Role In Neuronal Transmission Research Articles

Forced Treadmill Exercise Prevents Spatial Memory Deficits in Aged Rats Probably Through the Activation of Na+, K+-ATPase in the Hippocampus.

Regular physical activity has shown to improve the quality of life and to prevent age-related memory deficits. Memory processing requires proper regulation of several enzymes such as sodium-potassium adenosine triphosphatase (Na+, K+-ATPase) and acetylcholinesterase (AChE), which have a pivotal role in neuronal transmission. The present study investigated the effects of a treadmill running protocol in young (3 months), mature (6 months) and aged (22 months) Wistar rats, on: (a) cognitive function, as assessed in the Water maze spatial tasks; (b) Na+, K+-ATPase and AChE activities in the hippocampus following cognitive training alone or treadmill running combined with cognitive training. Animals of all ages were assigned to naïve (with no behavioral or exercise training), sedentary (non-exercised, with cognitive training) and exercised (20min of daily running sessions, 3 times per week for 4weeks and with cognitive training) groups. Cognition was assessed by reference and working memory tasks run in the Morris Water maze; 24 h after last session of behavioral testing, hippocampi were collected for biochemical analysis. Results demonstrated that: (a) a moderate treadmill running exercise prevented spatial learning and memory deficits in aged rats; (b) training in the Water maze increased both Na+, K+-ATPase and AChE activities in the hippocampus of mature and aged rats; (c) aged exercised rats displayed an even further increase of Na+, K+-ATPase activity in the hippocampus, (d) enzyme activity correlated with memory performance in aged rats. It is suggested that exercise prevents spatial memory deficits in aged rats probably through the activation of Na+, K+-ATPase in the hippocampus.

Ketamine upregulates eNOS expression in human astroglial A172 cells: Possible role in its antidepressive properties

Ketamine is a potent anti-depressive agent. Nitric oxide plays an essential role in neuronal transmission and cerebral blood flow and has been implicated in the pathophysiology of major depressive disorder as well as cardiovascular functioning. We investigated the effect of ketamine on eNOS expression in human A172 astroglial cells. Ketamine (50–500μM) increased eNOS expression at 4–24h in a concentration-dependent manner. This effect was mediated by NMDA receptor, Akt inhibition and ERK1/2 activation and was synergistically augmented by rapamycin. The combined effect on the vascular, immune and neuronal systems may be relevant to the rapid antidepressive effect of ketamine.

Probing the Selectivity of Monoamine Transporter Substrates by Means of Molecular Modeling

Probing the Selectivity of Monoamine Transporter Substrates by Means of Molecular Modeling

Membrane progesterone receptors localization in the mouse spinal cord

The recent molecular cloning of membrane receptors for progesterone (mPRs) has tremendous implications for understanding the multiple actions of the hormone in the nervous system. The three isoforms which have been cloned from several species, mPRα, mPRβ and mPRγ, have seven-transmembrane domains, are G protein-coupled and may thus account for the rapid modulation of many intracellular signaling cascades by progesterone. However, in order to elucidate the precise functions of mPRs within the nervous system it is first necessary to determine their expression patterns and also to develop new pharmacological and molecular tools. The aim of the present study was to profile mPR expression in the mouse spinal cord, where progesterone has been shown to exert pleiotropic actions on neurons and glial cells, and where the hormone can also be locally synthesized. Our results show a wide distribution of mPRα, which is expressed in most neurons, astrocytes, oligodendrocytes, and also in a large proportion of NG2 + progenitor cells. This mPR isoform is thus likely to play a major role in the neuroprotective and promyelinating effects of progesterone. On the contrary, mPRβ showed a more restricted distribution, and was mainly present in ventral horn motoneurons and in neurites, consistent with an important role in neuronal transmission and plasticity. Interestingly, mPRβ was not present in glial cells. These observations suggest that the two mPR isoforms mediate distinct and specific functions of progesterone in the spinal cord. A significant observation was their very stable expression, which was similar in both sexes and not influenced by the presence or absence of the classical progesterone receptors. Although mPRγ mRNA could be detected in spinal cord tissue by reverse transcriptase–polymerase chain reaction (RT–PCR), in situ hybridization analysis did not allow us to verify and to map its presence, probably due to its relatively low expression. The present study is the first precise map of the regional and cellular distribution of mPR expression in the nervous system, a prior requirement for in vivo molecular and pharmacological strategies aimed to elucidate their precise functions. It thus represents a first important step towards a new understanding of progesterone actions in the nervous system within a precise neuroanatomical context.

