Transduction Mechanisms of Drug Stimuli

Transduction Mechanisms of Drug Stimuli

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Transduction Mechanisms of Drug Stimuli. Editors view affiliations F. Colpaert R. Front Matter Pages Drugs as Chemical Stimuli. Pages Appel, R.

Weathersby, K. Cunningham, P. Callahan, R. Receptor Mechanisms of Opioid Drug Discrimination. Woods, A. Bertalmio, A. Young, W. Essman, G. Dykstra, A.

What Is Signal Transduction?

Bertalmio, J. Osmoreceptors respond to solute concentrations of body fluids. Additionally, pain is primarily a chemical sense that interprets the presence of chemicals from tissue damage, or similar intense stimuli, through a nociceptor. Physical stimuli, such as pressure and vibration, as well as the sensation of sound and body position balance , are interpreted through a mechanoreceptor.

Another physical stimulus that has its own type of receptor is temperature, which is sensed through a thermoreceptor that is either sensitive to temperatures above heat or below cold normal body temperature. Ask anyone what the senses are, and they are likely to list the five major senses—taste, smell, touch, hearing, and sight.

However, these are not all of the senses. The most obvious omission from this list is balance. Also, what is referred to simply as touch can be further subdivided into pressure, vibration, stretch, and hair-follicle position, on the basis of the type of mechanoreceptors that perceive these touch sensations. Other overlooked senses include temperature perception by thermoreceptors and pain perception by nociceptors.

Within the realm of physiology, senses can be classified as either general or specific.

Transduction mechanisms of drug stimuli

A general sense is one that is distributed throughout the body and has receptor cells within the structures of other organs. Mechanoreceptors in the skin, muscles, or the walls of blood vessels are examples of this type. General senses often contribute to the sense of touch, as described above, or to proprioception body movement and kinesthesia body movement , or to a visceral sense , which is most important to autonomic functions.

A special sense is one that has a specific organ devoted to it, namely the eye, inner ear, tongue, or nose. Each of the senses is referred to as a sensory modality. Modality refers to the way that information is encoded, which is similar to the idea of transduction. The main sensory modalities can be described on the basis of how each is transduced.

The chemical senses are taste and smell. The general sense that is usually referred to as touch includes chemical sensation in the form of nociception, or pain. Pressure, vibration, muscle stretch, and the movement of hair by an external stimulus, are all sensed by mechanoreceptors.

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Hearing and balance are also sensed by mechanoreceptors. Finally, vision involves the activation of photoreceptors. Listing all the different sensory modalities, which can number as many as 17, involves separating the five major senses into more specific categories, or submodalities , of the larger sense. An individual sensory modality represents the sensation of a specific type of stimulus. For example, the general sense of touch, which is known as somatosensation , can be separated into light pressure, deep pressure, vibration, itch, pain, temperature, or hair movement.

Only a few recognized submodalities exist within the sense of taste, or gustation.

Until recently, only four tastes were recognized: sweet, salty, sour, and bitter. Research at the turn of the 20th century led to recognition of the fifth taste, umami, during the mids. Very recent research has suggested that there may also be a sixth taste for fats, or lipids. Gustation is the special sense associated with the tongue. The surface of the tongue, along with the rest of the oral cavity, is lined by a stratified squamous epithelium. There are four types of papillae, based on their appearance Figure 2 : circumvallate, foliate, filiform, and fungiform. Within the structure of the papillae are taste buds that contain specialized gustatory receptor cells for the transduction of taste stimuli.

These receptor cells are sensitive to the chemicals contained within foods that are ingested, and they release neurotransmitters based on the amount of the chemical in the food. Neurotransmitters from the gustatory cells can activate sensory neurons in the facial, glossopharyngeal, and vagus cranial nerves. Just as with sodium ions in salty flavors, these hydrogen ions enter the cell and trigger depolarization. Sour flavors are, essentially, the perception of acids in our food. Increasing hydrogen ion concentrations in the saliva lowering saliva pH triggers progressively stronger graded potentials in the gustatory cells.

For example, orange juice—which contains citric acid—will taste sour because it has a pH value of approximately 3. Of course, it is often sweetened so that the sour taste is masked. The other tastes result from food molecules binding to a G protein—coupled receptor. A G protein signal transduction system ultimately leads to depolarization of the gustatory cell. The sweet taste is the sensitivity of gustatory cells to the presence of glucose dissolved in the saliva. The affinity for each of these molecules varies, and some will taste sweeter than glucose because they bind to the G protein—coupled receptor differently.

Bitter taste is similar to sweet in that food molecules bind to G protein—coupled receptors. However, there are a number of different ways in which this can happen because there are a large diversity of bitter-tasting molecules. Some bitter molecules depolarize gustatory cells, whereas others hyperpolarize gustatory cells. Likewise, some bitter molecules increase G protein activation within the gustatory cells, whereas other bitter molecules decrease G protein activation. The specific response depends on which molecule is binding to the receptor.

One major group of bitter-tasting molecules are alkaloids. Alkaloids are nitrogen containing molecules that are commonly found in bitter-tasting plant products, such as coffee, hops in beer , tannins in wine , tea, and aspirin. By containing toxic alkaloids, the plant is less susceptible to microbe infection and less attractive to herbivores. Therefore, the function of bitter taste may primarily be related to stimulating the gag reflex to avoid ingesting poisons.

Because of this, many bitter foods that are normally ingested are often combined with a sweet component to make them more palatable cream and sugar in coffee, for example. The highest concentration of bitter receptors appear to be in the posterior tongue, where a gag reflex could still spit out poisonous food.

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