PubMed · 72270
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J A Smith, E G Spokes, E D Bird, K P Minneman. 1977-10-29. Human post-mortem pineal metabolism.. https://doi.org/10.1016/s0140-6736(77)90865-0
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The intracortical distribution of the biogenic amines (BA), norepinephrine (NE), dopamine (DA) and serotonin (5-HT), was determined for the parietal and occipital cortical areas of the cat. Under microscopic control, slices of each region were dissected out into 4 fractions: (1) an upper gray fraction (G1); (2) a medium gray fraction (G2); (3) a lower gray fraction (G3) and (4) a white-matter fraction (W). The BA were assayed by means of specific and sensitive radioenzymatic techniques; using catechol-O-methyltransferase (COMT) for the catecholamines (CA), and N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT) for the 5-HT. In the two cortical regions studied, NE and DA were found to be distributed in an orderly laminar fashion. The highest levels of endogenous CA were measured in the superficial layers (fractions G1 and G2) while the white matter (fraction W) exhibited the lowest content of both NE and DA. DA represented 32--38% of the total CA content of the parietal cortex and 32--41% of the total CA content in the occipital cortex. In the parietal cortex, the distribution of 5-HT was similar in pattern to that of the CA, i.e., a decreasing concentration gradient with the highest endogenous levels in the G1 fraction and the lowest content in the W fraction. In the occipital cortex, the distribution was also found to be laminar for the gray matter but the W fraction showed a higher endogenous content than the lower gray fraction (G3). The release of NE, DA and 5-HT was studied by means of cortical superfusion in an in vivo preparation. The concentrations of BA measured in 30 min interval superfusates was fairly constant in a given experiment under basal conditions but varied widely from experiment to experiment. Variations in the basal overflow of NE were often independent of those found for DA and the basal overflow of 5-HT seemed independent of those of CA. The laminar intracortical distribution of endogenous NE, DA and 5-HT in cerebral cortex demonstrated by microdissection and biochemical assay techniques suggests a definite and structured pattern of aminergic innervation. Furthermore, the fact that these BA are released and a basal overflow can be detected and measured appears compatible with significant roles of NE, DA and 5-HT in synaptic transmission in the cerebral cortex.
A thin-layer chromatographic procedure for measuring pineal HIOMT activity is described, based on the methylation of NAS to melatonin. The method enables simple and accurate determination in small aliquots from a single pineal organ homogenate.
The visual pathway and central neural structures involved in the photic and endogenous regulation of the activity of pineal N-acetyltransferase and hydroxyindole-O-methyltransferase were investigated. The results indicate that the visual pathway regulating both enzymes is the retinohypothalamic tract, and that the inferior accessory optic tract is clearly not involved in the regulation of hydroxyindole-O-methyltransferase activity, as has been previously thought. In addition, the suprachiasmatic nucleus was found to be necessary for the generation of a rhythm in N-acetyltransferase activity in blinded animals, and to be responsible for the tonic elevation of hydroxyindole-O-methyltransferase activity in blinded animals. Finally, it was concluded that the rapid and large daily changes in N-acetyltransferase activity seen in a normal lighting cycle and the much slower and smaller changes in hydroxyindole-O-methyltransferase activity seen only after weeks in constant lighting conditions are mediated by the same neural tract; the different time courses of the effects of environmental lighting may be explained on the basis of different intracellular regulatory mechanisms.