Dopaminergic innervation of the rainbow trout pituitary and stimulatory effect of dopamine on growth hormone secretion in vitro

To elucidate which factors regulate growth hormone (GH) secretion in rainbow trout, dopaminergic innervation of the rainbow trout pituitary along with the action of dopamine in vitro, were studied. Brains with attached pituitaries were double-labeled for putative dopaminergic neuronal fibers and somatotropes, using fluorescence immunohistochemistry. A direct dopaminergic innervation to the proximal pars distalis (PPD) with dopaminergic fibers terminating adjacent to somatotropes was demonstrated. Growth hormone secretion from whole pituitaries was measured in perifusate using a homologous GH-RIA. Dopamine (DA; 10(-7)-2x10(-6) g ml(-1)) increased basal GH secretion, with the GH secretion normalizing again after the DA exposure was halted. When pituitaries were pre-treated with somatostatin-14 (SRIF-14; 10(-12)-10(-9) g ml(-1)), before being exposed to different doses of DA, there was an inhibition of GH secretion which was not reversed after treatment of SRIF-14 was halted, unless DA was added. It is concluded that dopamine can function as a GH secretagogue in the rainbow trout pituitary gland.

Transient alterations in neurotransmitter levels during a critical period of neural development in coho salmon (Oncorhyncus kisutch)

The time of parr-smolt transformation (PST) in salmon is a critical period of brain development during which the olfactory imprinting on the natal stream takes place. PST is associated with a surge of plasma thyroxine. We report here similar surges in the brain content of serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), dopamine (DA), norepinephrine (NE), and glutamine (Gln). Other putative neurotransmitters, such as glutamate and aspartate show no such change while gamma-amino-butyric acid (GABA) shows a minor elevation.

Lipoprotein profiles in Alaskan Siberian Yupik Eskimos

Coronary heart disease and diabetes, once rare in Eskimos, is on the increase in some Alaskan communities. As part of a detailed assessment of the prevalence of these diseases and associated risk factors in several villages, we report here on the plasma concentrations of lipoprotein and apoprotein in a sample of Siberian Yupik Eskimos aged 40-87 years living in the village of Gambell on St. Lawrence Island. Mean cholesterol levels for females were 242 mg/dl and 223 for males. LDL levels were 161 for females and 149 for males, while HDL levels were 67 for females and 58 for males. The mean ApoB and Apo-A1 values were 112 mg/dl and 167 mg/dl for males and females. Triglycerides were 73 for females and 77 for males. The allele frequency of APOE*3 and APOE*4 were .900 and .100 respectively. There was a total absence of the APOE*2 allele in this sample. Mean total cholesterol concentrations in this sample were markedly higher than those reported in 1958 from this village and from those recently reported for closely related Yupik Eskimos living in Siberia. The cholesterol levels were higher and the triglyceride levels were lower than in U.S. Indian populations. The data suggest the possibility of recent increased risk of cardiovascular disease for this Eskimo population. The new information indicates a need for comprehensive epidemiological studies to identify and characterize cardiovascular disease risk factors in all Alaska Native populations in order to provide a database for meaningful interventions. The lipoprotein profiles reported here are significantly different from Amerind groups, a finding that may reflect both dietary and genetic differences.

Distribution and changes in mu- and kappa-opiate receptors during the midlife neurodevelopmental period of Coho salmon, Oncorhynchus kisutch

