Biomedical subjects

E A Singer

Publications and source records attributed to E A Singer.

64 records · Page 4Linked to original sources

PubMed1986

Kainic acid induced seizures: changes in somatostatin, substance P and neurotensin.

The neuropeptides somatostatin, neurotensin and substance P were investigated in rats during and after limbic seizures induced by systemic injection of kainic acid (10 mg/kg, i.p.). Three hours after injection of the toxin, pronounced decreases (40-50%) in somatostatin-like immunoreactivity in frontal cortex, striatum, dorsal hippocampus and amygdala/pyriform cortex were observed. Concomitantly, neurotensin-like and substance P-like immunoreactivities were also reduced in the frontal cortex and the hippocampus. These early decreases in peptide levels may result from increased release and subsequent inactivation of the peptides during acute seizures. At later time intervals, 3, 10 and 30 days after injection of kainic acid, the initially decreased peptide levels were partially normalized. However, the reduction in somatostatin-like immunoreactivity in amygdala/pyriform cortex and striatum persisted up to 30 days. Neurotensin-like immunoreactivity remained decreased in the frontal cortex. On the other hand, neurotensin- and substance P-like immunoreactivities were increased in the striatum and substantia nigra 10-30 days after injection of kainic acid. These late changes in peptide levels may suggest destruction of peptidergic neurons or adaptive changes induced by the convulsions. Pretreatment of rats with cysteamine (100 mg/kg, i.p.), an agent which decreases brain somatostatin levels, had no effect on the intensity of kainic acid induced convulsions, although a slightly earlier onset of seizures was observed. The changes in peptide levels, especially the marked decreases in somatostatin content after systemic injection of kainic acid, suggest considerable acute and chronic alterations in peptidergic systems caused by limbic convulsions.

Amygdala↗

PubMed1986

Synthesis of alkyl-substituted arecoline derivatives as gamma-aminobutyric acid uptake inhibitors.

A series of N-methyltetrahydropyridine-3-carboxylic acids and methyl esters have been synthesized and biologically evaluated. Arecoline (6) was lithiated with LDA in THF to give 7, which was treated with various alkyl halides to afford exclusively the alpha-substituted products 8a-g. Thermodynamic reaction of 7 with carbonyl compounds gave the corresponding 5-substituted arecoline derivatives 10a-q. When phenyldiazonium tetrafluoroborate was used as electrophile, 8h and 9 were obtained. The relative stereochemistry of 10j-o was established by 1H NMR spectroscopy. Compound 12 was obtained by condensation of the silylketene acetal 11 with N-acetylindoxyl. Dehydration of 10a-c yielded 14a-c, respectively. Deprotection of the esters 14a, 14c, and 15 followed by chromatography on an ion-exchange resin gave the amino acids 16a, 16c, and 16d. The alcohol 17 was obtained by LiAlH4 reduction of the corresponding ester 14c. The amino acid 16c displayed a marked inhibitory effect on the synaptosomal uptake of gamma-amino[3H]butyric acid ([3H]GABA). The type of inhibition was competitive with a Ki of 12.9 microM. Compound 16d also inhibited [3H]GABA uptake but was about 10 times weaker than 16c. None of the biologically tested compounds (8a-g, 9, 10a-q, 12, 14a-c, 16a-d, 17) showed any effect in binding studies using [3H]GABA as ligand.

Animals↗

PubMed1986

Plasma protein(s) yields met-enkephalin-related peptides in near-micromolar concentrations when treated with pepsin.

Treatment of animal and human plasmas with pepsin yielded large quantities of immunoreactive methionine5-enkephalin (i-met-ENK). The concentrations measured after pepsin treatment were 0.1-0.5 microM, about 1000 times the normal circulating level of i-met-ENK (0.03-0.3 nM). The reaction was shown to be time and pH dependent and to involve the action of pepsin on a protein(s) of about 65,000 mol wt. Pepsin-generated i-met-ENK from rat plasma gave three major peaks during reverse phase HPLC, one of which (approximately 25% of the total) coeluted with methionine5-enkephalin sulfoxide and also completed in a radioreceptor assay for opiate-related substances. In addition, this material produced met-ENK-like effects on vascular permeability in rat skin and inhibited electrically induced contractions of the isolated guinea pig ileum in a naloxone-sensitive manner. The plasma substrate(s) that yielded i-met-ENK was distinguished from adrenal proenkephalins, since partially purified plasma substrate(s) did not liberate i-met-ENK upon digestion with trypsin and carboxypeptidase B. Although it is possible that these peptides differ from met-ENK in amino acid sequence, the results presented here suggest that met-ENK-related substances might be formed physiologically by the action of a pepsin-related processing enzyme(s) on plasma substrate(s). Such a mechanism would be analogous to that used in the renin-angiotensin system.

