as positive for TH. SIF cells (Small Intensely Fluorescent cells, ganglionic interneurons) were positive for GAP-43, TH and p38. One day after decentralization, GAP-43-LI and p38-LI in nerve terminals around principal neurons had disappeared. Some of the principal neurons showed a weak GAP-43-immunoreactivity. Three days post-decentralization, GAP-43- and p38-positive nerve terminals around the neurons had reappeared in considerable numbers and the intra-ganglionic nerve bundles were positive for both antibodies. In the control irides, GAP-43-LI and p38-LI were distributed in a varicose pattern in the nerve bundles, around blood vessels and in the network of terminals. Double labelling studies showed that GAP-43-LI was colocalized with TH-LI and p38-LI. The network of terminals in the dilator plate of the irides was quantified by measuring the fluorescence intensity of randomly selected areas, using CLSM. Three days after decentralization the intensity of GAP-43-LI and p38-LI had significantly increased. TH-LI had decreased 8 days after decentralization. The results indicate that GAP-43-LI and p38-LI are normally present in the nerve fibers and terminals of both pre- and post-ganglionic neurons in adult rats. The expression of GAP-43-LI and p38-LI in post-ganglionic neurons is preganglionically regulated, as indicated by the increased expression after decentralization. The expression of p38 in these neurons is probably regulated via mechanisms that are separate from those which regulate GAP-43, since it showed a different time course than that of GAP-43-LI.

Reduced electrical excitability of PC12 cells deficient in GAP-43: comparison with GAP-43-positive cells

The electrical excitability of 3 lines of rat pheochromocytoma (PC12) cells were determined under current-clamp recording conditions. In the presence of nerve growth factor (NGF), PC12(A) 'control' cells expressed high levels of GAP-43 protein, PC12(B) cells were highly deficient in GAP-43, and PC12(AB) cells, created by transfection of PC12(B) cells with a rat GAP-43 gene construct, expressed high levels of GAP-43. All 3 lines had similar resting membrane potentials, but significantly greater proportions of GAP-43-containing PC12(A) and PC12(AB) cells exhibited spiking in response to depolarizing current pulses. These spikes were resistant to TTX, were greatly enhanced in TEA and TTX, and were substantially reduced by L-type Ca(2+)-channel antagonists. GAP-43 expression may regulate PC12 cell excitability following NGF treatment, as reflected in a lower proportion of cells capable of discharging with Ca(2+)-spikes in a GAP-43-deficient cell line.

Developmental expression of GAP-43 and SNAP-25 in heterotopic rat cortical grafts

In situ hybridization techniques were used to assess (i) whether the temporal developmental profiles of the nervous system specific growth associated phosphoprotein (GAP-43) and the 25-kDa synaptosomal-associated protein (SNAP-25) are maintained in heterotopic cortical transplants, and (ii) whether the hybridization intensity in morphologically differentiated heterotopic transplants is comparable to that in the cortex of host animals. Cortical primordia at embryonic day 14 were stereotactically grafted into the striatum of adult recipient rats. Grafts at days 4, 7, 14, 35 and 56 after transplantation demonstrated developmental changes with a progressive decline of GAP-43 and a continuous up-regulation of SNAP-25 expression. Our data provide evidence of distinct molecular alterations during the differentiation process of cortical grafts, which are strikingly similar to previous studies investigating the temporal profile and intensity of GAP-43 and SNAP-25 gene expression in normal developing cortex of the rat.

Complex formation between gamma-immunoglobulin and calmodulin in calcium-free conditions

We show that gamma-immunoglobulin (IgG) binds calmodulin (CaM) in a Ca(2+)-independent manner, with Kd value of (1.7 +/- 0.5) x 10(-7) M. A single IgG molecule maximally bound 10 CaM molecules. The binding is to the heavy chain or Fab portion, but not the Fc portion, of the IgG molecules. Ca2+ greatly diminished the interaction between IgG and CaM, with IC50 = 8-9 microM. These data give a novel insight into protein-protein interactions.

