Drugs of abuse alter the way people think, feel, and behave by
disrupting neurotransmission, the process of communication between brain
cells. Over the past few decades, studies have established that
drug dependence
and addiction are features of an organic brain disease caused by drugs'
cumulative impacts on neurotransmission. Scientists continue to build
on this essential understanding with experiments to further elucidate
the physiological bases for drug abuse vulnerability as well as the full
dimensions and progression of the disease. The findings provide
powerful leads to new medications and behavioral treatments.
This second article in our
NIDA Notes Reference Series
discusses the central importance of studying drugs' effects on
neurotransmission and describes some of the most common experimental
methods used in this research. As with other articles in the series, we
provide illustrative references from articles published in
NIDA Notes.
What is Neurotransmission?
A person reads. The words on the page enter the brain through the
eyes and are transformed into information that is relayed, from cell to
cell, to regions that process visual input and attach meaning and
memory. When inside cells, the information takes the form of an
electrical signal. To cross the tiny intercellular gap that separates
one cell from the next, the information takes the form of a chemical
signal. The specialized chemicals that carry the signals across the
intercellular gaps, or synapses, are called neurotransmitters.
The ebb and flow of neurotransmitters—neurotransmission—is thus an
essential feature of the brain's response to experience and the
environment. To grasp the basic idea of neurotransmission, compare the
brain to a computer. A computer consists of basic units (semiconductors)
that are organized into circuits; it processes information by relaying
electric current from unit to unit; the amount of current and its route
through the circuitry determine the final output. The brain's
corresponding basic units are the neurons—100 billion of them; the brain
relays information from neuron to neuron using electricity and
neurotransmitters; the volume of these signals and their routes through
the organ determine what we perceive, think, feel, and do.
Of course, the brain, a living organ, is much more complex and
capable than any machine. Brain cells respond with greater versatility
to more types of input than any semiconductor; they also can change,
grow, and reconfigure their own circuits.
Neuroscientists seeking to understand why a drug is abused and the consequences of that abuse focus on two issues: