Sexually Dimorphic Effects of Histamine Degradation by Enteric Glial Histamine N-Methyltransferase (HNMT) on Visceral Hypersensitivity

Histamine is a neuromodulator that affects gut motility and visceral sensitivity through intrinsic and extrinsic neural pathways, yet the mechanisms regulating histamine availability in these pathways remain poorly understood. Here, we show that enteric glia contribute to histamine clearance in the enteric nervous system (ENS) through their expression of the enzyme histamine N-methyltransferase (HNMT). Glial HNMT expression was initially assessed using immunolabeling and gene expression, and functionally tested using CRISPR-Cas9 to create a Cre-dependent conditional Hnmt ablation model targeting glia. Immunolabeling, calcium imaging, and visceromotor reflex recordings were used to assess the effects on ENS structure and visceral hypersensitivity. Immunolabeling and gene expression data show that enteric neurons and glia express HNMT. Deleting Hnmt in Sox10+ enteric glia increased glial histamine levels and altered visceromotor responses to colorectal distension in male mice, with no effect in females. Interestingly, deleting glial Hnmt protected males from histamine-driven visceral hypersensitivity. These data uncover a significant role for glial HNMT in histamine degradation in the gut, which impacts histamine-driven visceral hypersensitivity in a sex-dependent manner. Changes in the capacity of glia to clear histamines could play a role in the susceptibility to developing visceral pain in disorders of the gut-brain interaction.

BQ788 reveals glial ETB receptor modulation of neuronal cholinergic and nitrergic pathways to inhibit intestinal motility: Linked to postoperative ileus

BACKGROUND AND PURPOSE

ET-1 signalling modulates intestinal motility and inflammation, but the role of ET-1/ETB receptor signalling is poorly understood. Enteric glia modulate normal motility and inflammation. We investigated whether glial ETB signalling regulates neural-motor pathways of intestinal motility and inflammation.

EXPERIMENTAL APPROACH

We studied ETB signalling using: ETB drugs (ET-1, SaTX, BQ788), activity-dependent stimulation of neurons (high K+ -depolarization, EFS), gliotoxins, Tg (Ednrb-EGFP)EP59Gsat/Mmucd mice, cell-specific mRNA in Sox10CreERT2 ;Rpl22-HAflx or ChATCre ;Rpl22-HAflx mice, Sox10CreERT2 ::GCaMP5g-tdT, Wnt1Cre2 ::GCaMP5g-tdT mice, muscle tension recordings, fluid-induced peristalsis, ET-1 expression, qPCR, western blots, 3-D LSM-immunofluorescence co-labelling studies in LMMP-CM and a postoperative ileus (POI) model of intestinal inflammation.

KEY RESULTS

In the muscularis externa ETB receptor is expressed exclusively in glia. ET-1 is expressed in RiboTag (ChAT)-neurons, isolated ganglia and intra-ganglionic varicose-nerve fibres co-labelled with peripherin or SP. ET-1 release provides activity-dependent glial ETB receptor modulation of Ca2+ waves in neural evoked glial responses. BQ788 reveals amplification of glial and neuronal Ca2+ responses and excitatory cholinergic contractions, sensitive to L-NAME. Gliotoxins disrupt SaTX-induced glial-Ca2+ waves and prevent BQ788 amplification of contractions. The ETB receptor is linked to inhibition of contractions and peristalsis. Inflammation causes glial ETB up-regulation, SaTX-hypersensitivity and glial amplification of ETB signalling. In vivo BQ788 (i.p., 1 mg·kg-1 ) attenuates intestinal inflammation in POI.

CONCLUSION AND IMPLICATIONS

Enteric glial ET-1/ETB signalling provides dual modulation of neural-motor circuits to inhibit motility. It inhibits excitatory cholinergic and stimulates inhibitory nitrergic motor pathways. Amplification of glial ETB receptors is linked to muscularis externa inflammation and possibly pathogenic mechanisms of POI.

LPAR1 regulates enteric nervous system function through glial signaling and contributes to chronic intestinal pseudo-obstruction

Gastrointestinal motility disorders involve alterations to the structure and/or function of the enteric nervous system (ENS) but the causal mechanisms remain unresolved in most cases. Homeostasis and disease in the ENS are processes that are regulated by enteric glia. Signaling mediated through type I lysophosphatidic acid receptors (LPAR1) has recently emerged as an important mechanism that contributes to disease, in part, through effects on peripheral glial survival and function. Enteric glia express LPAR1 but its role in ENS function and motility disorders is unknown. We used a combination of genetic, immunohistochemical, calcium imaging, and in vivo pharmacological approaches to investigate the role of LPAR1 in enteric glia. LPAR1 was enriched in enteric glia in mice and humans and LPA stimulated intracellular calcium responses in enteric glia, subsequently recruiting activity in a subpopulation of myenteric neurons. Blocking LPAR1 in vivo with AM966 attenuated gastrointestinal motility in mice and produced marked enteric neuro- and gliopathy. Samples from humans with chronic intestinal pseudo-obstruction (CIPO), a severe motility disorder, showed reduced glial LPAR1 expression in the colon and ileum. These data suggest that enteric glial LPAR1 signaling regulates gastrointestinal motility through enteric glia and could contribute to severe motility disorders in humans such as CIPO.

Histamine-dependent interactions between mast cells, glia, and neurons are altered following early-life adversity in mice and humans

Early-life adversity contributes to the development of functional bowel disorders later in life through unresolved mechanisms. Here, we tested the hypothesis that early-life adversity alters anatomical and functional interactions between mast cells and enteric glia. The effects of early-life stress were studied using the neonatal maternal separation (NMS) stress mouse model. Anatomical relationships between mast cells and enteric glia were assessed using immunohistochemistry and mast cell reporter mice (Mcpt5^Cre;GCaMP5g-tdT). Immunohistochemistry was used to assess the expression of histamine, histamine 1 (H1) receptors, and glial fibrillary acidic protein. Functional responses of glia to mast cell mediators were assessed in calcium imaging experiments using Sox10^CreERT2;GCaMP5g-tdT mice and cultured human enteric glial cells. NMS increases mast cell numbers at the level of the myenteric plexus and their proximity to myenteric ganglia. Myenteric glia respond to mediators released by activated mast cells that are blocked by H1 receptor antagonists in mice and humans and by blocking neuronal activity with tetrodotoxin in mouse tissue. Histamine replicates the effects of mast cell supernatants on enteric glia, and NMS increases histamine production by mast cells. NMS reduces glial responses to mast cell mediators in mouse tissue, while potentiating responses in cultured human enteric glia. NMS increases myenteric glial fibrillary acidic protein expression and reduces glial process length but does not cause neurodegeneration. Histamine receptor expression is not altered by NMS and is localized to neurons in mice, but glia in humans. Early-life stress increases the potential for interactions between enteric glia and mast cells, and histamine is a potential mediator of mast cell-glial interactions through H1 receptors. We propose that glial-mast cell signaling is a mechanism that contributes to enteric neuroplasticity driven by early-life adversity.NEW & NOTEWORTHY Early-life adversity places an individual at risk for developing functional gastrointestinal disorders later in life through unknown mechanisms. Here, we show that interactions between mast cells and glia are disrupted by early-life stress in mice and that histamine is a potential mediator of mast cell-glial interactions.

Enteric Glia Modulate Macrophage Phenotype and Visceral Sensitivity following Inflammation

Mechanisms resulting in abdominal pain include altered neuro-immune interactions in the gastrointestinal tract, but the signaling processes that link immune activation with visceral hypersensitivity are unresolved. We hypothesized that enteric glia link the neural and immune systems of the gut and that communication between enteric glia and immune cells modulates the development of visceral hypersensitivity. To this end, we manipulated a major mechanism of glial intercellular communication that requires connexin-43 and assessed the effects on acute and chronic inflammation, visceral hypersensitivity, and immune responses. Deleting connexin-43 in glia protected against the development of visceral hypersensitivity following chronic colitis. Mechanistically, the protective effects of glial manipulation were mediated by disrupting the glial-mediated activation of macrophages through the macrophage colony-stimulating factor. Collectively, our data identified enteric glia as a critical link between gastrointestinal neural and immune systems that could be harnessed by therapies to ameliorate abdominal pain.

