What impact might modern pharmaceuticals have on the broader areas of psychiatry and psychology? Theories of psychology have rested on argument, in the philosophical sense, rather than on scientifically based evidence (Eisenberg, 1976). In the years when psychology meant psychoanalysis, problems of the mind were generally believed to be environmentally-induced (Hunt, 1993). This represented a fundamental change from previously-held beliefs. For more than a millennium, mental and physical ailments were thought to be caused by an imbalance of bodily humors. These beliefs had very early origins. The ancient Roman anatomist, physician and philosopher, Galen, theorized a concept of the body functioning as a fluid mechanism. In his dissections, he took note of muscles and the whitish cords connected to them. Galen believed that movements of the body depended on muscles, and that the whitish cords (now known to be axon bundles from motor neurons) played a critical role (Churchland, 1988). He theorized that "psychic pneuma" traveled through these cords to produce movement. Galen had also dissected the ventricles of the brain, and believed that the "psychic pneuma" resided in them (Changeux, 1985).

Galen may have borrowed these concepts from Alcmaeon, an earlier Greek physician. Alcmaeon discovered the optic nerve during dissections on animals, and deduced that the nerve carried messages from the eyes to the optic lobe. He believed air (pneuma) to be the vital component of the mind, transmitting the perceptions of the sensory organs to the brain (Hunt, 1993).

Galen's theory of bodily fluids survived for centuries. In the Middle Ages, there were believed to be four types of these fluids: blood, phlegm, black bile and yellow bile (Changeux, 1985). Health was based upon a balance of these fluids. If there was too much or too little of a certain type of fluid, a person was thought to become choleric or melancholic. Patients were subject to treatments such as bloodletting in order to correct their balance of humors. While this may seem barbaric today, it was a commonly accepted practice for centuries. While many consider modern psychiatry much more advanced, however the "father of modern psychiatry" Benjamin Rush, advocated bloodletting. Drs. James Craik, Gustavus Brown and Elisha Dick, an apprentice of Rush, used this process on George Washington shortly before his death (Carol, 1957). Galen's concept of "psychic pneuma" ultimately became the "nervous fluid" of theories in the eighteenth century (Changeux, 1985).

Just as perceived causality for human behaviors went from the physical to the environmental, a reversal may occur. Kramer believes that fluoxetine undermines the Freudian hypothesis that inhibition of pleasure is merely a manner of defensiveness, guilt and sexual abuse (1993). A "biochemical imbalance" theory seems to have replaced Freud's psychological theory as the most widely accepted explanation for emotional pain and suffering (Breggin, 1994). A model of the mind based on the neural biochemicals is under formation (Osser, 1993). All behavior is now thought to be a reflection of brain function, the end result of interneuronal communication (Kandel, 1981). Fluoxetine may give insight to these models by giving a better understanding of the functioning of serotonin in the brain. By studying the conditions correlated with low and high serotonin levels, researchers may theorize about the functions and mechanisms of serotonin. The same would be true when selective inhibitors for the reuptake of other neurotransmitter like dopamine and norepinephrine are created. A functional model based on the concentrations of the neurohumors may compete with models based on environmental causality. However, one must also take into account the interaction between the physical and the environmental. One of the basic rules of modern genetics is that phenotype is a result of the interaction between the genotype and the outside world (Davis, 1986).

Interaction may also have a role in neurotransmission. The neurotransmitter may not only influence the expression of behavior, the conditions of the environment may have an effect on the levels of neurotransmitter as well. Neurotransmitters may serve as an instrumental factor or immediate cause of behavior and still themselves be effected by environmental forces. It is still possible for disorders to be induced by environmental conditions and at the same time exhibit irregular levels of a neurotransmitter.

Further advances will be made when more of the effects of neurotransmitters are known. One of the possible reasons why an increase or decrease in levels of a neurotransmitter has a wide range of effects is that the neurotransmitter is used all over the brain (Kruk, 1991). Different sections of the brain are known to have different functions. Therefore, any change in the overall level of the neurotransmitter may have global effects.

The commercial success of fluoxetine has sparked new research which may lead to the development of even more specific re-uptake inhibiting pharmaceuticals (Kramer, 1993). There may be more than one type of receptor triggered by a single neurotransmitter (Leonard, 1994). There has been knowledge of different receptor subtypes for over thirty years. In fact, ten different subtypes of serotonin receptors found in the rat brain (Leonard, 1994). Classification of receptor subtypes is based on proteins present which can be coupled to certain chemicals. For example the G-protein receptor subfamily, 5HT-1 can be coupled to adenylate cyclase and 5HT-2 can be coupled to phospantidyl inositol. The 5HT-3 receptors, previously called the "M" receptors, are now believed to be a family of subtypes (Leonard, 1994).

These subtypes of receptors may perform different functions. They may even be found in different concentrations in certain areas of the brain. A major advance may occur if pharmaceuticals were to be invented that would select for certain receptor sub-types. These pharmaceuticals could be even more specific in their effects. This would reduce side effects and provide greater insight into the physical mechanisms of the neurotransmitter and psychiatric disorders.

The neuroleptic model of brain functioning once again employs the concept of a balance of fluids. The various neurotransmitters flow at regulated levels: as long as the levels are normal the processes will run smoothly. When not at the appropriate levels, problems are expected to occur. The levels of the "fluids" that flow through the brain may not be the only determinant of brain function. For a simplistic comparison, if an internal combustion engine is structurally damaged or missing a component, it will not run well even if the amounts of fuel and oil are maintained at the optimum levels. Disorders may have a structural or organizational component. The way in which the neurons connect may be as important as the messages they send. This would prove to be a complex and difficult obstacle for researchers trying to make improvements in brain dysfunctioning caused by such structural irregularities. The manipulation of something as small and delicate as a neuron would be a great accomplishment. If functioning is dependent on the precise interconnection of neurons, then flooding the system with greater amounts of neurotransmitter may be like increasing the water pressure on a leaky plumbing system. It may seem to improve the performance of the system, but does not directly attack the problem and may even cause future troubles.