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The perception of taste is more complex than just the evaluation of sensations received from the taste buds of the oral cavity. It frequently represents the combined sensationsf from the gustatory, olfactory,mechancical and frequently the nocioreceptors of pain. This discussion is the latest in a series of discussion based on a major COMPREHENSIVE study of the

ELECTROLYTIC THEORY OF THE NEURAL PROCESS

Last update:              Activa™: See Citation Page

The gustatory modality is spatially diverse both in the diverse locations of the taste buds within the oral cavity, but also in the diversity of chemoreceptors within the individual taste bud. The result is a very complex variation in the perception of chemical stimulants with location within the oral cavity. The signals generated by the taste buds are transmitted to the central nervous system overy three differnt major nerves, n Vii, n. IX and n. X.  Conversely, there is little indication of any stage 2 signal processing occuring prior th the combining the the neural signals within the nucleus solitarius within the lower reaches of the central nervous system (the brain stem).  A complete block diagram of the gustatory modality of the neural system is presented for the first time.

THIS WEBPAGE IS IN AN EARLY STAGE OF ITS DEVELOPMENT.
The paper at upper right provides a complete justification for the employment of only four taste receptors in mammalian (and human) gustation. The first web pages supporting this area discuss;

• The TOP BLOCK DIAGRAM of GUSTATION
• The CHEMORECEPTORS, the gustaphores and olfactophores of both the taste an smell modalities.

Subsequent sections of this webpage will develop;

• Sensing of orbitals other than oxygen by the gustatory modality
• Sensing and perception of in9organics by the gustatory modality
• The four gustatory sensing channels in a theoretcial 3D perception space
• Comparison of predicted and observed Multi-Dimensional Scaling in gustation
• Expanding the AH,B framework of Shallebberger et al.
• A Umami perception defined by multiple fundamental gustaphores
• Bronsted acids, pungency and coolness as perceptons extrasensory to gustation
• Role of adaptation in taste persistence and stability

BLOCK DIAGRAM OF GUSTATION

CHEMORECEPTORS OF THE GUSTATORY PROCESS

There are only four gustaphores employed in evaluating the properties of myriad gustatory stimulants.  The functional and chemical description of these gustaphores differs significantly from their historical and behavioral science descriptions. The following table compares these descriptions.

C-Best--The natural environment contains few inorganic (Bronsted) acids, and these only in small amounts except in areas of volcanic activity. However, investigators have focused on them in evaluating the gustatory modality because of their ready availability and ease of calibration. The Electrolytic Theory of the Neuron clearly shows that it is the organic (Lewis) acids that are of primary interest to the gustatory modality of the neural system. The basic structure perceived as acidic is the carboxyl group, which in hydrated form is described chemically as a one-carbon diol.

This initial webpage will place the inorganic stimulants of gustation in a separate category in order to greatly simplify the description of the gustatory modality of terrestrial mammals. It appears the mammalian gustatory modality evolved based on the presence of various organic materials in the environment and the absolute need to replenish sodium ions lost within the terrestrial mammalian body. Later pages will build on the definition of the natrophore (discussed below) and the sodium sensitive gustatory receptors (GR's) to describe how the inorganic stimulants excite the sensory neurons of the gustatory modality.

G-Best--The recent focus on artificial sweeteners in the food industry has shown that it is not an exclusive propeerty of the sugars that are preceived as sweet. The Theory shows that it is actually a specific ligand that contributes to this sensation, a diol with the oxygen atoms separated by two carbon atoms.  By far the commonest form is the 1,2 cis-glycol ligand found in both aromatic and aliphatic molecules.

P-Best--The stimulants perceived as bitter have been associated with quinine since ancient times. However, quinine is not a simple form of the chemicals in this group. The primary form resulting in the bitter perception is a diol separating the two oxygen atoms by three carbons. This configuration is described as the picrophore in the Electrolytic Theory of the Neuron.  Picric is Greek for bitter.

The organic chemistry of the gustatory modality involves very complex chemical structures that are difficult to describe unequivocally using semantics (particularly among the G-Best and P-Best gustaphores) and very difficult to illustrate using two dimensional drawings. The terminology used here is based on Chapter 8 of the text, "The Neuron and Neural System."  This material is available as a Draft and cited elsewhere on this page.

