Neurotransmitters: The Chemical Messengers of the Brain

What are Neurotransmitters?

Doctor and nurse examining CT scan digital tablet
Hero Images/Getty Images

It is believed that the brain contains several hundred different types of chemical messengers (neurotransmitters) that act as communication agents between different brain cells. These chemical messengers are molecular substances that can affect mood, appetite, anxiety, sleep, heart rate, temperature, aggression, fear and many other psychological and physical occurrences.

Scientists have identified three major categories of neurotransmitters in the human brain:

1. Biogenic amine neurotransmitters have been studied the longest and are probably the best understood in terms of their relationship to psychological disturbances. Six of the main biogenic amine neurotransmitters are:

  • Norepinephrine, which influences sleep and alertness, is believed to be correlated to the fight or flight stress response.
  • Epinephrine is usually thought of as a stress hormone managed by the adrenal system, but it also acts as a neurotransmitter in the brain.
  • Dopamine influences body movement and is also believed to be involved in motivation, reward, reinforcement and addictive behaviors. Many theories of psychosis suggest that dopamine plays a role in psychotic symptoms.
    • Histamine is thought to influence arousal, attention, and learning. It is also released in response to an allergic reaction. Antihistamines, which are commonly used to treat allergies, have common side effects of sedation, weight gain, and low blood pressure.

      2. Peptide neurotransmitters are believed to be associated with the mediation of the perception of pain, stimulation of the appetite, regulation of mood and other multiple functions. Abnormalities in peptide neurotransmitters have been associated with the development of schizophrenia, eating disorders, Huntington’s disease and Alzheimer’s disease.

      • Cholecystokinin (CCK), a fairly new discovery, is a peptide that has received a lot of attention in the last decade. It is believed that CCK increases relaxation inducing GABA while decreasing dopamine. Studies have linked CCK with anxiety and panic attacks in people with panic disorder.

      3. Amino acid neurotransmitters are viewed by some experts as the main players in the neurotransmission process. There are two major amino acid neurotransmitters:

      • Gamma-aminobutyric acid (GABA) is a major inhibitory neurotransmitter that acts through a negative feedback system to block the transmission of a signal from one cell to another. It is important for balancing the excitation in the brain. Benzodiazepines (anti-anxiety drugs) work on the GABA receptors of the brain, inducing a state of relaxation.
      • Glutamate is an excitatory neurotransmitter and is the most abundant chemical messenger in the brain. It is believed to be involved in learning and memory. Certain diseases (such as Alzheimer’s disease) or brain injury (such as stroke) can cause too much glutamate to accumulate. This can set the stage for excitotoxicity, a process that can lead to damage or death of the affected brain cells.

        It is important to note that GABA and glutamate are carefully orchestrated to balance each other. Dysfunction of one of these amino acid neurotransmitters affects the function of the other. Some experts believe that their excitatory and inhibitory balance influences all brain cells.

        Neurotransmitters are Team Players

        All chemical messengers in the brain have immense interconnectivity. Their function relies on a system of checks and balances during each moment of life. If one part of the system fails, others can’t do their job properly. Panic disorder is just one of many physical and psychological illnesses that are believed to be influenced by the complex interacting of neurotransmitters.


        Beinfeld, Margery C. ”Cholecystokinin.” Psychopharmacology-4th Generation of Progress. 2000.

        Kaplan MD, Harold I. and Sadock MD, Benjamin J. Synopsis of Psychiatry, Eighth Edition. Baltimore: Williams & Wilkins. 1998.

        Paul, Steven M. "GABA and Glycine." Psychopharmacology-4th Generation of Progress. 2000.