Gastrointestinal neuroimmune disruption in a mouse model of Gulf War illness

Gulf War illness (GWI) is a chronic multisymptom disorder that is prominent in Gulf War veterans. Major unexplained symptoms of GWI include functional gastrointestinal disorders and undiagnosed illnesses, including neurologic disorders. Exposure to the antinerve gas drug pyridostigmine bromide (PB) is linked to the development of GWI, but the exact mechanisms remain unclear. Here, we tested the hypothesis that PB alters gut function by disrupting the neural and immune systems of the intestine. We exposed male and female mice to physiologically comparable amounts of PB that match the dose, route, and time frame of exposure experienced by Gulf War veterans and assessed the acute and chronic impacts on gastrointestinal functions, the functional architecture of the enteric nervous system, and immune responses in the gut and brain. Exposure to PB drove acute alterations to colonic motility and structure in both male and female mice that transitioned to chronic changes in gut functions. PB drove acute alterations to enteric neural and glial activity, glial reactivity, and neuron survival with glial reactivity persisting into the chronic phase in male mice. Despite having no effect on colonic permeability, exposure to PB caused major shifts in the expression of proinflammatory cytokines and chemokines in the colon and brain that suggest immunosuppressive effects. Interestingly, immune disruption was still evident in the colon and brain in female animals at 1 mo following exposure to PB. Together, our results show that the paradigm of PB exposure experienced by veterans of the Persian Gulf War contributes to long-lasting pathophysiology by driving enteric neuroinflammation, promoting immunosuppression, and altering functional anatomy of the colon in a sex-dependent manner.-Hernandez, S., Fried, D. E., Grubišić, V., McClain, J. L., Gulbransen, B. D. Gastrointestinal neuroimmune disruption in a mouse model of Gulf War illness.

Mineralocorticoid receptor antagonism prevents obesity-induced cerebral artery remodeling and reduces white matter injury in rats

OBJECTIVE

Midlife obesity is a risk factor for dementia development. Obesity has also been linked to hyperaldosteronism, and this can be modeled in rats by high fat (HF) feeding from weaning. Aldosterone, or activation of the mineralocorticoid receptor (MR) causes cerebrovascular injury in lean hypertensive rats. We hypothesized that rats fed a HF diet would show inward middle cerebral artery (MCA) remodeling that could be prevented by MR antagonism. We further proposed that the cerebral artery remodeling would be associated with white mater injury.

METHODS

Three-week-old male Sprague-Dawley rats were fed a HF diet ± the MR antagonist canrenoic acid (Canr) for 17 weeks. Control rats received normal chow (control NC). MCA structure was assessed by pressure myography.

RESULTS

The MCAs from HF fed rats had smaller lumens and thicker walls when compared to arteries from control NC rats; Canr prevented the MCA remodeling associated with HF feeding. HF feeding increased the mRNA expression of markers of cell proliferation and vascular inflammation in cerebral arteries and Canr treatment prevented this. White mater injury was increased in the rats fed the HF diet and this was reduced by Canr treatment. The expression of doublecortin, a marker of new and immature neurons was reduced in HF fed rats, and MR antagonism normalized this.

CONCLUSIONS

These data suggest that HF feeding leads to MR dependent remodeling of the MCA and this is associated with markers of dementia development.

The acute inhibition of enteric glial metabolism with fluoroacetate alters calcium signaling, hemichannel function, and the expression of key proteins

Glia play key roles in the regulation of neurotransmission in the nervous system. Fluoroacetate (FA) is a metabolic poison widely used to study glial functions by disrupting the tricarboxylic acid cycle enzyme aconitase. Despite the widespread use of FA, the effects of FA on essential glial functions such as calcium (Ca²⁺) signaling and hemichannel function remain unknown. Therefore, our goal was to assess specifically the impact of FA on essential glial cell functions that are involved with neurotransmission in the enteric nervous system. To this end, we generated a new optogenetic mouse model to study specifically the effects of FA on enteric glial Ca²⁺ signaling by crossing PC::G5-tdTomato mice with Sox10::creER^T2 mice. FA did not change the peak glial Ca²⁺ response when averaged across all glia within a ganglion. However, FA decreased the percent of responding glia by 30% (P < 0.05) and increased the peak Ca²⁺ response of the glial cells that still exhibited a response by 26% (P < 0.01). Disruption of Ca²⁺ signaling with FA impaired the activity-dependent uptake of ethidium bromide through connexin-43 (Cx43) hemichannels (P < 0.05) but did not affect baseline Cx43-dependent dye uptake. FA did not cause overt glial or neurodegeneration, but glial cells significantly increased glial fibrillary acid protein by 56% (P < 0.05) following treatment with FA. Together, these data show that the acute impairment of glial metabolism with FA causes key changes in glial functions associated with their roles in neurotransmission and phenotypic changes indicative of reactive gliosis.

