Neurotransmitters are chemicals in the nervous system that transmit nerve impulses across synapses between nerve cells and other nerve or muscle cells. Neurotransmitters are stored in the axons of neurons, and their release is triggered by electrical impulses. The effect that a neurotransmitter produces does not depend just on the particular chemical in question, but also on the receptor that receives the transmitted signal. For instance, a single neurotransmitter can promote either an excitatory or inhibitory post synaptic potential. Among the more than 300 neurotransmitters that have been identified are glutamate, GABA, glycine, dopamine, serotonin, adenosine, and acetylcholine. Improper production or function of neurotransmitters has been linked to a number of diseases and medical conditions, such as clinical depression and amyotrophic lateral sclerosis.

A sagittal section of rat brain (shown above) was immunofluorescently labeled for phosphorylated neurofilaments (expressed in neurons) with mouse anti-NF-P antibodies followed by goat anti-mouse secondary antibodies conjugated to Alexa Fluor 488. In addition, glial fibrillary acidic protein (expressed in various astroglia and neural stem cells) was targeted with rabbit anti-GFAP antibodies visualized with goat anti-rabbit secondary antibodies conjugated to Alexa Fluor 568. Cell nuclei were labeled with the popular nuclear counterstain Hoechst 33342. Images were recorded in grayscale with a 12-bit digital camera coupled to a Nikon Eclipse 80i microscope equipped with bandpass emission fluorescence filter optical blocks. During the processing stage, individual image channels were pseudocolored with RGB values corresponding to each of the fluorophore emission spectral profiles.