Differential distribution of protein kinase C (PKC alpha beta and PKC gamma) isoenzyme immunoreactivity in the chick brain

Protein kinase C (PKC) is involved in neural plasticity. The phosphorylation of the myristoylated alanine-rich protein kinase C substrate (MARCKS) in the left intermediate and medial hyperstriatum ventrale (IMHV) of the chick brain has been shown previously to correlate significantly with the strength of learning in filial imprinting. The distribution of PKC alpha, beta I, beta II and PKC gamma in the brain of 1-day-old dark-reared chicks was determined immunocytochemically, using the monoclonal antibodies MC5 and 36G9, raised against purified PKC alpha beta and PKC gamma, respectively. PKC gamma-stained cells were distributed widely in the telencephalon, including all hyperstriatal structures (including the IMHV), the hippocampus, neostriatum, ectostriatum and archistriatum. There were fewer stained cells in the septum and the least cellular staining was in the paleostriatum primitivum. Fluorescent double-labelling with neuron-specific enolase (NSE) and with the glial calcium-binding protein S100 suggested that PKC gamma immunoreactivity was present in neurones but not in glia. The distribution of PKC alpha beta-stained cells was more limited, with staining in the archistriatum, hippocampus and septum but not in the hyperstriatum. However, there was PKC alpha beta-staining of some fibres in the IMHV (but little elsewhere in the hyperstriatum ventrale), in the neostriatum, paleostriatal complex and the lobus parolfactorius. Double-labelling with NSE and S100 revealed PKC alpha beta/S100-positive glial cells present in the paleostriatal region only. There was some PKC alpha beta-staining of putative neurones in the hippocampus, septum and archistriatum. The differential distribution of PKC isoenzymes suggests that in the IMHV some axonal inputs contain PKC alpha beta whereas some postsynaptic cells contain the gamma form of PKC.

Innervation of the rat gastrointestinal sphincters: changes during development and aging

The effect of age on the adrenergic and peptidergic innervation of the lower oesophageal, pyloric and ileocaecal sphincters of the rat was investigated using immunohistochemical techniques. The distribution of nerve fibres containing the neuronal protein, growth associated protein-43, was also studied to determine the integrity of the enteric nervous system during development and aging. The four age groups examined were 2-3 days, 6 weeks, 3 months and 25 months old rats. Using protein gene product 9.5 antibody (a non-specific general neuronal marker), it was revealed that the myenteric ganglia in all sphincter regions were compactly arranged and were smaller in size at neonatal stage getting more spaced out and larger in size with age. There was no obvious change in the structure of the neutral elements with age. In the lower oesophageal sphincter, calcitonin gene-related peptide- and substance P-like immunoreactive nerve fibres showed notable changes in density and fluorescence intensity with age, decreasing and increasing, respectively, with no obvious change in vasoactive intestinal polypeptide- and growth-associated protein-like immunoreactivity. A slight increase in dopamine-beta-hydroxylase-like immunoreactivity was seen in old age. In the pyloric sphincter, there was an increase in calcitonin gene-related peptide- and substance P-like immunoreactivity with a less notable increase in dopamine-beta-hydroxylase-like immunoreactivity. A decrease in vasoactive intestinal polypeptide- and growth-associated protein-43-like immunoreactivity in the circular muscle of the sphincter was seen in old age. In the ileocaecal sphincter there was a marked increase in growth associated protein-43-, vasoactive intestinal polypeptide-, dopamine-beta-hydroxylase and substance P-like immunoreactivity. There was a decrease in the density of calcitonin gene-related peptide-like immuno-reactive nerve fibres in old age. In summary, two main conclusions can be drawn from the results of the present study. First, there was an age-related differential change in the density of immunoreactive nerve fibres containing various neuroactive substances. This indicates a level of plasticity of the various enteric nerve types and may reflect the degree of importance of the different neurotrasmitters in the physiological activities of the specific sphincter.(ABSTRACT TRUNCATED AT 400 WORDS)

