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PubMed1991

Calmodulin-dependent protein kinase II. Multifunctional roles in neuronal differentiation and synaptic plasticity.

One of the most important mechanisms for regulating neuronal functions is through second messenger cascades that control protein kinases and the subsequent phosphorylation of substrate proteins. Ca2+/calmodulin-dependent protein kinase II (CaM-kinase II) is the most abundant protein kinase in mammalian brain tissues, and the alpha-subunit of this kinase is the major protein and enzymatic molecule of synaptic junctions in many brain regions. CaM-kinase II regulates itself through a complex autophosphorylation mechanism whereby it becomes calcium-independent following its initial activation. This property has implicated CaM-kinase II as a potential molecular switch at central nervous system (CNS) synapses. Recent studies have suggested that CaM-kinase II is involved in many diverse phenomena such as epilepsy, sensory deprivation, ischemia, synapse formation, synaptic transmission, long-term potentiation, learning, and memory. During brain development, the expression of CaM-kinase II at both protein and mRNA levels coincides with the active periods of synapse formation and, therefore, factors regulating the genes encoding kinase subunits may play a role in the cell-to-cell recognition events that underlie neuronal differentiation and the establishment of mature synaptic functions. Recent findings have demonstrated that the mRNA encoding the alpha-subunit of CaM-kinase II is localized in neuronal dendrites. Current speculation suggests that the localized translation of dendritic mRNAs encoding specific synaptic proteins may be responsible for producing synapse-specific changes associated with the processing, storage, and retrieval of information in neural networks.

Amino Acid Sequence↗
PubMed2003

The role of synaptic GTPase-activating protein in neuronal development and synaptic plasticity.

Synaptic GTPase-activating protein (SynGAP) is a neuronal RasGAP (Ras GTPase-activating protein) that is selectively expressed in brain and highly enriched at excitatory synapses, where it negatively regulates Ras activity and its downstream signaling pathways. To investigate the physiological role of SynGAP in the brain, we have generated mutant mice lacking the SynGAP protein. These mice exhibit postnatal lethality, indicating that SynGAP plays a critical role during neuronal development. In addition, cell biological experiments show that neuronal cultures from mutant mice have more synaptic AMPA receptor clusters, suggesting that SynGAP regulates glutamate receptor synaptic targeting. Moreover, electrophysiological studies demonstrated that heterozygous mutant mice have a specific defect in hippocampal long-term potentiation (LTP). These studies show that the regulation of synaptic Ras signaling by SynGAP is important for proper neuronal development and glutamate receptor trafficking and is critical for the induction of LTP.

Animals↗
PubMed2005

Comparative localization of two serotonin receptors and sensorin in the central nervous system of Aplysia californica.

Aplysia californica is a powerful model for understanding the cellular and molecular mechanisms underlying modulation of neuronal plasticity and learning. In the central nervous system of Aplysia, serotonin is associated with various behaviors. For example, it induces short-, intermediate-, and long-term synaptic changes in sensory neurons during learning and inhibits the afterdischarge of the bag cells that initiate egg-laying behavior. Little is known about the nature and contribution of serotonin receptors involved in the numerous serotonin-mediated physiological responses in Aplysia. Recently, two G(i)-coupled serotonin receptors (5-HT(ap1) and 5-HT(ap2)) were cloned. We now report that, by using in situ hybridization to express the profile of these receptors, we are able to gain critical insight into their roles in the behavior of Aplysia. We compared their distribution to that of sensorin-A, a peptide specifically found in sensory neurons. We wished to determine their involvement in some simple forms of behavioral modifications. 5-HT(ap1) and 5-HT(ap2) mRNAs are expressed in all ganglia of the Aplysia central nervous system. Stronger signal was observed with the 5-HT(ap2) antisense probe than with the 5-HT(ap1) antisense probe. Notably, mRNA coding for the receptors was found in several identified neurons, in the bag cells, in characterized serotonergic neurons, and in neurons of the mechanosensory clusters that expressed sensorin. We also observed heterogeneity of receptor expression between R2 and LPl1 and among neurons of a single cluster of sensory neurons. These results suggest that 5-HT(ap1) and 5-HT(ap2) receptors may regulate the response to serotonin and/or its release in several neurons.

