Transforming growth factor-beta 1 in the rat brain: increase after injury and inhibition of astrocyte proliferation.

Transforming growth factor-beta 1 (TGF-beta 1) has been shown to up-regulate the synthesis of nerve growth factor (NGF) in cultured rat astrocytes and in neonatal brain in vivo (Lindholm, D., B. Hengerer, F. Zafra, and H. Thoenen. 1990. NeuroReport. 1:9-12). Here we show that mRNA encoding TGF-beta 1 increased in rat cerebral cortex after a penetrating brain injury. The level of NGF mRNA is also transiently increased after the brain trauma, whereas that of brain-derived neurotrophic factor remained unchanged. In situ hybridization experiments showed a strong expression of TGF-beta 1 4 d after the lesion in cells within and in the vicinity of the wound. Staining of adjacent sections with OX-42 antibodies, specific for macrophages and microglia/brain macrophages, revealed a similar pattern of positive cells, suggesting that invading macrophages, and perhaps reactive microglia, are the source of TGF-beta 1 in injured brain. Both astrocytes and microglia express TGF-beta 1 in culture, and TGF-beta 1 mRNA levels in astrocytes are increased by various growth factors, including FGF, EGF, and TGF-beta itself. TGF-beta 1 is a strong inhibitor of astrocyte proliferation and suppresses the mitotic effects of FGF and EGF on astrocytes. The present results indicate that TGF-beta 1 expressed in the lesioned brain plays a role in nerve regeneration by stimulating NGF production and by controlling the extent of astrocyte proliferation and scar formation.

Selective tonicity-induced expression of the neutral amino-acid transporter SNAT2 in oligodendrocytes in rat brain following systemic hypertonicity.

Sodium-coupled neutral amino-acid transporter member 2 (SNAT2) belongs to the family of neutral amino-acid transporters. SNAT2 is encoded by the gene Slc38a2, whose expression was reported to increase in vitro in fibroblasts, endothelial and renal cells exposed to a hypertonic medium. SNAT2 tonicity-induced expression brings about cellular accumulation of amino-acid, which contributes to osmoadaptation to hypertonicity. Since brain osmoadaptation is observed in relationship to neurological disorders resulting from pathological osmotic imbalances in blood plasma, we have investigated, through immunocytochemistry, SNAT2 expression in brain of rats subjected to systemic hypertonicity. Following prolonged systemic hypertonicity (24 h), small, strongly immunolabeled elements were observed that were not present in sham-treated animals. They were evenly distributed in the gray matter, with a lower density in the forebrain and a higher density in the brain stem. However the highest density by far was observed in white matter, where they were frequently aligned in chain-like rows. These observations suggested an oligodendrocyte location that was further established by double immunofluorescent labeling, using the oligodendrocyte phenotypic markers 2'-3'-cyclic nucleotide 3'phosphodiesterase and carbonic anhydrase II. SNAT2-positive elements were found associated with oligodendrocyte cell bodies, while oligodendrocyte processes were devoid of labeling. A quantitative analysis performed in the cerebral cortex indicated that virtually all SNAT2-positive elements were associated with oligodendrocyte cell bodies and conversely that the overwhelming majority of oligodendrocytes showed SNAT2 immunolabeling. The tonicity-induced expression of SNAT2 was not observed following acute systemic hypertonicity (6 h). Our results suggest that the osmoadaptation of brain oligodendrocytes to hypertonicity relies upon amino-acid accumulation through the tonicity-induced expression of SNAT2. The possible significance of these findings in relationship to the selective loss of oligodendrocytes observed in osmotic demyelination syndrome is discussed.

[Pathophysiology of the glutamate and the glycine transporters: new therapeutic targets]. / Fisiopatologia de los transportadores de glutamato y de glicina: nuevas dianas terapeuticas.

INTRODUCTION: The amino acids glutamate and glycine, apart from their role in protein synthesis, are two fundamental neurotransmitters in the central nervous system of mammals. The first one is ubiquitous and is involved in excitatory pathways of the neocortex, the retina and the cerebellum, and the second is involved in inhibitory pathways of brain caudal areas. However, both share their way of acting by integrating into the functioning of glutamate receptors of the NMDA type fundamentals in the regulation of motor, sensory and cognitive systems. AIM: To highlight the need for a fine regulation of glutamate and glycine concentrations in the intracellular and extracellular spaces of the nervous system through the action of very specific transporters for both neurotransmitters located in the plasma membrane of neurons and glial cells. DEVELOPMENT: The role of the glutamate and glycine transporters in glutamatergic and glycinergic neurotransmission and in the functioning of the nervous system is described. The pathological consequences of imbalances in these signaling pathways are pointed out. We also describe its involvement in pathologies such as schizophrenia, chronic pain, cerebral ischemia, diseases such as hereditary hyperekplexia and the non-ketotic hyperglycinemia, and neurodegenerative disorders. CONCLUSIONS: The knowledge at molecular level of the way of acting of these transporters for glutamate and glycine is allowing the identification and development of new therapeutic strategies for pathologies such as those described above and the development of new drugs.