Ultrastructural examination of B-50(GAP-43) immunoreactivity in rat jejunal villi

The lamina propria of rat jejunum is densely innervated with nerve fibres extending to the tips of the villi. A large number of these nerve fibres were previously shown to be B-50-immunoreactive at the light microscope level, whereas neurofilament immunoreactivity was found to be sparse in the mucosa. In this study we used immunoelectron microscopy to determine what proportion of nerve fibres in the lamina propria express B-50. Jejuna from male Lewis rats were immunolabelled for B-50 and neurofilament proteins. For electron microscopy, postembedding immunogold-silver techniques and LR White embedded tissues were used. Light microscopical immunostaining was performed by the streptavidin-biotin-peroxidase technique on deparaffinized tissue sections. We found that all ultrastructurally identifiable nerve profiles in jejunum were B-50 immunoreactive. Immunoelectron microscopy for neurofilament proteins failed to label fibres in the villi, whereas myelinated nerves in tongue sections processed in parallel (positive controls) were strongly neurofilament-protein-immunoreactive. The dominant B-50-positive and neurofilament-protein-negative phenotype supports the hypothesis of ongoing modelling or plasticity of intestinal mucosal nerves.

Immunocytochemical localization of growth-associated protein GAP-43 in early human development

Fibers labelled with antibody to the growth associated protein (GAP-43) were observed as early as 4 gestational weeks (g.w.) in the nervous system of human embryos. At 6 g.w. these fibers could be traced throughout the brainstem and the diencephalon. None of the immunolabeled fibers entered the telencephalic wall at that point, but 2 weeks later at 8 g.w., GAP-43 positive fibers were observed below the newly formed cortical plate of the cerebral cortex. GAP-43 positive fiber bundles had the same distribution as those previously labeled with tyrosine hydroxylase antibodies at the same age. These results strongly suggest that this growth associated protein is localized in the early growing dopaminergic fibers.

Neuronal pathfinding is abnormal in mice lacking the neuronal growth cone protein GAP-43

GAP-43 has been termed a "growth" or "plasticity" protein because it is expressed at high levels in neuronal growth cones during development and during axonal regeneration. By homologous recombination, we generated mice lacking GAP-43. The mice die in the early postnatal period. GAP-43-deficient retinal axons remain trapped in the chiasm for 6 days, unable to navigate past this midline decision point. Over the subsequent weeks of life, most GAP-43-deficient axons do enter the appropriate tracts, and the adult CNS is grossly normal. There is no evidence for interference with nerve growth rate, and cultured neurons extend neurites and growth cones in a fashion indistinguishable from controls. Thus, the GAP-43 protein is not essential for axonal outgrowth or growth cone formation per se, but is required at certain decision points, such as the optic chiasm. This is compatible with the hypothesis that GAP-43 serves to amplify pathfinding signals from the growth cone.

Anatomic basis of cognitive-emotional interactions in the primate prefrontal cortex

Recognition that posterior basal and medial parts of the prefrontal cortex belong to the cortical component of the limbic system was important in understanding their anatomic and functional organization. In primates, the limbic system has evolved along with the neocortex and maintains strong connections with association areas. Consequently, damage to limbic structures in primates results in a series of deficits in cognitive, mnemonic and emotional processes. Limbic cortices differ in their structure and connections from the eulaminate areas. Limbic cortices issue widespread projections from their deep layers and reach eulaminate areas by terminating in layer I. By comparison, the eulaminate areas receive projections from a more restricted set of cortices and when they communicate with limbic cortices they issue projections from their upper layers and terminate in a columnar pattern. Several of the connectional and neurochemical characteristics of limbic cortices are observed as a transient feature in all areas during development. Anatomic evidence suggests that limbic areas retain some features observed in ontogeny, which may explain their great plasticity and involvement in learning and memory, but also their preferential vulnerability in several psychiatric and neurologic disorders.

