| Popis: |
There is an extensive body of indirect evidence from animal studies which indicates that the “biogenic amines” act as central nervous system (CNS) neurotransmitters, particularly in critical integrative brain pathways. The catecholamines (CA) norepinephrine (NE) and dopamine (DA), the indoleamine (IA) serotonin (5-HT), and the quaternary alkyl-amine acetylcholine (ACh) are the brain amines on which most interest has been focused. In addition, the brain has also been found to contain and form other adrenergic amines, such as phenylethylamine (PEA) and octopamine, and indoleamines such as tryptamine, etc. One or more of these amines may act as co-transmitters, modulators, or regulators of synaptic transmission mediated by chemically related transmitters. Thus, tryptamine may be a modulator of serotonergic synapses [1] and PEA may be a modulator of CA synapses [1,2], as evidenced by studies on the ocular sympathetic system [3]. Octopamine appears to be co-transmitter in sympathetic nerves [4]. Based on the metabolic and functional unity of the neuron [5], Dale [6] proposed that a neuron releases the same transmitter at all its endings. Although Dale’s law has been interpreted to mean that there is only one transmitter, this latter assumption does not appear to hold true. Sabelli and associates [7] have thus proposed to extend Dale’s principle as follows: Each neuron releases at all its endings the same transmitter and metabolically related co-transmitters, and contains the same receptors throughout its surface membrane. In addition, there may be cells which contain the metabolic machinery for producing more than one family of transmitters; for instance, sympathetic neurons contain not only CA and metabolically related amines (octopamine, PEA) but also ACh [7–12] and possibly histamine [7,12,13]. Thus, we may have to allow for complex interactions at the synapse. One biogenic amine may affect the metabolism or levels of another, and there may be complex interactions between monoaminergic systems and other neurotransmitters or neuromodulator systems. |
