Mapping and targeted viral activation of pancreatic nerves in mice reveal their roles in the regulation of glucose metabolism

A lack of comprehensive mapping of ganglionic inputs into the pancreas and of technology for the modulation of the activity of specific pancreatic nerves has hindered the study of how they regulate metabolic processes. Here we show that the pancreas-innervating neurons in sympathetic, parasympathetic and sensory ganglia can be mapped in detail by using tissue clearing and retrograde tracing (the tracing of neural connections from the synapse to the cell body), and that genetic payloads can be delivered via intrapancreatic injection to target sites in efferent pancreatic nerves in live mice through optimized adeno-associated viruses and neural-tissue-specific promoters. We also show that, in male mice, the targeted activation of parasympathetic cholinergic intrapancreatic ganglia and neurons doubled plasma-insulin levels and improved glucose tolerance, and that tolerance was impaired by stimulating pancreas-projecting sympathetic neurons. The ability to map the peripheral ganglia innervating the pancreas and to deliver transgenes to specific pancreas-projecting neurons will facilitate the examination of ganglionic inputs and the study of the roles of pancreatic efferent innervation in glucose metabolism.

Estimating glomerular filtration rate in youth with obesity and type 2 diabetes: the iCARE study equation

BACKGROUND

The validity of pediatric estimated glomerular filtration rate equations (eGFRs) in early stages of CKD including hyperfiltration is unknown. The purpose of this study was to develop an eGFR equation for adolescents with obesity and type 2 diabetes (T2D).

METHODS

eGFRs were developed from iohexol-derived GFRs (iGFRs) in 26 overweight/obese (BMI > 85th percentile) youth and 100 with T2D from the iCARE (Improving renal Complications in Adolescents with T2D through REsearch) cohort. Twenty percent of the cohort was withheld as a validation dataset. Linear regression analyses were used to develop the best formula based on body size, sex, creatinine, urea, ± cystatin C. Comparable validity of commonly used eGFR equations was assessed.

RESULTS

Mean age 15.4 + 2.4 years, BMI Z-score 2.5 + 1.2, 61% female, and mean iGFR 129.0 + 27.7 ml/min/ 1.73 m². The best adjusted eGFR formula (ml/min/1.73 m²) was 50.7 × BSA^0.816 × (height (cm)/creatinine)^0.405 × 0.8994 if sex = female | 1 otherwise. It resulted in 53.8% of eGFRs within 10% of measured iGFR and 96.2% within 30%. Bland-Altman 95% limits of agreement in the external dataset were - 37.6 to 45.5 ml/min/1.73m² (bias = 3.96), and the correlation was 0.62. This equation performed better than all previously published creatinine-based eGFRs. cystatin C did not significantly improve results; however, some other cystatin C formulas also performed well.

CONCLUSIONS

The iCARE equation provides a more accurate creatinine-based eGFR in obese youth with and without T2D. Further studies are warranted to evaluate within-subject variability and applicability to lower GFRs and other populations.

Differential effects of hypothalamic long-chain fatty acid infusions on suppression of hepatic glucose production

Our objective was to investigate whether the direct bilateral infusion of the monounsaturated fatty acid (MUFA) oleic acid (OA) within the mediobasal hypothalamus (MBH) is sufficient to reproduce the effect of administration of OA (30 nmol) in the third cerebral ventricle, which inhibits glucose production (GP) in rats. We used the pancreatic basal insulin clamp technique (plasma insulin ∼20 mU/ml) in combination with tracer dilution methodology to compare the effect of MBH OA on GP to that of a saturated fatty acid (SFA), palmitic acid (PA), and a polyunsaturated fatty acid (PUFA), linoleic acid (LA). The MBH infusion of 200 but not 40 pmol of OA was sufficient to markedly inhibit GP (by 61% from 12.6 ± 0.6 to 5.1 ± 1.6 mg·kg(-1)·min(-1)) such that exogenous glucose had to be infused at the rate of 6.0 ± 1.2 mg·kg(-1)·min(-1) to prevent hypoglycemia. MBH infusion of PA also caused a significant decrease in GP, but only at a total dose of 4 nmol (GP 5.8 ± 1.6 mg·kg(-1)·min(-1)). Finally, MBH LA at a total dose of 0.2 and 4 nmol failed to modify GP compared with rats receiving MBH vehicle. Increased availability of OA within the MBH is sufficient to markedly inhibit GP. LA does not share the effect of OA, whereas PA can reproduce the potent effect of OA on GP, but only at a higher dose. It remains to be determined whether SFAs need to be converted to MUFAs to exert this effect or whether they activate a separate signaling pathway to inhibit GP.

Sensory and sympathetic nervous system control of white adipose tissue lipolysis

Circulating factors are typically invoked to explain bidirectional communication between the CNS and white adipose tissue (WAT). Thus, initiation of lipolysis has been relegated primarily to adrenal medullary secreted catecholamines and the inhibition of lipolysis primarily to pancreatic insulin, whereas signals of body fat levels to the brain have been ascribed to adipokines such as leptin. By contrast, evidence is given for bidirectional communication between brain and WAT occurring via the sympathetic nervous system (SNS) and sensory innervation of this tissue. Using retrograde transneuronal viral tract tracers, the SNS outflow from brain to WAT has been defined. Functionally, sympathetic denervation of WAT blocks lipolysis to a variety of lipolytic stimuli. Using anterograde transneuronal viral tract tracers, the sensory input from WAT to brain has been defined. Functionally, these WAT sensory nerves respond electrophysiologically to increases in WAT SNS drive suggesting a possible neural negative feedback loop to regulate lipolysis.

Basolateral carbonic anhydrase IV in the proximal tubule is a glycosylphosphatidylinositol-anchored protein

Carbonic anhydrase (CA) IV facilitates HCO(3) reabsorption in the renal proximal tubule by catalyzing the reversible hydration of CO(2). CAIV is tethered to cell membranes via a glycosylphosphatidylinositol (GPI) lipid anchor. As there is basolateral as well as apical CAIV staining in proximal tubule, the molecular identity of basolateral CAIV was examined. Biotinylation of confluent monolayers of rat inner medullary collecting duct cells stably transfected with rabbit CAIV showed apical and basolateral CAIV, and in the cell transfectants expressing high levels of CAIV, a transmembrane form was targeted to the basolateral membrane. Basolateral expression of CAIV ( approximately 46 kDa) was confirmed in normal kidney tissue by Western blotting of vesicle fractions enriched for basolateral membranes by Percoll density fractionation. We examined the mode of membrane linkage of basolaterally expressed CAIV in the kidney cortex. CAIV detected in basolateral or apical membrane vesicles exhibited similar molecular size by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis following deglycosylation, and was equally sensitive to phosphatidylinositol-specific phospholipase C digestion, indicating that CAIV is expressed on the basolateral membrane as a GPI-anchored protein. Half of the hydratase activity of basolateral vesicles was resistant to SDS denaturation, compatible with being CAIV. Thus, GPI-anchored CAIV resides in the basolateral membrane of proximal tubule epithelia where it may facilitate HCO(3) reabsorption via association with kNBC1.

The role of carbonic anhydrases in renal physiology

Carbonic anhydrase (CA) catalyzes the reversible hydration of CO(2). CA is expressed in most segments of the kidney. CAII and CAIV predominate in human and rabbit kidneys; in rodent kidneys, CAXII, and CAXIV are also present. CAIX is expressed by renal cell carcinoma (RCC). Most of these isoforms, except for rodent CAIV, have high turnover rates. CAII is a cytoplasmic enzyme, whereas the others are membrane-associated; CAIV is anchored by glycosylphosphatidylinositol linkage. Membrane polarity is apical for CAXIV, basolateral for CAXII, and apical and basolateral for CAIV. Luminal membrane CAs facilitate the dehydration of carbonic acid (H(2)CO(3)) that is formed when secreted protons combine with filtered bicarbonate. Basolateral CA enhances the efflux of bicarbonate via dehydration of H(2)CO(3). CAII and CAIV can associate with bicarbonate transporters (e.g., AE1, kNBC1, NBC3, and SCL26A6), and proton antiporter, NHE1 in a membrane protein complex called a transport metabolon. CAXII and CAXIV may also be associated with transporters in normal kidney and CAIX in RCCs. The multiplicity of CAs implicates their importance in acid-base and other solute transport along the nephron. For example, CAII on the cytoplasmic face and CAIV on the extracellular surface provide the 'push' and 'pull' for bicarbonate transport by supplying and dissipating substrate respectively.

Glomerular filtration rate via plasma iohexol disappearance: pilot study for chronic kidney disease in children

To guide the design of a nation-wide cohort study of chronic kidney disease in children, we determined how iohexol plasma disappearance curves could be used in children to measure glomerular filtration rate (GFR). Iohexol (5 ml) was administered intravenously and blood samples were obtained at 10, 20, 30, 60, 120, 240, 300, and 360 min after injection (N=29) and assayed by high performance liquid chromatography. Four urines were also collected following the injection. Intra-assay coefficient of variation (CV) in serum was 1.3% at 100 mg/l, 2.6% at 15 mg/l, and 3.4% for duplicate unknowns. GFR(9) was computed from iohexol dose and area under the nine-point blood disappearance curve, using double exponential modeling. Only 2.8% of 254 data points deviated by >3 CV from the curves. GFR(4) calculated from 10, 30, 120, and 300 min points correlated well with GFR(9) (r=0.999) and showed no bias (means+/-s.d. of GFR(9) and GFR(4)=59.3+/-36.3 and 59.4+/-36.0 ml/min per 1.73 m(2)). Relationship of GFR(9) and one-compartment GFR followed quadratic equation as previously reported by Brochner-Mortensen, allowing GFR to be calculated from 120 and 300 min points. This GFR(2) correlated well with GFR(9) (r=0.986). Estimated GFR from Schwartz height/creatinine formula correlated with GFR(9)(r=0.934) but overestimated GFR by 12.2 ml/min per 1.73 m(2). Urine iohexol clearance was poorly correlated (r=0.770) with GFR(9) owing to variability in urine collections (median CV=24%). GFR can be measured accurately using four-point iohexol plasma disappearance (in most cases, two points suffice); estimated GFR and urinary clearances are less useful.

Acute and chronic administration of immunomodulators induces anorexia in Zucker rats

To investigate the possible involvement of leptin signaling in lipopolysaccharide (LPS) anorexia, we compared the anorectic effect of LPS in genetically obese (fa/fa) Zucker rats and in their lean (Fa/?) counterparts. The effects of interleukin-1beta (IL-1beta) and muramyl dipeptide (MDP) were also tested. LPS [100 microg/kg body weight (BW)], IL-1beta (2 microg/kg BW) and MDP (2.2 mg/kg BW) injected intraperitoneally (i.p.) at lights out reduced food intake similarly in obese and lean rats. LPS injection at 500 or 1000 microg/kg BW (i.p.) also reduced food intake and BW similarly in obese and lean rats, but obese regained BW faster than lean rats. LPS (2.45 microg or 9.8 microg/h/rat) administered chronically with i.p. implanted osmotic pumps reduced food intake similarly on experimental day 1, regardless of the genotype. After day 3, the lean rats' anorectic response and recovery were dose-dependent, whereas the anorectic response in obese rats was minimally affected by dose (significant dose effect only on day 3). Again, obese rats regained lost BW faster than lean rats. These results do not support a role for leptin as the sole mediator of anorexia induced by bacterial products (LPS and MDP) and IL-1beta.

Role for CD14, TLR2, and TLR4 in bacterial product-induced anorexia

The cell surface component CD14 and the toll-like receptors 2 and 4 (TLR2 and TLR4) are important in mediating the immune responses to bacterial products in mammals. Using mice genetically deficient in CD14, TLR2, or TLR4, we studied the role of these molecules in the anorectic effects of LPS and muramyl dipeptide (MDP). CD14 or TLR2 knockout (KO) and TLR4-deficient (TLR4-DEF) mice as well as corresponding wild-type (WT) colittermates were injected intraperitoneally at dark onset with LPS (2 microg/mouse), MDP (10 mg/kg), interleukin-1 beta (IL-1 beta, 150 ng/mouse), or vehicle, and food intake was recorded. LPS and MDP reduced food intake in WT mice of all genotypes tested. The anorectic effect of LPS was attenuated (P < 0.04) in CD14-KO and TLR4-DEF mice but not in TLR2-KO (P > 0.05). The anorectic effect of MDP was blunted in CD14-KO and TLR2-KO (P < 0.02) mice but not in TLR4-DEF mice. IL-1 beta reduced food intake similarly in all genotypes tested. These results indicate that CD14 is involved in mediating the anorectic effects of both LPS and MDP. Furthermore, TLR4 and TLR2 are specifically involved in mediating the anorectic effects of LPS and MDP, respectively. The results are consistent with the hypothesis that TLR4 functions as the true LPS receptor and that TLR2 is involved in recognition of gram-positive bacterial products.

A role for cyclooxygenase-2 in lipopolysaccharide-induced anorexia in rats

Because nonselective cycloooxygenase (COX) inhibition attenuated anorexia after lipopolysaccharide (LPS) administration, we tested the ability of resveratrol (2.5, 10, and 40 mg/kg) and NS-398 (2.5, 10, and 40 mg/kg), selective inhibitors of the two COX isoforms COX-1 and -2, respectively, to attenuate LPS (100 microg/kg ip)-induced anorexia. NS-398 (10 and 40 mg/kg) administered with LPS at lights out attenuated LPS-induced anorexia, whereas resveratrol at all doses tested did not. Because prostaglandin (PG) E(2) is considered the major metabolite synthesized by COX, we measured plasma and cerebrospinal fluid (CSF) PGE(2) levels after LPS administration. LPS induced a time-dependent increase of PGE(2) in CSF but not in plasma. NS-398 (5, 10, and 40 mg/kg) blocked the LPS-induced increase in CSF PGE(2), whereas resveratrol (10 mg/kg) did not. These results support a role of COX-2 in mediating the anorectic response to peripheral LPS and point at PGE(2) as a potential neuromodulator involved in this response.

Within-meal gut feedback signaling

During a meal, multiple gastrointestinal sites are stimulated by ingested nutrients and their digestion products, initiating local gastrointestinal actions and producing a variety of potential feedback signals that can contribute to meal termination. During ingestion, gastric emptying is rapid, allowing a significant portion of ingested nutrients to enter the intestine. Gastric and duodenal vagal afferent fibers increase their electrophysiological activity in relation to the mechanical presence of ingested nutrients. On reaching the duodenum, nutrients also activate vagal chemosensitive elements and stimulate the release of a variety of brain gut peptides including cholecystokinin (CCK). CCK also activates vagal afferent fibers directly and modifies the response properties of vagal mechanosensitive fibers to gastric and duodenal loads. Blocking or eliminating these feedback signals results in increased meal size demonstrating their role in meal termination.

Intracerebroventricular CART peptide reduces food intake and alters motor behavior at a hindbrain site

Peptides from cocaine- and amphetamine-regulated transcript (CART) reduce food intake in rats when injected into the lateral ventricle. Hypothalamic and hindbrain sites important in the control of feeding contain CART-immunoreactive fibers. To further define the site of CART's anorectic action, we compared feeding and other behavioral responses to third or fourth ventricular (3V, 4V) CART-(55-102) in 6-h food-deprived rats, both before and after cerebral aqueduct occlusion. 3V CART reduced the volume of Ensure consumed and resulted in fewer observations of eating and grooming within the 30-min test session. These reductions were significantly attenuated by aqueduct obstruction. 4V CART suppressed Ensure intake and resulted in decreased observations of feeding both with and without aqueduct blockade. 3V CART produced flat-backed postures and movement-associated tremors that were prevented by aqueduct obstruction. 4V CART also produced these signs, both with and without aqueduct blockade. We conclude that the major hypophagic effect of intracerebroventricular CART is mediated at a hindbrain site. The association of CART-induced feeding suppression with altered motor behavior questions the specificity of intracerebroventricular CART for actions on feeding.

Excessive sugar intake alters binding to dopamine and mu-opioid receptors in the brain

Palatable food stimulates neural systems implicated in drug dependence; thus sugar might have effects like a drug of abuse. Rats were given 25% glucose solution with chow for 12 h followed by 12 h of food deprivation each day. They doubled their glucose intake in 10 days and developed a pattern of excessive intake in the first hour of daily access. After 30 days, receptor binding was compared to chow-fed controls. Dopamine D-1 receptor binding increased significantly in the accumbens core and shell. In contrast, D-2 binding decreased in the dorsal striatum. Binding to dopamine transporter increased in the midbrain. Opioid mu-1 receptor binding increased significantly in the cingulate cortex, hippocampus, locus coeruleus and accumbens shell. Thus, intermittent, excessive sugar intake sensitized D-1 and mu-1 receptors much like some drugs of abuse.

Intracerebroventricular CART peptide reduces rat ingestive behavior and alters licking microstructure

Intracerebroventricular administration of cocaine- and amphetamine-regulated transcript (CART) peptides reduces food intake and increases c-Fos in brain areas involved in the control of feeding. To discern behavioral mechanisms through which CART alters the microstructure of feeding, we injected CART-(55--102) (0.1, 0.5, 1, 2 microg, and saline controls) into the lateral ventricle of male Sprague-Dawley rats 5 min before dark onset and, using lickometers, monitored the ingestion of an Ensure liquid diet for the first 6 h of dark. At a threshold dose of 1 microg, CART dose dependently 1) decreased intake of Ensure in licks; 2) decreased meal size, but did not alter meal duration or number; 3) reduced initial lick rate of meals; and 4) significantly reduced burst number, licks/burst, and licks/cluster. CART dose dependently increased interlick interval (0.5 microg threshold, 192 +/- 4 vs. 183 +/- 3 ms, control; 1 microg: 201 +/- 1 ms; 2 microg: 214 +/- 6 ms). These data suggest that altered oral motor function, and possibly palatability perception, may be fundamental to the anorexigenic action of CART.

A role for NPY overexpression in the dorsomedial hypothalamus in hyperphagia and obesity of OLETF rats

Otsuka Long-Evans Tokushima Fatty (OLETF) rats lacking CCK-A receptors are hyperphagic, obese, and diabetic. We have previously demonstrated that these rats have a peripheral satiety deficit resulting in increased meal size. To examine the potential role of hypothalamic pathways in the hyperphagia and obesity of OLETF rats, we compared patterns of hypothalamic neuropeptide Y (NPY), proopiomelanocortin (POMC), and leptin receptor mRNA expression in ad libitum-fed Long-Evans Tokushima (LETO) and OLETF rats and food-restricted OLETF rats that were pair-fed to the intake of LETO controls. Pair feeding OLETF rats prevented their increased body weight and elevated levels of plasma insulin and leptin and normalized their elevated POMC and decreased NPY mRNA expression in the arcuate nucleus. In contrast, NPY expression was upregulated in the dorsomedial hypothalamus (DMH) in pair-fed OLETF rats. A similar DMH NPY overexpression was evident in 5-wk-old preobese OLETF rats. These findings suggest a role for DMH NPY upregulation in the etiology of OLETF hyperphagia and obesity.

Distal renal tubular acidosis with severe hypokalaemia, probably caused by colonic H(+)-K(+)-ATPase deficiency

We describe a 21 month old male infant who presented with failure to thrive associated with severe hypokalaemia and metabolic acidosis, together with hypomagnesaemia. Evaluation revealed marked renal and probable faecal potassium wasting, distal renal tubular acidosis, mild urinary magnesium wasting, and a normal gastric pH (gastric H(+)-K(+)-ATPase). Hypokalaemic forms of metabolic acidosis, such as diabetic ketoacidosis and proximal renal tubular acidosis were ruled out from the clinical picture. The hypokalaemia of distal renal tubular acidosis usually improves with alkali therapy, but this was not observed: despite correction of acidosis with 5 mmol/kg potassium citrate per day, an additional 5 mmol/kg potassium chloride was required to bring serum potassium to 3.5 mmol/l. At 3 years of age potassium was provided in the absence of potential alkali and acidosis ensued; serum bicarbonate fell to 10 mmol/l. Although a specific genetic analysis is not yet possible, the abnormalities are consistent with a novel form of distal renal tubular acidosis. The pathophysiology probably does not stem from defects in the vacuolar H(+)-ATPase but more likely from deficient activity of the colonic isoform of H(+)-K(+)-ATPase that is resident in the medullary collecting duct and mediates potassium absorption and proton secretion.

Maturation of carbonic anhydrase IV expression in rabbit kidney

Carbonic anhydrase (CA) IV facilitates renal acidification by catalyzing the dehydration of luminal H(2)CO(3). CA IV is expressed in proximal tubules, medullary collecting ducts, and A-intercalated cells of the mature rabbit kidney (Schwartz GJ, Kittelberger AM, Barnhart DA, and Vijayakumar S. Am J Physiol 278: F894-F904, 2000). In view of the maturation of HCO transport in the proximal tubule and collecting duct, the ontogeny of CA IV expression was examined. During the first 2 wk, CA IV mRNA was expressed in maturing cortex and medulla at ~20% of adult levels. The maturational increase was gradual in cortex over 3-5 wk of age but surged in the medulla, so that mRNA levels appeared higher than those in the adult medulla. In situ hybridization showed very little CA IV mRNA at 5 days, with increases in deep cortex and medullary collecting ducts by 21 days. Expression of CA IV protein in the cortex and medulla was minimal at 3 days of age but then apparent in the juxtamedullary region, A-intercalated cells and medullary collecting ducts by 18 days; there was little labeling of the proximal straight tubules of the medullary rays. Thus CA IV expression may be regulated to accommodate the maturational increase in HCO absorption in the proximal tubule. In the medullary collecting duct, there is a more robust maturation of CA IV mRNA and protein, commensurate with the high rate of HCO absorption in the neonatal segment.

Meal-related stimuli differentially induce c-Fos activation in the nucleus of the solitary tract

Feedback signals arising from the oral cavity and upper gastrointestinal tract contribute to the control of meal size. To assess how these signals are integrated at central sites involved in ingestive control, we compared levels of c-Fos activation in the nucleus of the solitary tract (NTS) and area postrema (AP) in response to meal ingestion or gastric and duodenal infusions in the rat. Ingestion of a liquid diet to satiety induced significant fos-like immunoreactivity (FLI) at multiple levels of the NTS and within the AP. The restriction of intake to one-half the normal ingestion of a rat did not result in significant FLI, although gastric infusion of this liquid diet volume did. Fast bolus infusion resulted in greater FLI than did the same volume infused at a rate to mimic that of normal ingestion. Prior experience with gastric infusions did not affect the amounts of FLI within the NTS or AP. In rats with pyloric cuffs blocking flow from the stomach to the intestine, combined gastric load and duodenal nutrient elicited significantly greater FLI than either gastric or duodenal infusions alone. These data demonstrate that neural activation arising from meal-related stimuli are integrated at the level of the NTS.

Plasticity of intercalated cell polarity: effect of metabolic acidosis

The cortical collecting duct (CCD) is capable of secreting H(+) or HCO3(-) depending on the acid-base status in vivo. Transport is a function of two types of intercalated cells in the CCD: A-intercalated cells secrete H(+) and B-intercalated cells secrete HCO3(-). Metabolic acidosis results in a decrease in HCO3(-) secretion and an increase in H(+) secretion by the respective cells. Using a model of metabolic acidosis in vitro, we have shown that the down-regulation of HCO3(-) secretion occurs by endocytosis of apical anion exchangers in B-intercalated cells. The finding of basolateral anion exchangers in some adapted B-intercalated cells is consistent with a reversal of functional epithelial polarity. Plasticity of polarity is also observed in cultured intercalated cells: high-density plating results in converting B- to A-intercalated cells via the deposition of the novel protein hensin in the extracellular matrix. A key problem in renal physiology is to investigate the role of hensin in mediating the adaptation of the CCD to acidosis in vitro and in vivo.

Influence of dispersants on the bioavailability and trophic transfer of petroleum hydrocarbons to larval topsmelt (Atherinops affinis)

Use of chemical dispersants as oil spill clean-up agents may alter the normal behavior of petroleum hydrocarbons (PH) by increasing their functional water solubility, resulting in increased bioavailability and altered interactions between dispersant, oil, and biological membranes. The objective of this research was to determine the impact of dispersing agents on PH bioavailability and trophic transfer to larval fish from primary levels of a marine food chain. Uptake, bioaccumulation, depuration, and metabolic transformation of a model PH, [14C]naphthalene, were measured and compared for Prudhoe Bay crude oil (PBCO) dispersed with Corexit 9527(R) (DO) and undispersed preparations of the water-accommodated fraction (WAF) of PBCO. The model food chain consisted of a primary producer, Isochrysis galbana; and a primary consumer, the rotifer, Brachionus plicatilis; and larval topsmelt, Atherinops affinis. Direct aqueous (AQ) exposure was compared with combined aqueous and dietary (AQ&D) exposure. Dispersants altered the uptake and depuration processes of naphthalene, independent of aqueous concentrations, in primary trophic species of a marine food chain. The amount of naphthalene taken up by topsmelt was initially significantly (P < or = 0.05) enhanced in the presence of dispersant, reaching a maximum more quickly than undispersed samples. Dispersion treatment significantly increased naphthalene dispension in topsmelt (P < or = 0.05) from both AQ and AQ&D exposures. No significant change in naphthalene uptake by fish was observed with the addition of contaminated food for either WAF or DO medium; however, both uptake and depuration rate constants varied significantly with route of exposure consistent with greater naphthalene turnover. The majority (> or = 72%) of naphthalene-derived radioactivity from fish tissue following all exposures was in the parent form, with smaller quantities of alpha- and beta-naphthols, alpha- and beta-naphthyl sulfates, and an unidentified derivative.

