Indole metabolism in the pineal organ of the pigeon with special reference to melatonin-synthesizing cells

By means of radioimmunoassay a clear-cut peak of melatonin concentration was found in the pineal organ of the pigeon at the middle of the scotophase (Coisin et al. 1982a). The aim of the present study was to identify the cell type responsible for the nocturnal indole metabolism, including melatonin synthesis, in the pineal of this avian species. After a short-term incubation or organ culture in the presence of [3H]-indolic precursors, [3H]-5-hydroxytryptophan or [3H]-5-hydroxytryptamine, the relative amounts of deaminated and acetylated products occurring in the pineal organ were measured by the use of thin layer chromatography and liquid-scintillation counting. It was possible to modify the relative amounts of deaminated and acetylated indoles by the application of some inhibitors of monoamine oxidase and cyclic nucleotide phosphodiesterase. Irrespective of the experimental conditions, high-resolution autoradiography combined with the above-mentioned radiochemical experiments showed that the cells of the receptor line (modified photoreceptor cells) are responsible for indole storage and metabolism, and very probably also for melatonin biosynthesis. The other cell types of the pineal parenchyma did not display significant labeling.     

Effects of α2-Adrenergic Agonists and Antagonists on Photoreceptor Membrane Currents

Type B photoreceptors of the nudibranch mollusc Hermissenda crassicornis receive excitatory synaptic potentials (EPSPs) whose frequency is controlled by potential changes of a neighboring cell known as the S optic ganglion cell which is thought to be electrically coupled to the presynaptic source of these EPSPs, the E optic ganglion cell. The frequency of the EPSPs increases when a conditioned stimulus (light) is paired with an unconditioned stimulus (rotation) during acquisition of a Pavlovian conditioned response. The results of the present study are consistent with an adrenergic origin for these EPSPs. Noradrenergic agonists (greater than 100 microM), norepinephrine and clonidine, only slightly depolarize the type B cell but clearly prolong its depolarizing response to light. Serotonin, by contrast, causes hyperpolarization of the type B cell's resting potential as well as after a light step. Clonidine reduces voltage-dependent outward K+ currents (IA, an early current, ICa2+-K+, a late Ca2+-dependent current) that control the type B cell's excitability (and thus its light response and membrane potential). These effects of clonidine are reduced or blocked by the alpha 2-receptor antagonist, yohimbine (0.5 microM), but not the alpha 1-blocker, prazosin. The same yohimbine concentration also blocked depolarizing synaptic excitation of the type B cell in response to depolarization of a simultaneously impaled S optic ganglion cell. Histochemical techniques (both the glyoxylic acid method of de la Torre and Surgeon and the formaldehyde-induced fluorescence or Falck-Hillarp method) demonstrated the presence of a biogenic amine(s) within a single neuron in each optic ganglion as well as three or four cells within the vicinity of previously identified visual interneurons. No serotonergic neurons were found within the optic ganglion or in proximity to visual interneurons. A clonidine-like synaptic effect on type B cells, therefore, could amplify conditioning-specific changes of membrane currents by increasing type B depolarization and possibly, as well, by elevating intracellular second messengers.     

Comparison of bacterial indicators and sampling programs for drinking water systems

A total of 48 French villages were selected for a survey of water quality from February 1983 to June 1984 as part of an epidemiological study conducted in the rural area of the Rh?ne-Alpes region. Water samples were collected and analyzed on a weekly basis in each village. Bacteriological analysis of each water sample included enumeration of standard plate count bacteria, total and thermotolerant coliforms, and fecal streptococci. The water quality regulations are examined as to the analysis frequency, the volume of samples, and the relationship between the various bacterial indicators. Analyzing 300-ml, instead of 100-ml, samples tends to generate better information on single water samples. However, if many samples are analyzed over time from the same community, the value of using large volumes of water samples is diminished. The comparisons between bacterial indicators showed that the information obtained from the various indicators was very similar. However, fecal streptococci had a better predictive value of a negative test than coliforms with respect to the French standards.     