TITLE: Fisiopatologia de los transportadores de glutamato y de glicina: nuevas dianas terapeuticas.Introduccion. Los aminoacidos glutamato y glicina, aparte de su papel en la sintesis de proteinas, son dos neurotransmisores fundamentales en el sistema nervioso central de los mamiferos. El primero es ubicuo y esta implicado en vias excitatorias de la neocorteza, la retina y el cerebelo, y el segundo esta asociado a vias inhibitorias de zonas caudales del cerebro. Sin embargo, ambos comparten su manera de actuar al integrarse en el funcionamiento de los receptores de glutamato del tipo NMDA, fundamentales en la regulacion de sistemas motores, sensitivos y cognitivos. Objetivo. Evidenciar la necesidad de una regulacion exquisita de las concentraciones de glutamato y de glicina en los espacios intra y extracelulares del sistema nervioso mediante la actuacion de transportadores muy especificos para ambos neurotransmisores localizados en la membrana plasmatica de las neuronas y de las celulas de la glia. Desarrollo. Se describe el papel de los transportadores de glutamato y glicina en la neurotransmision glutamatergica y glicinergica, y en el funcionamiento del sistema nervioso. Se señalan las consecuencias patologicas de los desequilibrios en estas vias de señalizacion. Tambien se describe su participacion en patologias como la esquizofrenia, el dolor cronico, la isquemia cerebral, la hiperplexia hereditaria, la hiperglicinemia no cetosica o trastornos neurodegenerativos. Conclusiones. El conocimiento de la forma molecular de actuar de los transportadores de glutamato y de glicina esta permitiendo la identificacion y el desarrollo de nuevas estrategias terapeuticas para patologias como las descritas y el desarrollo de nuevos farmacos.

Efflux and exchange of glycine by plasma membrane vesicles isolated from glioblastoma cells.

The efflux and exchange of glycine were studied in plasma membrane vesicles isolated from cultured glioblastoma cells. The mechanism of glycine translocation has been probed by comparing the ion dependence of net efflux to that of exchange. Dilution-induced efflux requires the simultaneous presence of internal sodium and chloride, while influx is dependent on the presence of these two ions on the outside (Zafra, F. and Giménez, C. (1986) Brain Res. 397, 108-116). Glycine efflux from the membrane vesicles is stimulated by external glycine, this exchange being dependent on external sodium, but not on external chloride. The parallelism observed in influx and efflux processes suggests that glycine is translocated in both directions across the membrane, probably by interacting with the carrier. To account for all the observed effects of external ions, glycine concentrations and membrane potential on glycine influx and efflux, a kinetic model of the Na+/Cl-/glycine cotransport system is discussed.

The role of chloride ions on the transport of glycine in plasma membrane vesicles from glial cells.

The high-affinity transport system for glycine in plasma membrane vesicles from C6 glioma cells is dependent on Na+ and also on the presence of Cl- in the incubation medium. This anion requirement is relatively specific for Cl-, since other anions are also capable of stimulating the glycine transport in the following order of decreasing efficacy: Cl- greater than Br- greater than SCN- congruent to I- greater than NO3- greater than F-. Chloride ions raise the Vmax for transport and, to a lesser extent, act on the Km. The data provided by direct measurements of the coupling of sodium and chloride to the transport of glycine by using a kinetic approach suggest a stoichiometry for the translocation cycle catalyzed by the glycine transporter of two sodium ions and one chloride ion per glycine zwitterion.

Regulation by phorbol esters of the glycine transporter (GLYT1) in glioblastoma cells.

