Nicotinic Receptors

Abstract

Fast neurotransmission in the central and peripheral nervous systems is mediated by the activity of ligand‐gated ion channels. Nicotinic acetylcholine receptors (nAChRs) belong to the family of cation‐permeable channels and result from the assembly of five subunits that form both the ligand‐binding site and the ionic pore. Sixteen genes encoding for these receptors have been identified in mammals and show differential expression throughout the body. Endogenously activated by ACh, nAChRs are the primary target of nicotine contained in tobacco leaves and mediate its addiction. The use of a partial agonist of nicotinic receptors significantly reduces craving and show good outcomes in smoking cessation. Spontaneous variations occurring in the genes encoding for nAChRs are associated with neurological diseases such as myasthenia gravis, to genetically transmissible epilepsies and to nicotine dependence. Dysfunction of the nAChR transmission is associated with diseases including schizophrenia, autism and neurodegenerative diseases such as Alzheimer's. Small molecules have recently shown beneficial outcomes in Alzheimer disease opening new avenues to treat neurological affections. Key Concepts: Neurotransmission is mediated by integral membrane proteins and can be subdivided into ligand‐gated ion channels and G‐coupled proteins. Nicotinic acetylcholine receptors belong to the family of cationic ligand‐gated ion channels that comprises four transmembrane domains and result from the assembly of five subunit around an axis of pseudosymmetry. Nicotinic acetylcholine receptors are key players in nicotine addiction and the primary target for this natural alkaloid that is contained in tobacco leaves. Nicotinic acetylcholine receptors at the neuromuscular junction play a determinant role in mediating transmission from the motor nerve to the muscle cell. Impairment of these receptor function leads to myasthenia gravis, which can be decomposed in its most common form to an autoimmune disease and in rarer forms in mutations of one or more genes. Dysfunction of the cholinergic system is associated with cognitive impairment and with neurological diseases such as schizophrenia, autism, genetically transmissible epilepsies and neurodegenerative diseases such as Alzheimer's. The development of small chemical molecules such as the partial agonist varenicline is shown to help in smoking cessation programmes and, more recently, for α7 EVP‐6124 in the treatment of Alzheimer disease.

Together but Separate: Relationships and Boundaries between North and South Koreans in Multiethnic Britain

“…Ethnic identity and boundaries have become significant in a situation of intensified intergroup contact and economic exchange. 19 Most North Korean immigrants in London live around New Malden and work for businesses run by South Korean immigrants. This particular settlement pattern of North Korean immigrants provides an ideal case for observing and analyzing more closely how an immigrant group has delimited the boundaries between "Us" and "Them."…”

“…According to Marger, "modern societies are stratified along several dimensions," 20 such as class and, in multiethnic societies, ethnicity; and, like other forms of stratification, ethnic stratification is "a system of structured social inequality." 21 In most multiethnic societies, "a hierarchical arrangement of ethnic groups emerges in which one establishes itself as the dominant group, with maximum power to shape the nature of ethnic relations," and "other, subordinate ethnic groups exert less power, corresponding to their place in the hierarchy, extending down to the lowest ranking groups, which may wield little or no power." 22 Thus, the concept of ethnic stratification, in explaining majority-minority or dominant-subordinate systems, helps in understanding changes in the relationship between North and South Koreans in a new migration context.…”

“…According to Marger,38 in a multiethnic society, group rank is determined mainly on the basis of distance from the dominant group in terms of culture and physical features: those most like the dominant group are more highly ranked and those most unlike it are ranked correspondingly low. Thus, a system of ethnic stratification is a ranking of groups, each made up of people with presumed common cultural or physical characteristics interacting in patterns of dominance and subordination, referred to as majority-minority or dominant-subordinate systems.…”