Pro-inflammatory and anti-inflammatory cytokine mRNA induction in the periphery and brain following intraperitoneal administration of bacterial lipopolysaccharide

Gram-negative bacteria-derived lipopolysaccharide (LPS or endotoxin) is known to play an important role in immune and neurological manifestations during bacterial infections. LPS exerts its effects through cytokines, and peripheral or brain administration of LPS activates cytokine production in the brain. In this study, we investigated cytokine and neuropeptide mRNA profiles in specific brain regions and peripheral organs, as well as serum tumor necrosis factor (TNF)-alpha protein levels, in response to the intraperitoneal administration of LPS. For the first time, the simultaneous analysis of interleukin (IL)-1beta system components (ligand, signaling receptor, receptor accessory proteins, receptor antagonist), TNF-alpha, transforming growth factor (TGF)-beta1, glycoprotein 130 (IL-6 receptor signal transducer), OB protein (leptin) receptor, neuropeptide Y, and pro-opiomelanocortin (opioid peptide precursor) mRNAs was done in samples from specific brain regions in response to peripherally administered LPS. The same brain region/organ sample was assayed for all cytokine mRNA components. Peripherally administered LPS up-regulated pro-inflammatory cytokine (IL-1beta and/or TNF-alpha) mRNAs within the cerebral cortex, cerebellum, hippocampus, spleen, liver, and adipose tissue. LPS also increased plasma levels of TNF-alpha protein. LPS did not up-regulate inhibitory (anti-inflammatory) cytokine (IL-1 receptor antagonist and TGF-beta1) mRNAs in most brain regions (except for IL-1 receptor antagonist in the cerebral cortex and for TGF-beta1 in the hippocampus), while they were increased in the liver, and IL-1 receptor antagonist was up-regulated in the spleen and adipose tissue. Overall, peripherally administered LPS modulated the levels of IL-1beta system components within the brain and periphery, but did not affect the neuropeptide-related components studied. The data suggest specificity of transcriptional changes induced by LPS and that cytokine component up-regulation in specific brain regions is relevant to the neurological and neuropsychiatric manifestations associated with peripheral LPS challenge.

Neonatal Borna disease virus infection (BDV)-induced damage to the cerebellum is associated with sensorimotor deficits in developing Lewis rats

Neonatal Borna disease virus (BDV) infection of the brain produces developmental damage to the cerebellum in Lewis rats, with minimal classical inflammatory responses. In the present study, we assessed the consequences of this damage by measuring motor coordination and postural skills in developing (postnatal days 4 to 30) Lewis rats that were neonatally infected with BDV. Neonatal BDV infection-induced motor impairments were selective and correlated with the time course of BDV damage to cerebellar development. BDV-induced motor deficits were not seen until the end of postnatal week 2. By postnatal week 3, BDV-infected rats had deficits in negative geotropism, fore- and hind limb placing and grasping. BDV-infected rats also exhibited deficits in the ability to hold on to a bar and to cross a suspended bar. Neonatal BDV infection induced impairments in the acoustic startle response. Compared to controls, neonatally BDV-infected rats exhibited attenuated habituation of the acoustic startle at postnatal day (PND) 23 and decreased startle responsiveness at PND 30. Prepulse inhibition of the acoustic startle remained unaltered in BDV-infected rats. The data demonstrate that neonatal BDV brain infection of rats can be a valuable animal model system for studying the relationship between abnormal brain development and resultant behavioral deficits. Further studies of this model may elucidate specific pathogenic mechanisms that that may have implications in the study of neurodevelopmental human disorders.

Role of basolateral carbonic anhydrase in proximal tubular fluid and bicarbonate absorption

Membrane-bound carbonic anhydrase (CA) is critical to renal acidification. The role of CA activity on the basolateral membrane of the proximal tubule has not been defined clearly. To investigate this issue in microperfused rabbit proximal straight tubules in vitro, we measured fluid and HCO(3)(-) absorption and cell pH before and after the extracellular CA inhibitor p-fluorobenzyl-aminobenzolamide was applied in the bath to inhibit only basolateral CA. This inhibitor was 1% as permeant as acetazolamide. Neutral dextran (2 g/dl, molecular mass 70,000) was used as a colloid to support fluid absorption because albumin could affect CO(2) diffusion and rheogenic HCO(3)(-) efflux. Indeed, dextran in the bath stimulated fluid absorption by 55% over albumin. Basolateral CA inhibition reduced fluid absorption ( approximately 30%) and markedly decreased HCO(3)(-) absorption ( approximately 60%), both reversible when CA was added to the bathing solution. In the presence of luminal CA inhibition, which reduced fluid ( approximately 16%) and HCO(3)(-) ( approximately 66%) absorption, inhibition of basolateral CA further decreased the absorption of fluid (to 74% of baseline) and HCO(3)(-) (to 22% of baseline). CA inhibition also alkalinized cell pH by approximately 0.2 units, suggesting the presence of an alkaline disequilibrium pH in the interspace, which would secondarily block HCO(3)(-) exit from the cell and thereby decrease luminal proton secretion (HCO(3)(-) absorption). These data clearly indicate that basolateral CA has an important role in mediating fluid and especially HCO(3)(-) absorption in the proximal straight tubule.

Leptin amplifies the feeding inhibition and neural activation arising from a gastric nutrient preload

Leptin affects food intake by reducing meal size, suggesting that it may modulate the efficacy of within-meal satiety signals. To assess whether leptin would amplify the feeding inhibitory actions of a nutrient gastric preload, we compared liquid diet food intake and patterns of c-Fos activation in response to intraventricular leptin (3.5 microg), intragastric Ensure (10 ml over 10 min), or their combination. Leptin alone did not affect Ensure intake but significantly increased the suppression of intake produced by the intragastric preload. Within the nucleus of the solitary tract (NTS), leptin alone did not stimulate c-Fos but significantly elevated the number of c-Fos positive cells in response to intragastric Ensure at medial and rostral levels. Within the paraventricular nucleus (PVN), both leptin and the gastric load stimulated c-Fos expression, but the combination resulted in significantly greater number of c-Fos positive cells. These data demonstrate that leptin modulates the feeding inhibition produced by meal-related signals and suggest that this modulation occurs at the levels of the NTS and PVN.

The role of gastrointestinal vagal afferents in the control of food intake: current prospects

Meals are the functional units of food intake in humans and mammals, and physiologic approaches to understanding the controls of meal size have demonstrated that the presence of food in the upper gastrointestinal tract plays a critical role in determining meal size. The vagus nerve is the primary neuroanatomic substrate in the gut-brain axis, transmitting meal-related signals elicited by nutrient contact with the gastrointestinal tract to sites in the central nervous system that mediate ingestive behavior. This article describes progress in examining the role of the vagal gut-brain axis in the negative-feedback control of meal size from four perspectives: neuroanatomic, neurophysiologic, molecular, and behavioral. Vagal afferents are strategically localized to be sensitive to meal-related stimuli, and their central projections are organized viscerotopically in the caudal brainstem. Vagal afferents are sensitive to mechanical, chemical, and gut and peptide meal-related stimuli and can integrate multiple such modalities. Meal-elicited gastrointestinal stimuli activate distinct patterns of c-fos neural activation within caudal brainstem sites, where gut vagal afferents terminate. Results of selective chemical and surgical vagal deafferentation studies have refined our understanding of the sites and types of critical gastrointestinal feedback signals in the control of meal size. Recent behavioral, molecular, and neurophysiologic data have demonstrated brainstem sites where centrally acting neuropeptides may modulate the processing of gut vagal afferent meal-related signals to alter feeding. Investigations of the structure and function of splanchnic visceral afferents and enterics and characterization of the integrative capacities of the hindbrain and forebrain components of the gut-brain axis are critical next steps in this analysis.

