Tadataka Yamada

Altered neuropeptide concentrations in cerebrospinal fluid of psychiatric patients

Immunoreactive somatostatin, bombesin, and cholecystokinin were measured in cerebrospinal fluid of normal subjects and patients with anorexia nervosa, depression, mania, and schizophrenia. Somatostatin-like immunoreactivity was decreased in anorexic and depressed patients. Bombesin-like immunoreactivity tended to be decreased in schizophrenics. Cholecystokinin-like immunoreactivity did not differ between groups. These data suggest a possible function for neuropeptides in regulation of human behavior.

Rapid Sequestration and Degradation of Somatostatin Analogues by Isolated Brain Microvessels

Abstract: Somatostatin (SRIF) is a putative peptide neurotransmitter that may interact with brain capillaries following neurosecretion of the peptide. The present studies investigate the binding and metabolism of SRIF analogues in isolated bovine brain microvessels. 125I [Tyr1]SRIF was rapidly degraded by capillary aminopeptidase with a half‐time of approximately 3 min at 23°C. The microvessel aminopeptidase had a low affinity and high capacity for the peptide, Km= 76 μM and Vmax= 74 nmol min−1. 125I‐[Tyr11]SRIF was converted to free iodotyrosine at a much slower rate, presumably by a lower‐activity endopeptidase. 125I‐[Tyr 11]SRIF was rapidly bound by microvessels, whereas another basic peptide, [Tyr8]bradykinin, or an acidic peptide, CCK8, or a neutral peptide, leucine enkephalin, were bound to a considerably less extent. The binding of 125I‐[Tyr11]SRIF to the capillaries was nonsaturable up to a concentration of 1 μg/ml of unlabeled peptide, and the binding reaction was extremely rapid, reaching equilibrium within 5 s at either 0°C or 37°C. Approximately 20% of the SRIF bound by the microvessels was resistant to acid wash and presumably represented internalized peptide. In addition, the 125I‐[Tyr11]SRIF bound rapidly to the endothelial cytoskeleton remaining after a 1% Triton X‐100 extraction of the microvessels. The peptide‐cytoskeletal binding reaction was nonsaturable up to 1 μg/ml of unlabeled [Tyr11]SRIF, but it was inhibited by 0.5% polylysine or 0.8 M KC1 and was stimulated by 1 mM dithiothreiotol. These studies suggest that brain microvessels rapidly sequester and degrade SRIF analogues and that this may represent one mechanism for rapid inactivation of the neuropeptides subsequent to neurosecretion.

Peptides are in the eye of the beholder

Neuroactive peptides, previously identified in central neurons and thought to be neurotransmitters or modulators, have been recently described in ocular tissues. The uvea (iris, ciliary body and choroid) contains extrinsic nerve fibers immunoreactive for substance P and VIP; exogenous application of these peptides evokes physiological reactions in the eye. At least eight neuroactive peptides have been localized to retinal neurons, generally the intrinsic, local-circuit amacrine cells. In the best studied retina, that of the pigeon, the local- ization of each peptide within a unique amacrine cell type implies that the multiple structural types described by Cajal are functionally distinctive neurons. Physiological explorations suggest functions for two of the retinal peptides, substance P and enkephalin, in visual information processing, and a biochemical study indicates that at least one peptide, somatostatin, is synthesized within the retina.

Regional distribution of somatostatin-like immunoreactivity in the human brain.

The regional distribution and chromatographic characteristics of somatostatin-like immunoreactivity (SLI) were studied in autopsy specimens of 8 human brains. SLI concentrations in 8 different regions of these brains ranged from (mean +/- S.E.) 756.3 +/- 363.4 pmol/g tissue in anterior hypothalamus to 1.6 +/- pmol/g in cerebellum. Chromatography of the extracts of human brain cortex, anterior hypothalamus, thalamus and amygdala on Sephadex G-50 disclosed one major peak which corresponded to the elution peak of synthetic somatostatin. Since the human brains were obtained at autopsy 11-36 h after death, the effects of temperature and time lapse between death and tissue extraction on SLI concentration and chromatographic pattern in rat brain were examined. After storage at 4 degrees C or 23 degrees C for 2 h and 8 h, a significant increase in SLI concentration was noted, although by 24 h in increase was no longer observed. A gradual loss in the eluting forms of SLI on gel chromatography was observed with storage at 4 degrees C or 23 degrees C.

Binding of ethacrynic acid to hepatic glutathione S-transferases in vivo in the rat

Abstract Ethacrynic acid is a substrate for rat glutathione S -transferases in vitro (1,2). In their study defining the importance of the glutathione S -transferases in the hepatic metabolism and biliary excretion of ethacrynic acid, Wallin et al . (3) suggested that a small but consistent portion of the administered drug was bound selectively and covalently to the transferases. Such an association would represent a unique example of covalent binding of a drug to the metabolizing enzyme without prior microsomal enzyme activation. We have undertaken these studies, therefore, to characterize the binding of ethacrynic acid to the glutathione S -transferases and to delineate the selectivity of this binding.