NEW & NOTEWORTHY

Our study shows that the acute impairment of enteric glial metabolism with fluoroacetate (FA) alters specific glial functions that are associated with the modification of neurotransmission in the gut. These include subtle changes to glial agonist-evoked calcium signaling, the subsequent disruption of connexin-43 hemichannels, and changes in protein expression that are consistent with a transition to reactive glia. These changes in glial function offer a mechanistic explanation for the effects of FA on peripheral neuronal networks.

Sirtuin-3 Is Expressed by Enteric Neurons but It Does not Play a Major Role in Their Regulation of Oxidative Stress

Gut inflammation contributes to the development of gut motility disorders in part by disrupting the function and survival of enteric neurons through mechanisms that involve oxidative stress. How enteric neurons regulate oxidative stress is still poorly understood. Importantly, how neuron autonomous antioxidant mechanisms contribute to the susceptibility of enteric neurons to oxidative stress in disease is not known. Here, we discover that sirtuin-3 (Sirt3), a key regulator of oxidative stress and mitochondrial metabolism, is expressed by neurons in the enteric nervous system (ENS) of the mouse colon. Given the important role of Sirt3 in the regulation of neuronal oxidative stress in the central nervous system (CNS), we hypothesized that Sirt3 plays an important role in the cell autonomous regulation of oxidative stress by enteric neurons and that a loss of Sirt3 increases neuronal vulnerability during intestinal inflammation. We tested our hypothesis using a combination of traditional immunohistochemistry, oxidative stress measurements and in vivo and ex vivo measures of GI motility in healthy and inflamed wild-type (wt) and Sirt3 null (Sirt3^−/−) mice. Our results show that Sirt3 is widely expressed by neurons throughout the myenteric plexus of the mouse colon. However, the deletion of Sirt3 had surprisingly little effect on gut function and susceptibility to inflammation. Likewise, neither the genetic ablation of Sirt3 nor the inhibition of Sirt3 with antagonists had a significant effect on neuronal oxidative stress. Therefore, we conclude that Sirt3 contributes very little to the overall regulation of neuronal oxidative stress in the ENS. The functional relevance of Sirt3 in enteric neurons is still unclear but our data show that it is an unlikely candidate to explain neuronal vulnerability to oxidative stress during inflammation.

Agonist-evoked Ca2+ signaling in enteric glia drives neural programs that regulate intestinal motility in mice

BACKGROUND & AIMS

Gastrointestinal motility is regulated by enteric neural circuitry that includes enteric neurons and glia. Enteric glia monitor synaptic activity and exhibit responses to neurotransmitters that are encoded by intracellular calcium (Ca2+) signaling. What role evoked glial responses play in the neural regulation of gut motility is unknown. We tested how evoking Ca2+ signaling in enteric glia affects the neural control of intestinal motility.

METHODS

We used a novel chemogenetic mouse model that expresses the designer receptor hM3Dq under the transcriptional control of the glial fibrillary acidic protein (GFAP) promoter (GFAP::hM3Dq mice) to selectively trigger glial Ca2+ signaling. We used in situ Ca2+ imaging and immunohistochemistry to validate this model and assessed gut motility by measuring pellet output and composition, colonic bead expulsion time, small intestinal transit time, total gut transit time, colonic migrating motor complex (CMMC) recordings and muscle tension recordings.

RESULTS

hM3Dq receptor expression is confined to GFAP-positive enteric glia in the intestines of GFAP::hM3Dq mice. In these mice, application of the hM3Dq agonist clozapine-N-oxide (CNO) selectively triggers intracellular Ca2+ responses in enteric glia. Glial activation drove neurogenic contractions in the ileum and colon but had no effect on neurogenic relaxations. CNO enhanced the amplitude and frequency of CMMCs in ex vivo preparations of the colon and CNO increased colonic motility in vivo. CNO had no effect on the composition of fecal matter, small intestinal transit or whole gut transit.

