User:Jtwsaddress42/Projects/Project 3/Sections/Chapter 3/The Antiquity Of Cellular Communication Systems

Cellular communication systems evolved early in the evolution of cells, if its foundations weren't already present at the point of membrane-cellwall encapsulation at the origin of cells. For bacteria, genetic exchange between partners via transduction, transformation and/or conjugation requires at least a minimal form of cell to cell communication. The evolution of social bacteria shows us that quorum sensing is a common phenomena in bacteria - Not only are they able to communicate between others of their own species, but they can communicate with other species as well. Eukaryotes exhibit an even greater range of social communication between individual cells in response to epigenetic events. What all these cell to cell communication systems hold in common are membrane-embedded macro-molecular systems that link environmental events occurring external to the cell to metabolic and genetic response elements within the cell.

Many of the biogenic amines and catecholamines identified as "neurotransmitters", were identified as such because they were first discovered in the nervous systems of animals. Like the phenomena of neuroid conduction in pre-neural cells, some of these substances have an evolutionary history that is much deeper than the origin of animals. Many so called "Neurotransmitters" predate animals, therefore neurons as well.

The antiquity of the amino acid and purinergic transmitters is obvious because of their metabolic functions, but the biogenic amines are the mainstay of the global neurotransmitter fountains embedded in the integrating reticulum of the reticular activating system - and, the deeper history of the ancient role of these biogenic amines is little discussed, explored, or known about.

Many "neurotransmitters" have been found to be utilized by single celled organisms, usually for the coordination of growth and metabolism in colonial contexts. These molecules were connected to biological mechanisms of communication between cells long before animals and nervous systems existed - and, a clear understanding of their roles in this context sheds light on their modern role in animal nervous systems.

Receptors, Signal Transduction & Second-messenger Systems
Most cell-membrane bound receptors facing the exterior of the cell are coupled to second-messenger systems that communicate with the enzyme complexes, organelles, metabolism, and genome in the interior of the cell.

The main signal transduction pathways in cells are:


 * Calmodulin pathway network - Ca2+, ligand-gated calcium ion channels, Ca2+-dependent enzymes
 * cAMP-dependent pathway - adenosine triphosphate (ATP) and adenylate cyclase
 * G protein signaling cascade - guanosine triphosphate (GTP) and guanylate cyclase
 * Inositol phosphate system - inositol trisphosphate (IP3) and diacylglycerol (DAG)

Transmitter Systems & Combinatorial Transmitter Logic
At the 1984 Conference of the Cognitive Neuroscience Institute, American neuroscientist Ira B. Black (March 18, 1941 – January 10, 2006) summarized the consensus the conference had come to regarding some of the key features and dynamics of memory at the cellular level in neurons.

Black goes on to examine the Catecholamine transmitters and the many components within the metabolic, genetic, and macro-molecular architecture of each specific transmitter system that are subject to regulatory action. "Metabolism of individual transmitters is organized into relatively discrete, self-contained functional units." Black lists the following components as being typical of a catecholamine neurotransmitter system:


 * biosynthetic enzymes,
 * storage vesicles,
 * receptor apparatus with its coupled second-messenger system components,
 * mechanism for high-affinity neuronal reuptake activation/deactivation,
 * catebolic enzymes.

He points out that this is a minimal system and has multiple potential points of regulation that are properly responsive to environmental changes, thereby allowing the system to be fine-tuned over physiological time. These are the component of a single neurotransmitter system, but neurons are capable of harboring multiple neuron transmitter systems within the cell - making it possible to employ a transmitter logic that is enormously sophisticated and selective.

In Neural Darwinism, Gerald Edelman picks up on the idea that a diversification of neurotranmitter substances in vertebrates added additional potential to regulate a highly variant neural architecture.

Neurotransmitter and receptor combinations provide an additional level of degeneracy at each synaptic cleft within each neuron, at the pre- and post-synaptic points of contact on the neuronal cell body, axon, dendritic tree of itself and its contacts. Additionally, degenerate receptor types for a specific transmitter, can allow the transmitter to serve a variety of functions depending on the coupling.