Immunohistochemical detection of biogenic amines in the photophores of the midshipman fish Porichthys notatus

Abstract

Biogenic amines are known to be present in the luminescence organs (photophores) of the teleost midshipman fish Porichthys notatus, but their distribution within the photophores was unknown until now. The cellular localization of endogenous monoamines was therefore investigated in the photophores of this fish by peroxidase–antiperoxidase immunohistochemistry with antibodies against serotonin, noradrenaline, and adrenaline. Strong serotonin-like immunoreactivity was detected exclusively within the light-emitting cells (photocytes). By contrast, strong noradrenaline immunostaining was present in axonal processes surrounding the photocytes and the lens border cells, and light staining was also observed within the photocytes. Adrenaline immunostaining was strongest in lens border cells, weak in photocytes, and absent in axonal processes. These observations support previous experimental results which suggest that noradrenaline is the excitatory neurotransmitter for light emission in this fish. The non-neuronal distribution of serotonin and adrenaline in the photophore suggests that these amines, or mere metabolites of adrenaline, play a neuromodualtory or paracrine role related to regulation of luminescence.