Chemical theories on depression: The brain consists of about ten thousand million neurons, or nerve cells, each cell having the capacity to conduct a tiny electric charge to others, via seven or eight thousand interconnections. The tail of each cell spreads into thousands of fibers, each ending with a swelling called a terminal button. The electric charge passes from the head of the cell to the tail, and ends in the thousands of terminal buttons. Between the terminal buttons of one cell and the head of the next cell are microscopic gaps called synapses. The electric current cannot jump the synapse, hut instead causes a change in the chemicals within the synapse, this change then causing a current to start in the head of the next cell. These chemicals are called neurotransmitters because they effectively transmit electrical charge from one neuron to the next. A few neurotransmitters have been isolated. They are divided into two groups, called the mono amines and the catecholamines.
Chemical Theories on Depression
The main chemical theory of depression is that a depletion of brain mono amine transmitters reduces the amount of “excitement” in the brain. The first evidence of a possible link between such chemical changes and depression came from observation of the effects of certain drugs, including some drugs which used to be used for high blood pressure, which sometimes caused depression and which reduce mono amine levels. Many researchers tried to correlate depression with actual levels of brain amines (or at least their breakdown products) but the results were variable and inconclusive.
On the evidence, there can be no simple chemical cause which explains depression. If it were only a matter of mono amine depletion, it would be hard to explain why the drugs that deplete mono amines (and they do this in a gross way compared to the body’s own subtle changes) do not always cause depression: in fact, they do so fairly rarely. It i also difficult to explain why some other drugs which deplete mono amines are not known to be associated with depression. Perhaps the presumed chemical changes often follow, rather than initiate, depression.
There is no doubt that someone in dark grey or black depression undergoes physical changes way beyond a mere change of mood, and such changes could well involve a change in brain amines. But since gross drug-induced amine depletion does not usually cause depression, there must be many other factors involve.