Letter | Published:

Immunoreactive thyrotrophin releasing factor in gastropod circumoesophageal ganglia

Abstract

REPORTS have indicated that thyrotrophin releasing factor (TRF) is stored in extrahypothalamic as well as hypothalamic brain regions of many vertebrates from the primitive larval lamprey to the more advanced mammals1–4. Although TRF is found in the brain of many poikilotherms, administration of synthetic TRF (pGlu-His-ProNH2) to these animals does not activate thyroid gland function5–7. Thus, it has been proposed that, in these animals, TRF modulates synaptic transmission rather than releasing thyrotrophin (thyroid stimulating hormone)1. Furthermore, the administration of TRF to hypophysectomised rodents potentiates the effect of the L-dopa on behaviour8, thus supporting the hypothesis that TRF modulates monoaminergic transmission in higher vertebrates as well. Further support for a role of TRF in synaptic transmission is the finding that administration of the synthetic tripeptide leads to an increase in noradrenaline turnover in rat brain9–11. Because these reports imply first, that TRF may influence monoaminergic transmission and second, that, in lower vertebrates, this role of TRF may be more important than that of regulating TSH release, we have investigated whether TRF is present in invertebrates which do not produce thyroid hormones but exhibit monoaminergic neurotransmission. We found immunoreactive TRF in the circumoesophageal ganglia of various gastropods. Species studied were the landsnail Mesodon roemeri (Connecticut Valley Biological Supply Co., Massachusetts), Planorbis corneus (Mogul Ed Corp., Wisconsin), Helesoma trivolbis and Viviparus malleatus (Ann Arbor Biological Center, Michigan).

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