Biomedical subjects

David R Brown

Publications and source records attributed to David R Brown.

82 records · Page 5Linked to original sources

PubMed2002

Mayhem of the multiple mechanisms: modelling neurodegeneration in prion disease.

This review examines recent attempts to advance the understanding of the mechanism by which neurones die in prion disease. Prion diseases or transmissible spongiform encephalopathies are characterized by the conversion of a normal glycoprotein, the prion protein, to a protease-resistant form that is suggested to be both the infectious agent and the cause of the rapid neurodegeneration in the disease. Death of the patient results from this widespread neuronal loss. Thus understanding the mechanism by which the abnormal form of the prion protein causes neuronal death might lead to treatments that would prevent the life-threatening nature of these diseases.

Animals↗

PubMed2002

Endocannabinoids as physiological regulators of colonic propulsion in mice.

BACKGROUND & AIMS: Activation of enteric cannabinoid CB1 receptors inhibits motility in the small intestine; however, it is not known whether endogenous cannabinoids (anandamide and 2-arachidonylglycerol) play a physiologic role in regulating intestinal motility. In the present study, we investigated the possible involvement of endocannabinoids in regulating intestinal propulsion in the mouse colon in vivo. METHODS: Intestinal motility was studied measuring the expulsion of a glass bead inserted into the distal colon; endocannabinoid levels were measured by isotope-dilution gas chromatography-mass spectrometry; anandamide amidohydrolase activity was measured by specific enzyme assays. CB1 receptors were localized by immunohistochemistry. RESULTS: Anandamide, WIN 55,212-2, cannabinol (nonselective cannabinoid agonists), and ACEA (a selective CB1 agonist) inhibited colonic propulsion; this effect was counteracted by SR141716A, a CB1 receptor antagonist. Administered alone, SR141716A increased motility, whereas the inhibitor of anandamide cellular reuptake, VDM11, decreased motility. High amounts of 2-arachidonylglycerol and particularly anandamide were found in the colon, together with a high activity of anandamide amidohydrolase. CB1 receptor immunoreactivity was colocalized to a subpopulation of choline acetyltransferase-immunoreactive neurons and fiber bundles in the myenteric plexus. CONCLUSIONS: We conclude that endocannabinoids acting on myenteric CB1 receptors tonically inhibit colonic propulsion in mice.

Amides↗

PubMed2002

Physical activity, sports participation, and suicidal behavior among college students.

PURPOSE: To evaluate the relationship between physical activity, sports participation, and suicidal behavior among college students (N = 4,728). METHODS: Data from the 1995 National College Health Risk Behavior Survey were analyzed. Students were classified as engaging in frequent vigorous activity 6-7 d.wk-1, vigorous activity 3-5 d.wk-1, moderate activity, low activity, or no activity. Sports participation was dichotomized into "yes" or "no" participation. Suicidal behavior was defined as thoughts about, plans for, or attempts at suicide during the 12 months before completing the survey. Data were stratified by sex and multivariable logistic regression modeling, calculated odds ratios (ORs) (adjusted for age, race/ethnicity, Body Mass Index/weight perception, cigarette smoking, episodic heavy alcohol use, drug use, and either activity level or sport participation) for suicidal behavior as associated with physical activity and sports participation. RESULTS: Adjusted ORs show that men in the "low activity" group were at almost half the odds (adjusted OR = 0.54; P < 0.015) of reporting suicidal behavior than men in the "not active" group. Women who engaged in moderate or frequent vigorous activity were at greater odds of reporting suicidal behavior compared with inactive women; OR = 1.76 (P < 0.035) and 1.99 (P < 0.034) respectively. Sports participation was protective against suicidal behavior. Adjusted ORs show that men who did not participate in sports were 2.5 times (P < 0.0003) more likely to report suicidal behavior than men who were sports participants. Women not participating in sports had 1.67 times the odds of reporting suicidal behavior than women sports participants (P < 0.05). CONCLUSIONS: Associations were found between sports participation/selected patterns of physical activity and suicidal behavior. Causal factors mediating the relationships need to be identified.

Adolescent↗

PubMed2002

Predominance of delta-opioid-binding sites in the porcine enteric nervous system.