Carbonic anhydrase IV is expressed in H(+)-secreting cells of rabbit kidney

Carbonic anhydrase (CA) IV is a membrane-bound enzyme that catalyzes the dehydration of carbonic acid to CO(2) and water. Using peptides from each end of the deduced rabbit CA IV amino acid sequence, we generated a goat anti-rabbit CA IV antibody, which was used for immunoblotting and immunohistochemical analysis. CA IV was expressed in a variety of organs including spleen, heart, lung, skeletal muscle, colon, and kidney. Rabbit kidney CA IV had two N-glycosylation sites and was sialated, the apparent molecular mass increasing by at least 11 to approximately 45 kDa in the cortex. Medullary CA IV was much more heavily glycosylated than CA IV from cortex or any other organ, such modifications increasing the molecular mass by at least 20 kDa. CA IV was expressed on the apical and basolateral membranes of proximal tubules with expression levels on the order of S2 > S1 > S3 = 0. Because CA IV is believed to be anchored to the apical membrane by glycosylphosphatidylinositol, the presence of basolateral CA IV suggests an alternative mechanism. CA IV was localized on the apical membranes of outer medullary collecting duct cells of the inner stripe and inner medullary collecting duct cells, as well as on alpha-intercalated cells. However, CA IV was not expressed by beta-intercalated cells, glomeruli, distal tubule, or Henle's loop cells. Thus CA IV was expressed by H(+)-secreting cells of the rabbit kidney, suggesting an important role for CA IV in urinary acidification.

Cloning of rabbit Cct6 and the distribution of the Cct complex in mammalian tissues

Cct6 protein is one of the subunits of the Cct complex involved in ATP-dependent folding of cellular proteins. We used the cDNA of the human CCT6 subunit to obtain a full-length cDNA from a rabbit kidney cortex library. Two transcripts of 2 and 2.5 kb were detected in rabbit kidney and liver by Northern analysis. The rabbit CCT6 was 93% identical to the human gene; the deduced amino acid sequence was 97% identical. A phylogenetic analysis of Cct6 proteins from mouse, rabbit, human, and yeast showed greater similarities of Cct6 protein among the species than among other Cct subunits. The ATP-binding sites were perfectly conserved among mammals and yeast, supporting the role of Cct complex in ATP-dependent protein folding. Using a polyclonal antibody to human Cct6 protein and Western analysis, we found expression of this subunit in a variety of rabbit organs and tissues, as well as in bovine testes, human lymphocytes, human and rabbit reticulocytes, and in two cultured kidney cell lines. We also found Cct1 protein by Western analysis in several rabbit organs as well as in bovine testes. These data characterize the rabbit Cct6 subunit and compare it to its homologues. The Western analyses support the concept that Cct complex is widely distributed among tissues and highly conserved among eukaryotes.

Role of endogenous CCK in the inhibition of gastric emptying by peptone and Intralipid in rats

To assess the role of endogenous cholecystokinin in the control of gastric emptying of peptone solutions and Intralipid suspensions, we examined the ability of a dose range of the CCK-A antagonist, devazepide to accelerate the gastric emptying of various caloric concentrations of peptone and Intralipid in rats. In the absence of devazepide, both peptone and Intralipid emptying slowed with increasing concentration. Devazepide's effect on peptone gastric emptying diminished with increasing peptone concentration. The threshold dose for accelerating the emptying of 0.2 kcal/ml peptone was lower than the threshold dose for affecting 0.5 kcal/ml peptone and devazepide had no effect on the gastric emptying of 1.0 kcal/ml peptone. In contrast, devazepide affected Intralipid gastric emptying at all three Intralipid concentrations and the threshold dose decreased with increasing Intralipid concentration. However, the magnitude of the effect of devazepide on peptone or Intralipid gastric emptying was partial and did not increase as a function of concentration. These data demonstrate a role for endogenous CCK in the emptying of peptone and Intralipid but suggest that endogenous CCK does not account for the increased slowing of gastric emptying evident with increased caloric concentration.

Effects of neonatal rat Borna disease virus (BDV) infection on the postnatal development of the brain monoaminergic systems

Effects of neonatal Borna disease virus infection (BDV) on the postnatal development of brain monoaminergic systems in rats were studied. Tissue content of norepinephrine (NE), dopamine (DA) and its metabolite, 3,4-dihydroxyphenol acetic acid (DOPAC), and serotonin (5-HT) and its metabolite, 5-hydroxyindole-3-acetic acid (5-HIAA) were assayed by means of HPLC-EC in frontal cortex, cerebellum, hippocampus, hypothalamus and striatum of neonatally BDV-infected and sham-inoculated male Lewis rats of 8, 14, 21, 60 and 90 days of age. Both NE and 5-HT concentrations were significantly affected by neonatal BDV infection. The cortical and cerebellar levels of NE and 5-HT were significantly greater in BDV-infected rats than control animals at postnatal days (PND) 60 and 90. Tissue content of NE in hippocampus was unaffected. In hippocampus, neonatally BDV-infected rats had lower 5-HT levels at PND 8 and significantly elevated levels at PND 21 and onwards. Neither striatal levels of 5-HT nor hypothalamic levels of 5-HT and NE were affected by neonatal BDV infection, suggesting that the monoamine systems in the prenatally maturing brain regions are less sensitive to effects of neonatal viral infection. 5-HIAA/5-HT ratio was not altered in BDV-infected rats indicating no changes in the 5-HT turnover in the brain regions damaged by the virus. Neither DA nor DOPAC/DA ratio was affected by neonatal BDV infection in any of the brain regions examined. The present data demonstrate significant and specific alterations in monoaminergic systems in neonatally BDV-infected rats. This pattern of changes is consistent with the previously reported behavioral abnormalities resulting from neonatal BDV infection.

Salvage treatment for recurrent squamous cell carcinoma of the oral cavity

BACKGROUND

Squamous cell carcinoma (SCCA) of the oral cavity recurs with a frequency of 25%-48%, a fact that usually portends a poor prognosis. Recent studies have reported salvage cure rates as high as 67%. Investigators have also claimed that restaging recurrent tumors provides useful prognostic information, although this has not been demonstrated with tumors of the oral cavity. The purposes of this study were: (1) to report the patterns of recurrent SCCA of the oral cavity; (2) to examine the benefit of restaging oral cavity tumors, and (3) to compare different treatment modalities in the management of recurrent SCCA of the oral cavity. Materials and Methods Thirty-eight patients who developed recurrent SCCA of the oral cavity were reviewed. Salvage treatment consisted of surgery, chemotherapy, radiation therapy, or a combination of these modalities. Survival analysis was based on the stage of the primary and recurrent tumors and the type of salvage treatment received.

RESULTS

The overall recurrence rate was 28%. Local recurrence was most common (58%) followed by locoregional (27%) and regional recurrence (16%). Patients who recurred more than 6 months after completion of their primary treatment had improved survival compared with those who recurred within 6 months of initial treatment. Individuals with stage I-II primary tumors had significantly improved salvage time and total survival time compared with those with stage III-IV primary tumors (p < 0.005 and p < 0.001). Conversely, the stage of the recurrent tumor was not predictive of either improved salvage time or total survival time. Patients who underwent salvage surgery had significantly improved salvage time and total survival time compared with those who received chemotherapy and/or radiation therapy (p < 0.001 and p < 0.002). The overall salvage cure rate was 21%. Neither the stage of the primary or recurrent tumors nor the type of salvage treatment received significantly correlated with an improved cure rate. However, the group of patients who underwent salvage surgery approached a statistically significant improvement in cure rate (p = 0.08).

CONCLUSIONS

Squamous cell carcinoma of the oral cavity is most likely to recur at the primary site. The stage of the primary tumor is significantly correlated with survival even after recurrence, but the stage of the recurrent tumor is not significantly correlated with survival. Patients most likely to benefit from retreatment are those who (1) have primary tumors stage I-II, (2) recur greater than 6 months after their initial treatment, and (3) develop recurrences that are amenable to salvage surgery.

NBC3 expression in rabbit collecting duct: colocalization with vacuolar H+-ATPase

We have recently cloned and characterized a unique sodium bicarbonate cotransporter, NBC3, which unlike other members of the NBC family, is ethylisopropylamiloride (EIPA) inhibitable, DIDS insensitive, and electroneutral (A. Pushkin, N. Abuladze, I. Lee, D. Newman, J. Hwang, and I. Kurtz. J. Biol. Chem. 274: 16569-16575, 1999). In the present study, a specific polyclonal antipeptide COOH-terminal antibody, NBC3-C1, was generated and used to determine the pattern of NBC3 protein expression in rabbit kidney. A major band of approximately 200 kDa was detected on immunoblots of rabbit kidney. Immunocytochemistry of rabbit kidney frozen sections revealed specific staining of the apical membrane of intercalated cells in both the cortical and outer medullary collecting ducts. The pattern of NBC3 protein expression in the collecting duct was nearly identical to the same sections stained with an antibody against the vacuolar H+-ATPase 31-kDa subunit. In addition, the NBC3-C1 antibody coimmunoprecipitated the vacuolar H+-ATPase 31-kDa subunit. Functional studies in outer medullary collecting ducts (inner stripe) showed that type A intercalated cells have an apical Na+-dependent base transporter that is EIPA inhibitable and DIDS insensitive. The data suggest that NBC3 participates in H+/base transport in the collecting duct. The close association of NBC3 and the vacuolar H+-ATPase in type A intercalated cells suggests a potential structural/functional interaction between the two transporters.