Adult↗

PubMed1984

Substance P is markedly increased in plasma of patients with hepatic coma.

Substance P (determined as immunoreactive substance P [i-SP]), noradrenaline, and adrenaline were measured in plasma of 18 patients with hepatic coma (stage I-IV), 16 healthy controls, and 10 critically ill patients without evidence of hepatocellular disease. Plasma i-SP (119 +/- 13 fmol/ml) was significantly higher in patients with hepatic coma than in healthy controls (13 +/- 2 fmol/ml) or control patients (23 +/- 4 fmol/ml). Plasma i-SP rose in parallel with plasma noradrenaline and adrenaline. There was a significant direct correlation between plasma i-SP and noradrenaline. Increase in plasma i-SP and noradrenaline was associated with a decrease in systemic vascular resistance and an increase in cardiac index and was most pronounced in those patients who finally died in coma. Deterioration in the dying patients was accompanied by a further significant increase in plasma i-SP. Immunoreactivity was identified as authentic SP by high performance liquid chromatography in 3 representative patients. Accumulation of the vasodilating peptide SP in plasma of patients with hepatic coma may be important in the pathogenesis of the cardiovascular disturbances associated with this disease.

Adolescent↗

PubMed1984

Parallel secretion of endogenous 5-hydroxytryptamine and histamine from mast cells stimulated by vasoactive peptides and compound 48/80.

The peptides, neurotensin, substance P, somatostatin, and bombesin, several analogues and fragments of neurotensin and compound 48/80, all caused the secretion of both endogenous 5-hydroxytryptamine (5-HT) and histamine. There was no differential effect of any of the secretagogues tested on the secretion of 5-HT and histamine. Amitriptyline prevented the secretion of histamine in response to stimulation by neurotensin, substance P, somatostatin or compound 48/80 but was without effect on the secretion of endogenous 5-HT.

Amitriptyline↗

PubMed1984

Stimulation of luteinizing hormone release after stereotaxic microinjection of neurotensin into the medial preoptic area of rats.

Neurons immunoreactive to luteinizing hormone-releasing hormone (LHRH) are localized to the medial preoptico-septal region of the rat hypothalamus, an area known to be essential for the regulation of the surge of luteinizing hormone (LH) that precedes ovulation. The effect of neurotensin (NT) on circulating LH levels following its discrete microinjection into this region was evaluated. Within 30 min after the stereotaxic microinjection of 40 ng of NT in 50 nl into the medial preoptic area (MPOA) just rostral to the organum vasculosum of the lamina terminalis in ovariectomized (OVX), anesthetized rats, plasma LH levels rose from 417 +/- 36 to 923 +/- 113 ng/ml (p less than 0.001). There was also a significant increase (p less than 0.001) in plasma LH levels following the microinjection of 50 ng of norepinephrine in 50 nl in this same site. Similarly, levels of LH increased from 48 +/- 7 to 110 +/- 19 ng/ml (p less than 0.004) following the microinjection of NT into the rostral MPOA on the morning of proestrus in anesthetized rats. In contrast, saline, substance P, leu-enkephalin and LHRH microinjected in the rostral MPOA of OVX rats had no significant effect on circulating levels of LH. The microinjection of NT 0.4 mm rostral or caudal to this area was also without effect. The presence of two binding sites with KdS of 4.2 and 29 nM and site concentrations of 0.11 and 0.68 pmol/mg in tissue homogenates of the rostral MPOA were also established. These data suggest a role for NT in the central regulation of LH release.

Animals↗

PubMed1982

In vivo synthesis of substance P in the corpus striatum of the rat and its transport to the substantia nigra.