N-Best--While the perception of sodium in solution has been recognized as a primary stimulant of gustation since ancient times, its means of stimulating the gustatory modality has not. The Sodium ion cannot exist as a positive ion in an aqueous solution. The ion is immediately complexed with the water molecules into a coordinate chemistry structure, typically Na⁺(H₂O)₆  This structure can also be considered an inorganic diol with a single sodium ion separating the two oxygen atoms. Each Na⁺(H₂O)₆ complex actually contains multiple diol ligands and each molecule of an ionizable sodium compound represents a stimulant presenting multiple gustaphores simultaneously.

The ramifications of this discussion, as they apply to both taste and smell, are continued at GUSTAPHORES.

GUSTATORY RECEPTORS (GR's) of GUSTATION

In the course of developing the stereochemistry of the natural sugars and seeking to define why they are perceived as sweet, Shallenberger & Acree^2,3, defined the unique geometry found among their sugars, and the artificial sweeteners as well. They showed the potential for each of the sugars to form a dual coordinate bond with a putative sensory neuron gustatory receptor (GR), where the distance between the two coordinate bonds was 2.6 angstrom. All of the gustaphores defined above are based on this same stereochemical structure, but with different d-values, their spacing in Angstrom.

With the gustaphores of gustation defined as above, along with their respective dual coordinate bond spacing, d-values, it is now possible to describe the gustatory receptors (GR's) within the Electrolytic Theory of the Neuron.

It has been known since at least the 1970's that the neurolemma consisted of a variet of phospholipids but their purpose was unknown¹. Lehninger unknowingly documented the phospholipids forming the four gustatory receptors at that time.  As noted in Chapter 8 of "The Neuron and the Neural System," other orbitals besides oxygen can participate in the gustatory process besides oxygen, specifically nitrogen. The challenge is to identify a set of GR's that can coordinate bond with the gustaphores defined above. This bonding must be compatible with the matching stereochemistry of the gustaphores and the receptors.  The simplest means of satisfying these requirements are to employ receptor ligands similar to the gustaphore ligands. This greatly simplifies the task.

C-Best GR--One of the identified lipids of the lemma, phosphatidyl serine, exhibits a carboxyl group and is most appropriate for forming the C-Best gustatory receptor (GR) of the sensory neurons. As a result, a dual coordinate bond is formed between the respective oxygen and hydroxyl groups. This GR can coordinate bond with a wide variety of Lewis acids.

P-Best GR--One of the identified lipids of the lemma, phosphatidyl 3"-O-aminoacyl glycerol has an oxygen and an amine separated by two carbons in an aliphatic configuration. As a result, it exhibits a d-value of 4.2 Angstrom and the geometry necessary to form a dual coordinate bond between the picrophores and the P-Best sensory neurons and is defined here as the picric GR.

G-Best GR--One of the identified lipids of the lemma, phosphatidyl galactos has an oxygen and a hydroxyl group separated by a d-value of 2.6 Angstrom due to its 1,2 cis-glycol configuration involving O-3 and O-4 of an aromatic structure. As a result, it exhibits the geometry necessary to form a dual coordinate bond between a wide variety of glycophores (including the common sugars)and is defined here as the "sweet" or G-Best GR.

The labels cis- and trans- take on very specific, and extended, definitions in order to be consistent when applied to both aromatic and aliphatic molecules.   Shallenberger & Acree discuss this situation³.  Organic Chemistry texts note the Newman diagram for the cyclic compounds are particularly complicated because they are not planar molecules; even the same arrangement of atoms may be present in multiple puckered forms, the "chair", "half-chair", "boat" and "twist" or skewed-boat forms.  Each form typically exhibits a different potential energy⁴.

N-Best GR--One of the identified lipids of the lemma, phosphatidyl inositol has an oxygen and a hydroxyl group separated by a d-value of 3.3 Angstrom due to its 1,2 trans-glycol configuration involving O-3 and O-4 of an aromatic structure. As a result, it exhibits the geometry necessary to form a dual coordinate bond with a hydrated sodium ion and is defined here as the hydrated sodium GR, as opposed to the salty GR in order to avoid confusion with the common salt, NaCl.

