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Biomedical subjects

D Grundy

Publications and source records attributed to D Grundy.

At least 109 records · Page 6Linked to original sources
PubMed1989

Responses of vagal efferent fibres to stimulation of gastric mechano- and chemoreceptors in the anaesthetized ferret.

The involvement of gastric tension receptors and mucosal chemoreceptors in vagal reflexes was assessed directly by recording single efferent fibres from the cervical vagus nerve in the urethane anaesthetised ferret. 32/39 fibres responded to distension of the gastric corpus, mainly with excitation of firing, 24/39 fibres responded to antral distension, with a higher proportion showing a reduction in firing. Fifty-seven percent of fibres showed a convergent input from corpus and antrum. The magnitude of these responses was large (usually greater than 50%) and of short latency (less than 1 s). Responses to chemical perfusions in the antrum were seen in 14/31 efferent fibres, most of which showed excitation. Latency of response was variable (5-120 s) and may have been influenced by diffusion through the antral mucous barrier. These data indicate a complex arrangement of vagal reflexes involved in pre-pyloric regulation of gastric emptying by mechanical and chemical stimuli in the lumen.

Action Potentials↗
PubMed1989

Pre-pyloric mechanisms regulating gastric motor function in the conscious dog.

Reflex mechanisms regulating gastric motor function were studied in four conscious dogs, whose stomachs had been surgically divided into separate corporal and antral pouches. Interactions between the corpus and antrum were investigated in fasted animals by balloon distension of each region. During the quiescent phase (phase I) of the migrating motor complex (MMC), distending the corpus with volumes greater than 80 ml resulted in contractions of the corpus, which persisted for as long as the distending stimulus was applied. This corporal distension also initiated antral contractions which were greater if the antrum was moderately distended and also greater with a larger corporal distending volume up to 300 ml. Graded 5 ml inflation of the antrum during the quiescent phase of the MMC stimulated antral contractions. This antral response to antral distension was augmented when the corpus was inflated but was only statistically significant with antral volumes below 25 ml. Distension of the antrum with volumes greater than 12.5 ml caused inhibition of corporal contractions during both the active phase of a migrating complex or when stimulated by corporal inflation. The degree of inhibition was proportional to the distending stimulus and was present for the duration of the applied distension. For antral volumes of 50 ml the inhibition persisted for a variable time after the stimulus was withdrawn. The inhibition of corporal activity by antral distension was still effective after blocking acid secretion with cimetidine (100 mg), which would eliminate spillage of acid into the jejunum as a cause of the inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Intrathecal baclofen and the H-reflex.

Baclofen was given intrathecally to six patients with severe lower limb spasticity due to traumatic spinal cord injury. The effects of the drug on spasticity and the ratio between the maximum amplitude of the H reflex and the M response from the soleus (Hmax/Mmax ratio) were assessed. In each patient, spasticity was reduced following intrathecal baclofen and in four patients there was a reduction in the amplitude of the H reflex and Hmax/Mmax ratio. These results suggest that the Hmax/Mmax ratio may be helpful in establishing optimum drug dosage, particularly when the drug is used on a chronic basis.

Adult↗
PubMed1989

Space: a testbed for basic biomedical sciences.

In Space many bodily functions adjust to the absence of gravity. Our understanding of these homeostatic processes have depended on studies on man and other animals. The present paper briefly reviews how such studies may benefit some terrestrial medical problems.

Adaptation, Physiological↗
PubMed1989

Physiological problems for man in space.

This article discusses some of the problems facing man in space. Many of these problems are manifested only on return to Earth when the de-conditioned body again has to withstand the effects of gravity.

Adaptation, Physiological↗
PubMed1989

Calcium metabolism and the osteopenia of space flight.

This paper briefly reviews the subject of bone remodelling and calcium homeostasis and considers the changes that occur in the microgravity environment of space. The effectiveness of exercise as a countermeasure to bone demineralisation is discussed.

Bone Demineralization, Pathologic↗
PubMed1989

Food for thought--nutritional problems in space.

The present paper discusses how the study of nutritional problems in space have proceeded, the way microgravity may alter nutritional requirements and how these may be met during long term missions in space.

Dietary Carbohydrates↗
PubMed1988

Speculations on the structure/function relationship for vagal and splanchnic afferent endings supplying the gastrointestinal tract.

This paper discusses some of the unsettled issues in the study of the afferent innervation of the gastrointestinal (GI) tract. Afferent fibres in the vagus and splanchnic nerves have been studied electrophysiologically and much has been learnt from single fibre recordings. Splanchnic afferent fibres generally terminate in multiple mechanosensitive endings in the mesentery and serosa where they are in a position to monitor tension on the mesenteric attachments. Other mechanoreceptors following a mainly vagal pathway behave as if they are functionally in-series with the muscle elements of the gut wall and signal muscle tension generated passively by distension and actively during contraction. A third group of afferent endings supply the GI mucosa where they are in a position to signal information on the physical and chemical environment of the gut lumen. A complex picture of mucosal sensitivity has emerged with subpopulations of receptors with polymodal sensitivity and quality-specific mechanoreceptors, thermoreceptors and chemoreceptors. Unfortunately, there is little concensus amongst the different research groups because of different experimental paradigms. One group describes specific chemoreceptors, other groups fail to find them. In this minireview I have speculated on the cause of the often conflicting data on GI afferents and the implications this has for the interpretation of visceral receptor mechanisms.