The high-affinity glycine transporter in neurons and glial cells is the primary means of inactivating synaptic glycine. The effects of 12-O-tetradecanoylphorbol ester (TPA), a potent activator of protein kinase C (PKC), on the high-affinity Na(+)-dependent glycine transport were investigated in C6 cells, a cell line of glial origin. Incubation of C6 cells with TPA led to concentration- and time-dependent decrease in the glycine transport that could be completely suppressed by the addition of the PKC inhibitor staurosporine. The TPA effect could be mimicked by oleoylacetylglycerol and exogenous phospholipase C. Northern and Western blot analysis indicate that C6 cells express the GLYT1 glycine transporter. Incubation of COS cells transiently transfected with a full-length clone of the GLYT1 transporter in the presence of TPA, produces a decrease in glycine uptake.

Immunohistochemical localization of the amino acid transporter SNAT2 in the rat brain.

SNAT2 is a neutral amino acid carrier that belongs to the system A family. Since its function in the nervous system remains unclear, we have analyzed its distribution in the rat CNS using specific antisera. Although SNAT2 is expressed widely in the CNS, it is enriched in the spinal cord and the brainstem nuclei, especially those of the auditory system. At the cellular level, SNAT2 was preferentially located in neuronal cell bodies and processes, although it was also strongly expressed in the meninges and ependyma. In astrocytes, the localization of SNAT2 was more restricted since it was intensely expressed in the perivascular end-feet, glia limitans, cerebellar astrocytes and Bergmann glia, but it was less intense in astrocytes of the cerebral parenchyma. Among neurons, the primary sensory neurons of the mesencephalic trigeminal nucleus appeared to be those that most strongly express SNAT2, but many other neurons, including cortical pyramidal cells and their dendrites were also intensely stained. In several regions the transporter was detected in axons, especially in the brainstem, and its presence in both dendrites and axons was confirmed by confocal microscopy and ultrastructural studies. However, while SNAT2 was observed in the large principal dendrites and the small distal dendrites, it was only found in axonal shafts and was excluded from terminals. Some glutamatergic neurons were among the more intensely labeled cells whereas SNAT2 was not detected on GABAergic neurons. The expression of SNAT2 partially coincides with that reported for SNAT1, especially in glutamatergic neurons. Hence, both proteins could fulfill complementary roles in replenishing glutamate pools and be differentially regulated under different physiological conditions. They also seem to co-localize in non-neuronal cells probably contributing to amino acid fluxes through the blood-brain barrier.

Molecular biology of glycinergic neurotransmission.

Glycine is a major inhibitory neurotransmitter in the spinal cord and brainstem of vertebrates. Glycine is accumulated into synaptic vesicles by a proton-coupled transport system and released to the synaptic cleft after depolarization of the presynaptic terminal. The inhibitory action of glycine is mediated by pentameric glycine receptors (GlyR) that belong to the ligand-gated ion channel superfamily. The synaptic action of glycine is terminated by two sodium- and chloride-coupled transporters, GLYT1 and GLYT2, located in the glial plasma membrane and in the presynaptic terminals, respectively. Dysfunction of inhibitory glycinergic neurotransmission is associated with several forms of inherited mammalian myoclonus. In addition, glycine could participate in excitatory neurotransmission by modulating the activity of the NMDA subtype of glutamate receptor. In this article, we discuss recent progress in our understanding of the molecular mechanisms that underlie the physiology and pathology of glycinergic neurotransmission.

Developmental expression of the glycine transporter GLYT2 in the auditory system of rats suggests involvement in synapse maturation.

The synaptic action of many neurotransmitters is terminated by specific transporters that remove the molecules from the synaptic cleft and help to replenish the transmitter supply. Here, we have investigated the spatiotemporal distribution of the glycine transporter GLYT2 in the central auditory system of rats, where glycinergic synapses are abundant. In adult rats, GLYT2 immunoreactivity was found at all relay stations, except the auditory cortex. Many immunoreactive puncta surrounded the neuronal somata in the cochlear nuclear complex, the superior olivary complex, and the nuclei of the lateral lemniscus. In contrast, diffuse neuropil labeling was seen in the inferior colliculus and the medial geniculate body. The punctate perisomatic labeling and the diffuse neuropil labeling were very similar to the staining pattern described previously with glycine antibodies in the auditory system, suggesting that GLYT2 is a reliable marker for glycinergic synapses. However, there was a discrepancy between cytoplasmic GLYT2 and glycine labeling, as not all neuron types previously identified with glycine antibodies displayed somatic GLYT2 immunoreactivity. During development, GLYT2 immunoreactivity appeared between embryonic days 18 and 20, i.e., shortly after the time when the earliest functional synapses have been established in the auditory system. Labeling turned from a diffuse pattern to a clustered, punctate appearance. The development was also characterized by an increase of the signal intensity, which generally lasted until about postnatal day 10. Thereafter, a decrease occurred until about postnatal day 21, when the mature pattern was established in most nuclei. Because of the perinatal onset of GLYT2 immunoreactivity, we speculate that the transporter molecules participate in the process of early synapse maturation.

