An Overview of Rodent Models of Obesity and Type 2 Diabetes.

Many animal models that are currently used in appetite and obesity research share at least some main features of human obesity and its comorbidities. Hence, even though no animal model replicates all aspects of "common" human obesity, animal models are imperative in studying the control of energy balance and reasons for its imbalance that may eventually lead to overt obesity. The most frequently used animal models are small rodents that may be based on mutations or manipulations of individual or several genes and on the exposure to obesogenic diets or other manipulations that predispose the animals to gaining or maintaining excessive weight. Characteristics include hyperphagia or changes in energy metabolism and at least in some models the frequent comorbidities of obesity, like hyperglycemia, insulin resistance, or diabetes-like syndromes. Some of the most frequently used animal models of obesity research involve animals with monogenic mutations of the leptin pathway which in fact are useful to study specific mechanistic aspects of eating controls, but typically do not recapitulate "common" obesity in the human population. Hence, this review will mention advantages and disadvantages of respective animal models in order to build a basis for the most appropriate use in biomedical research.

The Quinpirole Hypolocomotive Effects are Strain and Route of Administration Dependent in SHR and SLA16 Isogenic Rats.

The SHR and SLA16 inbred strains present behavioral differences in anxiety/emotionality that could be under the influence of dopaminergic neurotransmission. In order to investigate the role of D2 receptors in modulating such differences, an agonist (quinpirole) and an antagonist (haloperidol) of this receptor were administered, either via systemic injection (IP), or microinjected into the ventral area of the hippocampus (vHIP). Quinpirole and haloperidol IP decreased locomotor activity, only in SLA16 rats in the open-field (OF), and in both strains in the elevated plus-maze (EPM). Quinpirole also increased the preference for the aversive areas of the EPM. Quinpirole vHIP decreased locomotor activity in both strains. Haloperidol vHIP did not elicit behavioural changes and no differences in the levels of D2 receptors and of dopamine transporter in the hippocampus were found. Results indicate that systemic activation/blocking of D2 receptors caused a strain-dependent hypolocomotion, whereas activation of D2 receptors in the vHIP, but not D2 receptor antagonism, regardless of dose, decreased general locomotor activity in the two strains. Therefore, we suggest that genomic differences in the chromosome 4 can influence the locomotor activity regulated by the D2 dopaminergic receptor, especially in the vHIP.

Altered expression of GABAA receptors (α4, γ2 subunit), potassium chloride cotransporter 2 and astrogliosis in tremor rat hippocampus.

Impaired GABAergic inhibitory neurotransmission plays an essential role in the pathogenesis of epilepsy. GABA(A) receptor (GABA(A)R), potassium chloride cotransporter 2 (KCC2) and astrocytes are of particular importance to GABAergic transmission and thus involved in the development of increased seizure susceptibility. The tremor rat (TRM: tm/tm), a genetic mutant discovered in a Kyoto-Wistar colony, can manifest both absence-like seizures and tonic convulsions without any external stimuli. So far, there are no reports that can elucidate the effects of GABA(A)R (α4, γ2 subunit), KCC2 and astrocytes on TRMs. The present study was undertaken to detect the expressions of GABA(A)R α4, GABA(A)R γ2 and KCC2 in TRMs hippocampus at mRNA and protein levels. In this work, mRNA and protein expressions of GABA(A)R α4 were significantly elevated while GABA(A)R γ2 and KCC2 were both evidently decreased in TRMs hippocampus by real-time RT-PCR and western blot, respectively. Furthermore, a dramatic elevation of KCC2 protein level was found after cerebroventricular injection with K252a to TRMs than that in the DMSO-treated TRMs. Besides, our present study also demonstrated that GFAP (a major component of astrocyte) immunoreactivity was much more intense in TRMs hippocampal CA1, CA3 and DG regions than that in control group with immnohistochemistry and confocal microscopic analyses. The protein expression of GFAP was also markedly elevated in TRMs hippocampus, suggesting that astrogliosis appeared in the TRM model. These data demonstrate that altered expressions of GABA(A)R (α4, γ2) and KCC2 and astrogliosis observed in TRMs hippocampus may provide us good therapeutic targets for the treatment of genetic epilepsy.

Receptor fingerprinting the circling ci2 rat mutant: insights into brain asymmetry and motor control.

