A variety of drugs which were thought to selectively effect the synthesis, release or reuptake of the biogenic monoamines, and thereby deplete their stores in brain, were administered to rats. The animals were given intraperitoneal injections of reserpine, α-methyl-meta-tyrosine, α-methyl-para-tyrosine, para-cholorophenylalanine and tetrabenazine, and were killed at intervals known to cause maximum depletion of serotonin, dopamine and norepinephrine. When compared to saline controls, the drugs depleted the respective monoamines, as expected, but changes in the levels of acetylcholine, alanine, glycine, γ-aminobutyric acid, and aspartate and glutamate were also observed.

1.1. The concentration of free tryptophan, bound tryptophan and tyrosine was compared in the plasma of the rat and the pigeon.2.2. The content of tryptophan, 5-hydroxytryptophan, serotonin, 5-hydroxyindoleacetic acid, tyrosine, dopamine and norepinephrine was determined concurrently, and the distribution of these compounds was compared in four major brain areas of the two species.3.3. The plasma levels of free tryptophan and tyrosine were higher in the pigeon than in the rat.4.4. The content of tryptophan, 5-hydroxytryptophan and tyrosine was higher in brain parts of the pigeon than the rat.5.5. The content of serotonin was higher in the telencephalon of the pigeon, while the content of norepinephrine was higher in the telencephalon of the rat.6.6. The content of 5-hydroxyindoleacetic acid was higher in brain parts of the rat than the pigeon.

A rapid and sensitive method for separation and concurrent assay of 14 compounds at the picomole level in individual rat brain parts is described. The putative amino acid neurotransmitters (aspartate, γ-aminobutyric acid, glutamate, and glycine) are extracted from a 20–30 mg portion of the tissue with 5% TCA and assayed as their respective DNP-amino acid methyl ester derivatives by glc. Four other putative neurotransmitters (acetylcholine, dopamine, norepinephrine, and serotonin) and some of their precursors and metabolites (choline, tryptophan, 5-hydroxytryptophan, 5-hydroxyindoleacetic acid, and tyrosine) are extracted in 1n formic acid-acetone (v/v:15/85) from the remaining tissue. The lipids are removed with a heptane-chloroform (v/v:8/1) wash and the aqueous phase is dried at 37°C under N2. The dried extract is dissolved in water (pH 4). With one portion of this solution, acetylcholine and choline are assayed using a radioenzymatic method whereas with the rest, dopamine, norepinephrine, serotonin, 5-hydroxyindoleacetic acid, 5-hydroxytryptophan, tryptophan, and tyrosine are separated with three ion exchange resins arranged in tandem. These compounds are assayed fluorometrically with modified microadaptations of previously reported methods.