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Biomedical subjects

D F Sharman

Publications and source records attributed to D F Sharman.

At least 55 records · Page 3Linked to original sources
PubMed1982

In vitro release of endogenous catecholamines from the neural and intermediate lobe of the hypophysis.

This paper shows for the first time that the dopamine present in the neural and intermediate lobe (NIL) of the pituitary gland can be released in vitro by depolarization of the tissue with increased [K+]. The release is Ca++ dependent. This observation is in accordance with the concept that dopamine has a function as a neural transmitter substance in the NIL. At a [Ca++] of 2.5 mM it was also possible to measure the norepinephrine release from the NIL. The dopamine release from the NIL was unaffected by GABA. In contrast, the release of dopamine (but not of norepinephrine) from the medial-basal hypothalamus was enhanced by GABA.

Animals↗
PubMed1981

Cerebral dopamine, apomorphine and oral activity in the neonatal pig.

Neonatal piglets in which oral stimulation associated with feeding was reduced by intragastric tube feeding displayed an increase in stereotyped snout rubbing, licking and chewing behaviour. An investigation of a possible neurochemical basis for this behaviour was made by using sensitive radioenzymatic and microfluorimetric assays to estimate the concentrations of the catecholamines and of the dopamine metabolites homovanillic acid (HVA) and 3,4-dihydroxyphenyl-acetic acid (DOPAC) in different brain regions. These observations revealed that the increased non-nutritive oral activity of such piglets did not appear to be caused by an increased release of dopamine in the brain, since it was not associated with increases in the concentrations of the acidic metabolites of dopamine in either the caudate nucleus, the putamen, the nucleus accumbens, the olfactory tubercle, the hypothalamus, or the substantia nigra. The only neurochemical changes observed were small decreases in the concentration of HVA in the putamen and the nucleus accumbens. A lack of effect on catecholamine concentrations in any of the six brain regions examined suggested that the environmental manipulation caused no changes in the development of catecholamine-containing nerve endings. Subcutaneous injection of apomorphine was found to increase the non-nutritive oral activity of piglets. Apparent conditioning effects of the environment on apomorphine-induced stereotyped behaviour however, prevented any satisfactory testing of possible changes in cerebral dopamine receptor sensitivity following reduced oral stimulation.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1980

Observations on pituitary and cerebral catecholamines in Brattleboro rats.

The combined neural and intermediate lobes (N.I.L.) of the pituitary glands of Brattleboro rats contained significantly more noradrenaline (NA) than those of normal controls of the same age. In addition, in 4 and 6 months old rats the N.I.L. of the homozygotes (Di-rats) contained about twice as much NA as those of the heterozygotes (non-Di-rats). In the enlarged and hyperaemic neural lobes of the Di-rats enlarged blood vessels could be seen. They were surrounded by a rich network of nerve fibres which displayed catecholamine fluorescence. The NA concentrations in the medial basal hypothalamus (M.B.H.) of 4, 6, and 9 months old Di-rats were significantly higher than those of the non-Di-rats and of controls of the same age. This may contribute to the diminished ACTH secretion in Brattleboro rats. The total amount of DA contained in the N.I.L. of 9 months old Di-rats was 20% lower than in the non-Di-rats of the same age. The concentrations of homovanillic acid (HVA) in the corpora striata of 4 months old Di- and non-Di-rats was significantly higher than in older Brattleboro rats and in control rats of various strains and ages. At 9 months it was nearly twice as high in the Di-rats as in the non-Di-rats. The concentrations of dihydroxyphenylacetic acid in the striata of 4--6 months old Di- and non-Di-rats were higher than those of Long Evans rats of the same age.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1978

Responses of the pituitary-adrenal system of the pig to environmental changes and drugs.

1 The reactivity of the pituitary-adrenal axis of the young pig was tested for its suitability as a sensitive index for any discomfort that might be experienced under certain conditions of intensive husbandry.2 In a thermoneutral environment, most undisturbed piglets showed only slight variations in the plasma concentrations of adrenocorticotrophic hormone (ACTH) and corticosteroids.3 Stimuli such as exposure to ambient temperatures of +40 degrees C or -5 degrees C were required to cause large rises in the plasma concentrations of ACTH and corticosteroids.4 Apparently milder stimuli, such as change of environment, slight frustration or changes in ambient temperatures between +5 degrees C and +30 degrees C only rarely caused a significant rise in plasma corticosteroids. Thus changes in plasma corticosteroid concentrations are not a sensitive index for the reaction of a piglet to its environment.5 Increases in plasma ACTH concentrations occurred faster than those of the corticosteroids, were larger when expressed as a percentage of the basal values and occurred following relatively small disturbances such as omission of the reward in an operant behaviour test when corticosteroid changes were often not detectable. Thus rises in plasma ACTH might be a useful indication that a given situation is disturbing to a pig. The reaction of plasma ACTH concentrations to chronic irritations as they might occur in intensive husbandry remains to be investigated.6 Azaperone (2 mg/kg i.m.), a drug which is used as a sedative in pigs, caused a rise of about 50% in plasma corticosteroid concentrations. It did not diminish the large steroid output seen when the animals were exposed to high and low ambient temperatures.

Abdomen↗