Animals↗
PubMed1993

Astrocyte subtypes in the rat olfactory bulb: morphological heterogeneity and differential laminar distribution.

Despite increased recognition of the importance and heterogeneity of astrocyte functions throughout the central nervous system (CNS) relatively little attention has been paid to morphological diversity among astrocytes. Recent studies have indicated that subsets of astrocytes are involved in glial-axonal interactions critical to both development and reinnervation of the rat olfactory bulb. Here, we have characterized the morphologies and distribution of astrocytes within anatomically and functionally distinct layers of the adult main olfactory bulb (MOB). Using a known immunohistochemical marker for astrocytes, glial fibrillary acidic protein (GFAP), and the classic gold sublimate method, we identified six astrocyte subtypes based on their morphology and distribution: (1) unipolar, (2) irregular, (3) wedge-shape, (4) circular, (5) semicircular, and (6) elongate. Unipolar, irregular and wedge-shape astrocytes have not been previously described in the CNS. The unipolar and irregular types are located exclusively in the olfactory nerve layer. Wedge-shape astrocytes are unique to, and are the major subtype in, the glomerular layer. These three morphologically unique astrocyte subtypes may correspond to olfactory nerve layer (ONL) and glomerular layer (GL) astrocytes, which express molecules that regulate axonal growth or synaptogenesis during development and/or regeneration of the olfactory nerve. In the glomerular layer, astrocytes are highly organized with respect to the glomeruli. Individual astrocytes are loyal to a single glomerulus. In the external plexiform layer, astrocytes are spaced relatively uniformly. In the granule cell layer, astrocytes appear to compartmentalize granule cell aggregates, recently shown to be coupled by tight junctions. The distribution and patterns of astrocyte processes and the density of GFAP immunoreactivity are distinctive for each of the layers of the olfactory bulb. The spacing of astrocytes and the organization of their processes may be important to compartmentalization of neuronal functions. High levels of GFAP immunoreactivity correlated with layers of high neuronal plasticity. The morphological diversity and differential distribution of astrocytes in the olfactory bulb reported here support growing evidence for functional diversity of astrocytes and important interactions among specific astrocyte and neuron subtypes. It is reasonable to hypothesize, therefore, that as for neurons, morphologically distinctive astrocyte subtypes may correspond to functionally specific classes.

Animals↗
PubMed2001

Acute stress and dexamethasone rapidly increase hippocampal somatostatin synthesis and release from the dentate gyrus hilus.

Somatostatin is a neuropeptide whose facilitatory action in the generation of long-term potentiation (LTP) in the hippocampal dentate gyrus has been associated with memory processes. Since stress and memory seem to share some neural pathways, we studied somatostatin release from dentate gyrus hilar cells of the hippocampus in unanesthetized free-moving rats subjected to stress or dexamethasone treatments. In parallel, the number of dentate gyrus hilar cells expressing somatostatin mRNA was quantified by nonradioactive in situ hybridization in these two experimental conditions. Rats were stereotaxically implanted with a push-pull cannula in the dentate gyrus hilar region. Animals were perfused 1 week later in basal or stress (30 min immobilization stress) conditions. The other group was intraperitoneally injected with the synthetic glucocorticoid dexamethasone (3 mg/kg b.w.). Samples were collected every 15 min for somatostatin radioimmunoassay. In parallel, in other groups of animals undergoing the same treatments, brains were removed for in situ hybridization studies with an oligonucleotide labeled with digoxigenin that recognizes somatostatin-14. The results showed that stress induced a significant increase in somatostatin release from dentate gyrus hilar cells 30-45 min after immobilization stress application. Dexamethasone-injected animals exhibited a similar response 45 min after drug administration. In situ hybridization analysis revealed that the two treatments significantly increased the number of cells expressing somatostatin mRNA in the hilar region. In conclusion, somatostatin interneurons of the hippocampal hilar region appear to be a novel stress stimulus target. Their rapid reactivity, expressed as modifications of both somatostatin release and number of cells expressing somatostatin mRNA, provides an interesting model of neuronal plasticity.

Acute Disease↗
PubMedDate not supplied

Neurons bearing neurofibrillary tangles are responsible for selected synaptic deficits in Alzheimer's disease.