Circling behaviour of the ci2 rat mutant, a model for hyperkinetic movement disorders, is associated with an abnormal asymmetry in striatal dopaminergic activity. Since it is more likely that imbalances in several neurotransmitter systems result in the cascade of neurochemical disturbances underlying disorders involving motor dysfunctions, we measured the densities of 12 neurotransmitter receptors in the basal ganglia and vestibular nuclei of adult circling mutants (ci2/ci2), non-circling littermates (ci2/+) and controls from the background strain (LEW/Ztm). In controls, the left caudate putamen (CPu) contains lower kainate and the left globus pallidus higher AMPA densities than their right counterparts. The medial vestibular nucleus of mutants ipsilateral to the preferred direction of rotation contained higher M2 densities than the contralateral one. ci2/+ animals presented no interhemispheric differences, did not differ behaviourally from controls, but contained lower GABAA densities in the CPu, nucleus accumbens (Acb) and reticular (Rt), ventromedial (VM) and ventral posterolateral (VPL) thalamic nuclei. Mutants contained lower GABAA (CPu, Acb, Rt, VPL) but higher nicotinic (Rt, VM) densities than controls and higher GABAA (CPu, VM) densities than ci2/+ rats. Hyperactivity level of mutants was positively correlated with the adenosine A2A receptor densities in the ipsilateral Acb, but negatively correlated with those of the ipsilateral thalamus. Concluding, ci2/ci2 mutants show alterations in GABAA, cholinergic and A2A receptor densities. Our data add to the hypothesis that motor disorders such as hyperkinesias cannot be explained solely by absolute functional increases or decreases in the dopaminergic system, but are due to imbalances in several neurotransmitter systems.

Upregulation of brain expression of P-glycoprotein in MRP2-deficient TR(-) rats resembles seizure-induced up-regulation of this drug efflux transporter in normal rats.

PURPOSE: The multidrug resistance protein 2 (MRP2) is a drug efflux transporter that is expressed predominantly at the apical domain of hepatocytes but seems also to be expressed at the apical membrane of brain capillary endothelial cells that form the blood-brain barrier (BBB). MRP2 is absent in the transport-deficient (TR(-)) Wistar rat mutant, so that this rat strain was very helpful in defining substrates of MRP2 by comparing tissue concentrations or functional activities of compounds in MRP2-deficient rats with those in transport-competent Wistar rats. By using this strategy to study the involvement of MRP2 in brain access of antiepileptic drugs (AEDs), we recently reported that phenytoin is a substrate for MRP2 in the BBB. However, one drawback of such studies in genetically deficient rats is the fact that compensatory changes with upregulation of other transporters can occur. This prompted us to study the brain expression of P-glycoprotein (Pgp), a major drug efflux transporter in many tissues, including the BBB, in TR(-) rats compared with nonmutant (wild-type) Wistar rats. METHODS: The expression of MRP2 and Pgp in brain and liver sections of TR(-) rats and normal Wistar rats was determined with immunohistochemistry, by using a novel, highly selective monoclonal MRP2 antibody and the monoclonal Pgp antibody C219, respectively. RESULTS: Immunofluorescence staining with the MRP2 antibody was found to label a high number of microvessels throughout the brain in normal Wistar rats, whereas such labeling was absent in TR(-) rats. TR(-) rats exhibited a significant up-regulation of Pgp in brain capillary endothelial cells compared with wild-type controls. No such obvious upregulation of Pgp was observed in liver sections. A comparable overexpression of Pgp in the BBB was obtained after pilocarpine-induced seizures in wild-type Wistar rats. Experiments with systemic administration of the Pgp substrate phenobarbital and the selective Pgp inhibitor tariquidar in TR(-) rats substantiated that Pgp is functional and compensates for the lack of MRP2 in the BBB. CONCLUSIONS: The data on TR(-) rats indicate that Pgp plays an important role in the compensation of MRP2 deficiency in the BBB. Because such a compensatory mechanism most likely occurs to reduce injury to the brain from cytotoxic compounds, the present data substantiate the concept that MRP2 performs a protective role in the BBB. Furthermore, our data suggest that TR(-) rats are an interesting tool to study consequences of overexpression of Pgp in the BBB on access of drugs in the brain, without the need of inducing seizures or other Pgp-enhancing events for this purpose.

