…as neurotransmitters but also as neuromodulators. As neuromodulators, they do not act directly as neurotransmitters but rather increase or decrease the action of neurotransmitters. Well-known examples are the opioids (e.g., enkephalins), so named because they are endogenous (produced in the human body) peptides (short chains of amino acids) with a…

…transmitter substances but also of neuromodulators. Neuromodulators are substances that do not directly activate ion-channel receptors but that, acting together with neurotransmitters, enhance the excitatory or inhibitory responses of the receptors. It is often impossible to determine, in the presence of many substances, which are transmitters and which are modulators.…

…fungus secretes a number of neuromodulatory agents, particularly guanobutyric acid and sphingosine, near both the central and peripheral nervous systems of its host. The fungus also contains a slew of unusual bacteria-like toxins, which may impair the chemical signals that allow the ant to communicate with other members of its…