«AMPA Receptors Recent cloning efforts have clearly demonstrated that AMPA and kainate receptors are distinct receptor complexes, although they can be activated ...» Document abstract
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psychology
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26/11/2007
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SummaryGlutamate Receptors Glutamate receptors are found throughout the brain and are expressed on both neurons and glia, although not all glutamate receptor subtypes are found on both cell types. Glutamate receptors, sometimes referred to as excitatory amino acid receptors, were initially classified into N-methyl-D-aspartate (NMDA), quisqualate, and kainate receptors on the basis of their preferential activation by these exogenous agonists. More recently, five categories of glutamate receptors (NMDA, kainate, a-amino-3-hydroxy-5-methylisoxazole-4-propionic acid [AMPA], L-2-amino-4-phosphonobutyrate (L-AP4), and trans-1-aminocyclopentane-1,3-dicarboxylic acid [ACPD] receptors) have been established on the basis of pharmacological, electrophysiological, and molecular biological criteria. The L-AP4 receptor type is defined by its agonist and acts as an inhibitory autoreceptor, while the quisqualate receptors of the previous classification have been subdivided by means of more-specific agonists into AMPA and ACPD receptors. AMPA and Kainate receptors are sometimes collectively referred to as non-NMDA receptors. NMDA, kainate and AMPA receptors are ionotropic glutamate receptors; the L-AP4 and ACPD receptors are grouped as metabotropic receptors. Ionotropic receptors are ligand-gated cation-specific channels that are activated rapidly (milliseconds), whereas metabotropic receptors coupled to G proteins and second-messenger systems function more slowly on a scale of several hundred milliseconds to seconds.
Table of Contents- AMPA Receptors Recent cloning efforts have clearly demonstrated that AMPA and kainate receptors are distinct receptor complexes, although they can be activated by the same agonists.
- Kainate Receptors Although kainate is an effective agonist of AMPA receptors, it also activates its own distinct class of ionotropic receptors, the kainate-preferring receptors.
- NMDA receptors have a number of distinct recognition sites for endogenous and exogenous ligands, each with discrete binding domains. At present there are at least seven pharmacologically distinct sites through which compounds can alter the activity of this receptor.
- Metabotropic Receptors Not as much is known about the last group of glutamate receptors, the metabotropic receptors.
«GABAA receptors are heteromeric in that the receptor can comprise at least four types of subunit proteins, termed a, b, g, and d. It is pentameric in that each ...» Document abstract
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Language : english
psychology
presentation
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26/11/2007
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SummaryGABAA Receptor The GABAA receptor is a member of the superfamily of ligand-activated ion channels in the cell membrane. GABA type A (GABAA) receptors are most closely related to strychnine-sensitive glycine receptors, more distantly related to acetylcholine nicotonic receptors and serotonin 5-hydroxytryptamine (5-HT) [5-HT] type receptors, and even more distantly related to glutamate ionotropic receptors (AMPA and kainate receptors and NMDA receptors). GABAA receptors are heteropentameric protein complexes, which when activated undergo a series of conformational changes that form an open channel (pore) selectively permeable to anions, specifically chlorine anion (Cl–) and to a lesser degree (HCO–3). Receptor activation normally results in an influx of Cl– which rapidly and transiently hyperpolarizes the membrane, a process generally referred to as the generation of an inhibitory postsynaptic potential. The increase in Cl– flux also decreases the resistance of the membrane, which acts as a shunt to impede the ability of depolarizing excitatory postsynaptic potentials to elicit action potentials (nerve impulses).
Table of Contents- GABAA receptors are heteromeric in that the receptor can comprise at least four types of subunit proteins, termed a, b, g, and d. It is pentameric in that each receptor has a total of five proteins
- A variety of pharmacological agents can influence the activity of GABAA receptors
- GABAB Receptors The metabotropic GABAB receptors are a member of the superfamily of G-protein-coupled receptors expressed in the cell membrane.
- However, it is likely that a breakdown in the regulation of glutamate is a major factor.
- Epilepsy Epilepsy is a group of neurological disorders characterized by spontaneous recurrent seizures.
- Although many neurobiological factors may contribute to seizure formation, a prominent feature of most seizures is an abnormal and excessive firing of glutamatergic neural pathways.
- Kindling, which is a gradual induction of a hyperexcitable neuronal state, can occur by focal repetitive subconvulsive stimulation of the hippocampus, amygdala, or some other brain areas.