Sequential modification of membrane currents with classical conditioning

Pavlovian conditioning of the nudibranch mollusc Hermissenda crassicornis was previously shown to produce long-lasting reduction of two K+ currents measured across the Type B photoreceptor soma membrane (Alkon et al., 1982a; Alkon et al., 1985). Pavlovian conditioning of the rabbit was also shown to be followed by persistent K+ current reduction (Disterhoft et al., 1986). Here we report the first evidence that Ca2+ currents can also be modified by conditioning. The amplitude of the currents rather than their voltage-dependence remains reduced at least 1-2 d after conditioning (but not control procedures). Conditioning-induced changes of both K+ and Ca2+ currents increased as a function of training, the Ca2+ currents only changing substantially with greater than or equal to 250 trials. The later changes of the Ca2+ current may function to limit the magnitude of excitability increases due to associative learning.     

Regulation of chicken pineal arylalkylamine-N-acetyl transferase by postsynaptic alpha 2-adrenergic receptors

The present investigation sought to characterize the adrenergic inhibition of arylalkylamine-N-acetyltransferase in cultured chicken pineal glands. Arylalkylamine-N-acetyltransferase, the melatonin rhythm generating enzyme, displays daily oscillations of activity that are driven by a circadian oscillator. Norepinephrine released at sympathetic nerve endings inhibits the enzyme and appears to play a role in maintaining a circadian rhythm of melatonin release. Chicken pineal glands were isolated in organ culture and the effects of adrenergic agents on the night time peak of N-acetyltransferase activity were studied. Norepinephrine and clonidine prevented 50 to 65% of the nocturnal rise of N-acetyltransferase activity. When applied at middark, norepinephrine and clonidine caused a 50 to 65% inhibition of N-acetyltransferase activity in 2 hours. Dose-response studies indicated clonidine was 100 times more potent than norepinephrine or cirazoline at inhibiting N-acetyltransferase activity. Inhibition of N-acetyltransferase activity was also observed, at micromolar concentration with epinephrine, UK 14,304 and alpha-methylnorepinephrine but not with phenylephrine, isoproterenol or dopamine. Epinephrine and clonidine actions were antagonized by yohimbine but not by prazosin. Destruction of the presynaptic compartment by bilateral superior cervical ganglionectomy did not affect the clonidine-induced inhibition of N-acetyltransferase and its reversal by yohimbine. It is concluded that the adrenergic inhibition of N-acetyltransferase activity in chicken pineal gland probably occurs via stimulation of postsynaptic alpha 2-adrenergic receptors.     

Indirect estimation of the maximal aerobic power of a male and female population from Brussels aged 6 to 23 years. Comparison with a direct technic for measuring maximal oxygen consumption

Validation of the maximal multistage 20 m shuttle run test with 1 min steps has been compared with a stepwise load increase on a bicycle ergometer among 201 male and female subjects ranging from 14 to 30 years. A slight underestimation of VO2 max (5.2%) amounting to 2.71 ml . min-1 . kg-1 was observed for the multistage shuttle test as compared to the bicycle test (r = 0.72). The analysis of the biological values collected after exercise does not show major differences between the two tests (plasma lactate, urinary total protein and albumin, creatinine). The renal handling of plasma proteins appears to be equally disturbed under the influence of exhaustive exercise. Maximal aerobic power regularly increases with age in both sexes, being more pronounced however for boys (1.16 to 3.37 l . min-1) than for girls (1.17 to 2.43 l . min-1) from 6 to 20 years old. Boys nearly sustain 50 ml . min-1 . kg-1 throughout childhood. On the contrary, from 8 years on girls progressively reduce their VO2 max down to 37.1 ml . min-1 . kg-1 at the age of 19. The decrease is more pronounced during the 11-16 years period. The present results constitute tentative norms on 1,025 brussels male and female subjects ranging from 6 to 23 years.