Gastric and duodenal features of meals mediate controls of liquid gastric emptying during fill in rhesus monkeys

To study the dynamics of liquid gastric emptying in rhesus monkeys under conditions that simulated gastric fill during a meal, we measured the gastric emptying of liquid glucose at various concentrations and volumes when administered intragastrically at rates ranging from 12.5 to 37.5 ml/min. Glucose gastric emptying was faster during than following the period of gastric fill. At a single glucose concentration, volume infused rather than the rate of filling determined the volume emptied. Lower glucose concentrations emptied more slowly than physiological saline. As glucose concentration increased, emptying during fill slowed. Duodenal glucose infusions greatly slowed the rate of saline emptying during fill, demonstrating duodenal feedback control. Although casein hydrolosate emptied more rapidly than glucose, the dynamics of volume and concentration dependency and the role of duodenal feedback were similar. These data reveal that both gastric volume and duodenal negative feedback controls important in gastric emptying following stomach filling also contribute to its control during fill.

Inhibition of gastric emptying by bombesin-like peptides is dependent upon cholecystokinin-A receptor activation

The amphibian peptide bombesin (BN) and the related mammalian peptides gastrin-releasing peptide (GRP) and neuromedin B (NMB) inhibit gastric emptying in rats. Exogenous administration of BN stimulates the release of cholecystokinin (CCK), a gastrointestinal peptide that also potently inhibits gastric emptying. To determine whether the inhibition of gastric emptying by BN-like peptides is mediated by a CCK-dependent mechanism, we examined the ability of the CCK-A receptor antagonist, devazepide, to block the inhibition of saline gastric emptying produced by BN, GRP18-27 and NMB. Using the same dosages as in the gastric emptying experiment, we also evaluated the effect of devazepide on feeding suppression produced by systemically administered BN. Our results showed that devazepide completely blocked the suppression of gastric emptying produced by BN, GRP18-27 and NMB but had no effect on BN-induced suppression of food intake. These results suggest that BN-like peptides inhibit gastric emptying through an indirect mechanism that is dependent upon CCK-A receptor activation. In contrast, the suppression of food intake by BN, in this experimental paradigm, is independent of CCK-A receptors.

Mechanisms of HCO(-)(3) secretion in the rabbit connecting segment

The connecting tubule (CNT) contains alpha-(H(+)-secreting) and beta-(HCO(-)(3)-secreting) intercalated cells and is therefore likely to contribute to acid-base homeostasis. To characterize the mechanisms of HCO(-)(3) transport in the rabbit CNT, in which there is little definitive data presently available, we microdissected the segments from the superficial cortical labyrinth, perfused them in vitro, measured net HCO(-)(3) transport (J(HCO(-)(3))) by microcalorimetry, and examined the effects of several experimental maneuvers. Mean +/- SE basal J(HCO(-)(3)) was -3.4 +/- 0.1 pmol. min(-1). mm(-1) (net HCO(-)(3) secretion), and transepithelial voltage was -13 +/- 1 mV (n = 47). Net HCO(-)(3) secretion was markedly inhibited by removal of luminal Cl(-) or application of basolateral H(+)-ATPase inhibitors (bafilomycin or concanamycin), maneuvers that inhibit beta-intercalated cell function. Net HCO(-)(3) secretion was not affected by inhibitors of alpha-intercalated cell function (basolateral Cl(-) removal, basolateral DIDS, or luminal H(+)-ATPase inhibitors). Net HCO(-)(3) secretion was stimulated by isoproterenol and inhibited by acetazolamide. These data indicate that 1) CNTs secrete HCO(-)(3) via an apical DIDS-insensitive Cl(-)/HCO(-)(3) exchanger, mediated by a basolateral bafilomycin- and concanamycin-sensitive H(+)-ATPase; 2) inhibition of cytosolic carbonic anhydrase decreases HCO(-)(3) secretion; and 3) stimulation of beta-adrenergic receptors increases HCO(-)(3) secretion. The failure to influence net HCO(-)(3) transport by inhibiting alpha-intercalated cell apical H(+)-ATPases or basolateral Cl(-)/HCO(-)(3) exchange suggests that the CNT has fewer functioning alpha-intercalated cells than the cortical collecting duct. These are the first studies to examine the rate and mechanisms of HCO(-)(3) secretion by the rabbit CNT; this is clearly an important segment in mediating acid-base homeostasis.

Decreased responsiveness to dietary fat in Otsuka Long-Evans Tokushima fatty rats lacking CCK-A receptors

Adult Otsuka Long-Evans Tokushima fatty (OLETF) rats lack functional cholecystokinin A (CCK-A) receptors, are diabetic, hyperphagic, and obese, and have patterns of ingestion consistent with a satiety deficit secondary to CCK insensitivity. Because dietary fat potently stimulates CCK release, we examined how dietary fat modulates feeding in adult male OLETF rats and their lean [Long-Evans Tokushima (LETO)] controls. High-fat feeding produced sustained overconsumption of high-fat diet (30% corn oil in powdered chow) over a 3-wk period in OLETF but not LETO rats. We then assessed the ability of gastric gavage (5 ml, 1-2 kcal/ml x 15 s) or duodenal preloads (1 kcal/ml, 0.44 ml/min x 10 min) of liquid carbohydrate (glucose), protein (peptone), or fat (Intralipid) to suppress subsequent 30-min 12.5% glucose intake in both strains. In OLETF rats, gastric and duodenal fat preloads were significantly less effective in suppressing subsequent intake than were equicaloric peptone or glucose. These results demonstrate that OLETF rats fail to compensate for fat calories and suggest that their hyperphagia and obesity may stem from a reduced ability to process nutrient-elicited gastrointestinal satiety signals.

Persistent neonatal Borna disease virus (BDV) infection of the brain causes chronic emotional abnormalities in adult rats

Neonatal Borna disease virus (BDV) brain infection results in selective developmental damage to the hippocampal dentate gyrus and the cerebellum. When mature, neonatally BDV-infected rats show extreme locomotor hyperactivity and reduced freezing behavior in novel environments. Traditional interpretation of both of these behavioral abnormalities would suggest decreased anxiety in infected rats compared to normal animals. However, it also possible that the locomotor hyperactivity in infected rats reflects higher rather than reduced anxiety, and is the result of increased escape responses to aversive stimuli. The present experiments were undertaken to test a hypothesis about elevated anxiety in neonatally BDV-infected adult Lewis rats by studying their species-specific fear-related responses. Compared to normal subjects, BDV-infected rats exhibited locomotor hyperactivity and elevated defecation in a highly aversive, brightly lit open field. As expected, in a less aversive, dimly lit open field, uninfected controls increased ambulation, whereas infected rats significantly decreased locomotor activity and defecation. Unlike uninfected rats, BDV-infected rats exhibited an attenuated freezing response immediately after loud auditory stimuli. On the contrary, immediate freezing responses following footshock were comparable in the two groups of animals indicating an intact ability to freeze in BDV-infected rats. Despite a decreased baseline startle responsiveness, BDV-infected rats demonstrated increased sensitization of the startle response by preceding footshocks, suggesting a tendency toward elevated escape responses. Compared to normal subjects, BDV-infected rats showed decreased conditional freezing and elevated conditional defecation response in the context previously paired with aversive stimulation indicating sparing of an autonomic component of fear conditioning. The findings indicate that neonatally BDV-infected adult rats are hyperreactive to aversive stimuli, possibly as a result of chronic emotional abnormalities.

