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Biomedical subjects

G W Bennett

Publications and source records attributed to G W Bennett.

At least 109 records · Page 6Linked to original sources
PubMed1981

Location and release of TRH and 5-HT from amphibian skin.

The occurrence and release of thyrotrophin-releasing hormone (TRH) and 5-hydroxytryptamine (5-HT) from amphibian skin have been described by previous investigators. In the present study, the precise location and site of release of TRH and 5-HT from the skin of Rana pipiens and Xenopus laevis have been examined using a combination of procedures including immunohistochemistry, HPLC, and radioimmunoassay. The results indicate that TRH is located specifically within the dermal glands of these species, and that both TRH and 5-HT are discharged from these glands following adrenergic stimulation. The origin and functional significance of these substances in amphibian skin granular glands are discussed.

Animals↗
PubMed1981

Electrochemical monitoring of 5-hydroxytryptamine release in vitro and related in vivo measurements of indoleamines.

1. Electrochemical techniques have been used to measure release of endogenous 5HT from brain regions in vitro and to record electrochemical changes induced by drugs acting on 5HT neurones in the anaesthetised and unanaesthetised rat in vivo. 2. 5HT release in vitro was observed in all regions studied. The highest level of basal release was observed in the nucleus accumbens/septal region and hypothalamus and the lowest in the striatum. 3. High potassium (55 mM) increased release of 5HT in all regions, where their basal release was observed. 5HT release was also increased by p-chloroamphetamine (1-10 microM). 4. In rats anaesthetised with pentobarbitone, three electrochemical peaks were observed in the striatum, nucleus accumbens and frontal cortex at + 0.12 V, +0.2 V and + 0.35 V using a micro-graphite paste electrode and differential pulse voltammetry. 5. The peak at + 0.12 V was increased by micro-infusion of ascorbic acid (5 X 10(-6) M) and that at + 0.35 V by micro-infusion of 5HT (5 X 10(-6) M) and 5-hydroxyindole acetic acid (5HIAA) (5 X 10(-6) M). 6. p-Chlorophenylalanine (2 X 150 mg/kg) caused the loss of the peak at + 0.35 V. Fenfluramine (10 mg/kg) also decreased the peak at + 0.35 V. 7. The results indicate the validity of the in vitro technique and demonstrate the future potential of the in vivo method, though further studies are needed to determine the precise chemical nature of the changes in oxidation following administration of drugs acting on 5HT neurones.

Action Potentials↗
PubMed1980

Dopamine stimulates the degradation of gonadotropin releasing hormone by rat synaptosomes.

Immunohistochemical studies have shown the existence of synapses between nerve endings containing dopamine and gonadotropin releasing hormone (LH-RH) respectively in the hypothalamic median eminence. It is generally accepted that this transmitter is involved in the regulation of gonadotropin secretion as a modulator of LH-RH release, although the evidence is conflicting and both inhibitory and excitatory actions of dopamine have been reported. In vitro studies support the excitatory effect and low doses of dopamine have been shown to release LH-RH from incubated hypothalamic fragments and synaptosomes. This report describes studies with nerve endings isolated from the rat hypothalamus in which dopamine at higher concentrations than those used previously has been found to stimulate the degradation of LH-RH but not thyrotropin releasing hormone (TRH). This mechanism seems to be physiological in that it is calcium-dependent, requires the structural integrity of the nerve endings and fluctuates with the reproductive state of the animal.

Animals↗
PubMed1979

Metabolic and secretory processes in nerve-endings isolated from post-mortem brain.

Isolated nerve ending particles (synaptosomes) prepared from rat and human cerebral cortex, after varying conditions of post-mortem storage were shown to possess good structural and morphological integrity and metabolic activity. Respiration, potassium retention, lactate dehydrogenase content, and stimulus-induced release of transmitter candidate amino acids, as well as the neuropeptide somatostatin, were measured. These preparations from post-mortem material showed properties which were closely comparable with similar preparations from fresh material. The relevance of these findings to studies on human post-mortem material is discussed.

Aged↗
PubMed1979

Prostaglandins and the release of LHRH from hypothalamic synaptosomes. Effects of indomethacin pretreatment.

The possible role of prostaglandins (PGs) in the hypothalamic control of ovulation has been investigated by studying the effects of indomethacin (ID) and PGs on the release of luteinizing hormone-releasing hormone (LHRH) from hypothalamic synaptosomes. Female rats were chronically pretreated with ID on diestrus 2 (D2) and proestrus (P), or on diestrus 1 (D1) and D2. Basal LHRH release from hypothalamic synaptosomes prepared from rats pretreated on D2/P was reduced to 48% after a 20-min incubation period, compared with sham-treated animals. ID pretreatment on D1/D2 caused a similar but less marked reduction in LHRH release (to 66% of controls at 20 min). Extraction of the LHRH remaining within the synaptosomal pellet showed that ID pretreatment also reduced the synaptosome content of LHRH. (15S)-15-methyl PGE2 (15-E2) (10(-4) and 10(-6) M) added to the incubating medium stimulated the release of LHRH BY APPROXIMATELY 40%, but this effect was only observed in synaptosomes prepared from ID-treated rats. PGE2 (10(-4) and 10(-6) M) had no significant effect in either sham-treated or ID-treated groups.

Animals↗
PubMed1975

Release of corticotrophin releasing factor and other hypophysiotropic substances from isolated nerve-endings (synaptosomes).

Synaptosomes isolated from the sheep and the rat hypothalamus contain corticotrophin releasing factor, vasopressin, prolactin-release inhibiting factor and probably all of the substances which participate in the regulation of adenohypophysial function. Electrical field stimulation or depolarizing concentrations (55 mmol/l) of potassium ions cause a release of these factors from the incubated nerve-endings in a calcium-dependent manner. It is suggested that synaptosomes may provide a valuable approach to the study of mechanisms involved in hypothalamic neurosecretion in vitro.

Adrenocorticotropic Hormone↗