CONCLUSIONS

Glial excitability encoded by intracellular Ca2+ signaling functions to modulate excitatory enteric circuits. Selectively triggering glial Ca2+ signaling might be a novel strategy to improve gut function in motility disorders.

Enteric glia mediate neuron death in colitis through purinergic pathways that require connexin-43 and nitric oxide

BACKGROUND AND AIMS

The concept of enteric glia as regulators of intestinal homeostasis is slowly gaining acceptance as a central concept in neurogastroenterology. Yet how glia contribute to intestinal disease is still poorly understood. Purines generated during inflammation drive enteric neuron death by activating neuronal P2X7 purine receptors (P2X7R), triggering ATP release via neuronal pannexin-1 channels that subsequently recruits intracellular calcium ([Ca²⁺]_i) responses in the surrounding enteric glia. We tested the hypothesis that the activation of enteric glia contributes to neuron death during inflammation.

METHODS

We studied neuroinflammation in vivo using the 2,4-dinitrobenzenesulfonic acid model of colitis and in situ using whole-mount preparations of human and mouse intestine. Transgenic mice with a targeted deletion of glial connexin-43 (Cx43) [GFAP∷Cre^ERT2+/-/Cx43^f/f ] were used to specifically disrupt glial signaling pathways. Mice deficient in inducible nitric oxide (NO) synthase (iNOS^-/-) were used to study NO production. Protein expression and oxidative stress were measured using immunohistochemistry and in situ Ca²⁺ and NO imaging were used to monitor glial [Ca²⁺]_i and [NO]_i.

RESULTS

Purinergic activation of enteric glia drove [Ca²⁺]_i responses and enteric neuron death through a Cx43-dependent mechanism. Neurotoxic Cx43 activity, driven by NO production from glial iNOS, was required for neuron death. Glial Cx43 opening liberated ATP and Cx43-dependent ATP release was potentiated by NO.

CONCLUSIONS

Our results show that the activation of glial cells in the context of neuroinflammation kills enteric neurons. Mediators of inflammation that include ATP and NO activate neurotoxic pathways that converge on glial Cx43 hemichannels. The glial response to inflammatory mediators might contribute to the development of motility disorders.

Tumor necrosis factor-α inhibition attenuates middle cerebral artery remodeling but increases cerebral ischemic damage in hypertensive rats

Hypertension causes vascular inflammation evidenced by an increase in perivascular macrophages and proinflammatory cytokines in the arterial wall. Perivascular macrophage depletion reduced tumor necrosis factor (TNF)-α expression in cerebral arteries of hypertensive rats and attenuated inward remodeling, suggesting that TNF-α might play a role in the remodeling process. We hypothesized that TNF-α inhibition would improve middle cerebral artery (MCA) structure and reduce damage after cerebral ischemia in hypertensive rats. Six-week-old male stroke-prone spontaneously hypertensive rats (SHRSP) were treated with the TNF-α inhibitor etanercept (ETN; 1.25 mg·kg(-1)·day(-1) ip daily) or PBS (equivolume) for 6 wk. The myogenic tone generation, postischemic dilation, and passive structure of MCAs were assessed by pressure myography. Cerebral ischemia was induced by MCA occlusion (MCAO). Myogenic tone was unchanged, but MCAs from SHRSP + ETN had larger passive lumen diameter and reduced wall thickness and wall-to-lumen ratio. Cerebral infarct size was increased in SHRSP + ETN after transient MCAO, despite an improvement in dilation of nonischemic MCA. The increase in infarct size was linked to a reduction in the number of microglia in the infarct core and upregulation of markers of classical macrophage/microglia polarization. There was no difference in infarct size after permanent MCAO or when untreated SHRSP subjected to transient MCAO were given ETN at reperfusion. Our data suggests that TNF-α inhibition attenuates hypertensive MCA remodeling but exacerbates cerebral damage following ischemia/reperfusion injury likely due to inhibition of the innate immune response of the brain.

Improvement in middle cerebral artery structure and endothelial function in stroke-prone spontaneously hypertensive rats after macrophage depletion

BACKGROUND

Inflammation is involved in the pathogenesis of hypertension. Hypertensive animals have an increased number of perivascular macrophages in cerebral arteries. Macrophages might be involved in remodeling of the cerebral vasculature. We hypothesized that peripheral macrophage depletion would improve MCA structure and function in hypertensive rats.