Gut vagal afferent lesions increase meal size but do not block gastric preload-induced feeding suppression

Subdiaphragmatic vagal afferent (SVA) signals arising from gut sites may provide critical feedback for the control of food intake within a meal. To evaluate the role of SVAs in both spontaneous and scheduled meals, food intake was assessed in two paradigms in male Sprague-Dawley rats. In the first study, control (Con) rats (n = 6) and rats with subdiaphragmatic vagal deafferentation (SDA) (n = 7) had 12-h nightly access to Ensure liquid diet (1 kcal/ml). SDA rats had larger and fewer meals and maintained initial rapid rates of licking, yet total numbers of licks were unaffected. In the second study, Con (n = 8) and SDA (n = 7) rats had scheduled access to 12. 5% liquid glucose after overnight food deprivation. Glucose intake was assessed after 5-ml gastric preloads of 0.9% saline or glucose, peptone, and Intralipid solutions at three concentrations (0.5, 1, and 2 kcal/ml). Glucose and peptone preloads suppressed intake similarly in Con and SDA rats, whereas Intralipid was ineffective. These results suggest that meal-related SVA signals 1) are not critical in determining preload-induced feeding suppression after deprivation, yet 2) contribute to satiety during spontaneous meals.

Central leptin modulates behavioral and neural responsivity to CCK

The mechanisms through which leptin, the protein product of the ob gene, affects food intake remain to be determined. To assess whether the actions of leptin depend on modulation of within-meal satiety signals, we measured the effect of third ventricular leptin administration on the satiety actions of CCK. Leptin (10 micrograms) administered 1 h before 30-min access to a liquid diet had no effect on intake when administered alone, but doses of 3.5 or 10 micrograms dose dependently increased the suppression of intake produced by 1 nmol/kg CCK. Examination of patterns of c-Fos activation induced by 3.5 micrograms leptin and 1 nmol/kg CCK revealed that the combination produced significant c-Fos activation within the area postrema and the caudal and medial nucleus of the solitary tract (NST) compared with either leptin or CCK treatments alone. The leptin-CCK combination also resulted in increased c-Fos activation within the paraventricular nucleus of the hypothalamus above that produced by leptin alone. These data suggest that the actions of leptin in food intake are mediated through its ability to modulate responsivity to within-meal satiety signals.

Meal-synchronized CEA in rats: effects of meal size, intragastric feeding, and subdiaphragmatic vagotomy

Within a feeding schedule of intermittent food access, large meals have the ability to induce activity at the same time the next day [circadian ensuing activity (CEA)]. In these experiments, we evaluated the minimum meal size necessary to induce CEA and whether oral-pharyngeal factors and afferent vagal activity played necessary roles in the induction of the underlying process. In experiment 1, every 33 h rats were given two meals separated by a 2-h interval. The size of the first meal was varied, while total intake every feeding cycle was held constant. When the initial meal was <10 g (34 kcal) CEA occurred later, indicating that such a meal size was subthreshold for inducing CEA. In experiment 2, rats were given intragastric (IG) meals every 33 h, before and after complete subdiaphragmatic vagotomy. IG nutrient meals induced CEA, indicating that extensive oral-pharyngeal experience was not necessary for CEA induction. CEA occurred in vagotomized rats but, compared with intact rats, appeared to occur later relative to nutrient infusion, indicating that afferent vagal activity may be sufficient but not necessary to induce CEA.

Postnatal development of carbonic anhydrase IV expression in rabbit kidney

Carbonic anhydrase (CA) IV activity facilitates renal acidification by catalyzing the dehydration of luminal carbonic acid. CA IV has been localized to the proximal tubules and medullary collecting ducts. Maturation of CA IV expression has been considered to be important in the development of renal acid excretion. The purpose of the present study was to determine the maturational expression of CA IV in rabbit kidney. A guinea pig polyclonal antibody to purified rabbit lung microsomal membrane CA IV was generated. Immunoblotting of membrane proteins after peptide-N-glycosidase F treatment revealed two N-glycosylation sites and reduction in size from approximately 52 to 35 kDa; there appeared to be heavier glycosylation in the medulla. In membrane and total proteins from the kidney cortex, CA IV was 15-30% of the adult level during the first 2 wk of life but increased to mature levels by 5 wk of age. The maturational pattern in the cortex was confirmed by measuring SDS-resistant CA hydratase activity. In the medulla, both membrane and total proteins were generally less than one-fourth of the adult level of CA IV during the first 2 wk of life before reaching mature levels by 5 wk of age. Immunohistochemistry showed staining in proximal tubules (apical > basolateral), with maximal label in the S2 segment. CA IV also appeared on the apical membranes of a minority cell type of the cortical collecting duct, presumably the alpha-intercalated cell. Several labeled cells also appeared to be the process of being extruded from medullary collecting ducts of 1- to 2-wk rabbits. The antibody did not reliably detect medullary CA IV expression in sections from mature rabbits. These studies indicate that there is a substantial postnatal increase in expression of CA IV in the maturing kidney in both the cortex and medulla. The disappearance of intercalated cells in the maturing rabbit medullary collecting duct may be part of a normal renal developmental program as previously reported [J. Kim, J.-H. Cha, C. C. Tisher, and K. M. Madsen. Am. J. Physiol. 270 (Renal Fluid Electrolyte Physiol. 39): F575-F592, 1996]. It is likely that the maturation of CA IV expression contributes to the increase in renal acidification observed early in postnatal life.

Interactions between gastric volume and duodenal nutrients in the control of liquid gastric emptying

We examined the relationships between gastric volume and duodenal glucose load in the regulation of gastric emptying in adult male rhesus monkeys. Intragastric glucose loads (0.125 g/ml) of volumes ranging from 150 to 375 ml empty from the stomach at the same rate from 20 to 120 min. However, to achieve these equivalent emptying rates, progressively larger volumes were emptied in the initial 20 min with increasing gastric volume. Duodenal glucose infusions dose dependently inhibited the 10-min emptying of various volumes of intragastric saline. Although increasing gastric volume resulted in increased emptying, duodenal glucose right-shifted the relationship between initial gastric volume and volume emptied. These data demonstrate that liquid nutrient gastric emptying represents an interaction between gastric volume and nutrient-induced duodenal feedback. For controlled duodenal caloric delivery rates to be established, sufficient nutrient emptying must occur to increase the magnitude of duodenal feedback to withhold a given gastric volume.

Viral teratogenesis: brain developmental damage associated with maturation state at time of infection

The rat brain continues to mature after birth and is particularly vulnerable to developmental damage following perinatal insult. Borna disease virus (BDV) infection of postnatal day one (PND-1) rat brain causes a non-encephalitic, persistent infection associated with developmental neuroanatomical and behavioral abnormalities. To test the hypothesis that BDV infection during different brain developmental stages yields variable pathological and clinical disease sequelae, rats were examined for BDV-induced neuroanatomical and behavioral abnormalities following inoculation with BDV on PND-15, and the findings were compared to those resulting from inoculation on PND-1. Similar to rats inoculated with BDV on PND-1, PND-15 inoculated rats developed a persistent infection associated with body weight stunting, abnormal salt taste preference and hippocampal neuron degeneration. However, unlike rats infected with BDV on PND-1, PND-15 inoculated rats did not show signs of cerebellar hypoplasia or hyperactivity. Thus, the risk of BDV-induced damage to specific brain regions, and their associated behaviors, appears, in part, dependent upon the brain's developmental stage at time of BDV-infection. These studies provide evidence of the selective vulnerability of specific neuroanatomic regions and behaviors in developing nervous system to virus-induced damage.

Borna disease virus-induced hippocampal dentate gyrus damage is associated with spatial learning and memory deficits

In neonatally inoculated rats, Borna disease virus (BDV) leads to a persistent infection of the brain in the absence of an inflammatory response and is associated with neuroanatomic, developmental, physiologic, and behavioral abnormalities. One of the most dramatic sites of BDV-associated damage in the neonatal rat brain is the dentate gyrus, a neuroanatomic region believed to play a major role in spatial learning and memory. The absence of a generalized inflammatory response to neonatal BDV infection permits direct effects of viral damage to the dentate gyrus to be examined. In this report, neonatally BDV-infected rats at various stages of dentate gyrus degeneration were evaluated in the Morris water maze, a swimming test that assesses the rats' capacity to navigate by visual cues. Our data demonstrate progressive spatial learning and memory deficits in BDV-infected rats that coincided with a gradual decline in the estimated hippocampal dentate gyrus neuron density.