The observation that neurons containing neurofibrillary tangles are usually adjacent to neurons free of any morphological indication of disease, suggests the hypothesis that it is NFT-bearing neurons that are primarily responsible for the loss of function in AD. Quantitative Golgi postmortem studies from our laboratories have indicated that there is in many regions of the brains of nondemented humans an age-related increase in dendritic extent of single neurons. In Alzheimer's disease, this normal, age-related increase in dendritic extent was not found, leading to the hypothesis that one of the neurobiological defects in AD is a failure of neuronal plasticity. Message levels of the growth-associated protein, GAP-43, in frontal association cortex (area 9/46) indicated that AD brains with the highest density of neurofibrillary tangle-bearing neurons, showed GAP-43 message levels decreased of the order of 6-fold relative to AD brains with the lowest density of NFT. Combined immunocytochemistry to differentiate tangle-bearing from tangle-free neurons with in situ hybridization to define relative GAP-43 message levels in single neurons revealed that grain density over tangle-bearing neurons containing nuclei was reduced 3-fold compared to that over adjacent tangle-free neurons. This reduction in expression of GAP-43 message in tangle-bearing neurons was selective, because using probes for other messages showed that grain density over tangle-bearing neurons was, on average, increased or similar to that over adjacent non-tangle-bearing neurons. Message levels for the synaptic vesicle-associated protein, synaptophysin, have also been found to be reduced in tangle-bearing neurons relative to adjacent tangle-free neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed2000

Identification and distribution of nitric oxide synthase in the brain of adult zebrafish.

Nitric oxide (NO) is proposed to be involved in developmental and plastic processes. We investigated the presence and distribution of nitric oxide synthase (NOS) in the zebrafish (Danio rerio) using molecular and histochemical techniques. A partial gene sequence corresponding to the neuronal NOS isoform (nNOS) was identified, and in situ hybridization revealed cellular nNOS mRNA expression throughout the brain of adult zebrafish, distributed in distinct central nuclei and in proliferation zones. NOS immunoreactivity and nicotinamide adenine dinucleotide phosphate diaphorase activity partly coincided with the nNOS mRNA expression, however was present also in additional neuronal and non-neuronal cell types. The results indicate the occurrence of different NOS isoforms in the adult brain, of which nNOS may participate in neurotransmission, and in mechanisms related to the continuous growth and neuronal plasticity of the teleost brain.

Age Factors↗
PubMed2005

Dendritic BC1 RNA in translational control mechanisms.

Translational control at the synapse is thought to be a key determinant of neuronal plasticity. How is such control implemented? We report that small untranslated BC1 RNA is a specific effector of translational control both in vitro and in vivo. BC1 RNA, expressed in neurons and germ cells, inhibits a rate-limiting step in the assembly of translation initiation complexes. A translational repression element is contained within the unique 3' domain of BC1 RNA. Interactions of this domain with eukaryotic initiation factor 4A and poly(A) binding protein mediate repression, indicating that the 3' BC1 domain targets a functional interaction between these factors. In contrast, interactions of BC1 RNA with the fragile X mental retardation protein could not be documented. Thus, BC1 RNA modulates translation-dependent processes in neurons and germs cells by directly interacting with translation initiation factors.

3' Flanking Region↗
PubMed2004

The relationships between neurons containing dopamine and nitric oxide synthase in the ventral tegmental area.

Ventral tegmental area (VTA) is a heterogeneous group of dopaminergic cells which contains interfascicular (IF), parabrachial (PBP) and rostral linear (RLi) nuclei. Neurons of this area are involved in the regulation of motor and motivational aspects of behavior and reveal high neuronal plasticity. Among many various neurotransmitters and neuromodulators, nitric oxide (NO) is localized in this region. In the present study, we investigated morphology and distribution of nitric oxide synthase (NOS)-positive neurons in VTA and their colocalization with dopaminergic neurons. The study was performed on six adult Wistar rats. After perfusional fixation, the brains were cut, immunostained for tyrosine hydroxylase (TH) and NOS and studied by confocal laser microscopy. In each of the three studied nuclei of VTA we investigated three different neuronal populations. Numerous TH-immunoreactive (TH-ir) and NOS-immunoreactive (NOS-ir) neurons are present in the studied region. Among them, a considerable number showed coexistence of both neurotransmitters. The populations of TH-ir and NOS-ir neurons interact with each other as manifested by the presence of NOS-ir endings on TH-ir neurons and vice versa. Taking the above into account, it may be suspected that NO is involved in the modulation of dopaminergic transmission.