METHODS

For macrophage depletion, six-week-old stroke-prone spontaneously hypertensive rats (SHRSP) were treated with CLOD, 10 mL/kg every three or four days, i.p., or vehicle (PBS lipo). MCA structure and function were analyzed by pressure and wire myography.

RESULTS

Blood pressure was not affected by CLOD. The number of perivascular CD163-positive cells per microscopic field was reduced in the brain of SHRSP+CLOD. CLOD treatment caused an improvement in endothelium-dependent dilation after intralumenal perfusion of ADP and incubation with Ach. Inhibition of NO production blunted the Ach response, and endothelium-independent dilation was not altered. At an intralumenal pressure of 80 mmHg, MCA from SHRSP+CLOD showed increased lumen diameter, decreased wall thickness, and wall-to-lumen ratio. Cross-sectional area of pial arterioles from SHRSP+CLOD was higher than PBS lipo.

CONCLUSIONS

These results suggest that macrophage depletion attenuates MCA remodeling and improves MCA endothelial function in SHRSP.

Temporary mineralocorticoid receptor antagonism during the development of hypertension improves cerebral artery dilation

Hypertension causes cerebral artery remodeling and increases the risk of stroke. Renin angiotensin system blockade during the development of hypertension has therapeutic effects even after treatment withdrawal. Mineralocorticoid receptor (MR) activation has been implicated in artery remodeling and impaired endothelial function. The possibility that there is a critical therapeutic window for MR antagonism has not been investigated. We hypothesized that temporary MR antagonism while hypertension develops would improve middle cerebral artery (MCA) structure and function in stroke-prone spontaneously hypertensive rats (SHRSP), even after treatment withdrawal. Six-week-old SHRSP were treated with spironolactone (25 mg/kg/day) from 6 to 12 weeks and when aged to 18 weeks, these rats were compared to age-matched untreated SHRSP. Surprisingly, temporary spironolactone treatment reduced the MCA outer and lumen diameter but had no effect on the wall thickness. Temporary spironolactone treatment improved nitric oxide and endothelium-derived hyperpolarizing factor mediated dilation but had no effect on blood pressure. Spironolactone treatment caused a very small reduction in the damage caused by permanent focal cerebral ischemia. These results suggest that temporary MR antagonism during the development of hypertension has divergent effects on the MCA, in that it causes a potentially detrimental reduction in the lumen diameter while improving vasodilation.

Abstract 351: Mineralocorticoid Receptor Antagonism During the Development of Hypertension Improves Cerebral Artery Endothelium Dependent Dilation Even After Treatment Withdrawal

Hypertension causes cerebral artery remodeling and increases the risk of stroke. Renin angiotensin system blockade during the development of hypertension has therapeutic effects even after treatment withdrawal. Mineralocorticoid receptor (MR) activation has been implicated in artery remodeling and impaired endothelial function. The possibility that there is a critical therapeutic window for MR antagonism has not been investigated. We hypothesized that temporary MR antagonism while hypertension develops would improve endothelium dependent dilation even after treatment withdrawal. Six-week-old male stroke prone spontaneously hypertensive rats (SHRSP) were treated with spironolactone (Spir; 25mg/kg/day, n=8) from 6-12 weeks then aged to 18 weeks. Age-matched untreated SHRSP were controls (n=8). The middle cerebral artery (MCA) was removed and mounted on a pressure myograph, endothelium dependent dilation was assessed by intralumenal perfusion of 2-methylthioadenosine 5′-triphosphate (2-MeS-ATP), or uridine 5′-triphosphate (UTP). Spir had no effect on blood pressure. The MCA diameter after the development of tone was not different between the groups (197.7 ± 8.7 vs. 199.1 ± 4.1 μm, Spir vs. control). Spir treatment increased nitric oxide (NO) mediated MCA dilation in response to 2-MeS-ATP (% change from baseline; 50.9 ± 5.0 vs. 28.0 ± 4.3, Spir vs. control, p<0.05 ANOVA). Spir treatment also increased UTP mediated dilation (% change from baseline; 48.4 ± 6.0 vs. 37.4 ± 6.7, Spir vs. control, p<0.05 ANOVA), and increased the MCAs sensitivity to UTP as evidenced by a reduction in the Log EC50 for UTP (-9.2 ±0.1 vs. -8.7±0.2 Spir vs. control, p<0.05 t-test). There was no difference in the response to sodium nitroprusside between the two groups (% change from baseline; 42.5 ± 7.2 vs. 47.0 ± 7.6, Spir vs. control). These results suggest that MR antagonism improves both NO and endothelium derived relaxing factor mediated dilation in MCAs when the antagonist is administered while hypertension develops. Intriguingly, the improved endothelial function persists even after several weeks of treatment withdrawal suggesting there may be a critical time window during which endothelial function can be permanently improved in cerebral arteries from SHRSP.

