Relationships between the effects of peripherally administered salmon calcitonin on calcaemia and brain biogenic amines.

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Abstract
The effects of s.c. administered salmon calcitonin on the biogenic amine neurotransmitters and metabolites were studied in discrete brain sections in order to evaluate the relationships between these central effects and the fall of serum calcium and to investigate the mechanisms of calcitonin-induced behavioral changes. The biogenic amines and metabolites were simultaneously determined by high-performance liquid chromatography with electrochemical detection in tissue samples obtained from rats treated with 10-80 MRC U/kg of the peptide. Some rats were pretreated with calcium lactate to inhibit the calcitonin-induced hypocalcaemia. Most of the effects, consisting of signs of serotonergic system activation, have been observed in the hypothalamus, accounting for some behavioral effects of the peripherally administered salmon calcitonin. It was speculated that the activation of the brain serotonergic system could result from two indirect and separate mechanisms: the first, which would involve enhanced serotonin synthesis, seemed to be facilitated by calcium availability. A second possible mechanism, which would involve enhanced serotonin release from the neurons, seemed to be mediated by the fall of calcium levels in the blood.