- Neuropathic Pain Activation of afferent C fibers with nociceptive stimuli produces pain sensations that are enhanced during pathological conditions.
- A pregnane-derived synthetic neurosteroid is in clinical trials for treatment of epilepsy.
- Substance Abuse Ethanol enhances GABA receptor function in some in vitro preparations potentially via a protein-binding site.
«Neurotransmitter receptors produce intracellular effects by one of two basic mechanisms: . In the wake of the recent proliferation ...» Document abstract
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Language : english
psychology
research papers
date published
13/11/2007
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SummaryUltimately the effects of monoamines on CNS function and behavior depend upon their interactions with receptor molecules. The binding of monoamines to these plasma membrane proteins initiates a series of intracellular events that modulate neuronal excitability. Unlike the transporters, multiple receptor subtypes exist for each monoamine transmitter. The initial classification of many receptor subtypes was based on radioligand binding studies. Receptor binding sites were identified on the basis of the rank order of binding affinities for a number of agonist and antagonist compounds. More recently, the molecular cloning of monoamine receptors has confirmed that many of the sites initially defined by these binding studies did indeed correspond to distinct receptor proteins encoded by unique genes. Molecular cloning has also led to the identification of previously unknown receptors, and to the introduction of powerful tools to characterize receptor structure and function.
Table of Contents- Neurotransmitter receptors produce intracellular effects by one of two basic mechanisms:
- In the wake of the recent proliferation of known receptors subtypes, much work needs to be done to determine the functional roles of individual receptors.
- The 5-HT1 receptors comprise the largest serotonin receptor subfamily, with human subtypes designated:
- At least three receptor subtypes mediate the effects previously attributed to a single 5HT2 receptor subtype.
- The 5-HT3 receptor is unique among monoaminergic receptors in its membership within the ligand-gated ion channel superfamily.
- The D1 receptor was initially distinguished from the D2 subtype by its high affinity for the antagonist SCH 23390 and its relatively low affinity for butyrophenones such as haloperidol
- The dopamine D2 receptor was initially distinguished from the D1 receptor on the basis of its high affinity for butyrophenones.
- The D3 and D4 receptors are considered to be D2-like on the basis of similarities in their gene structures, sequence homologies, and pharmacology.
- Like the a-adrenergic receptors described, b-adrenergic receptors (designated including subtypes b1, b2, and b3) are found both in the brain and in many peripheral tissues.
- Unlike H1 and H2 histamine receptors, H3 receptors are located presynaptically on axon terminals.
- Within the human brain, nicotinic acetylcholine receptors are found at highest densities within the hippocampal formation, neocortex, substantia nigra, ventral tegmental area, dorsal raphe nucleus, periaqueductal gray, and the basal forebrain cholinergic complex.
« Neuropeptide receptors have been associated with just about every type of second messenger signal transduction system that has been identified. . ...» Document abstract
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Language : english
biology
research papers
date published
26/11/2007
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SummaryNeuropeptide receptors have undergone the same process of discovery and characterization that receptors for other neurotransmitters have enjoyed. The process begins with the pharmacological characterization of the receptor's physicochemical binding properties by assessing the affinity of various metabolically derived and synthetic peptide fragments, and the native molecule, for the receptor binding site found in membrane preparations. Peptide receptor locations are mapped with radioactive or fluorescent tags that are inserted into peptide molecules, which often contain substituted amino acids at the most vulnerable peptidase cleavage sites. Previously, once the peptide receptor was characterized pharmacologically, it was usually purified from some relatively enriched biological tissue source or brain region by affinity column chromatography. After it had been purified, binding parameters and activity were recharacterized for the reconstituted purified receptor protein and structural information obtained by X-ray crystallography. This process was closely followed in the purification of the neurotensin-neuromedin N receptor.
Table of Contents- The neurotensin receptor was first characterized by photoaffinity labeling and cross-linking of radioiodinated ligands, which resulted in two labeled subunits of about 49 Kd and 51 Kd from rat brain synaptosomes.
- The much more powerful tools of molecular biology have been utilized more recently.
- Neuropeptide receptors have been associated with just about every type of second messenger signal transduction system that has been identified.
- Peptides are degraded to smaller fragments, and eventually to single amino acids, by specific enzymes termed peptidases.
- The metabolism of TRH has been investigated fairly completely, principally because of the limited number of fragments that can be generated from a tripeptide.
- The peptides involved in neuroendocrine regulation have cell bodies residing in the hypothalamus that receive feedback from all levels of the endocrine axes.