Afferent Pathways↗
PubMed1988

Reflex responses of vagal efferent fibres influenced by gastrointestinal mechanoreceptors to electrical afferent stimulation in the anaesthetized ferret.

Activity was recorded from 188 vagal efferent fibres, 90% of which showed responses to distension of the stomach and duodenum. Of thirty fibres tested with single-shock vagal stimulation, reflex action potentials were evoked in fifteen, ranging in latency from 39 to 318 ms. Responses at short latency showed little latency-jitter and high response-probability, and those at long latency showed opposite characteristics. This suggests that two pathways are present in the central organization of vagal reflexes to the gut.

Action Potentials↗
PubMed1987

Involvement of gastrointestinal mechano- and intestinal chemoreceptors in vagal reflexes: an electrophysiological study.

The role of gastrointestinal mechanoreceptors and intestinal chemoreceptors in the genesis of vago-vagal reflexes was assessed by recording single vagal efferent fibre discharge in the urethane-anaesthetized ferret during procedures known to activate discrete populations of gastrointestinal afferent fibres. Distension of the stomach, duodenum and jejunum was used to activate mechanoreceptors while perfusion of the intestinal loops with various chemical solutions was used to activate mucosal chemoreceptors. Mechanical stimulation of the stomach and/or intestine was effective in modulating vagal efferent discharge in 90% of units tested. The response (either excitation or inhibition of efferent firing) was characterized by its short-latency (less than 1 s), slow-adaptation, and rapid return on removal of the stimulus. In contrast, chemical stimulation was much less potent evoking clear-cut responses in only 26 of the 109 efferent units. Luminal HCl was the most effective stimulus accounting for 81% of the efferent responses although these were of long-latency (greater than 1 min), gradual in onset and poorly maintained. Other efferent responses to HCl and hypertonic saline were characterized by a long-latency, sudden increase in discharge associated with the prodrome of vomiting. We conclude that while the mechanosensitive afferent input is well represented in terms of the genesis of vagal reflexes, the chemosensitive afferent input may be more important in behavioural aspects of visceral stimuli like vomiting.

Animals↗
PubMed1987

Vagal afferent discharge from gastric mechanoreceptors during contraction and relaxation of the ferret corpus.

Vagal afferent fibres with mechanoreceptive fields in the gastric corpus were studied electrophysiologically in the urethane-anaesthetized ferret in an attempt to assess how changes in muscle tension and length modulate receptor discharge. Single afferent units were spontaneously active and increased their firing on distension of the corpus. During vagally evoked isovolumetric contractions and relaxations, the afferent discharge closely followed changes in intracorpus pressure. Under near-isotonic conditions, changes in both intracorpus pressure and afferent discharge were attenuated to similar degrees despite large changes in corpus volume, although the latter had a modulating influence on afferent discharge. These mechanoreceptors appeared to behave as tension receptors but were also influenced by muscle length as would occur if the receptor were associated with the laminar intramuscular septa of connective tissue which may serve as intramuscular tendons in this tissue.

Action Potentials↗
PubMed1987

Disruption of the jejunal migrating motor complex by gastric distension and feeding in the dog.

1. The jejunal motor response to gastric distension has been quantified in the conscious dog and compared with that of feeding in order to determine the role of the physical bulk of a meal in the conversion from fasted to fed motor activity. 2. In six dogs gastric distension abolished the cyclical migrating motor complex (m.m.c.) and evoked a pattern of continuous irregular jejunal motility similar to that seen postprandially, but only after a latency of 21.5 +/- 2.7 min compared to that of 7.1 +/- 1.2 min for the response to feeding. Computer analysis of distension and fed jejunal motility revealed similar distributions of intervals between contractions and contraction amplitudes with comparable mean values for both. 3. In two dogs with antrum and corpus surgically divided distension of the corpus had a similar effect on jejunal motility although the latency to both distension and feeding were considerably less. 4. By varying the period of distension it has been possible to control accurately the duration of the jejunal motor response and so assess its effectiveness in disrupting the timing of the m.m.c. The return to m.m.c. cycling following deflation was independent of preceding complexes. The occurrence of the post-distension activity front was closely related to the act of deflation itself (R = 0.94) following a latency of 26.2 +/- 2.1 min (n = 39). 5. It is concluded that the bulk of a meal contributes significantly to the early part of postprandial motility and is capable of disrupting the timing of subsequent migrating motor complexes.

Animals↗