Identification and distribution of aspartoacylase in the postnatal rat brain.

Aspartoacylase metabolizes N-acetylaspartic acid to produce L-aspartate and acetate. An aspartoacylase deficiency in humans is responsible for Canavan disease, a lethal autosomal recessive leukodystrophy. The role of aspartoacylase in the mammalian brain is unclear. Here we have generated and characterized a highly specific polyclonal antibody against aspartoacylase which recognizes a 37 kDa monomer and a dimer in normal but not in aspartoacylase-deficient rat tissue. Aspartoacylase protein expression sharply increases at P14, peaks at P28 and plateaus thereafter. Biochemical analysis reveals immunoreactivity in cytosolic but not in membrane fractions. Histologically, most abundant expression was observed in white matter tracts and thalamus. On the cellular level, aspartoacylase immunoreactivity is restricted to oligodendrocyte somata in both white and gray matter.

Production of knockout rats using ENU mutagenesis and a yeast-based screening assay.

The rat is a widely used model in biomedical research and is often the preferred rodent model in many areas of physiological and pathobiological research. Although many genetic tools are available for the rat, methods to produce gene-disrupted knockout rats are greatly needed. In this study, we developed protocols for creating N-ethyl-N-nitrosourea (ENU)-induced germline mutations in several rat strains. F1 preweanling pups from mutagenized Sprague Dawley (SD) male rats were then screened for functional mutations in Brca1 and Brca2 using a yeast gap-repair, ADE2-reporter truncation assay. We produced knockout rats for each of these two breast cancer suppressor genes.

Vulnerability of monoaminergic neurons in the brainstem of the zitter rat in oxidative stress.

In the monograph of Santiago Ramon y Cajal, he provided a detailed description about the morphological changes in degeneration and regeneration of peripheral and central nervous systems following lesions. He discussed factors that may promote or inhibit axonal growth after peripheral and/or central nerve injury. Cajal with a brilliant insight anticipated the existence of several factors acting on degeneration and regeneration. Free radicals have been proposed to be one of such factors. These highly reactive oxygen species-derived free radicals play a pathogenetic role in neurological disorders, including ischemia, trauma, Alzheimer's disease and Parkinson's disease (PD). In this review we will discuss the similarities and differences between the morphological changes under oxidant stress and Cajal's drawings of degeneration and regeneration following the central injury. The monoaminergic neuron systems in the brainstem appear vulnerable to these free radicals, which have also been implicated in the selective degeneration of the nigrostriatal DA system. We analyzed the degeneration of fibers and the neuronal cell death of brainstem monoaminergic neuron systems in a mutant rat, which has abnormal metabolism of oxygen species in the brain. The degeneration of DA cell bodies and fibers was characterized by swollen varicosities and clustered fibers.

Normotopic and heterotopic cortical representations of mystacial vibrissae in rats with subcortical band heterotopia.

The tish rat is a neurological mutant exhibiting bilateral cortical heterotopia similar to those found in certain epileptic patients. Previous work has shown that thalamocortical fibers originating in the ventroposteromedial nucleus, which in normal animals segregate as 'barrel' representations for individual whiskers, terminate in both normotopic and heterotopic areas of the tish cortex (Schottler et al., 1998). Thalamocortical innervation terminates as barrels in layer IV and diffusely in layer VI of the normotopic area. Discrete patches of terminals are also observed in the underlying heterotopic area suggesting that representations of individual vibrissa may be present in the heterotopic somatosensory areas. The present study examines this issue by investigating the organization of the vibrissal somatosensory system in the tish cortex. Staining for cytochrome oxidase or Nissl substance reveals a normal complement of vibrissal barrels in the normotopic area of the tish cortex. Dense patches of cytochrome oxidase staining are also found in the underlying lateral portions of the heterotopic area (i.e. the same area that is innervated by the ventroposteromedial nucleus). Injections of retrograde tracers into vibrissal areas of either the normotopic or heterotopic area produce topographically organized labeling of neurons restricted to one or a small number of barreloids within the ventroposteromedial nucleus of the thalamus. Physical stimulation of a single whisker (D3 or E3) elicits enhanced uptake of [(14)C]2-deoxyglucose in restricted zones of both the normotopic and heterotopic areas, demonstrating that single whisker stimulation can increase functional activity in both normotopic and heterotopic neurons. These findings indicate that the barrels are intact in the normotopic area and are most consistent with the hypothesis that at least some of the individual vibrissae are 'dually' represented in normotopic and heterotopic positions in the primary somatosensory areas of the tish cortex.