Animals↗
PubMed1997

Slow eye movements.

Monkeys and humans are able to perform different types of slow eye movements. The analysis of the eye movement parameters, as well as the investigation of the neuronal activity underlying the execution of slow eye movements, offer an excellent opportunity to study higher brain functions such as motion processing, sensorimotor integration, and predictive mechanisms as well as neuronal plasticity and motor learning. As an example, since there exists a tight connection between the execution of slow eye movements and the processing of any kind of motion, these eye movements can be used as a biological, behavioural probe for the neuronal processing of motion. Global visual motion elicits optokinetic nystagmus, acting as a visual gaze stabilization system. The underlying neuronal substrate consists mainly of the cortico-pretecto-olivo-cerebellar pathway. Additionally, another gaze stabilization system depends on the vestibular input known as the vestibulo-ocular reflex. The interactions between the visual and vestibular stabilization system are essential to fulfil the plasticity of the vestibulo-ocular reflex representing a simple form of learning. Local visual motion is a necessary prerequisite for the execution of smooth pursuit eye movements which depend on the cortico-pontino-cerebellar pathway. In the wake of saccades, short-latency eye movements can be elicited by brief movements of the visual scene. Finally, eye movements directed to objects in different planes of depth consist of slow movements also. Although there is some overlap in the neuronal substrates underlying these different types of slow eye movements, there are brain areas whose activity can be associated exclusively with the execution of a special type of slow eye movement.

Animals↗
PubMed1998

Kindling-induced neurogenesis in the dentate gyrus of the rat.

Kindling, a form of neuronal plasticity produced by repeated low intensity electrical brain stimulation, leads to epileptic seizures. To address possible causes of this phenomenon, we have prepared amygdala-kindled animals and measured neurogenesis, by bromodeoxyuridine incorporation. Early, when focal seizures were present, there was no evidence of a change in the rate of hippocampal neurogenesis. In contrast, during the later phases of kindling, when secondary generalization was well established and motor seizures were present, neurogenesis was enhanced by 75-140%, depending on the hippocampal region. Double labelling with the neuron-specific marker TOAD-64 demonstrated the presence of numerous new-born granule neurons in the kindled animals. We propose that the newly-born neurons contribute to the cellular changes and behavioral symptoms associated with this type of epileptiform brain plasticity.

Animals↗
PubMed2004

Increased expression of nitric oxide synthase in cultured neurons from adult rat colonic submucous ganglia.

Neuronal plasticity in the enteric nervous system (ENS) is probably a key step in intestinal adaptation during growth, maturation and ageing as well as in several pathophysiological situations. Studies on cultured myenteric neurons have revealed an increased vasoactive intestinal peptide (VIP) expression in neuronal nitric oxide synthase (NOS)-expressing neurons. In addition, both VIP and nitric oxide (NO) promote survival of cultured myenteric neurons. The aim of the present study was to investigate possible changes in the expression of VIP and NOS in cultured submucous neurons from adult rat large intestine. Submucous neurons were cultured as explants or as dissociated neurons for 3 and 8 days. Immunocytochemistry was used to determine the proportions of neurons containing VIP or NOS in preparations of uncultured controls (reflects the conditions in vivo) and in cultured explants of submucosa and dissociated submucous neurons. In situ hybridization was used to determine changes in the expressions of NOS and VIP mRNA. The relative number of NOS-expressing neurons increased significantly during culturing. The percentage of all neurons expressing NOS was 22% in controls, while approximately 50% of the cultured submucous neurons expressed NOS. VIP-expressing neurons constituted approximately 80% of all submucous neurons in controls as well as in cultured explants or dissociated neurons. Studies on coexistence revealed that the VIP-containing neurons were the ones that started to express NOS during culture. The induced expression of NOS in cultured adult submucous neurons indicates that nitric oxide, possibly in cooperation with VIP, is important for neuronal adaptation, maintenance and survival.

Animals↗
PubMed2007

Dopamine D1/5 receptor-mediated long-term potentiation of intrinsic excitability in rat prefrontal cortical neurons: Ca2+-dependent intracellular signaling.