Incorporation of [35S]methionine into substance P in the striatum of the rat and the subsequent transport of the labelled peptide to the substantia nigra has been demonstrated in vivo. After a 4-h infusion of [35S]methionine into the corpus striatum and an additional interval of 4 h radiolabelled substance P was found in the striatum and the substantia nigra of the animals. The criteria for concluding that the labelled product was substance P were: (a) gel chromatography and subsequent ion exchange chromatography of an acetic acid extract of the infused striatum of the ipsilateral substantia nigra yielded a peak of radioactivity co-eluting with endogenous immunoreactive substance P or a sample of synthetic substance P; (b) the radioactive material from this peak also co-chromatographed with synthetic substance P on high-voltage paper electrophoresis or high-pressure liquid chromatography; and (c) bound specifically to the substance antibody. Intracisternal injection of colchicine (70 microgram, i.c.) completely suppressed the appearance of radiolabelled substance P immunoreactive material in the substantia nigra. The data indicate that synthesis of substance P occurs in nerve cell bodies located in the corpus striatum and that substance P is transported to the substantia nigra by a colchicine sensitive mechanism.

Afferent Pathways↗

PubMed1982

Capsaicin does not change tissue levels of glutamic acid, its uptake, or release in the rat spinal cord.

Capsaicin treatment (50 mg/kg, subcutaneous) of newborn rats resulted in 1 75% decrease of substance P immunoreactivity in the dorsal spinal cord of the adult animal, but failed to affect levels of the proposed sensory neurotransmitter glutamic acid or to alter high-affinity uptake of [3H]glutamic acid into synaptosomes of the same tissue. Furthermore, capsaicin (30 microM) in vitro had no influence on the release of [3H]glutamic acid from spinal cord P2 fractions of untreated adult rats, but induced a marked release of substance P. The results suggest that, in contrast to substance P fibers, neurons containing glutamic acid are not sensitive to capsaicin. Eleven other neurochemical parameters measured in the spinal cord did not appear to be changed by the treatment with capsaicin, suggesting a considerable neurochemical selectivity of the lesion.

Animals↗

PubMed1981

Sedimentation and release properties of P2 fractions derived from rat cerebral cortex slices incubated with radiolabeled GABA for a short or long time period.

On homogenization of rat cerebral cortex slices previously incubated with [3H] GABA or [14C]GABA for 5 or 30 min, respectively, particles were recovered in P2 fractions which exhibited similar buoyant density, but different sedimentation velocity on linear sucrose density gradient centrifugation. The K+-evoked release of [3H]GABA from particles isolated from slices previously incubated for 5 min with [3H]GABA was increased in the presence of exogenous Ca2+. In contrast, the K+-evoked release from particles isolated from slices previously incubated for 30 min with [3H]GABA, was not influenced by the presence of exogenous Ca2+. These results suggest that, depending on the incubation time of slices, exogenously applied GABA can be detected in different pools. These pools not only seem to differ in their CA2+ dependency of K+-evoked release but also in their subcellular localization.

Animals↗

PubMedDate not supplied

Immunohistochemical and chromatographic studies of peptides with tachykinin-like immunoreactivity in the central nervous system of the lamprey.

The distribution and chemical properties of compounds with tachykinin-like immunoreactivity (TK-LI) in the spinal cord and brain of lampreys (Lampetra fluviatilis and Ichthyomyzon unicuspis) were investigated by means of immunohistochemistry and various chromatographic methods combined with radioimmunoassay. The distribution of TK immunoreactive fibers in the lamprey spinal cord was investigated with 13 different TK antisera which gave positive staining in pilot experiments. The antisera were raised against substance P (SP) (n = 6), physalaemin (PHY) (n = 1), neurokinin A (NKA) (n = 2), kassinin (KAS) (n = 2) or eledoisin (ELE) (n = 2). Pre-incubation of these antisera with their corresponding TKs abolished or reduced the immunostaining. Four different patterns of distribution were found with the 13 antisera, and they did not seem to be related to the TKs against which the antisera were raised. The different patterns could be explained by assuming the presence of the three different TKs. Six different antisera, raised against SP (n = 2), KAS (n = 2) or ELE (n = 2), were used for radioimmunoassay. The TK-LI material eluted as several separate components in various chromatographic systems. The central nervous system (CNS) of the lamprey did not contain measurable amounts of SP, NKA, neurokinin B (NKB), KAS or ELE. The present data imply that the lamprey CNS contains at least three different TKs probably different from SP, PHY, NKA, NKB, KAS or ELE; these are possibly new, not earlier described TKs. The three hypothetical TKs differ in their distribution.

Animals↗