Auditory and vestibular defects in the circling (ci2) rat mutant.

The circling rat is an autosomal recessive mutant (homozygous ci2/ci2) that displays lateralized circling behaviour, locomotor hyperactivity, ataxia and stereotypic head-movement. These abnormal behaviours occur in phases or bursts either spontaneously or in response to stress. Heterozygous (ci2/+) littermates display normal spontaneous behaviours. We have previously found that ci2/ci2 rats of both genders have a lower tissue content of dopamine in the striatum ipsilateral to the preferred direction of rotation, indicating that the rats turn away from the brain hemisphere with higher striatal dopaminergic activity. In view of the similarities of the motor syndrome of the ci2/ci2 mutant rat to that of mouse deafness mutants, the present study evaluated the hearing ability of the circling rat mutant by recording brainstem auditory-evoked potentials. To test for vestibular dysfunction, a swimming test was conducted. Histological methods were used to examine the cochlear and vestibular parts of the inner ear and the cochlear and vestibular brainstem nuclei for defects. The absence of auditory-evoked potentials demonstrated a complete hearing loss in the adult ci2/ci2 mutant rat, whereas heterozygous littermates exhibited auditory-evoked potentials with thresholds resembling those of other laboratory strains. Furthermore, the mutant rats were unable to swim. Histological analysis of the inner ear of adult mutants revealed virtually complete loss of the cochlear neuroepithelium, while no such hair cell degeneration was seen in the vestibular parts of the inner ear. However, part of the vestibular hair cells showed protrusions into the endolymphatic space, suggesting alterations in the cytoskeletal architecture. The histological findings in mutant circling rats strongly indicate that the hearing loss of the mutants is of the sensory neural type, the most prevalent type of hearing loss. In the cochlear nuclei of the brain stem of mutant rats, neurons exhibited an abnormal shape, reduced size and increased density compared to controls. In contrast, no abnormal neuronal morphology was seen in the vestibular nuclei, but a significantly reduced neuronal density was found in the medial vestibular nucleus. Abnormal vestibular function would be a likely explanation for the disturbed balance of mutant rats as exemplified by the ataxia and the inability to swim, whereas the previous data on these rats strongly indicate an involvement of the basal ganglia in the abnormal circling behaviour. The genetic defect in the mutant rats, thus, results in a clinical syndrome with features also seen in human genetic disorders with deafness and hyperkinesia, making the ci2/ci2 rat an excellent model for investigating both cochlear/vestibular dysfunction and hyperkinetic movement disorders.

Differential impact of predator or immobilization stressors on central corticotropin-releasing hormone and bombesin-like peptides in Fast and Slow seizing rat.

Lines of rats selectively bred for amygdala excitability, as reflected by kindling rates in response to electrical stimulation, also exhibit differences in tests of anxiety. Inasmuch as corticotropin-releasing hormone (CRH) and bombesin (BN) have been associated with anxiety, regional levels and release of these peptides, as well as plasma adrenocorticotropic hormone (ACTH) and corticosterone, were assessed in 'Slow' and 'Fast' seizing rats following predator exposure (ferret) or immobilization. Ferret exposure elicited a greater increase of plasma ACTH and corticosterone concentrations in the Slow than in the Fast rats. In contrast, immobilization provoked a greater rise of plasma ACTH levels in the Fast rats, paralleling the vigorous struggling observed in this line. In Slow rats, stressor exposure elicited increased levels of ir-BN at the anterior hypothalamus, and increased ir-CRH at the median eminence/arcuate nucleus (Me/Arc), paraventricular hypothalamic nucleus (PVN) and pituitary (Pit), whereas decreased levels of ir-BN were found at the nucleus tractus solitarius (NTS). Fast rats likewise showed decreased ir-BN at the NTS, but unlike the Slow rats, ir-CRH was reduced in the Me/Arc, PVN and Pit in response to both stressors. In vivo microdialysis experiments revealed that in response to ferret exposure, the Slow rats showed a greater CRH release at the central nucleus of the amygdala (CeA) as compared to Fast rats. However, immobilization elicited a more pronounced release of CRH in Fast than in Slow rats. Taken together, the results demonstrate that these two lines of rats show differential endocrinological and neurochemical response patterns to these stressors.