The super-effective gustaphores

The above figure also describes two-groups of super-effective gustaphores. These are gustaphores with an auxiliary structural element that influences the GR's very significantly. The result is a more complex stereochemical coordinate bond than envisioned above. When participating in the dual coordinate bond, these gustaphores introduce an additional bond between that element and an element of the GR. These elements are found in the G-Best and P-Best gustaphores. The result can be a major increase in the sensation delivered to the central nervous system.

Umami is dismissed as a distinct perception

During much of the 20th Century, investigators from the Eastern Hemisphere have promoted the concept of a distinct perception associated with a variety of chemicals that included the flavorant known as mono-sodium glutamate. In the context of this work, mono-sodium glutamate is clearly a stimulant consisting of two distinct gustaphores, a natrophore associated with the hydrated complex of the sodium ion and the glycophore associated with the 1,2 cis-glycol of the glutamate. Thus, the perception of umami is the result of two distinct sensations delivered to the central nervous system from two of the four primary gustatory receptors.

The potential for additional gustatory receptor types

There is a clear potential for sensory neurons to employ additional phospholipids modified to act as GR's, particularly for GR's with more carbon atoms in the chain between the orbitals of their diol ligands. However, very sophisticated statistical analyses, employing multidimensional scaling techniques, have shown there are only four primary gustatory receptor channels in the mammalian neural systems.

MAJOR CONCEPTUAL CHANGES

The Electrolytic Theory of the Neuron provides insights into the operation of the gustatory sensing modalities not achieveable under the more widely taught chemical theory of the neuron.

The theory is far more complete and mathematically rigorous than any other presented to date. It introduces three major paradigm shifts affecting concepts held true for the last 50 years, a super extended period considering the rate of changes in other scientific technologies.

The theory shows that;

• The gustatory modality is best understood using a set of functional stages identical to those used to interpret the visual and hearing modalities.
• The sensory neurons of gustation are functionally the same as the neurons of the visual and hearing modalities.
• The cilia of the sensory neurons exhibit specialized areas of type 2 lemma that appear as if coated with a liquid crystalline material that supports the transduction mechanism of taste. This material conceptually forms the Gustatory Receptors (GR's).
• The GR's of taste are primarily phospholipids combined with a set of amino acids. The amino acids can be considered simple peptides. However, they are specifically not proteins
• The GR's of taste are distinctly different from the olfactory receptors (OR's) of smell. with one exception.  Phosphatidylserine (PtdSer) is found in both modalities as the receptor for the sensing of organic (Lewis) acids.
• Molecular self-assembly, along with genetic coding, play important roles within the gustatory taste buds.
• The transduction process involves a non-reactive quantum-mechanical energy change that does not produce a chemical residue.
• The stimulant is stereochemically bonded to the GR's and then spontaneously decoupled (released).
• While coupled to the GR's, the dipole potential of the stimulant is measured.
• The sensory neurons exhibit adaptive qualities similar to those in hearing, vision and smell.
• The number and organization of the output signaling paths from the taste buds to the CNS is yet to be determined.
• The signals delivered to the CNS are processed very similarly to the way visual,hearing and smell signals are processed.
• As in hearing and vision, memory plays a major role in interpreting and identifying indivual stumulants.

A draft describing the overall gustatory process is available for review and comment by researchers and advanced students. Draft of Taste modality.

A CAUTION

Because of the revolutionary nature of some of the material presented, students subject to examination by their institution are encouraged to review the Cautions Page before proceeding.

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REFERENCES

1. Lehninger, A. (1970) Biochemistry. NY: Worth Publishing pp196-200

2. Shallenberger, R. & Acree. T. (1967) Molecular theory of sweet taste Nature vol 216, pp 480-482(

3. Shallenberger, R. & Acree, T. (1971) Chemical structure of compounds and their sweet and bitter taste In Beidler, L. ed. Taste: Handbook of Sensory Physiology, Vol IV, Part 2, Chap 12

4. Morrison, R. & Boyd, R. (1971) Organic Chemistry, 2nd Ed. Boston: Allyn & Bacon, Inc. pp 283-310

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