Stimulation of the trypanocidal and endoribonuclease activities by the interferon induced (2'-5') oligoadenylates.

Interferon or 2'-5' oligoadenylates (2'-5' An) activated the microbicidal activity of primary cultures of rat glia cells and of the mouse macrophage transformed cell line J774 against infection by Trypanosoma cruzi. Pretreatment with gamma-interferon (gamma-IFN) or 2'-5' A3 of rat glia cells or direct addition of these compounds during the incubation with the parasite enhanced the uptake of metacyclic trypanosomes by the cells. Furthermore, glia cells treated with gamma-IFN or 2'-5' A3 were able to restrict the growth and to eventually destroy intracellular amastigotes. Bacterial lipopolysaccharide (LPS) synergized with gamma-IFN as well as with 2'-5' A3 and 2'-5' A4, but not with dephosphorylated 'core' molecules or ATP, to induce a partial trypanocidal activity in J774 cells. In addition, those treatments with gamma-IFN or 2'-5' A3 activated to a similar extent an endoribonuclease, which degraded ribosomal RNA, in rat glia cells, suggesting a role of this enzyme in the mechanism of the trypanocidal activity of gamma-IFN.

The subcellular and cellular distribution of G protein-coupled receptor kinase 2 in rat brain.

G protein-coupled receptor kinase 2 has been found to phosphorylate and thus regulate the activity of several G protein-coupled receptors implicated in neuronal signalling pathways. Although this kinase was initially described as a soluble protein, our laboratory has recently found that a significant amount of G protein-coupled receptor kinase 2 is associated with microsomal membranes in liver and different types of cultured cells. In the present report we show that high G protein-coupled receptor kinase 2 specific activity and protein levels are present in microsomal fractions of rat brain homogenates. On the other hand, immunochemical detection using a new antibody raised against the N-terminus of the kinase revealed a specific and widely distributed staining in different areas of the central nervous system, and the association of G protein-coupled receptor kinase 2 with intracellular structures in nervous cells. Our results further suggest that this receptor kinase may be involved in the modulation of G protein-coupled receptor-mediated neurotransmission and that association with microsomal membranes may play a role in G protein-coupled receptor kinase 2 functions in the brain.

An ultrastructural study of the glycine transporter GLYT2 and its association with glycine in the superficial laminae of the rat spinal dorsal horn.

The glycine transporter GLYT2 is present in axonal boutons throughout the spinal cord, and its laminar distribution matches that of glycine-enriched axons, which are presumed to be glycinergic. In order to determine whether boutons which possess GLYT2 are glycine-enriched, we have carried out pre-embedding immunocytochemistry with antibody raised against GLYT2, and combined this with post-embedding detection of glycine, in the rat. GLYT2 immunoreactivity was present in boutons which formed symmetrical axodendritic, axosomatic or axoaxonic synapses, and was often seen in peripheral axons of type II synaptic glomeruli. One hundred and fifty GLYT2-immunoreactive boutons were analysed quantitatively, and in 142 (94.6%) of these the density of gold particles representing glycine-like immunoreactivity exceeded the background level (over presumed glutamatergic boutons) by at least a factor of two. Within immunoreactive boutons, the GLYT2 reaction product was associated with the plasma membrane, but often appeared as discrete clumps and was generally excluded from the region of the active sites of synapses. These results confirm that GLYT2 is associated with glycine-enriched axonal boutons in the superficial dorsal horn. They also suggest that GLYT2 is unevenly distributed on the plasma membrane of these boutons, and raise the possibility that it may be excluded from synaptic clefts.

Cellular distribution and regulation by cAMP of the GABA transporter (GAT-1) mRNA.

The high-affinity GABA transporter in neurons and glial cells is the primary means of inactivating synaptic GABA. In the present study, a rat GABA transporter (GAT-1)-specific probe was used to quantitate GAT-1 mRNA in cultured neurons and glial cells from rat brain. GAT-1 mRNA is expressed in neurons but not in pure cultures of astrocytes. Incubation of neurons with forskolin led to concentration- and time-dependent decreases in GAT-1 mRNA. This effect could be also achieved by chronic exposure of neurons to 8-Br-cAMP and dib-cAMP but not with 1,9-dideoxyforskolin. This effect on the levels of GAT-1 mRNA correlates with a decrease in the Na(+)-dependent GABA transport activity in neurons. Treatment with agents that increase cellular levels of cAMP did not affect GABA transport or GAT-1 mRNA expression in glial cells.