- Regional differences in CRF receptor regulation by corticosterone have also been reported, which have been shown to partly result from differential glycosylation of the CRF receptor.
- Alzheimer's Disease Dementia of the Alzheimer's Type represents up to two thirds of the demented population encountered in clinical practice, and over half of the nursing home beds in the United States are currently occupied by such patients.
- The CRF-containing interneurons of the cortex are also consistently depleted in Alzheimer's disease. As with SRIF, subcortical areas containing CRF neurons may be spared, but unlike SRIF, CRF receptors are increased in number (up-regulated) with no change in affinity.
- Corticotropin-Releasing Factor After a search spanning nearly three decades, CRF was isolated and characterized in 1981 as a 41-amino acid peptide.
- A series of studies have demonstrated significant elevations of CRF concentrations in the CSF of drug-free patients with major depression or following suicide.
- Like many other neuropeptide transmitters, central administration of SRIF produces a variety of behavioral and physiological effects.
- Decreased neurotensin concentrations in CSF have been reported in several populations of patients with schizophrenia when compared to controls or patients with other psychiatric disorders.
« Structure of Neurotransmitter Receptors Considerable information now exists about the primary structure of neurotransmitter receptors. . ...» Document abstract
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biology
research papers
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26/11/2007
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SummaryClasses of Neurotransmitters Much of the information transfer between neurons in the CNS occurs via chemical synapses. These synapses use a variety of messengers (neurotransmitters) that are released in a Ca2+-dependent fashion from presynaptic terminals and act on specific protein receptors to produce biochemical and excitability changes in the receiving cell. There are two primary groups of neurotransmitters—low–molecular-weight amines and neuroactive peptides. These agents act on two classes of receptors, ligand-gated ion channels, at which the binding of the transmitter directly opens ion channels in the membrane, and G protein coupled receptors. The activated G protein then acts on ion channels or alters biochemical second-messenger systems. Physiologists classify synaptic transmission according to the speed of transmission (fast or slow) and according to the nature of the response (excitatory or inhibitory).
Table of Contents- Currently, there are nine low–molecular-weight amines that serve as neurotransmitters.
- Conductance Mechanisms Underlying Neurotransmitter Actions
- Structure of Neurotransmitter Receptors Considerable information now exists about the primary structure of neurotransmitter receptors.
- The ligand-gated ion channels gated by extracellular ATP (called P2X receptors) are exceptions to the scheme described above and have structures more typical of the inwardly rectifying K+ channels.
- G-protein coupled receptors have a distinctly different structure from the ligand-gated ion channels.
« This unusual property of NMDA receptors provides a molecular mechanism for conferring associative properties on long-term potentiation. . ...» Document abstract
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biology
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26/11/2007
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SummaryIn its simplest form, the postsynaptic response to neurotransmitter release can be mediated by a single protein complex. For example, nicotinic acetylcholine receptors are self-contained stimulus-response modules that both detect a stimulus, acetylcholine, and generate a response, passage of ion currents. In a similar vein, other members of this superfamily of ionotropic receptors, including g-aminobutyric acid (GABA) and glutamate receptors, have the ability to function in a manner that is independent of the intracellular signaling pathways discussed. Thus, in contrast to growth factor or G-protein–coupled receptors, which often recruit elaborate cascades to elicit a response, the simplicity of self-sufficient ionotropic receptor complexes represents an optimal design for achieving reliability, precision, and speed. However, this view of ionotropic receptors as insulated from their social environment has had to be abandoned in the face of overwhelming evidence that this class of receptors is dynamically regulated by intraneuronal signaling pathways. Although these receptors do not rely on intraneuronal signaling pathways to operate ion channels, because these channels are an intrinsic feature of the receptor complex the linkage between ligand binding and ion channel gating is nevertheless subject to regulation by the network of intraneuronal signaling pathways just described. For example, phosphorylation of the GABA or glutamate receptors modulates their response to ligand exposure.
Table of Contents- Long-Term Depression The principle that ion channels are regulated by second messenger pathways is of central importance in considering how neuronal responses are altered by experience.
- Long-Term Potentiation The notion that coactivation of multiple second messenger pathways can have a qualitatively different impact than any one individually is also borne out in another well-known model of synaptic plasticity, long-term potentiation.
- This unusual property of NMDA receptors provides a molecular mechanism for conferring associative properties on long-term potentiation.
- Role of Phosphorylation The associative property of this model of synaptic plasticity has focused attention on deciphering the intraneuronal signaling pathways that mediate the long-term change in synaptic transmission triggered by NMDA receptor stimulation.