Effects of extracellular calcium concentration on the glutamate release by bioactive glass (BG60S) preincubated osteoblasts

Glutamate released by osteoblasts sharing similarities with its role in neuronal transmission is a very new scientific concept which actually changed the understanding of bone physiology. Since glutamate release is a calcium (Ca2+)-dependent process and considering that we have previously demonstrated that the dissolution of bioactive glass with 60% of silicon (BG60S) can alter osteoblast Ca2+-signaling machinery, we investigated whether BG60S induces glutamate secretion in osteoblasts and whether it requires an increase in intracellular Ca2+. Here we showed that the extracellular Ca2+ increase due to BG60S dissolution leads to an intracellular Ca2+ increase in the osteoblast, through the activation of an inositol 1,4,5-triphosphate receptor (InsP3R) and a ryanodine receptor (RyR). Additionally, we also demonstrated that glutamate released by osteoblasts can be profoundly altered by BG60S. The modulation of osteoblast glutamate released by the extracellular Ca2+ concentration opens a new window in the field of tissue engineering, since many biomaterials used for bone repair are able to increase the extracellular Ca2+ concentration due to their dissolution products.

Interactions between GABA-B 1 receptors and Kir 3 inwardly rectifying potassium channels

γ-aminobutyric acid (GABA) is the principal inhibitory neurotransmitter in the mammalian brain. It acts via both ionotropic GABA-A and metabotropic GABA-B receptors. We evaluated the interaction of receptors with members of the inwardly rectifying potassium (Kir 3) channel family, which also play an important role in neuronal transmission and membrane excitability. These channels are functionally regulated by GABA-B receptors. Possible physical interactions between GABA-B receptor and Kir 3 channels expressed in HEK cells were evaluated using Bioluminescence Resonance Energy Transfer (BRET) experiments, co-immunoprecipitation and confocal microscopy. Our data indicate that Kir 3 channels and Gβγ subunits can interact with the GABA-B 1 subunits independently of the GABA-B 2 subunit or Kir 3.4 which are ultimately responsible for their targetting to the cell surface. Thus signalling complexes containing GABA-B receptors, G proteins and Kir channels are formed shortly after biosynthesis most likely in the endoplasmic reticulum.

Dynamic Changes in Dopaminergic Neurotransmission Induced by a Low Concentration of Bisphenol‐A in Neurones and Astrocytes

One of the most common chemicals that behaves as an endocrine disruptor is the compound 4,4'-isopronylidenediphenol, called bisphenol-A (BPA). We previously reported that prenatal and postnatal exposure to BPA potentiated central dopaminergic neurotransmission, resulting in supersensitivity to psychostimulant-induced pharmacological actions. Many recent findings have supported the idea that astrocytes, which are a subpopulation of glial cells, play a critical role in neuronal transmission in the central nervous system. The present study aimed to investigate the role of neurone-astrocyte communication in the enhancement of dopaminergic neurotransmission induced by BPA. We found that treatment of mouse purified astrocytes and neurone/glia cocultures with BPA in vitro caused the activation of astrocytes, as detected by a stellate morphology and an increase in levels of glial fibrillary acidic protein. A low concentration of BPA significantly enhanced the Ca2+ responses to dopamine in both neurones and astrocytes. Furthermore, a high concentration of BPA markedly induced the activation of caspase-3, which is a marker of neuronal apoptotic cell death in mouse midbrain neurone/glia cocultures. By contrast, treatment with 17beta-oestradiol (E2) had no such effects. Prenatal and neonatal exposure to BPA led to an enhancement of the dopamine-dependent rewarding effect induced by morphine. These findings provide evidence that BPA alters dopamine responsiveness in neurones and astrocytes and that, at least in part, it may contribute to potentiate the development of psychological dependence on drugs of abuse.