The glycine transporter GLYT2 is a reliable marker for glycine-immunoreactive neurons.

The glycine transporter GLYT2 is present in neurons of the spinal cord, the brain stem and the cerebellum. This localization is similar to that of glycine immunoreactivity, suggesting a causal relationship between GLYT2 expression and glycine distribution. In this report, we analyzed if such a relationship does exist by using neuronal cultures derived from embryonic spinal cord. GLYT2 was synthesized in a small subpopulation of neurons where it was targeted both to dendrites and to axons, being the axonal content higher than the dendritic one. At early stages in the development of cultured spinal neurons, the highest GLYT2 levels were found in the axonal growth cones. As the culture matured, immunoreactivity extended to the axonal shaft. Double-immunofluorescence experiments indicated a perfect co-localization of GLYT2 and glycine immunoreactivity in cultured neurons. Moreover, the concentration of glycine into neurons expressing GLYT2 was proportional to the concentration of the transporter. This observation was reproduced in GLYT2-transfected COS cells. These evidences indicate that the high content of glycine observed in some neurons in culture is indeed achieved by the concentrative task performed by GLYT2, and that GLYT2 can be used as a reliable marker for identification of glycine-enriched neurons.

The synthesis of nerve growth factor and brain-derived neurotrophic factor in hippocampal and cortical neurons is regulated by specific transmitter systems.

Both nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) exert neurotrophic actions on the cholinergic neurons of the basal forebrain nuclei. These neurotrophic factors are synthesized by hippocampal and cortical neurons that are located in the projection field of the basal forebrain cholinergic neurons. Both in vivo and in vitro the levels of NGF- and BDNF-mRNAs are increased up to 20-fold by kainic acid via non-NMDA glutamate receptors. Enhancement of the effectiveness of the GABAergic system by benzodiazepam or direct GABA agonists blocks the effect of kainic acid and reduces the basic levels of NGF- and BDNF-mRNAs. Whereas the increases in both NGF- and BDNF-mRNAs above normal levels are mediated by non-NMDA receptors, maintenance of the normal levels of NGF- and BDNF-mRNAs seems to be mediated predominantly by NMDA receptors. The regulation of NGF and BDNF synthesis via specific transmitter systems is discussed in the context of the refined tuning of synaptic functions, the potential implications for memory functions, and the possible therapeutic consequences for the treatment of Alzheimer's disease.

Transforming growth factor-beta 1 stimulates expression of nerve growth factor in the rat CNS.

Transforming growth factor-beta 1 (TGF-beta 1) markedly increased the mRNA encoding nerve growth factor (NGF) in cultured rat astrocytes in a time- and concentration-dependent manner. The maximal effect of TGF-beta 1 (a 50-fold increase in NGF-mRNA) was reached after 24 h incubation. The TGF-beta-mediated increase in NGF-mRNA results from enhanced transcription as shown in nuclear run-on studies and in transfection assays using the NGF promoter linked to a chloramphenicol acetyltransferase (CAT) reporter gene. TGF-beta 1 also increased its own expression in astrocytes as well as that of the proto-oncogene c-fos. Intraventricular injection of TGF-beta 1 resulted in an increase of NGF-mRNA levels in the rat hippocampus (3-4 fold) showing that TGF-beta 1 is also effective in increasing NGF expression in vivo.

Characterization of glycine uptake in plasma membrane vesicles isolated from cultured glioblastoma cells.

C6 glioblastoma cells in culture were employed to isolate plasma membrane vesicles. After disruption of the glioblastoma cells by homogenization, membrane fractions were obtained by centrifugation on a discontinuous Ficoll density gradient. Fragmented membranes were found mainly in vesicular form. Transport of glycine has been demonstrated in membrane vesicles, using artificially imposed ion gradients as the sole energy source. The uptake of glycine is strictly dependent on the presence of Na+ and Cl- in the medium, and the process can be driven either by an Na+ gradient (out greater than in) or by a Cl- gradient (out greater than in) when the other essential ion is present. The process is stimulated by a membrane potential (negative inside) as demonstrated by the effect of ionophore valinomycin and anions with different permeabilities. The kinetic analysis shows that glycine is accumulated by two systems with different affinities.