- Actions of Psychotropic Drugs In addition to providing insight into the molecular mechanism underlying synaptic plasticity, studies of intraneuronal signaling pathways are also directly relevant to deciphering the mode of action of psychotropic drugs.
- Evidence supporting this theory has been provided by recent studies demonstrating that opiate withdrawal is attenuated in transgenic animals that are deficient in CREB.
« We also tested the effect of an alkaloid called atropine. We predicted that it would impair the action of acetylcholine, since it competes with its receptors. ...» Document abstract
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Language : english
medical studies
case study
date published
23/10/2007
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SummaryOne of the most important organs in the body is the heart. Of course, this organ is of great importance not only in humans but in all vertebrates. Blood, which carries nutrients, oxygen, and wastes from organ to organ within the body is pumped by the heart. Without the heart’s pumping action, blood would simply remain stagnant within the vessels of the body, and any vertebrate in this condition would die off very quickly.
Table of Contents- While the heart is essential to all vertebrates alike, it is important to note that there are some stark distinctions between the hearts of different vertebrates.
- Although the heart is able to initiate its own action potential and make itself beat, there are sympathetic and parasympathetic neurons that innervate it.
- As compared to the control, adding epinephrine sped up heart rate but, according to the readings, decreased contractile strength.
« Out of the many types of GABA(A) receptors in the nervous system, it is believed that only a few are affected by benzodiazepines. ...» Document abstract
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Language : english
biology
school essay
date published
17/09/2007
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SummaryThe GABA(A) receptor plays a vital role in the mammalian brain and is responsible for a large majority of inhibitory neurotransmissions in the central nervous system (Perrine 144). The GABA(A) receptor is a member of the ionotropic (ligand gated) family of receptors that uses GABA, otherwise known as γ-aminobutyric acid, as its ligand. The binding of GABA to the receptor opens the associated ion channel, which in this case is selectively permeable to chlorine ions as they pass down their electrochemical gradient. The negatively charged chlorine ions passing into the cell further negate the postsynaptic membrane potential, usually hyperpolarizing it. This makes it more difficult to depolarize the cell and decreases the probability of further propagation of action potential.
Table of Contents- The GABA(A) receptor plays a vital role in the mammalian brain and is responsible for a large majority of inhibitory neurotransmissions in the central nervous system
- The GABA(A) receptor consists of five glycoprotein subunits
- Other binding sites exist along the protein shell of the GABA(A) receptor complex, including binding sites for agonists (activating ligands) such as barbiturates(sedatives), certain steroids and benzodiazepines
- Diazepam, commonly known as Valium, with its trademark electron attracting group at the 7th position
- with an ' subunit but the aforementioned two GABA ligands are still necessary for the ion channel to open
- Out of the many types of GABA(A) receptors in the nervous system, it is believed that only a few are affected by benzodiazepines
- There exist three types of benzodiazepines, short lasting, intermediate lasting and long lasting.
- With all these positive effects of benzodiazepines, there is always the risk of taking too much.
- With all these positive effects of benzodiazepines, there is always the risk of taking too much.
« The parasympathetic sends signals through the Vagus nerve to Acetylcholine receptors on the heart which decreases cardiac output. ...» Document abstract
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Language : english
biology
case study
date published
02/10/2007
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SummaryThe heart is probably one of the most important muscles in an organism’s body. It is what drives the flow of nutrients, oxygen, and other vital cells across an organism’s body. In different organisms the heart can have slightly different anatomical features as compared to other organisms. In humans, the heart is divided into 4 chambers; the left and right atriums as well as the left and right ventricles. Each chamber is separated by muscle walls and by special valves, the semi lunar and cuspids, which allow blood to flow into appropriate chambers and to make sure oxygenated blood and deoxygenated blood do not mix, allowing for 100% separation.
Table of Contents- The heart is probably one of the most important muscles in an organism's body.
- The blood in the frog heart gets pumped through the different chambers and throughout the body by contraction of the muscle cells in the heart.
- It can be said that the modern Internet began with the formation of several online communities.
- Modern medicine now uses technology which records the depolarization of the heart and graphs them allowing us to calculate heart rates and strengths.
- Although the heart is able to regulate itself, the nervous system is able to regulate the strength and duration of contractions.
- In this experiment we measured the mechanical and electrical activity of the Frog heart.
- Based exclusively on the data our hypothesis is supported, but it can not be applied because it was not carried out under optimal conditions.
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