Adaptation of the outer medullary collecting duct to metabolic acidosis in vitro

Metabolic acidosis in vivo, as well as in vitro (1 h at pH 6.8 followed by 2 h at pH 7.4) stimulates H+-ATPase-dependent H+ secretion in outer medullary collecting ducts from the inner stripe (OMCDi) (S. Tsuruoka and G. J. Schwartz. J. Clin. Invest. 99: 1420-1431, 1997). Another group has shown that the adaptation to metabolic acidosis in vivo is mediated by an apical polarization of H+ pumps without an increase in total H+ pump mRNA or protein (B. Bastani, H. Purcell, P. Hemken, D. Trigg, and S. Gluck. J. Clin. Invest. 88: 126-136, 1991). To further address the mechanism of adaptation, we measured net HCO-3 absorption before and after applying protein/RNA synthesis and signal transduction inhibitors during the 1 h of low pH and a cytoskeletal inhibitor during the entire 3-h incubation. Net HCO-3 transport, measured by microcalorimetry, increased approximately 33% after in vitro acidosis. This increase was prevented by application during the first hour of anisomycin (10 microM) or actinomycin D (4 microM), but not by anisomycin applied during the 2-h incubation at pH 7.4. Similar results were obtained with the cell calcium chelator, 1, 2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester (BAPTA-AM, 20 microM), the calmodulin antagonist, calmidazolium (30 nM), the endoplasmic reticulum Ca-ATPase inhibitor, thapsigargin (100 nM), and the protein kinase C (PKC) inhibitor, staurosporine (100 nM), applied during the 1 h at pH 6.8, but not with BAPTA-AM or thapsigargin used during the 2-h incubation at pH 7. 4. Colchicine (10 microM) applied during the entire 3-h incubation also prevented this adaptive increase in H+ secretion, whereas lumicolchicine (10 microM, the inactive congener) did not. Colchicine also reversibly prevented any adaptive increases in transepithelial positive voltage. Thus the adaptation to acidosis in vitro required RNA and protein synthesis, changes in intracellular calcium and PKC activity, and intact microtubules. Time was required for the adaptation to occur, as the increase in HCO-3 transport was small after <3-h incubation. Protein synthesis and changes in cell calcium were critical during the initial period of low pH but not once the acid stimulus had been removed. Exocytosis of H+ pumps appears to occur continually during the entire 3-h incubation. These data would suggest that the synthesis and regulation of proteins involved in shuttling H+ pumps in cytoplasmic vesicles to the apical membrane via exocytosis are important for the OMCDi to adapt to low pH in vitro and probably to metabolic acidosis in vivo.

Vagal and splanchnic afferents are not necessary for the anorexia produced by peripheral IL-1beta, LPS, and MDP

We investigated the extrinsic gut neural mediation of the suppression of food intake in male Sprague-Dawley rats induced by peripheral intraperitoneal administration of 2 microg/kg interleukin-1beta (IL-1beta), 100 microg/kg bacterial lipopolysaccharide (LPS), and 2 mg/kg muramyl dipeptide (MDP). Food intake during the first 3 and 6 h of the dark cycle was measured in rats with subdiaphragmatic vagal deafferentation (n = 9), celiac superior mesenteric ganglionectomy (n = 9), combined vagotomy and ganglionectomy (n = 9), and sham deafferentation (n = 9). IL-1beta, LPS, and MDP suppressed food intake at 3 and 6 h in all surgical groups. The results demonstrate that neither vagal nor nonvagal afferent nerves from the upper gut are necessary for the feeding-suppressive effects of intraperitoneal IL-1beta, LPS, or MDP in the rat and suggest that peripheral administration of immunomodulators produces anorexia via a humoral pathway.

Duodenal nutrient exposure elicits nutrient-specific gut motility and vagal afferent signals in rat

Volume and chemical characteristics of meals in the gut have been proposed to generate vagal afferent signals that mediate the negative feedback control of ingestion and gastric emptying. Furthermore, duodenal nutrients elicit changes in gastrointestinal motility that may stimulate mechanosensitive vagal afferents. The degree to which the activity of an individual vagal afferent fiber can be modified by moth mechanical and nutrient properties in the gut remains unclear. The present studies evaluated the relationships between distal antral and proximal duodenal load-sensitive vagal afferent activity and gastroduodenal motility in response to duodenal nutrient exposure in ketamine-xylazine-anesthetized rats. Duodenal carbohydrate (glucose) and amino acid (peptone) infusions (0.2 ml/min, 0.2-0.5 kcal/ml) stimulated concentration-dependent increases in 1) antroduodenal contractions and 2) antral and duodenal vagal afferent activity beyond those attributable to osmolarity alone. In addition, duodenal peptone was more effective than equicaloric glucose in eliciting this vagal activity. These data demonstrate that the proximal duodenum can discriminate its nutrient chemical contents and that gastroduodenal load-sensitive vagal afferents indirectly transduce nutrient chemical information.

Diagnosis and treatment of renal tubular disorders

There is a wide variety of renal tubular disorders affecting children. Understanding the pathophysiology of each disease assists in the recognition and treatment of these diseases, which can have profound effects on a child's growth and development. We review some of the more common tubular disorders found in children, emphasizing those conditions in which recent advances have been made in understanding of the specific genetic or physiological defect responsible: Fanconi's syndrome, cystinuria, renal tubular acidosis, and the hypokalemic metabolic alkaloses. Current recommendations are presented for diagnosing and treating these conditions.

Disordered food intake and obesity in rats lacking cholecystokinin A receptors

Otsuka Long-Evans Tokushima Fatty (OLETF) rats develop obesity, hyperglycemia, and non-insulin-dependent diabetes mellitus and do not express cholecystokinin A (CCK-A) receptors, the receptor subtype mediating the satiety actions of CCK. In short-term feeding tests, male OLETF rats were completely resistant to exogenous CCK, and their response to bombesin was attenuated. Comparisons of liquid meal consumption in OLETF and control Long-Evans Tokushima (LETO) rats demonstrated that 1) OLETF rats had greater intakes during 30-min scheduled daytime meals and significantly larger and fewer spontaneous night-time meals and 2) although the initial rates of licking were the same, OLETF rats maintained the initial rate longer and the rate at which their licking declined was slower. In 24-h solid food access tests, OLETF rats consumed significantly more pellets than LETO controls, and this increase was attributable to significant increases in meal size. Together, these data are consistent with the interpretation that the lack of CCK-A receptors in OLETF rats results in a satiety deficit leading to increases in meal size, overall hyperphagia, and obesity.

Carbonic anhydrase II and IV mRNA in rabbit nephron segments: stimulation during metabolic acidosis

Carbonic anhydrase (CA) facilitates renal bicarbonate reabsorption and acid excretion. Cytosolic CA II catalyzes the buffering of intracellular hydroxyl ions by CO2, whereas membrane-bound CA IV catalyzes the dehydration of carbonic acid generated from the secretion of protons. Although CA II and IV are expressed in rabbit kidney, it is not entirely clear which segments express which isoforms. It was the purpose of this study to characterize the expression of CA II and CA IV mRNAs by specific segments of the nephron using semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) and to determine the effect of chronic metabolic acidosis on CA expression by those segments. Individual nephron segments (usually 1-2 mm) were isolated by microdissection and subjected to RT-PCR. Amplification was performed simultaneously for CA IV, CA II, and malate dehydrogenase (MDH), a housekeeping gene. The intensities of the PCR products were quantitated by densitometry. CA IV mRNA was expressed by S1 and S2 proximal tubules and by outer medullary collecting duct from inner stripe (OMCDi) and outer stripe and initial inner medullary collecting duct (IMCDi). CA II mRNA was expressed by S1, S2, and S3 proximal tubules, thin descending limb, connecting segment (CNT), and all collecting duct segments. Acid loading induced CA IV mRNA expression in S1 and S2 proximal tubules and in OMCDi and IMCDi. CA II mRNA was induced by acidosis in all three proximal segments and nearly all distal segments beginning with CNT. No upregulation of MDH mRNA expression occurred. These adaptive increases in CA II and IV mRNAs are potentially important in the kidney's adaptation to chronic metabolic acidosis.

Load-sensitive rat gastric vagal afferents encode volume but not gastric nutrients

To assess nutrient sensitivity in a population of gastric load-sensitive vagal afferents, their neurophysiological activity was examined in anesthetized rats with inflated pyloric cuffs after gastric infusion of a range of volumes of nutrient and equiosmotic saline solutions. Responses to physiological saline loads (1, 2, 4, and 8 ml) were compared with responses elicited by the same volume range of carbohydrate (12.5% glucose), protein (12.5% peptone), and equiosmotic hypertonic (750 mosM) saline. The threshold load volume of physiological saline required to increase gastric vagal afferent activity was 1 ml. Thereafter, there was a dose-dependent relationship between increasing gastric volume and firing rate and between gastric volume and pressure. The dose-response relationships elicited by glucose, peptone, and equiosmotic hypertonic saline loads did not differ from those elicited by physiological saline loads. These data identify a population of gastric load-sensitive vagal afferents unresponsive to the chemical composition of gastric contents and are consistent with a role for vagal gastric volume signals but not gastric nutrient content in the negative feedback control of ingestion.