NEUROCHEMICAL CORRELATES OF BEHAVIOUR–CONTENT OF TRYPTOPHAN, 5‐HYDROXYTRYPTOPHAN, SEROTONIN, 5‐HYDROXYINDOLEACETIC ACID, TYROSINE, DOPAMINE AND NOREPINEPHRINE IN FOUR BRAIN PARTS OF THE PIGEON DURING BEHAVIOURAL DEPRESSION FOLLOWING AN INJECTION OF TRYPTOPHAN1,2

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Abstract
Abstract— Pigeons working on a multiple lixed‐ratio 50, fixed interval 10 schedule of food reinforcement were injected with l‐tryptophan (300mg/kg; I.M.) and killed at various times before, during and after the period of behavioural depression following the administration of this amino acid (0, 25, 50, 90, 170 and 230 min). The levels of tryptophan, 5‐hydroxytryptophan, 5‐hydroxytryptamine, 5‐hydroxyindoleacetic acid, tyrosine, dopamine and norepinephrine were concurrently measured in 4 specific areas of the brain (telencephalon, diencephalon plus mesencephalon, pons plus medulla‐oblongata and cerebellum). The course of the increases in the level of 5‐hydroxytryptamine in the telencephalon, and subsequent return to pre‐injection levels, was temporally related to the onset of the decreased responding and gradual return to normal rates of responding. Changes in dopamine and norepinephrine were not correlated with the onset of and recovery from the decreased response rates. The data in this paper are discussed in terms of (a) the previously reported work with 5‐hydroxytryptophan and (b) the importance of the telencephalic serotonergic system in certain types of behavioural depression.
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