Mammalian Scribble Forms a Tight Complex with the βPIX Exchange Factor

Drosophila Scribble is implicated in the development of normal synapse structure and epithelial tissues, but it remains unclear how it plays a role and which process it controls [1–3]. The mammalian homolog of Scribble, hScrib, has a primary structure and subcellular localization similar to that of its fly homolog [4], but its function remains unknown. Here we have used tandem mass spectrometry to identify major components of the hScrib network. We show that it includes βPIX (also called Cool-1), a guanine nucleotide exchange factor (GEF), and its partner GIT1 (also called p95-APP1), a GTPase activating protein (GAP) [5–8]. βPIX directly binds to the hScrib PDZ domains, and the hScrib/βPIX complex is efficiently recovered in epithelial and neuronal cells and tissues. In cerebellar granule cell cultures, hScrib and βPIX are both partially localized at neuronal presynaptic compartments. Furthermore, we show that hScrib is required to anchor βPIX at the cell cortex and that dominant-negative βPIX or hScrib proteins can each inhibit Ca2+-dependent exocytosis in neuroendocrine PC12 cells, demonstrating a functional relationship between these proteins. These data reveal the existence of a tight hScrib/βPIX interaction and suggest that this complex potentially plays a role in neuronal transmission.

Differential involvement of PKC subspecies in neuronal function

Protein kinase C (PKC) is a key enzyme involved in various types of signal transduction, and it is most abundant in the nervous system. Available evidence suggests that PKC plays a prominent role in neuronal transmission. PKC is a member of a family consisting of at least eleven subspecies: alpha, beta I, beta II, gamma, delta, epsilon, eta, theta, mu, zeta and lambda. The individual role of each subspecies could not be demonstrated because of the homologous structure of the PKC subspecies. We studied the distinct functional roles of PKC subspecies in the central nervous system by defining the detailed localization of each subspecies. The immunocytochemical localization suggested that cPKCs (alpha, beta I, beta II, and gamma) function postsynaptically, while epsilon-PKC preferentially modulates the synaptic efficacy in the presynapse. GAP-43, a presynaptic PKC substrate involved in neuronal plasticity, was preferentially phosphorylated by epsilon-PKC rather than alpha, beta and gamma-PKC. As the epsilon-PKC could be activated by arachidonic acid, it is strongly suggested that in the case of LTP, the presynaptic epsilon-PKC is activated by arachidonic acid released postsynaptically and phosphorylates GAP-43, resulting in the increase in glutamate release.

Immunocytochemical localization of the α-, βI-, βII- and γ-subspecies of protein kinase C in the monkey visual pathway

We examined the distribution of α-, βI-, βII- and γ-subspecies of protein kinase C (PKC) in the monkey visual pathway, including the retina, the lateral geniculate nucleus (LGN) and the visual cortex (area 17). In the retina, α-PKC immunoreactivity was found in cone photoreceptor and in bipolar cells. βBI-PKC immunoreactivity was present in the ganglion cell layer and the optic nerve fibers. The βII- and γ-PKCs were not found in the retina. In the LGN, intense γ-PKC immunoreactivity was found in a part of magno and parvo cells. The LGN was negative for the α-, βI- and βII-PKC. All four PKC subspecies were present in the visual cortex but the distribution was distinct. The βI-PKC immunoreactive cells were scattered in all layers, while the α-PKC immunoreactive cells were prominent in layers II, III, IVb, IVc and VI, and the βII-PKC immunoreactive cells were found in layers II, III, IVb and VI. The intense γ-PKC immunoreactivity was present in the neuropils in layers I, IVa, IVc and VI and also in soma and dendrites in layers II and VI. It thus seems likely that each subspecies plays a specific role in neuronal transmission in the visual pathway.

