Neurotransmitter receptors muscarinic receptor

So, parasympathetic nerves use acetylcholine as a neurotransmitter and cholinomimetic drugs mimic the action of acetylcholine at its receptors. Muscarinic receptor subtypes are found on neuroeffector junctions. Nicotinic receptor subtypes are found on ganglionic synapses. Chohnomimetics can be classified as ... 

The convincing evidence from the experimental work presented here supports the conclusion that EGb is effective for the treatment of dementia and cerebral insufficiency. To sum up the major characteristics of the pharmacological activities of EGb, particularly in the CNS, the following conclusions can be readied. EGb improves hypoxic tolerance and protects cerebral neurons against apoptosis-, edema- and ischemia-induced injury. In addition, EGb inhibits age-related impairment of cerebral neurotransmitters, inducting muscarinic receptors, and 2-... 

As with most other neurotransmitter receptors, acetylcholine receptors are classified into ionotropic and metabotropic receptors. Ionotropic acetylcholine receptors are referred to as "nicotinic" because they are responsive to nicotine, an alkaloid compound present in cigarettes. Metabotropic acetylcholine receptors are referred to as "muscarinic" because they are sensitive to muscarine, a mushroom compound. Cholesterol has been reported to modulate the activity of both receptor types, yet most studies have been focused on the interaction... 

Acetylcholinesterase is a component of the postsynaptic membrane of cholinergic synapses of the nervous system in both vertebrates and invertebrates. Its structure and function has been described in Chapter 10, Section 10.2.4. Its essential role in the postsynaptic membrane is hydrolysis of the neurotransmitter acetylcholine in order to terminate the stimulation of nicotinic and muscarinic receptors (Figure 16.2). Thus, inhibitors of the enzyme cause a buildup of acetylcholine in the synaptic cleft and consequent overstimulation of the receptors, leading to depolarization of the postsynaptic membrane and synaptic block. 

Parasympathetic stimulation decreases heart rate. Acetylcholine, the neurotransmitter released from the vagus nerve (the parasympathetic nerve to the heart), binds to muscarinic receptors and causes the following effects ... 

Both nicotinic and muscarinic receptors are widespread in the CNS. Muscarinic receptors with a high affinity for pirenzepine (PZ), M, receptors, predominate in the hippocampus and cerebral cortex, whereas M2 receptors predominate in the cerebellum and brainstem, and M4 receptors are most abundant in the striatum. Central muscarinic and nicotinic receptors are targets of intense pharmacological interest for their potential roles in regulating abnormal neurological signaling in Alzheimer s disease, Parkinson s disease and certain seizure disorders. Nicotinic receptors are largely localized at prejunctional sites and control the release of neurotransmitters [10,11],... 

Acetylcholine. Most of the acetylcholine in the basal ganglia is found in the striatum, as the neurotransmitter of the large spiny interneurons, which account for about 3% of all striatal neurons. Both muscarinic and nicotinic cholinergic receptors are found in the striatum. Postsynaptic muscarinic receptors may inhibit transmitter release from... 

Several neurotransmitter and receptor changes are observed in Alzheimer s disease (Nordberg 1992). Losses occur in nicotinic receptors, but muscarinic receptors are relatively preserved. Reductions are also seen in serotonin 5-HTl and 5-HT2 receptors. Glutamate NMDA receptors decrease, while kainate receptors increase. j8-adrenergic and dopamine receptors are preserved. Decreases occur in receptors for somatostatin and neuropeptide Y, but corticotrophin-releasing factor receptors increase. Across all receptor subtypes for which there is a loss, the number of receptors decrease but the affinity constant remains unchanged. 

Muscarinic receptors have modulatory effects on numerous other neurotransmitters in the brain (van der Zee and Luiten 1999). Of particular interest are interactions between glutamate and cholinergic systems in learning and memory (Aigner 1995). 

Norepinephrine opens the pupil of the eye acetylcholine narrows it. Note that an antagonist of acetylcholine at the muscarinic receptor, atropine, has the same outcome as norepinephrine (see above). Norepinephrine is a bronchodilator in contrast, acetylcholine is a bronchoconstrictor. Norepinephrine increases the heart rate, chronotropy, whereas acetylcholine slows the heart rate, bradycardy. Norepinephrine decreases the rate of intestinal movements, whereas acetylcholine increases them. In all these cases, the effects of these neurotransmitters are opposed. 

Acetylcholine is an important neurotransmitter. It acts at nicotinic and muscarinic receptors. Antagonists at these receptors find use in clinical medicine. 

FIGURE 2.5 Cholinergic synapse. Acetylcholine hinds to muscarinic receptors (1) and nicotinic receptors (2). Acetylcholinesterase (AchE) cleaves the neurotransmitter acetylcholine into acetylCoA and choline. 

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