Excitement, substances causing

The absorption of light by a substance causes the formation of excited-state molecules. This excitation is followed by various elementary transformations which eventually lead to the deactivation or to the disappearance of those excited molecules. The absorption of light as well as each one of the elementary transformations of the original molecule in an excited state is a primary step. Specifically, a primary step may be (a) a transformation of the excited molecule into a different chemical species, as in steps 24, 15, and 14 of Figure 1, or (b) a radiative or nonradiative transition between different energy levels of the molecule, e.g., steps 02, 21, 22, 23, 13, 11, and 16 of Figure 1. Those corresponding to (a) are photochemical primary steps, while those of (b) are photophysical primary steps. 

MDMA.MDA(3,4-methylenedioxyamphetamine) gives by far the best high of this group. Its effects can best be described as being sort of like LSD without the extreme excited state caused by that substance. It was popularly known as "the love drug" because of the calm state of empathy so characteristic of its effect. It could also be a powerful aphrodisiac under the right circumstances. 

If opiates are not consumed, then the upregulated substances cause net excitation of the noradrenergic neurons -causing the characteristic withdrawal symptoms... 

Bufotenin 48, a poison occurring in the skin of toads, causes a rise in blood pressure and paralyses the spinal and cerebral motor centres. Psilocin 49, the psychoactive substance in the Mexican mushroom Teonanacatl, increases excitability and causes hallucinations ... 

A number of substances increase the sodium permeability of excitable membranes. Their effects on sodium channels are unclear. For example, when a substance causes a permeability increase which is blocked by TTX, then it may be acting directly on the channel or indirectly on some binding site or receptor adjacent to, or some distance from, the channel. It is not easy to distinguish these possibilities in many instances. 

Regarding the types of fibers acted upon by capsaicin, Szolcsanyi (1976, 1977) has shown that close arterial injections of the substance cause excitation exclusively of the slowest-conducting unmyelinated C2 fibers all others including Aap, A8, and C fibers remained unaffected. After desensitization with capsaicin, when this compound was no longer able to activate C fibers (Porszasz and Jancso, 1959), action potentials in these fibers could still be elicited by electrical stimulation of peripheral nerves, demonstrating that desensitization is not simply conduction block. Szolcsanyi... 

A considerable number of natural products are derived from indole. Very important is the essential amino acid tryptophan (133), a constituent of many proteins. Enzymatic conversion of tryptophan in living organisms produces additional natural products, for example, serotonin (134, 5-hydroxytryptamine) by hydroxylation and decarboxylation. It occurs in the semm of warm-blooded animals as a vasoconstrictor, and is one of the agents responsible for maintaining vascular tone. Moreover, it acts as a neurotransmitter, that is, it is essential for conducting impulses between nerve cells. Bufotenin (135), a poison occurring in the skin of toads, causes a rise in blood pressure and paralyzes the spinal and cerebral motor centers. Psilocin (136), the psychoactive substance in the Mexican mushroom Teonanacatl, increases excitability and causes hallucinations. 

Vasopressin, as the name indicates, influences blood pressure an injection of the substance causes a long-lasting elevation of blood pressure. Furthermore, it excites the smooth musculature of the intestines. In normal physiology, however, the effect on the kidney is most significant. Vasopressin inhibits diuresis, i.e. it helps in the reabsorption of water and consequently in the concentration of urine. Impaired production of vasopressin results in the syndrome called diabetes insipidus in which huge quantities of very dilute urine are excreted in one documented case, as much as 56 liters per day A corresponding thirst accompanies such a loss of liquid. Injection of the hormone relieves the symptoms. 

The simpler substance apoharmine according to Flury causes increased reflex excitability in the dog. In the frog it produces a like effect which with larger doses goes on to tetanus. Esterification of harmol with methylcarbamic acid induces affinities with the physostigmine type of drug. ... 

The effect of an external electric field is to produce an acceleration of the electrons in the direction of the field, and this causes a shift of the Fermi surface. It is a necessary condition for the movement of electrons in the fc-space that there are allowed empty states at the Fermi surface hence electrical conductivity is dependent on partially filled bands. An insulating crystal is one in which the electron bands are either completely full or completely empty. If the energy gap between a completely filled band and an empty band is small, it is possible that thermal excitation of electrons from the filled to the empty band will result in a conducting crystal. Such substances are usually referred to as intrinsic semiconductors. A much larger class of semiconductors arises from impurities... 

B) Phase-shift methods. The phase shift method for determining fluorescence lifetimes is based on the principle that if fluorescence is excited by suitably modulated light source, emitted radiation will also be similarly modulated. With reference to a scattering substance, emission from a fluorescent substance will introduce a time lag due to finite time between absorption and emission. This, by definition is the lifetime of the excited state. The time lag will cause a phase-shift relative to the exciting light. Phase fluorimetry requires a modulated light source and a phase sensitive detector. 

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