Parr-smolt transformation (PST) in coho salmon is associated with a plasma thyroid hormone (PT4) surge and a critical period of neural development that includes axonal sprouting, neurogenesis, and surges of select neurotransmitters. Here we provide a description of the selectivity, distribution, and the changes in the density of mu- and kappa-opiate receptors during PST, as revealed by quantitative in vitro autoradiography of [3H]Tyr-D-Ala-Gly-NMe-Phe-Gly-ol ([3H]DAMGO) and [3H]ethylketocyclazocine ([3H]EKC), respectively. The concentration of mu-receptors increased significantly in select cell groups in the early stages of parr-smolt transformation, until a peak was reached at the time coinciding with the peak of the PT4 surge. In other cell groups, the peaks occurred 1 or 2 weeks later. With one exception, this increase was followed by a decrease in concentration. The brain areas showing the highest concentrations are the dorsal nucleus of the ventral telencephalic area, the glomerular region, the granular layer of the valvula cerebelli, the nucleus diffuses of the inferior lobe, and the nucleus diffuses of the torus lateralis. Other regions with distinctly elevated mu-receptor concentrations are the stratum griseum centrale of the optic tectum and the preoptic area. The distribution of kappa-receptors is more diffuse, and the densities are considerably lower. The overlap in distribution of mu- and kappa-receptors is considerable, but significant exceptions are noted. For example, the dorsomedial nucleus of the dorsal telencephalic area, the habenular nucleus, and the dorsomedial nucleus of the thalamus exhibit a surge in density of kappa-receptors at the time of the PT4 surge, while the density of mu-receptors in these nuclei remain very low throughout parr-smolt transformation. The kappa-receptor containing cell groups are not identifiable until 3 weeks before the PT4 surge because of low densities. The most prominently labeled kappa-receptor regions are the ventral and dorsal nuclei of the ventral telencephalic area, the medial and dorsal zones of the dorsal telencephalic area, the optic tectum (all layers), the dorsomedial nucleus of the thalamus, the torus lateralis of the ventral hypothalamus, and the preoptic area. An increase of mu- and kappa-opiate receptor densities in specific brain regions may reflect roles in the alteration of brain organization, olfactory imprinting, neuroendocrine activity or other physiological activities. The overall distribution of these receptors are relatively more extensive in salmon than in other vertebrates so far studied.

Transient serotonin-immunoreactive neurons coincide with a critical period of neural development in coho salmon (Oncorhynchus kisutch)

In coho salmon (Oncorhynchus kisutch), smolt transformation has been shown to be associated with sequential surges of neurotransmitters in the brain. In order to determine if the surge of serotonin (5-HT) is correlated with structural changes, we have used immunocytochemistry to observe changes in the serotonin immunoreactivity before, during and after the 5-HT surge. The following stages were studied: 12-month-old freshwater presmolts, 17-month-old freshwater presmolts, 18-month-old saltwater smolts, 19-month-old saltwater postsmolt, 24-month-old postsmolt, and adult spawners. In the 17-month-old samples, but not at any other stage, we found a set of transient (serotonin-immunoreactive) 5-HT-immunoreactive neurons in the lateral preoptic area, as well as a discrete population of 5-HT-immunoreactive neurons in the lateral part of the dorsal right habenular nucleus. In addition, a higher density of serotonergic fibers was found in the telencephalon at this stage compared to the following two stages. Since the transient 5-HT-immunoreactive structures presented here do not appear simultaneously with the 5-HT total brain concentration surge, we conclude that they are unlikely to be the source of the 5-HT surge, but are probably related to other developmental changes in the brain associated with smolt transformation.

Pseudomonas cepacia 2,2-dialkylglycine decarboxylase. Sequence and expression in Escherichia coli of structural and repressor genes

A 3969-base pair PstI-PstI fragment of Pseudomonas cepacia DNA containing the gene for the pyridoxal 5'-phosphate dependent 2,2-dialkylglycine decarboxylase (pyruvate) (EC 4.1.1.64) was cloned in Escherichia coli. The insert was sequenced by the dideoxy method using nested deletions from both ends, revealing a central 1302-base pair region that codes for the decarboxylase subunit. The recombinant enzyme was expressed in E. coli, purified to homogeneity, and sequenced at the amino terminus. Also, a cofactor-labeled active site peptide was sequenced. The carboxyl terminus of the deduced amino acid sequence is homologous with the carboxyl terminus of mammalian ornithine aminotransferase; the active site sequence is similar to the active site sequences of several other aminotransferases. No homologies with known decarboxylase sequences could be found. Expression of the decarboxylase gene is negatively controlled by a 687-nucleotide sequence upstream of and diverging from the structural gene. Expression is induced by S-isovaline, 2-methylalanine, and D-2-aminobutanoic acid, but not by glycine, D- or L-alanine, L-2-aminobutanoic acid, R-isovaline, or other alkyl amino acids.