The effects of photoperiod on growth rate and circulating thyroid hormone levels in the red drum, Sciaenops ocellatus: evidence for a free-running circadian rhythm of T(4) secretion.

Previous studies with red drum and other species have indicated that diurnal rhythms of circulating thyroid hormones (thyroxine, T(4), and 3-5-3'-triiodo-L-thyronine, T(3)) are synchronized to the light cycle, and not to time of feeding. In this study we set out to address the effects of various lighting regimes on thyroid hormone levels in the red drum. The first experiment was undertaken to determine the effects of long and short photoperiods on diurnal thyroid hormone rhythms, growth rate, feed efficiency and food consumption. Red drum raised under a long photoperiod (16L:8D) grew significantly larger and exhibited greater feed efficiency than their short photoperiod (8L:16D) counterparts. There were no changes in food consumption or the diurnal profile of plasma thyroid hormones, e.g. increased peak amplitude or duration, that would explain this increase in growth rate and feed efficiency. The second experiment was undertaken to determine if diurnal thyroid hormone rhythms in the red drum originate from an endogenous circadian clock. To address this question, red drum were housed under a 12L:12D photoperiod and fed once daily at variable times before the lighting was switched to constant dim illumination for up to 3 days. The rhythm of circulating T(4) levels persisted for two complete cycles with constant amplitude in fish that continued to be fed during constant dim illumination, and did not appear to entrain to feeding. The T(4) rhythm also persisted for three complete cycles under constant conditions in feed-restricted fish, although with a diminished amplitude over time. To our knowledge, these data provide the first evidence for a free-running circadian rhythm of plasma T(4) levels in a fish. These findings implicate the involvement of an endogenous circadian clock that determines when the hypothalamo-pituitary-thyroid axis is activated.

The effects of photoperiod and feeding on the diurnal rhythm of circulating thyroid hormones in the red drum, Sciaenops ocellatus.

Available data in cyprinid and salmonid species indicate that nutrient intake sustains thyroidal rhythmicity and that time of feeding may influence the amplitude, but not the phase, of diurnal thyroid hormone cycles. Several experiments were conducted to characterize the nature of thyroidal rhythmicity in a more derived perciform teleost, the red drum. These studies were designed to test the following hypotheses: (1) that feeding time will alter the amplitude of the thyroid hormone rhythm without altering its phase and (2) that food deprivation will diminish the amplitude of the thyroid hormone rhythm. Circulating T(4) levels in this species exhibit high-amplitude diurnal rhythms, whereas circulating T(3) levels fluctuate within a more narrow range. Fish were reared under a 12L:12D photoperiod and fed 5% body weight once daily either at dawn or at dusk. Feeding time had no discernible effect on the phase of the T(4) cycle, but altered the amplitude of the cycle. Dawn-fed fish had significantly greater mean peak levels of T(4) than dusk-fed fish, although there was no difference in daily mean levels in both groups of fish. When red drum were deprived of food, significant declines in plasma glucose, HSI, and liver glycogen content occurred within 3 days. When red drum were sampled once per day after 3, 7, or 11 days of food deprivation there were no consistent changes in circulating T(4) and T(3) levels compared to those of fed controls. However, significant declines in circulating T(4) and T(3) levels in response to food deprivation were detected with a diurnal sampling protocol. Within 3 days of food deprivation, T(4) levels were significantly reduced compared to those in fed controls and not significantly different from T(4) levels after 10 days of food deprivation. T(3) levels exhibited a stepwise decline in circulating levels during food deprivation. These data indicate that both feeding time and nutrient status exert their effects on thyroid hormone rhythms by modifying the amplitude of these cycles. These data also underscore the importance of incorporating a consideration of endocrine rhythmicity into sampling protocols.

Felbamate increases [3H]glycine binding in rat brain and sections of human postmortem brain.

The anticonvulsant compound felbamate (2-phenyl-1,3-propanediol dicarbamate; FBM) appears to inhibit the function of the N-methyl-D-aspartate (NMDA) receptor complex through an interaction with the strychnine-insensitive glycine recognition site. Since we have demonstrated previously that FBM inhibits the binding of [3H]5, 7-dichlorokynurenic acid (DCKA), a competitive antagonist at the glycine site, we assessed the ability of FBM to modulate the binding of an agonist, [3H]glycine, to rat forebrain membranes and human brain sections. In contrast to its ability to inhibit [3H]5,7-DCKA binding, FBM increased [3H]glycine binding (20 nM; EC50 = 485 microM; Emax = 211% of control; nH = 1.8). FBM, but not carbamazepine, phenytoin, valproic acid or phenobarbital, also increased [3H]glycine binding (50 nM; EC50 = 142 microM; Emax = 157% of control; nH = 1.6) in human cortex sections. Autoradiographic analysis of human brain slices demonstrated that FBM produced the largest increases in [3H]glycine binding in the cortex, hippocampus and the parahippocampal gyrus. Because various ions can influence the binding of glycine-site ligands, we assessed their effects on FBM-modulation of [3H]glycine binding. FBM-enhanced [3H]glycine binding was attenuated by Zn++ and not inhibited by Mg++ in human brain. These results suggest that FBM increases [3H]glycine binding in a manner sensitive to ions which modulate the NMDA receptor. These data support the hypothesis that FBM produces anticonvulsant and neuroprotective effects by inhibiting NMDA receptor function, likely through an allosteric modulation of the glycine site.

Selective introduction of TMS groups in tryptamines: preparation of N1-TMS derivatives of tryptamines.

Indolethylamines (tryptamines) with a primary animofunction react with Regisil under controlled conditions to yield a mono TMS derivative. Mass spectrometry to these derivatives shows that the TMS group is substituted on the indolic nitrogen (N1) and not the primary amino nitrogen. This is confirmed by converting these compounds to their isothiocyanate derivatives. The GC and GC-MS data of some typical compounds are presented.

The simultaneous determination by selected ion monitoring of the levels of homovanillic, isohomovanillic, 3,4-dihydroxyphenylacetic and 3-methoxy-4-hydroxymandelic acids in single biological samples.

Methods for the determination and quantitation of homovanillic, isohomovanillic, 3,4-dihydroxyphenylacetic and 3-methoxy-4-hydroxymandelic acids in single samples of biological material by gas chromatography, gas chromatographic mass spectrometry and selected ion monitoring during gas chromatographic mass spectrometry are described. Examples of the levels of these four acid metabolites of catecholamines in serum and CSF of untreated dog, cat and human, in urine of parkinsonian subjects treated with varying doses of L-DOPA and in CSF of dogs which had received 1 g of L-DOPA per day for 7 weeks are presented.