Characterization of the 5' region of the rat brain glycine transporter GLYT2 gene: identification of a novel isoform.

We have identified two alternative 5' ends for the GLYT2 glycine transporter in rat brain DNA by using rapid amplification of cDNA ends (RACE) analysis. Study of the genomic DNA revealed that the isoform diversity is generated by alternative use of exons 1a or 1b, respectively. Upon translation, the mRNA corresponding to the novel isoform GLYT2b would yield a protein five amino acids longer than the previously characterized isoform GLYT2a. Both forms display similar regional distribution and kinetics characteristics. However, whereas GLYT2a is able to actively accumulate glycine into transfected COS cells, GLYT2b seems only to exchange (or release) glycine.

Glycine, glycine receptor subunit and glycine transporters in the rat parabrachial and Kölliker-Fuse nuclei.

In the present study, we investigated the expression and distribution of key molecules in the parabrachial (PB) and Kölliker-Fuse nuclei (KF) that determine glycinergic signal transduction. By means of immunocytochemistry, we analyzed the amino acid glycine (Gly), the glycine transporters 1 and 2 (GlyT1, GlyT2), and the ligand binding glycine receptor-subunit alpha 1 (GlyR alpha 1). Gly-immunoreactivity (-ir) was mainly found in varicose fibers and presumed terminal boutons; Gly-ir cell bodies were only occasionally seen. Immunoreactivity for GlyT2 was located in axons while GlyT1-staining was diffuse in the neuropil. Immunolabeling for GlyR alpha 1 occurred mostly as granular staining diffusely distributed throughout the neuropil. Only in the superior lateral PB, the lateral crescent of the PB, and caudally in the KF did GlyR alpha 1-ir outline cell bodies and primary and higher-order dendrites. Furthermore, our data demonstrate a distinct codistribution of immunoreactivities for Gly, GlyT2. and GlyR alpha 1 in a specific set of PB nuclei and in the KF. Strong staining was consistently seen in the internal lateral PB, the ventral lateral PB, the lateral crescent, the medial PB adjacent to the superior cerebellar peduncle, and the rostral two-thirds of the KF. Moderate to weak immunostaining was present in the superior, central, and dorsal lateral PB, the external medial PB, the medioventral part of the medial PB, and caudally in the KF. In contrast, remaining nuclei such as the external lateral PB and the waist area were essentially devoid of Gly-ir profiles, GlyT2-ir, and GlyR alpha 1-ir. Immunoreactivity for GlyT1 was evenly distributed throughout all nuclei of the medial and lateral PB, including the external lateral PB and the waist area, while the KF was only weakly stained. Our data provide evidence that glycinergic mechanisms might play a role for neural processing in most nuclei of the PB and in the KF. Only the external lateral PB and the waist area are apparently not subject to glycinergic inhibition.

[Molecular bases of hereditary hyperekplexia]. / Bases moleculares de la hiperplexia hereditaria.

INTRODUCTION: Hereditary hyperekplexia is a rare clinical syndrome typically characterized by sudden and generalized startle in response to trivial but unexpected tactile or acoustic stimulations. Typically it is accompanied by a temporally but complete muscular rigidly, and usually it manifests shortly after birth. Some affected infants die suddenly from lapses in cardiorespiratory function. Mental development usually is normal. AIM: To summarize and update the molecular bases underlying the hereditary hyperekplexia syndrome. DEVELOPMENT: Approximately 30% of the individuals suffering hereditary hyperekplexia show mutations on a gene located on chromosome 5q32 with a dominant or recessive trait. This gene encodes the alpha subunit of the strychnine-sensitive glycine receptor, which plays a crucial role in inhibitory glycinergic neurotransmission that process sensory and motor information. About 70% of the patients with hyperekplexia do not show genetic defects in the glycine receptor gene; this suggested that additional genes might be affected in this disease. Recent studies have reveals that mutations in the neuronal glycine transporter GLYT2 are a second major cause of hyperekplexia. CONCLUSIONS: Hereditary hyperekplexia is a complex genetic disease in which several genes can be implicated, all of them directly or indirectly involved in inhibitory glycinergic neurotransmission. Two major proteins involved in hyperekplexia are the strychnine-sensitive glycine receptor (GlyR) and the neuronal glycine transporter GLYT2. Implication of secondary additional accompanying or interacting proteins in glycinergic terminals are not ruled out.