Neurotransmitter receptors locations

GABA Gamma aminobutyric acid, a neurotransmitter. Acts upon GABA receptors located especially in the nervous system. 

When the action potential reaches the synaptic bouton, depolarisation triggers the opening of voltage-operated calcium channels in the membrane (Figure 2.5). The concentration gradient for Ca2+ favours the passive movement of this ion into the neuron. The subsequent rise in cytoplasmic Ca2+ ion concentration stimulates the release of neurotransmitter into the synaptic cleft, which diffuses across this narrow gap and binds to receptors located on the postsynaptic neuronal membrane (Figure 2.5). 

G -protein-coupled receptors are often located on the presynaptic plasma membrane where they inhibit neurotransmitter release by reducing the opening of Ca2+ channels like inactivation and breakdown of the neurotransmitter by enzymes, this contributes to the neuron s ability to produce a sharply timed signal. An a2 receptor located on the presynaptic membrane of a noradrenaline-containing neuron is called an autoreceptor but, if located on any other type of presynaptic neuronal membrane (e.g., a 5-HT neuron), then it is referred to as a heteroreceptor (Langer, 1997). Autoreceptors are also located on the soma (cell body) and dendrites of the neuron for example, somatodendritic 5-HTia receptors reduce the electrical activity of 5-HT neurons. 

Postsynaptic receptor A receptor located on the postsynaptic neuronal membrane mediating the physiological effects of the neurotransmitter. 

Purines such as ATP and adenosine play a central role in the energy metabolism of all life forms. This fact probably delayed recognition of other roles for purines as autocrine and paracrine substances and neurotransmitters. Today it is recognized that purines are released from neurons and other cells and that they produce widespread effects on multiple organ systems by binding to purinergic receptors located on the cell surface. The principal ligands for... 

Numerous neurotransmitter receptors are located in the vomiting center, CTZ, and GI tract. Examples of such receptors include cholinergic and histaminic, dopaminergic, opiate, serotonin, neurokinin (NK), and benzodiazepine receptors. Theoretically, chemotherapeutic agents, their metabolites, or other emetic compounds trigger the process of emesis through stimulation of one or more of these receptors. 

Another example of molecular communication is found in a neuronal synapse, which is a communication junction between two neurons as shown in Fig.2. The presynaptic membrane releases the neurotransmitter molecule that is recognized and captured by the receptor located on the surface of the postsynaptic membrane. 

In contrast to the ionotropic receptors, the metabotropic receptors are monomeric in structure and unique in that they show no structural similarity to the other G-protein-coupled neurotransmitter receptors. They are located both pre- and postsynaptically and there is experimental evidence that they are involved in synpatic modulation and excitotoxicity, functions which are also shared with the NMDA receptors. To date, no drugs have been developed for therapeutic use which are based on the modulation of these receptors. 

Synaptic cleft Gap of about 100 300 pm in diameter between two neurons. A neurotransmitter is released from the first neuron into the synaptic cleft and may interact with a receptor located on the membrane of the second neuron to trigger reactions leading to the propagation of information... 

The 5-HT3 receptor is the only monoamine neurotransmitter receptor that functions as a lig-and-gated ion channel, controlling the flux of Na-i- and K+ ions. 5-HT3 receptors are located on parasympathetic nerve terminals in the gastrointestinal tract, and high densities are found in areas of the brain associated with the emetic response, such as the area postrema. The antiemetic effects of 5-HT3 antagonists, such as ondansetron, result from actions at these sites. 5-HT3 receptors in the dorsal horn of the spinal cord have been implicated in nociception and development of new 5-HT3 receptor-related compounds may have potential as non-opioid, non-addictive analgesics. 

For pharmacodynamic agents acting within one species (human), selectivity may also be achieved by differences in accumulation, when similar receptors are located in cells or in membranes of different character. The neurotransmitter receptors, for example, are similar, but are found in a variety of highly differentiated cells whose membranes are unlikely to possess the same physical characteristics. 

The most popular OTC sleep aids are those that contain antihistamines such as diphenhydramine or doxylamine (Table 3.1). As noted in Chapter 1, nerve cells in the brain communicate with each other by secreting chemicals called neurotransmitters. One such neurotransmitter that regulates sleep is histamine. When histamine is released by a nerve cell, it diffuses over to the target nerve cell and binds to specialized proteins called receptors located on the outer surface of the nerve cell. These receptors are specially designed to bind only histamine, and when they do, the target nerve cell will become either activated or deactivated. In the brain, histamine serves the function of keeping us awake, and when drugs such as antihistamines are taken, they block the ability of histamine receptors to bind histamine. 

The actions of neurotransmitters are mediated mostly through their interactions with receptors located either at presynaptic or postsynaptic sites. These receptors function in a coordinated fashion to elicit excitation (depolarization) or inhibition (hyperpolarization) within and between neuronal subsystems. A basic inadequacy in this interplay is believed to lead to pathologic states... 

Ferkany JW, Zaczek R, Coyle JT (1982) Kainic acid stimulates excitatory amino acid neurotransmitter release at presynaptic receptors. Nature 298 757-9 Fink K, Gothert M, Molderings G, Schlicker E (1989) N-methyl-D-aspartate (NMDA) receptor-mediated stimulation of noradrenaline release, but not release of other neurotransmitters, in the rat brain cortex receptor location, characterization and desensitization. Naunyn Schmiede-berg s Arch Pharmacol 339 514-21... 

---