Neurotransmitter control of hypothalamic-pituitary-thyroid functions in rats

The possible roles of monoamine neurotransmitters in the regulation of the hypothalamic-pituitary-thyroid axis were examined in the rat. Rats were treated acutely and repeatedly with drugs which are presumed to alter neurotransmitter functional activity. These drugs include neurotransmitter precursors (tryptophan and L-DOPA), synthesis inhibitors (p-chlorophenylalanine and alpha-methyltyrosine), uptake inhibitors (desipramine and zimelidine) and lithium carbonate. The hormone levels measured were hypothalamic TRH and SLI content and serum TSH, T4 and T3. We conclude that augmented serotonergic or dopaminergic activity may inhibit TRH release, but that release from these inhibitions is not sufficient to stimulate TRH release. The release of TRH seems to be mediated by norepinephrine. Lithium treatment results in increased hypothalamic TRH.

Hypergastrinemia Develops Within 24 Hours of Truncal Vagotomy in Dogs

Postvagotomy hypergastrinemia may result from withdrawal of tonic vagal inhibitory mechanism(s) or from G-cell hyperplasia secondary to diminished acid secretion. Early development of hypergastrinemia, after vagotomy, would favor the first mechanism, whereas delayed development would favor the second. We sought to distinguish between these two mechanisms and to determine whether alterations in somatostatin release might mediate postvagotomy hypergastrinemia. We measured plasma concentrations of gastrin and somatostatinlike immunoreactivity basally and in response to meal (pH controlled at 5.5) and to insulin hypoglycemia before and after truncal vagotomy in 11 dogs. Basal and postprandial hypergastrinemia were established within 24 and 48 h after vagotomy, respectively. Basal and meal-stimulated plasma somatostatinlike immunoreactivity concentrations were unaltered by vagotomy, although insulin hypoglycemia-induced rises in plasma somatostatinlike immunoreactivity were abolished by vagotomy. Our data suggest that neither G-cell hyperplasia nor alterations in somatostatin release explain postvagotomy hypergastrinemia in the dog. The observations support the hypothesis that postvagotomy hypergastrinemia results from the withdrawal of a tonic vagal inhibitory mechanism of gastrin release that is independent of somatostatin. Whether the tonic vagal inhibition of gastrin is direct or indirect is unknown.

Biosynthesis of Somatostatin-Like Immunoreactivity by Frog Retinas In Vitro

Abstract: Somatostatin‐like immunoreactivity has been localized to a wide variety of central nervous system neurons, including the retina. We utilized the unique advantages the retina provides for in vitro studies of nerves to examine the biosynthesis of somatostatin. Extracts of frog retinas pulse‐labeled with [35S]cysteine for various time periods revealed uptake of radioactivity into material adsorbable by anti‐somatostatin antibody linked to affinity beads. This uptake increased in a curvilinear fashion for 4 h and was inhibited by cycloheximide (0.2 mM) or by boiling the retinas prior to labeling. Pulse‐chase experiments revealed that affinity‐adsorbable radioactivity from retinal extracts decreased with time of incubation in chase medium; 89% of this decrease could be accounted for by increases in the affinity‐adsorbable radioactivity of the chase medium. Chromatography of the retinal extracts on Sephadex G50 (superfine) revealed four elution peaks, whereas only one peak, co‐eluted with somatostatin‐14, could be identified in the medium. Chromatographic elution patterns of affinity‐adsorbable radioactivity from extracts of pulse‐labeled retinas incubated in chase medium for various times showed a gradual shift of radioactivity from the earlier‐eluting peaks to the later ones. These studies indicate that biosynthesis of somatostatin occurs in frog retinas in vitro. The retina may be a useful model for further study of peptidergic neurons.

Bombesin-like immunoreactivity in human cerebrospinal fluid.

Abstract Bombesin-like immunoreactivity (BLI) was detected in the cerebrospinal fluid of healthy human volunteers. The mean concentration+-S.E. for 29 subjects was34.4 +- 1.8fmol/ml. Chromatography of human spinal fluid BLI on Sephadex G50 revealed a single peak which coeluted with bombesin nonapeptide.

Thyrotropin-releasing hormone levels decrease in hypothalamus of aging rats.

Because hypothalamic and extrahypothalamic levels of thyrotropin-releasing hormone immunoreactivity (TRH-IR) undergo profound changes during the prenatal and early postnatal period in rats, similar effects with advanced aging were anticipated. For this reason we measured hypothalamic and reproductive tissue levels of TRH-IR, hypothalamic levels of somatostatin (SRIF), and beta-endorphin (EP), serum levels of prolactin (Prl), growth hormone (GH), thyrotropin (TSH), and thyroxine (T4) in young, sexually mature and 24-28 month-old male Long-Evans and Sprague-Dawley rats. Hypothalamic and prostatic levels of TRH-IR were consistently reduced as were the levels of T4 in old rats compared to young controls. Aging did not change the ratio of TRH to the major TRH-like peptide in prostates, as determined by high pressure liquid chromatography (HPLC) or the levels of hypothalamic SRIF and EP. All of the hypothalamic TRH-IR in both old and young male rats consisted of TRH by HPLC. Falling hypothalamic TRH levels and TRH secretory capacity may play a role in the blunted TSH response to cold stress in old rats.