Increased levels of GAP-43 protein in schizophrenic brain tissues demonstrated by a novel immunodetection method

Studies on the molecular basis of neurological and psychiatric disorders often rely on the precise determination of specific proteins in brain tissues. In this study, we have developed a method for measuring the levels of the neural-specific growth-associated protein, GAP-43, in human postmortem brain specimens. This rapid and quantitative method is based on immunodetection procedures. Briefly, synaptosomal plasma membranes (SPMs) are deposited onto polyvinylidene difluoride (PVDF) membranes via a dot-blotting apparatus, followed by specific GAP-43 detection using a monospecific polyclonal antibody. Overall, the dot-blot procedure provided several advantages over Western blots and one-dimensional and two-dimensional polyacrylamide gels. The assays were more sensitive, reproducible, and allowed the rapid and simultaneous determination of multiple samples. Using this technique, we examined the levels of the GAP-43 protein in Brodmann's areas 17, 20, and 10 of schizophrenic and age-, sex-, and postmortem interval (PMI) matched controls. These studies revealed an increase in the levels of GAP-43 in visual association and frontal cortices (areas 20 and 10) of schizophrenic brains. Given the relationship of GAP-43 expression with the establishment and remodeling of neural connections, our results support the hypothesis that schizophrenia is associated with a perturbed organization of synaptic connections in associative areas of the human brain.

In vivo induction of the growth associated protein GAP43/B-50 in rat astrocytes following transient middle cerebral artery occlusion

Immunohistochemistry was used to investigate the induction of growth-associated protein GAP43/B-50 in the astrocytes of rat cerebrum in vivo following ischemic injury produced by 30 min of transient middle cerebral artery occlusion. Three days after operation, GAP43 immunoreactivity first appeared in some astrocytic populations surrounding the infarcted lesion. Induction of GAP43 in those astrocytes persisted for up to 14 days and disappeared at 30 days postoperation. Double-immunofluorescence staining confirmed that the GAP43-immunoreactive astrocytes examined were all positive for glial fibrillary acidic protein. Our present data suggest that certain astrocytes could be induced to synthesize GAP43 in vivo in response to an ischemic insult in adult rats.

Selective expression of neurotrophin-3 messenger RNA in muscle spindles of the rat

The expression of neurotrophin-3 messenger RNA was studied by in situ hybridization in rat muscle spindles from the first embryonic stages of their formation until their mature appearance in adult animals. The first expression of neurotrophin-3 messenger RNA in developing muscles was observed at E19 in the firstly formed intrafusal fiber, the nuclear bag2 fiber. High levels of neurotrophin messenger RNA were found in the equatorial region of these intrafusal fibers in thin lines of cytoplasma around and between the packed-up nuclei. From E21 on, neurotrophin-3 messenger RNA was also present in the nuclear bag1 type intrafusal fiber. The expression of neurotrophin-3 messenger RNA in nuclear chain fibers, which were found in muscle spindles from day 6 after birth, was low and insignificant in comparison to the expression in the nuclear bag fibers. After completion of muscle spindle formation around the third week after birth, high levels of neurotrophin-3 messenger RNA remained present in the intrafusal fibers throughout life. During the entire period of muscle formation, examined from E15 on, as well as in mature muscles, no neurotrophin-3 messenger RNA could be detected in extrafusal fibers by in situ hybridization. The exclusive intramuscular expression of neurotrophin-3 messenger RNA in intrafusal fibers during development as well as in mature stages suggests the involvement of neurotrophin-3 in the formation and the maintenance of muscle spindles.