Classical acetylcholine receptors do not play a direct role in neuronal transmission of photic information in the suprachiasmatic nucleus in rats

Acetylcholine is said to be involved in the neuronal transmission of photic information in the suprachiasmatic nucleus (SCN). The purpose of this study was to specify what subtypes of acetylcholine receptors play a major role using in vivo system and to examine the interaction of acetylcholine and excitatory amino acid receptors. To evaluate the effect of a selective agonist or antagonist for the nicotinic or muscarinic receptor on the neuronal transmission in the SCNT, N-acetyltransferase (NAT) activity in the pineal gland was measured after microinjection at this site. In the case of pretreatment with an antagonist, light stimulation was given after 20 min. Carbamilcholine chloride (carbachol) mimicked and only α-bungarotoxin (α-BTX) blocked the light effect; however, more selective agonists or antagonists were not effective. As for the interaction of these two cholinergic agents with an agonist or antagonist for N- methyl- d-aspartate (NMDA) receptor, α-BTX or d-2-amino-5-phosphonovalerate ( d-APV) significantly blocked the suppressive effect of NMDA or carbachol, respectively. These data suggest that classical acetylcholine receptors do not play a direct role in neuronal transmission of photic information in the SCN in rats.

Immunohistochemical localization of guanine nucleotide-binding protein in rat retina

The localization of a guanine nucleotide-binding protein, Go, in rat retina has been immunohistochemically examined by use of affinity-purified antibody against the alpha-subunit of Go. Dense Go-immunoreactive products are localized in the inner and outer plexiform layers which are considered as the region of synaptic interplay between neuronal components of the retina. Weak Go-immunoreactivity is also found in the neuropil of the ganglion cell layer and the inner nuclear layer. The selective enrichment of Go in synaptic zones of the retina suggests its major role in neuronal transmission within the retina.

ONTOGENESIS OF ENZYME SYSTEMS DEAMINATING DIFFERENT MONOAMINES

1 A detailed investigation into the postnatal development of the activity of the enzyme monoamine oxidase (MAO) in the rat and domestic pig was carried out. 2 MAO activity was measured in littermate male rats aged between 3 and 122 days belonging to six breeding colonies. The tissues studied were three brain regions in which monoamines may play a role in neuronal transmission (septum, hypothalamus, corpus striatum) and, for comparison, in the cerebellum. Liver, heart and adrenal glands were the peripheral organs studied. The following substrates were used to measure MAO activity in each tissue homogenate: kynuramine, tyramine, dopamine, tryptamine and 5-hydroxytryptamine (5-HT). 3 MAO activity towards kynuramine, tyramine and dopamine increased after birth in all brain regions and also in the liver, to reach maximal values between days 40 and 80. In the heart and the adrenal glands enzyme activity remained low up to 30-40 days and then increased steeply. This was the case in all litters examined. 4 All tissues deaminated more tyramine than dopamine. In the liver, the ratio of the quantities of tyramine deaminated/dopamine deaminated was approx. 2 at all ages. In the homogenates of whole brains (including or excluding the hypothalamus and striatum) this ratio was also 2 at all ages. In contrast in the isolated striatum and hypothalamus it was first much higher and reached a value of 2 only at an age of about 20 days. This may indicate an independent development of a dopamine and a tyramine deaminating enzyme system in discrete brain regions. It was suggested, that the low ability to deaminate dopamine in discrete brain regions may be due to the local presence of an enzyme inhibitor which becomes too diluted to be active in homogenates of whole brain. 5 Deamination of tryptamine in the striatum decreased between day 5 and 20 in 3 out of 4 colonies tested. There was a large fall in the deamination of 5-HT in all tissues of one group of rats, but in another 4 groups the tissues of the 5 day old rats deaminated smaller amounts of 5-HT than those of the older rats. 6 Purified hypothalamic mitochondria from 40 day old rats deaminated more tyramine and dopamine but not tryptamine per mg protein than those from 5 day old rats. 7 In the domestic pig there was a significant rise in the values in hippocampal MAO activity towards dopamine and tyramine from the foetus (55 day gestation) to the 1 week old piglet. A further steady rise up to week 6 was indicated, but this rise was not statistically significant. The difference between rat and pig probably reflected the much higher degree of maturity of the latter at birth. 8 In the hippocampus of the pig the ratio between the amount of tyramine deaminated/dopamine deaminated decreased from greater than 10 (foetus) to 4.8 in the 6 week old pig and 2 in the adult.