Brain activation chemical control

Codeine also activates pain-control circuits that descend from the section of the brain called the midbrain to the spinal cord, causing the release of naturally produced opioids called endorphins and enkephalins. The endorphins and enkaphalins bind to and activate receptors on cells in the spinal cord that prevent the transmission of pain signals. As discussed in Chapter 3, endorphins and enkephalins are your body s natural chemicals that allow you to feel no pain. ... 

Even when effective in controlling behavior, Ritalin and other stimulants have side effects common with use of amphetamines. These include nervousness, insomnia, and perhaps some more long-term problems such as dependency, slowed growth, or depression. Critics sometimes note the similarity between cocaine and the active chemical ingredient in Ritalin, methylphenidate. Both stimulate the dopamine system of the brain, but cocaine does so quickly and methylphenidate does so slowly. The similarities show in the abuse of Ritalin for its pleasure-inducing qualities. 

The following findings are of particular interest activation of the area of the human brain known to be an important source of the chemically distinct brain activation pattern in animal REM activation of a vast area of the limbic forebrain which is known to mediate emotion and to motivate behaviour in humans activation of the limbic areas controlling emotion, especially fear and activation of multimodal association areas of the brain. 

In essence, all of the older benzodiazepines that are structurally related to chlordiazepoxide and diazepam are termed 1,4-benzodiazepines. The chemical structure of some commonly used benzodiazepines is shown in Figure 9.2. They enhance the actions of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) in the brain. As a consequence, they affect the activities of the cerebellum (concerned with balance and coordination), the limbic areas of the brain and the cerebral cortex (thought and decision making, fine movement control). 

With more links in the chain, brains have more opportunities to make adjustments—there are more knobs and controls with which to fine-tune the activities of neurons. Current theories of learning and memory identify the plasticity—adjustability—of synapses as the mechanism by which brains acquire and store information. Intelligence evolves from the continual tweaking of chemical transmission in the brain. 

The nervous system has several properties in common with the endocrine system, which is the other major system for control of body function. These include high-level integration in the brain, the ability to influence processes in distant regions of the body, and extensive use of negative feedback. Both systems use chemicals for the transmission of information. In the nervous system, chemical transmission occurs between nerve cells and between nerve cells and their effector cells. Chemical transmission takes place through the release of small amounts of transmitter substances from the nerve terminals into the synaptic cleft. The transmitter crosses the cleft by diffusion and activates or inhibits the postsynaptic cell by binding to a specialized receptor molecule. In a few cases, retrograde transmission may occur from the postsynaptic cell to the presynaptic neuron terminal. 

A population-based case-control study on brain cancer was carried out in some areas in the United States with petroleum refining and chemical manufacturing industries (i.e., activities suspected of being associated with brain cancer) and is described in detail in the monograph on dichloromethane (see this volume). Probability, intensity, duration and calendar time of life-long individual exposures to each of six chlorinated aliphatic hydrocarbons, including 1,1,1-trichloroethane, were assessed through an ad-hoc job-exposure matrix. Whereas risk excesses of some consistency were associated with exposure to other chlorinated aliphatic hydrocarbons, exposure to 1,1,1-trichloroethane showed little indication of an association with brain cancer (Heineman et al., 1994). 

From the viewpoint of the chemist, the brain presents an almost limitless frontier. The brain, as a center for communication control, has been shown by anatomists and physiologists to be composed of a network of neurons that make contact with one another mostly by release of chemicals at synaptic junctions (neurotransmission). There are astronomical numbers of these synaptic junctions,and there 1s also a complex array of chemical transmitters and chemical modulators Involved 1n neurotransmission. Many of these transmitters and modulators have not yet been identified. The physiological actions of these substances are diverse (they both excite and depress activity) so we must also postulate that many different molecular structures are Involved 1n receptor functions even for the very same transmitter or modulator. 

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