Selective myelin defects in the anterior medullary velum of the taiep mutant rat.

The taiep rat is a myelin mutant in which initial hypomyelination is followed by progressive demyelination of the CNS. An in vitro study suggests that accumulation of microtubules within oligodendrocytes is the cause of the taiep myelin defects (Song et al., 1999). In this article, we analyze microtubule accumulation in relation to taiep myelin defects in vivo in the anterior medullary velum (AMV), a CNS tissue that enables entire oligodendrocyte units to be resolved. Immunohistochemical analysis demonstrated notably high levels of beta-tubulin and the microtubule associated protein tau in the somata and processes of taiep oligodendrocytes. This was correlated with markedly reduced expression of the myelin proteins, proteolipid protein (PLP), myelin basic protein (MBP), 2',3 -cyclic nucleotide 3'-phosphodiesterase, and both large (L) and small (S) isoforms of myelin-associated glycoprotein (MAG). Moreover, PLP and L-MAG, which are dependent on the microtubule system for intracellular transport, accumulated in the perinuclear cytoplasm of the taiep oligodendrocyte. The myelin deficit was most marked in the area of the AMV populated by the small somata oligodendrocytes that have fine long processes that support numerous myelin sheaths of small diameter axons. Type III/IV oligodendrocytes, which have large somata and short processes that support a small number of myelin sheaths of large diameter axons, were also affected to a certain degree in compact myelin sheath formation. These results support the hypothesis that myelin loss and oligodendrocyte disruption in the taiep mutant result from a defect in the microtubule system that transports myelin components from the somata to the myelin sheath.

The pck rat: a new model that resembles human autosomal dominant polycystic kidney and liver disease.

BACKGROUND: The pck rat is a recently identified model of polycystic kidney disease (PKD) and liver disease (PLD) that developed spontaneously in the rat strain Crj:CD/SD. Its pattern of inheritance is autosomal recessive. METHODS: To characterize this new model, we studied pck rats derived from F9 breeding pairs from Charles River Japan and control Sprague-Dawley rats. Blood and tissues (kidneys, liver, and pancreas), obtained from these rats at 1, 7, 21, 70, and 182 days of age, were used for biochemical determinations, light and electron microscopy, and immunohistochemistry. RESULTS: The pck rats develop progressive cystic enlargement of the kidneys after the first week of age, and liver cysts are evident by day 1. The renal cysts developed as a focal process from thick ascending loops of Henle, distal tubules, and collecting ducts in the corticomedullary region and outer medulla. Flat and polypoid epithelial hyperplasia were common in dilated tubules and cysts. Apoptosis was common and affected normal, as well as dilated tubules, but less frequently cysts lined by flat epithelium. The basement membranes of the cyst walls exhibited a variety of alterations, including thinning, lamellation, and thickening. Focal interstitial fibrosis and inflammation were evident by 70 days of age. Segmental glomerulosclerosis and segmental thickening of the basement membrane with associated effacement of the podocyte foot processes were noted in some rats at 70 days of age. The PKD was more severe in male than in female pck rats, as reflected by the higher kidney weights, while there was no gender difference in the severity of the PLD. Mild bile duct dilation was present as early as one day of age. With age, it became more severe, and the livers became markedly enlarged. Even then, however, there was only a mild increase in portal fibrosis, without formation of fibrous septae. Slight elevations of plasma blood urea nitrogen levels were detected at 70 and 182 days of age. CONCLUSIONS: The pck rat is a new inherited model of PKD and PLD with a natural history and renal and hepatic histologic abnormalities that resemble human autosomal dominant PKD. This model may be useful for studying the pathogenesis and evaluating the potential therapies for PKD and PLD. The identification of the pck gene may provide further insight into the pathogenesis of autosomal dominant PKD.

Impaired nitric oxide production in coronary endothelial cells of the spontaneously diabetic BB rat is due to tetrahydrobiopterin deficiency.