Prefrontal cortex (PFC) dopamine D1/5 receptors modulate long- and short-term neuronal plasticity that may contribute to cognitive functions. Synergistic to synaptic strength modulation, direct postsynaptic D1/5 receptor activation also modulates voltage-dependent ionic currents that regulate spike firing, thus altering the neuronal input-output relationships in a process called long-term potentiation of intrinsic excitability (LTP-IE). Here, the intracellular signals that mediate this D1/5 receptor-dependent LTP-IE were determined using whole cell current-clamp recordings in layer V/VI rat pyramidal neurons from PFC slices. After blockade of all major amino acid receptors (V(hold) = -65 mV) brief tetanic stimulation (20 Hz) of local afferents or application of the D1 agonist SKF81297 (0.2-50 microM) induced LTP-IE, as shown by a prolonged (>40 min) increase in depolarizing pulse-evoked spike firing. Pretreatment with the D1/5 antagonist SCH23390 (1 microM) blocked both the tetani- and D1/5 agonist-induced LTP-IE, suggesting a D1/5 receptor-mediated mechanism. The SKF81297-induced LTP-IE was significantly attenuated by Cd(2+), [Ca(2+)](i) chelation, by inhibition of phospholipase C, protein kinase-C, and Ca(2+)/calmodulin kinase-II, but not by inhibition of adenylate cyclase, protein kinase-A, MAP kinase, or L-type Ca(2+) channels. Thus this form of D1/5 receptor-mediated LTP-IE relied on Ca(2+) influx via non-L-type Ca(2+) channels, activation of PLC, intracellular Ca(2+) elevation, activation of Ca(2+)-dependent CaMKII, and PKC to mediate modulation of voltage-dependent ion channel(s). This D1/5 receptor-mediated modulation by PKC coexists with the previously described PKA-dependent modulation of K(+) and Ca(2+) currents to dynamically regulate overall excitability of PFC neurons.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed2001

Relationships between neuronal cell adhesion molecule and LHRH neurons in the urodele brain: a developmental immunohistochemical study.

Polysialic acid (PSA), a homopolymer attached to neural cell adhesion molecule (NCAM) is considered a major hallmark of vertebrate cell migration. We studied the distribution of PSA-NCAM by immunohistochemistry, during brain development, in two urodele amphibians, Pleurodeles waltl and the neotenic newt Ambystoma mexicanum. In both species a gradual increase of immunolabelling was observed throughout the brain from developmental stage 30 to stage 52. At the onset of metamorphosis, some differences became evident: in Pleurodeles immunostaining was gradually restricted to the olfactory system while in Ambystoma, PSA-NCAM maintained a more extended distribution (for example throughout the telencephalic walls) suggesting, for the brain of this latter species, a rather preserved neuronal plasticity. The aim of the present work was to correlate the above described PSA-NCAM-immunoreactivity (IR) with the distribution of luteinizing hormone-releasing hormone (LH-RH) containing neurons, which represent a well known example of neural elements migrating from the olfactory placode. LHRH-IR, undetectable till stage 30, was later found together with PSA-NCAM-IR in both the olfactory system and septo-hypothalamic areas. Such observations further support a role of PSA in providing a migration route toward the establishment of a part, at least, of the urodele LHRH system. The possible functional meaning of the LHRH-containing neurons localized between dorsal and ventral thalamus of Ambystoma, never reported before in this area, almost devoid of PSA-NCAM-IR, is discussed.

Ambystoma mexicanum↗
PubMed2006

The plasticity of the DRG neurons belonging to different subpopulations after dorsal rhizotomy.

1. The plasticity of sensory neurons following the injury to their axons is very important for prognosis of recovery of afferent fibers with different modality. It is evident that the response of dorsal root ganglion (DRG) neurons after peripheral axotomy is different depending on the deficiency in neurotrophic factors from peripheral region. The loss of cells appears earlier and is more severe in B-cells (small, dark cells with unmyelinated axons) than in A-cells (large, light cells with myelinated axons). 2. We studied using immunohistochemical methods the response of DRG neurons to dorsal rhizotomy and combined injury of central and peripheral neuronal processes. A quantitative analysis of DRG neurons tagged by the selective markers isolectin B4 (IB4) and the heavy molecular component of the neurofilament triplet (NF200) antibody, selective for subpopulations of small and large/medium DRG neurons, respectively, was performed after dorsal rhizotomy, peripheral axotomy, and their combination. 3. The number of NF200(+)-neurons is reduced substantially after both dorsal rhizotomy and peripheral axotomy, while the decrease of IB4(+)-neurons is observed only in combined injury, i.e., dorsal rhizotomy accompanied with sciatic nerve injury. 4. Our results show that distinct subpopulations of DRG neurons respond differently to the injury of their central processes. The number of NF200(+)-neurons decreases to greater degree following dorsal rhizotomy in comparison to IB4(+)-neurons.