The antidiarrheal and constipating actions of opioids are mediated in part by enteric neurons, which lie within the wall of the small intestine and colon, but the differential expression of specific, high-affinity opioid-binding sites in ganglionated plexuses within functionally distinct intestinal segments has not been examined. We determined the saturation binding characteristics under Na+-free conditions of the nonselective opioid receptor (OPR) ligand [3H][(5alpha,7alpha)-17-(cyclopropylmethyl)-4,5-epoxy-18,19-dihydro-3-hydroxy-6-methoxy-alpha, alpha-dimethyl-6,14-ethenomorphinan-7-methanol] (diprenorphine) and the respective delta-, kappa-, and mu-OPR ligands [3H]naltrindole, D-(5alpha,7alpha,8beta)-(-)-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxoaspiro-(4,5)dec-8-yl]benzeneacetamide ([3H]U-69,593), and [3H][D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO) in neuronal membranes isolated from myenteric and submucosal plexuses of porcine small intestine and colon. Naloxone-displaceable [3H]diprenorphine-binding sites (KD values ranging from 0.2-0.5 nM and Bmax = 50-95 fmol/mg of protein) were found in both subregions from all gut segments examined. High-affinity [3H]naltrindole sites (KD = 60-140 pmol) were at highest densities (approximately 60 fmol/mg of protein) in submucosal plexus of the ileum and distal colon myenteric plexus and were at lowest densities (8-9 fmol/mg of protein) in the submucosal plexuses of cecum and distal colon. [3H]U-69,593 sites (KD = 0.3-4 nM) were present only in the myenteric plexuses of all segments examined, with highest densities in cecum and proximal colon (44-47 fmol/mg of protein). [3H]DAMGO-binding sites were expressed at relatively low densities in the enteric plexuses of all gut regions. These results indicate that delta-OPRs predominate in the porcine enteric nervous system with a more circumscribed expression of kappa- and mu-OPRs.

Animals↗

PubMed2002

Heart rate-arterial blood pressure relationship in conscious rat before vs. after spinal cord transection.

This experiment quantified the initial disruption and subsequent adaptation of the blood pressure (BP)-heart rate (HR) relationship after spinal cord transection (SCT). BP and HR were recorded for 4 h via an implanted catheter in neurally intact, unanesthetized rats. The animals were then anesthetized, and their spinal cords were severed at T(1)-T(2) (n = 5) or T(4)-T(5) (n = 6) or sham lesioned (n = 4). BP was recorded for 4 h daily over the ensuing 6 days. The neurally intact rat showed a positive cross correlation, with HR leading BP at the peak by 1.8 +/- 0.8 (SD) s. The cross correlation in unanesthetized rats (n = 2) under neuromuscular blockade was also positive, with HR leading. After SCT at T(1)-T(2), the cross correlation became negative, with BP leading HR, and did not change during the next 6 days. The cross correlation also became negative 1-3 days after SCT at T(4)-T(5), but in four rats by day 6 and thereafter the cross correlation progressively reverted to a positive value. We propose that the positive cross correlation with HR leading BP in the intact rat results from an open-loop control that depends on intact supraspinal input to sympathetic preganglionic neurons in the spinal cord. After descending sympathetic pathways were severed at T(1)-T(2), the intact vagal pathway to the sinoatrial node dominated BP regulation via the baroreflex. We suggest that reestablishment of the positive correlation after SCT at T(4)-T(5) was attributable to the surviving sympathetic outflow to the heart and upper vasculature reasserting some effective function, perhaps in association with decreased spinal sympathetic hyperreflexia. The HR-BP cross correlation may index progression of sympathetic dysfunction in pathological processes.

Animals↗

PubMed2002

Copper-dependent functions for the prion protein.

Prion diseases such as bovine spongiform encephalopathy and Creutzfeldt-Jakob disease are fatal neurodegenerative diseases. These diseases are characterized by the conversion of a normal cellular protein, the prion protein, to an abnormal isoform that is thought to be responsible for both pathogenesis in the disease and the infectious nature of the disease agent. Understanding the biology and metabolism of the normal prion protein is therefore important for understanding the nature of these diseases. This review presents evidence for the normal function of the cellular prion protein, which appears to depend on its ability to bind copper (Cu). There is now considerable evidence that the prion protein is an antioxidant. Once the prion protein binds Cu, it may have an activity like that of a superoxide dismutase. Conversion of the prion protein to an abnormal isoform might lead to a loss of antioxidant protection that could be responsible for neurodegeneration in the disease.

