One of the class of neurotransmitter is acetylcholine (2-acetoxy-N,N,N-trimethylethanaminium) that are present on both central nervous system (CNS) and peripheral nervous system (PNS), particularly the autonomic nervous system of PNS. Nicholls (1994) stated that it is released within the pre- and post-ganglionic parasympathetic neurons, certain postganglionic sympathetic fibers, and preganglionic sympathetic neurons. On the other hand, with an assist from some associated neurons, it allows the activation of anti-excitatory actions in CNS (Whittaker & Roed, 1981).
According to Whittaker (1981), the cholinergic system is originated from large cell between the medial septum and nucleus ...view middle of the document...
NnAChR is found mainly on neurons and have homologous subunits that have pair of cysteine residue for binding of transmitter. This 130kDa (80kDa α-subunit and 50kDa non-α-subunit) receptor is regulated through second messenger, in which vasoactive intestinal peptide (VIP) from PKA activation that increases the cAMP causes the improvement in peak conductance of cell-based patch at the ganglion neurons.
ACh is terminated through rapid hydrolysis by AChE at the Neuromuscular Junction (NMJ) and cholinergic synapses (Waymire, 2014). Acetylcholinesterase (AChE) hydrolyse ACh rapidly after it dissociate from its receptor, becoming acetate and choline for the reaccumulation at its terminal through the Na+ coupled transporter (Hucho, 1986). Low amount of ACh (ACh deficiency) may causes dementia and some of the major diseases that causes low ACh deficiency are myasthenia gravis and Alzherimer’s disease (WiseGeek, 2014).
Another class of neurotransmitter is biogenic amines, which are divided into two main derivatives; the tyrosine-derived catecholamine (dopamine, norepinehrine, and epinephrine) as well as tryptophan-derived monoamine like 5-hydroxtrptamine (serotonin) (Mason, Losos, & Singer, 2011). Nicholls (1994) explained that dopamine, norepinephrine and serotonin cell bodies are originated from respective regions of CNS; substantia nigra, locus coeruleus and raphe nuclei, which control sleep and mood.
According to Nicholls (1994), synthesis of biogenic amines occurs by sequential conversion of tyrosine to dopamine and then norepinephrine by tyrosine hydrolase, L-aromatic amino acid decarboxylase and dopamine β-hydrolase. The transition of tryptophan to serotonin follows a similar oxidation-decarboxylation mechanism, however with only single oxidation step (Katz, 1999). An extensively studied vesicle involved in packaging the biogenic amines that is the chromaffin vesicle which facilitates uptake of the neurotransmitter by V-type proton pump with the aid of ATP and transporter protein, generating proton motive force by establishment of pH gradient (Nicholls, 1994).
The vesicular exocytosis of biogenic amines is governed by electrical stimulation associated to down-regulation by presynaptic autoreceptors, for instance α2 autoreceptor for norepinephrine release and D2 receptor for dopamine release (Katz, 1999; Nicholls, 1994). In terms of the...