Graduate Thesis Or Dissertation
 

The relationship between environmental lighting and hydroxyindole-o-methyltransferase activity in the pineal gland of steelhead trout (Salmo gairdneri)

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  • Pineal hydroxyindole-0-methyltransferase (HIOMT) activity was monitored over a 24 h period under three different photoperiods, 16L:8D, 8L: 16D, and 12 L:12D. It was observed that in all three groups of fish HIOMT activity was high' during the dark portion of the photoperiod in comparison to activity during the light portion. Also, in all groups there was a sharp rise in HIOMT activity in the first four hours after the onset of darkness. Capping the fish to eliminate direct illumination of the pineal failed to abolish the characteristic pattern of response seen previously. Blinding and constant dark conditions did abolish the characteristic rhythm, as did blinding followed by surgical exposure of the pineal. These results lead us to conclude that pineal HIOMT activity in juvenile steelhead trout is dependent on photoperiod. Furthermore, lighting information reaches the gland via the eyes. It was further observed that pineal HIOMT activity response to light is affected by the background color on which the fish are hled. On a white background HIOMT activity shows peak activity during the light portion of the photoperiod with low activity associated with the dark portion.
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