Endothelial cells (EC) from diabetic BioBreeding (BB) rats have an impaired ability to produce NO. This deficiency is not due to a defect in the constitutive isoform of NO synthase in EC (ecNOS) or alterations in intracellular calcium, calmodulin, NADPH or arginine levels. Instead, ecNOS cannot produce sufficient NO because of a deficiency in tetrahydrobiopterin (BH(4)), a cofactor necessary for enzyme activity. EC from diabetic rats exhibited only 12% of the BH(4) levels found in EC from normal animals or diabetes-prone animals which did not develop disease. As a result, NO synthesis by EC of diabetic rats was only 18% of that for normal animals. Increasing BH(4) levels with sepiapterin increased NO production, suggesting that BH(4) deficiency is a metabolic basis for impaired endothelial NO synthesis in diabetic BB rats. This deficiency is due to decreased activity of GTP-cyclohydrolase I, the first and rate-limiting enzyme in the de novo biosynthesis of BH(4). GTP-cyclohydrolase activity was low because of a decreased expression of the protein in the diabetic cells.

Increased H2O2, vascular endothelial growth factor and receptors in the retina of the BBZ/Wor diabetic rat.

Hyperglycemia in diabetes induces increased levels of hydrogen peroxide (H2O2), a reactive oxygen species generated by reduced nicotinamide adenine dinucleotide (NADH) oxidase. Nontoxic levels of H2O2 increase endothelial cell permeability. Using a model of non-insulin-dependent diabetes, the BBZ/Wor rat, we investigated retinal levels of H2O2, vascular endothelial growth factor (VEGF) and its receptors, VEGF-R1 and VEGF-R2 by transmission electron microscopy at sites of the blood-retinal barrier (BRB). H2O2 localization was done by the cerium NADH oxidase method, and extravasation of endogenous serum albumin was used to document disruption of the BRB. Higher levels of H2O2 were detected in blood vessels of diabetic (78.7 +/- 4.84%) as compared with vessels from nondiabetic rats (39.0 +/- 4.47%). VEGF immunoreactivity was statistically higher in the inner BRB (24.67 +/- 0.33 colloidal gold particles/63 microm2 vs. 21.52 +/- 0.43 colloidal gold particles/63 microm2, p = .0001) and outer BRB (42.56 +/- 0.45 colloidal gold particles/63 microm2 vs. 15.51 +/- 0.51 colloidal gold particles/63 microm2, p = .0001) of diabetic rats as compared with age matched nondiabetic control rats. VEGF-R1 immunoreactivity was significantly higher in diabetic retinas in both the inner BRB (21.66 +/- 0.75 colloidal gold particles/63 microm2 vs. 12.69 +/- 0.61 colloidal gold particles/63 microm2, p = .0001) and outer BRB (22.76 +/- 2.36 colloidal gold particles/63 microm2 vs. 8.53 +/- 2.67 colloidal gold particles/63 microm2, p = .0013). VEGF-R2 was statistically higher in the inner BRB (8.97 +/- 0.57 colloidal gold particles/63 microm2 versus 7.03 +/- 0.65 colloidal gold particles/63 microm2, p = .0419) but not in the outer BRB (29.42 +/- 1.25 colloidal gold particles/63 microm2 vs. 28.07 +/- 1.42 colloidal gold particles/63 microm2, p = .4889). H2O2 levels correlated with increased VEGF (correlation coefficient = 0.82, p = .001) in this model of nonproliferative diabetic retinopathy. These results support that hyperglycemia is one factor that induces retinal endothelial cells in vivo to increase H2O2 via NADH oxidase and stimulates increases in VEGF resulting in disruption of the BRB.

Effect of repeated seizure experiences on tyrosine hydroxylase immunoreactivities in the brain of genetically epilepsy-prone rats.

The genetically epilepsy-prone rat (GEPR) is a model of generalized tonic/clonic epilepsy, and has functional noradrenergic deficiencies that act as partial determinants for the seizure predisposition and expression. The present study investigated the effect of repeated seizure experiences by acoustic stimulation (110 dB, 10 times) on the immunoreactivities of tyrosine hydroxylase (TH), a rate-determining enzyme in the synthesis of norepinephrine, in brain regions of GEPRs. TH immunoreactivity in locus coeruleus, the major noradrenergic nucleus in brain, was lower in GEPRs than control Sprague-Dawley rats. It was also decreased in several regions including inferior colliculus of GEPRs. Repeated experiences of audiogenic seizures further decreased TH immunoreactivities in locus coeruleus and inferior colliculus of GEPRs. The results from the present study suggest that the lower immunoreactivities of TH in locus coeruleus and inferior colliculus contribute, at least in part, to the noradrenergic deficits in GEPRs, and repeated seizure experiences further intensified these noradrenergic deficits, which may be related to the altered seizure expression by repetitive audiogenic seizure in GEPRs.