The development of hypertension and hyperaldosteronism in a rodent model of life-long obesity

Aldosterone has been linked to the deleterious cardiovascular effects of obesity in humans. The association of aldosterone with obesity in rodents is less well defined, particularly in models of diet-induced obesity. We hypothesized that adrenal aldosterone production and aldosterone synthase expression would be increased in rats with obesity-induced hypertension. Male Sprague Dawley rats were fed a high-fat (HF: 36% fat) or control diet from 3 wk of age, and mean arterial pressure (MAP) was measured by telemetry. MAP was increased after 4 wk of HF diet; this was 6 wk before changes in body weight. Mineralocorticoid receptor antagonism did not prevent the HF-induced increase in MAP. After 17 wk on the diets, HF rats had increased body and fat weights (abdominal and epididymal) and were insulin resistant (Homeostasis Model Assessment index: 3.53 ± 0.43 vs. 8.52 ± 1.77; control vs. HF, P < 0.05). Plasma aldosterone levels were increased in the HF rats (64.14 ± 14.96 vs. 206.25 ± 47.55 pg/ml; control vs. HF, P < 0.05). This occurred independently of plasma renin activity (4.8 ± 0.92 vs. 4.73 ± 0.66 ng/ml/h, control vs. HF). The increase in aldosterone was accompanied by a 2-fold increase in adrenal aldosterone synthase mRNA expression and zona glomerulosa hypertrophy. Rats were also studied after 8 wk of HF diet, a time when MAP, but not body weight, was increased. At this time plasma aldosterone was unchanged but plasma renin activity was increased (4.4 ± 0.5 vs. 8.1 ± 1.3 ng/ml/h; control vs. HF, P < 0.05). These studies suggest that rats fed a HF diet from weaning may be a useful model for studying obesity-associated hyperaldosteronism.

Doxycycline, a matrix metalloprotease inhibitor, reduces vascular remodeling and damage after cerebral ischemia in stroke-prone spontaneously hypertensive rats

Matrix metalloproteases (MMPs) are a family of zinc peptidases involved in extracellular matrix turnover. There is evidence that increased MMP activity is involved in remodeling of resistance vessels in chronic hypertension. Thus we hypothesized that inhibition of MMP activity with doxycycline (DOX) would attenuate vascular remodeling. Six-week-old male stroke-prone spontaneously hypertensive rats (SHRSP) were treated with DOX (50 mg·kg(-1)·day(-1) in the drinking water) for 6 wk. Untreated SHRSP were controls. Blood pressure was measured by telemetry during the last week. Middle cerebral artery (MCA) and mesenteric resistance artery (MRA) passive structures were assessed by pressure myography. MMP-2 expression in aortas was measured by Western blot. All results are means ± SE. DOX caused a small increase in mean arterial pressure (SHRSP, 154 ± 1; SHRSP + DOX, 159 ± 3 mmHg; P < 0.001). Active MMP-2 expression was reduced in aorta from SHRSP + DOX (0.21 ± 0.06 vs. 0.49 ± 0.13 arbitrary units; P < 0.05). In the MCA, at 80 mmHg, DOX treatment increased the lumen (273.2 ± 4.7 vs. 238.3 ± 6.3 μm; P < 0.05) and the outer diameter (321 ± 5.3 vs. 290 ± 7.6 μm; P < 0.05) and reduced the wall-to-lumen ratio (0.09 ± 0.002 vs. 0.11 ± 0.003; P < 0.05). Damage after transient cerebral ischemia (transient MCA occlusion) was reduced in SHRSP + DOX (20.7 ± 4 vs. 45.5 ± 5% of hemisphere infarcted; P < 0.05). In the MRA, at 90 mmHg DOX, reduced wall thickness (29 ± 1 vs. 22 ± 1 μm; P < 0.001) and wall-to-lumen ratio (0.08 ± 0.004 vs. 0.11 ± 0.008; P < 0.05) without changing lumen diameter. These results suggest that MMPs are involved in hypertensive vascular remodeling in both the peripheral and cerebral vasculature and that DOX reduced brain damage after cerebral ischemia.