Prenatal haloperidol induces a selective reduction in the expression of plasticity-related genes in neonate rat forebrain

Haloperidol, a dopamine receptor antagonist clinically used as an antipsychotic drug, induces long-term deleterious effects in offspring development when administered prenatally. However, the basis for this overall response to the drug remains unknown. Here we describe that prenatal administration of haloperidol in rats induces a drastic and selective reduction in the expression of plasticity-related genes in neonate forebrain, but not in mesencephalon. GABAergic and enkephalinergic markers such as glutamic acid decarboxylase activity and mRNA, and preproenkephalin mRNA were also diminished in forebrain. However, the expression of other genes such as epidermal growth factor-receptor, glial fibrillary acidic protein, and several proto-oncogenes (src, fos and myc), and a cholinergic marker such as choline acetyltransferase activity were unaltered. In addition, haloperidol promoted a significant decrease in mitotic cell number and cellular density in the striatum, one of the forebrain regions with the highest dopamine receptor density. These findings suggest that prenatal dopamine receptor occupancy may be a critical factor in controlling the development of forebrain target cells through mechanisms involving changes in the expression of plasticity-related genes.

c-Fos induction in the rat spinal dorsal horn partially deafferented by dorsal rhizotomy

The 4th and 5th segments of the lumbar (the L4 and L5) dorsal horn receive primary input from the sciatic receptive fields through the L4 and L5 dorsal roots. Noxious stimulation of the hindpaw with formalin induces c-Fos in neurons in superficial laminae (I and II) of these dorsal horn segments. Rhizotomy of the L5 dorsal root 2 days before stimulation resulted in a marked reduction in the number of neurons with c-Fos protein-like immunoreactivity (fos-neurons). At 3 weeks after the L5 rhizotomy, the number of fos-neurons in laminae I and II significantly increased compared to that at 2 days post-rhizotomy. This result indicates that chronic partial deafferentation by dorsal rhizotomy increases responsiveness of superficial dorsal horn neurons to spared primary input.

Igloo, a GAP-43-related gene expressed in the developing nervous system of Drosophila

GAP-43 (growth-associated protein, 43 × 10(3) M(r)) is an essential, membrane-associated, neuronal phosphoprotein in vertebrates. The protein is abundantly produced in the growth cones of developing and regenerating neurons, and it is phosphorylated upon induction of long-term potentiation (LTP). Prior work has identified GAP-43-like proteins only in chordates. In this paper, a nervous system-specific gene from Drosophila melanogaster is described that encodes two proteins sharing biochemical activities and sequence homology with GAP-43. The region of homology encompasses the calmodulin-binding domain and protein kinase C (PKC) phosphorylation site of GAP-43. The fly proteins are shown to bind Drosophila calmodulin (CaM), and are phosphorylated by purified PKC after a fashion predicted from prior work with vertebrate GAP-43. GAP-43 is modified by palmitoylation. An amino-terminal myristoylation site is described for the Drosophila protein, which may play a similar role in membrane association in the fly. While a small family of GAP-43-related genes has been recognized in vertebrates, only a single gene appears to be present in the fly. As the Drosophila gene encodes two proteins, each with multiple calmodulin-binding domains and repeated sites for PKC phosphorylation, it may afford functions provided by the family of vertebrate genes.

De novo synthesis of GAP-43: in situ hybridization histochemistry and light and electron microscopy immunocytochemical studies in regenerating motor neurons of cranial nerve nuclei in the rat brain