Animals↗
PubMed1994

Identification and characterization of rhythmic nociceptive and non-nociceptive spinal dorsal horn neurons in the rat.

The properties of rhythmic low-threshold and multireceptive spinal dorsal horn neurons were determined. Multiple neuron recordings were made via a single electrode in the lumbar spinal cord of pentobarbital-anesthetized or decerebrate, unanesthetized, spinalized rats. The background activity of a total of 223 neurons was analysed: 21.0% of 176 fully characterized neurons were low threshold, 73.3% multireceptive and 5.7% nociceptive-specific neurons. Twenty of 100 neurons tested were driven by antidromic stimulation at the upper cervical cord. To identify and evaluate rhythmic harmonic oscillations in the discharges of spinal dorsal horn neurons during background activity and steady-state noxious heat-evoked responses, interspike interval, autocorrelation and autospectral analysis were performed. The background activity of 99 of the 223 neurons (44.4%) of our sample was rhythmic. The distribution of the fundamental spectral frequencies has a bimodal shape, the first band between 0.5 and 2 Hz and the second between 6 and 13 Hz. Low-threshold and multireceptive neurons had a similar incidence of rhythmicity (54.1 and 43.4%, respectively). Only one of 20 neurons with long ascending projections presented rhythmic background activity. Activation of heat-sensitive nociceptors within the cutaneous receptive fields of the neurons had a strong anti-rhythmic effect in nine of 15 (60%) neurons. No change was observed in the pattern of autospectra of non-rhythmic neurons or low-threshold neurons during noxious stimulation. Twenty-four of 37 (66.6%) rhythmic neurons retained their rhythmic background discharges during reversible cold-block spinalization at the upper thoracic cord. The incidence of neurons with burst-like discharges was highest among multireceptive neurons (98/129, 75.9%) and non-rhythmic neurons (89/124, 71.8%). Thus, rhythmicity exists in sensory neurons of the spinal dorsal horn probably generated within its local neuronal network and partially modulated by supraspinal descending systems. Rhythmicity is depressed by activity in primary afferent nociceptors. The role of rhythmicity for information transfer and neuronal plasticity is discussed.

Action Potentials↗
PubMed2004

Matrix metalloproteinases and their endogenous inhibitors in neuronal physiology of the adult brain.

More than 20 matrix metalloproteinases (MMPs) and four of their endogenous tissue inhibitors (TIMPs) act together to control tightly temporally restricted, focal proteolysis of extracellular matrix. In the neurons of the adult brain several components of the TIMP/MMP system are expressed and are responsive to changes in neuronal activity. Furthermore, functional studies, especially involving blocking of MMP activities, along with the identification of MMP substrates in the brain strongly suggest that this enzymatic system plays an important physiological role in adult brain neurons, possibly being pivotal for neuronal plasticity.

Adult↗
PubMed2001

Neurosteroids: recent findings.

The term neurosteroid applies to those steroids that are synthesized in the nervous system, from cholesterol or other blood-borne steroidal precursors, and that accumulate in the nervous system to levels that are at least in part independent from steroidogenic gland secretion. Both glial cells and neurons participate in neurosteroid biosynthesis and metabolism. Several neurosteroids are involved in auto/paracrine mechanisms involving regulation of target gene expression and/or effects on membrane receptors (particularly those for neurotransmitters). An additional unexpected mechanism of steroid action is reported here: pregnenolone binds to neural microtubule-associated protein of type 2 (MAP2) and increases both the rate and extent of tubulin polymerization, forming microtubules of normal electron microscopic appearance. This novel mechanism may play a role in regulating microtubule formation and dynamics and thus neuronal plasticity and function.

Animals↗