Lesions that simulate gunshot wounds - further examples II

A variety of postmortem and antemortem defects may be misinterpreted as gunshot wounds. In this paper, we present an additional series of lesions that simulate gunshot wounds. We briefly discuss each case, emphasizing various aspects of the scene investigation, clinical correlation and autopsy that are important in each case.

Lesions that simulate gunshot wounds

A variety of postmortem and antemortem defects can be misinterpreted as true antemortem injuries. In this paper, we present a collection of six cases with defects which simulate gunshot wounds. We briefly discuss each case and emphasize the importance of scene investigation, clinical correlation and careful examination in such cases.

Investigation of the 1987 Indianapolis Airport Ramada Inn incident

On October 20, 1987, a military reserve aircraft lost power during a transcontinental flight and attempted an emergency landing at The Indianapolis International Airport. The pilot ejected and the disabled and pilotless aircraft struck a bank building. It then skidded across the street and entered the lobby of The Airport Ramada Inn where it exploded. This incident was unusual in that the fatal injuries occurred in individuals on the ground and not in the occupant of the aircraft. Seven people were killed in the lobby area and two were trapped in a laundry where they died of smoke inhalation. A tenth person died of burns ten days later. Minor injuries were reported among four hotel guests, two firefighters and the Air Force pilot. A multiagency mass disaster-plan had been formulated and rehearsed in preparation for the Panamerican Games, which had been held in Indianapolis in August 1987. A number of volunteers arrived before a security perimeter was established. They began an undocumented removal of the bodies from the scene and were about to remove valuables for "safekeeping" when stopped by coroners' office personnel. Fatalities resulted from smoke inhalation, burns or a combination. Bodies were identified by a combination of dental records, personal effects and visual means within 24 hours. The problems encountered in managing this disaster scene will also be compared with previously reported incidents.

Undiagnosed, untreated acute lymphoblastic leukemia presenting as suspected child abuse

Natural disease being mistaken for child abuse is rare. A two-year-old child was found unresponsive at home and transported to a local hospital, where she expired in the emergency room. Several cutaneous contusions were observed. Prior to the autopsy it was learned that an anonymous report of "child abuse" had been previously filed concerning this child. At autopsy there were multiple metasynchronous cutaneous contusions, but no radiologic or gross evidence of other injuries. A pericardial effusion, massive hepatosplenomegaly and generalized lymphadenopathy were apparent. The bone marrow, liver, spleen, lymph nodes, kidneys, pancreas, heart, stomach, and dura mater showed a monotonous lymphocytic infiltrate. Immunocytochemical studies confirmed the diagnosis of acute lymphoblastic leukemia of childhood. This case reaffirms the need for an objective examination of all cases by a forensic pathologist.

Concealment of the body in drug deaths

Discovery of a concealed body often leads to the assumption that the manner of death was homicide. However, in cases where death has resulted from illicit drug use or drug abuse, the body may be concealed to protect persons involved in drug abuse or drug marketing.

Amanita phalloides mushroom poisoning: a cluster of four fatalities

A group of four illegal aliens had been without food for several days when they found a group of wild mushrooms growing in a field in Southern California. Each man consumed a meal of one to six fried mushrooms. Two days after eating the mushrooms, all four men developed abdominal pain, nausea, diarrhea, and intractable vomiting. Three days after consuming the mushrooms, all four were hospitalized and their clinical courses rapidly deteriorated to refractory hepatorenal failure and coma. Three of the victims died three days after admission to the hospital and the fourth died eight days after admission. The autopsy findings are presented and the mechanism of Amanita phalloides mushroom poisoning is discussed.

Human cannibalism: a case report

Human cannibal cases are relatively rare in modern civilized societies. We report a single case of familial cannibalism that occurred in Oklahoma in 1977. The investigation posed unique problems in pathology, psychiatry, criminalistics, and serology.