In order to investigate the modulation of the synthesis and the subcellular localization of the growth associated protein GAP-43 in neuronal cell bodies we have taken advantage of the well known regenerative properties of axotomized motor neurons of the facial and hypoglossal nuclei. Alterations in the levels of GAP-43 mRNA containing cells were studied by in situ hybridization histochemistry. The protein localization was examined using immunohistochemistry at the light and electron microscopic levels. Neurons from the control side showed undetectable levels of both GAP-43-like immunoreactivity and GAP-43 mRNA levels. Whereas axotomized neurons exhibited a marked increase in GAP-43 mRNA levels and in GAP-43-like immunoreactivity. Three to 50 days after axotomy, motor neurons ipsilateral to the lesion displayed a dense reticular or filamentous perinuclear distribution of the immunoreactivity in somata and proximal dendritic processes, corresponding to the location of the Golgi apparatus in these neurons. At the electron microscopic level the immunoreactivity was located in the cisternae of the Golgi complex and found to be associated with trans-side vesicles of these complexes. The myelinated fibers of the transectomized facial nerve also presented an intense GAP-43-like immunoreactivity. Twenty-one days after the axotomy a decay in the number of immunostained neurons and in the intensity of immunolabeled somata was observed. Our study reveals a rapid induction of GAP-43 mRNA and protein after axotomy. The localization of the newly synthesized GAP-43-like immunoreactivity to the Golgi apparatus seen in the present work suggests an early association of this protein with newly formed membranes prior to transport toward the terminals through the axons.

Increased expression of growth-associated protein GAP-43/B-50 following cerebral hemitransection or striatal ischemic injury in the substantia nigra of adult rats

The substantia nigra receives massive inhibitory gamma-aminobutyric acid (GABA)-ergic inputs, deafferentation of which is supposed to lead to anterograde transsynaptic regression of the nigral neurons. An immunohistochemical technique was used to examine growth-associated protein GAP-43 expression following cerebral hemitransection or transient middle cerebral artery occlusion (MCAO) in the substantia nigra of adult rats. GAP-43 expression was transiently elevated in the substantia nigra pars reticulata (SNr) neurons, but not in the pars compacta neurons at 3 and 4 days post-hemitransection. Massive striatal ischemic injury produced by transient MCAO also caused an increase in GAP-43 synthesis in the SNr neurons at 3 and 4 days after operation. The present findings raise the possibility that deafferentation of the GABAergic inputs leading to transneuronal regression of the SNr neurons is responsible for the elevated expression of GAP-43 in the substantia nigra of adult rats.

Differential localization of SCG10 and p19/stathmin messenger RNAs in adult rat brain indicates distinct roles for these growth-associated proteins

SCG10 is a developmentally regulated, growth-associated protein (GAP) that was isolated as a neuronal marker of the neural crest. It was recently found that SCG10 shares an amino acid sequence similarity with a phosphoprotein named stathmin or p19 of which phosphorylation is induced by nerve growth factor and vasoactive intestinal peptide in PC12 cells and striatal neurons, respectively. While expression of SCG10 messenger RNA dramatically decreases during postnatal development, significant levels of expression still persist into adulthood. To examine possible roles of SCG10 in the adult brain, we examined the distribution of messenger RNAs encoding SCG10 and p19/stathmin as well as GAP-43 in adult rat brain sections by northern blot, RNase protection and in situ hybridization. SCG10 transcripts are found at high levels in long-distance projecting neurons and neurons with extensive dendritic arbors, while p19/stathmin messenger RNA was weakly distributed over most brain areas. Both messenger RNAs are expressed in neuronal subpopulations but not in glia, although the overall distribution of the transcripts of these two structurally related genes is distinct. The spatial and temporal expression profiles of SCG10 messenger RNA is comparable to that of GAP-43, another neuronal GAP, in the developing nervous system, however the expression of SCG10 messenger RNA in the adult brain is distinct from that of GAP-43, especially in the hippocampus and brain stem, where the dentate granule cells and sensory and motor neurons of brainstem express SCG10 but not GAP-43. These results suggest that SCG10 may have a unique role in the neuronal growth-response of subsets of mature neurons, and that SCG10 plays a stathmin-like function at nerve terminals, to which it may be rapidly transported by means of membrane attachment due to a hydrophobic domain present in SCG10 but not in p19/stathmin. This suggests that SCG10 may play a role in structural plasticity in the adult brain.