Animals↗

PubMed2002

Molecular advances in understanding inherited prion diseases.

The prion diseases are neurodegenerative disorders that have attracted great interest because of the possible link between bovine spongiform encephalopathy (BSE) and variant Creutzfeldt-Jakob disease (CTD) in humans. Possible transmission of these diseases has been linked to a single protein termed the prion protein. This protein is an abnormal isoform of a normal synaptic glycoprotein. The majority of prion diseases does not appear to be caused by transmission of an infectious agent but occur spontaneously with no known cause. The strongest supporting evidence that the prion protein is the causative agent in prion disease comes from specific inheritable forms of prion disease which are linked to single point mutations in the prion protein gene. Paradoxically, these point mutations, although autosomal dominant with 100% penetrance do not lead to disease until late in life. Molecular techniques are now being used extensively to determine how these point-mutations alter the prion protein's normal structure and activity. This review deals with the latest insights into how inherited mutations in the prion protein gene lead to neurodegenerative disease.

Animals↗

PubMed2001

Chemical coding of neurons expressing delta- and kappa-opioid receptor and type I vanilloid receptor immunoreactivities in the porcine ileum.

Opioid drugs have profound antidiarrheal and constipating actions in the intestinal tract and are effective in mitigating abdominal pain. Mediators of intestinal inflammation and allergy produce increased mucosal secretion, altered bowel motility and pain due to their ability to evoke enteric secretomotor reflexes through primary afferent neurons. In this study, the distribution of delta- and kappa-opioid receptor (DOR and KOR, respectively) immunoreactivities in chemically identified neurons of the porcine ileum was compared with that of the capsaicin-sensitive type 1 vanilloid receptor (VR1). DOR and VR1 immunoreactivities were observed to be highly localized in choline acetyltransferase (ChAT)- and calcitonin gene-related peptide (CGRP)-positive neurons and nerve fibers of the submucosal and myenteric plexuses and both receptors exhibited frequent colocalization. In the inner submucosal plexus, they also were colocalized in substance P (SP)-positive neurons. Neurons in the outer submucosal plexus expressed DOR immunoreactivity alone or in combination with VR1. KOR-immunoreactive neurons were found only in the myenteric plexus; these cells coexpressed immunoreactivity to ChAT, CGRP, vasoactive intestinal peptide (VIP) or nitric oxide synthase (NOS). In addition, some KOR-positive neurons coexpressed immunoreactivities to DOR and VR1. Based on their neurochemical coding, opioid and vanilloid receptor-immunoreactive neurons in the submucosal and myenteric plexuses may include primary afferents and constitute novel therapeutic targets for the palliation of painful intestinal inflammatory, hypersensitivity and dysmotility states.

Animals↗

PubMedDate not supplied

Impact of physical activity on medical expenditures among adults downhearted and blue.

OBJECTIVE: To examine inactivity-associated medical expenditures in adults, controlling for frequency of feeling downhearted/blue. METHODS: Using the 1987 National Medical Expenditure Survey (N=12,250), expenditures were analyzed by comparison and multivariate models. Expenditures were updated to 2003 dollars. RESULTS: Medical expenditure was 354 dollars (t=3.80, P<0.01) lower for active than inactive persons: 6.1% of the expenditure (133 dollars in 1987, 429 dollars in 2003) was inactivity associated. The total inactivity-associated expenditure was near 12 billion dollars in 1987 (38 billion dollars in 2003). CONCLUSIONS: Medical expenditure increased with frequency of feeling downhearted/blue and was higher for inactive than active people.

Adolescent↗

PubMedDate not supplied

A Preliminary analysis of medical expenditures among active and sedentary US adults with mental disorders.

OBJECTIVE: To determine whether leisure-time physical activity is associated with lower direct annual medical expenditures among a sample of adults with mental disorders. METHODS: Using the 1995 National Health Interview Survey and 1996 Medical Expenditure Panel Survey, differences between medical expenditures for sedentary and active persons were analyzed using t-tests. RESULTS: The per capita annual direct medical expenditure was US 2785 dollars higher for sedentary than for active persons (P<0.05). The total expenditure associated with sedentary behavior was US 31.7 billion dollars (US 19.1 billion dollars in men; US 12.6 billion dollars in women). CONCLUSIONS: Physical activity is associated with a reduced economic burden among people with mental disorders.

Adult↗