Different pathways of canalicular secretion of sulfated and non-sulfated fluorescent bile acids: a study in isolated hepatocyte couplets and TR- rats.

BACKGROUND/AIMS: Fluorescent bile acids have proved useful for characterizing bile salt transport mechanisms. The aim of this study was to further validate the use of lysyl-fluorescein conjugated bile acid analogues as surrogate bile acids. METHODS: We analyzed biliary excretion kinetics of cholyl lysyl fluorescein (CLF), lithocholyl lysyl fluorescein (LLF) and sulfo-lithocholyl lysyl fluorescein (sLLF), both in the isolated rat hepatocyte couplet model and in TR- rats with a selective canalicular transport defect of non-bile acid organic anions. RESULTS: CLF and LLF, which like their natural nonsulfated bile acid congeners are expected to be handled by the canalicular bile salt export pump, were transferred into the bile canaliculus much faster than sLLF, a putative substrate for the canalicular multispecific organic anion transporter in both the in vivo and the in vitro models employed. The contention that different transport systems are involved in sulfated and non-sulfated lysyl fluorescein conjugated bile acids biliary excretion was supported further by studies using TR- rats, in which the cumulative biliary excretion of sLLF was reduced to 6% as compared with that of normal Wistar rats, in good agreement with values for its naturally-occurring radiolabeled parent compound sulfoglycolithocholate. In contrast, CLF and LLF were reduced to 66% and 52%, similar values to these for their congeners, [14C] glycocholate and [14C] lithocholate. CONCLUSION: The close similarity in behavior of lysyl fluorescein conjugated bile acids to that of their naturally-occurring parent compounds in these different models gives support for both sulfated and nonsulfated lysyl fluorescein conjugated bile acids as substitute molecules for studies of bile acid transport.

Cellular distribution of iron in the brain of the Belgrade rat.

In this study, we investigated the cellular distribution of iron in the brain of Belgrade rats. These rats have a mutation in Divalent Metal Transporter 1, which has been implicated in iron transport from endosomes. The Belgrade rats have iron-positive pyramidal neurons, but these are fewer in number and less intensely stained than in controls. In the white matter, iron is normally present in patches of intensely iron-stained oligodendrocytes and myelin, but there is dramatically less iron staining in the Belgrade rat. Those oligodendrocytes that stained for iron did so strongly and were associated with blood vessels. Astrocytic iron staining was seen in the cerebral cortex for both normal rats and Belgrade rats, but the iron-stained astrocytes were less numerous in the mutants. Iron staining in tanycytes, modified astrocytes coursing from the third ventricle to the hypothalamus, was not affected in the Belgrade rat, but was affected by diet. The results of this study indicate that Divalent Metal Transporter 1 is important to iron transport in the brain. Iron is essential in the brain for basic metabolic processes such as heme formation, neurotransmitter production and ATP synthesis. Excess brain iron is associated with a number of common neurodegenerative diseases. Consequently, elucidating the mechanisms of brain iron delivery is critical for understanding the role of iron in pathological conditions.

Elevated neuropeptide Y and corticotropin-releasing factor in the brain of a novel epileptic mutant rat: Noda epileptic rat.

Noda epileptic rat (NER) is a new epileptic rat strain, which was developed by inbreeding rats with spontaneous tonic-clonic seizures in a stock of Crj:Wistar. In the present study, possible changes of two neuropeptides, neuropeptide Y (NPY) and corticotropin-releasing factor (CRF), in the brains of NER were investigated. Increased contents of immunoreactive (IR) NPY were found in the striatum and amygdala of 8-week NERs with partial seizure, while these changes extended to the limbic region including hippocampus in 16-week NERs with fully developed generalized tonic-clonic seizure. IR-CRF were elevated only in the entorhinal and pyriform cortex of both 8-week and 16-week NERs. Generalized tonic-clonic seizure in NERs induced a transient increase of NPY mRNA in the granular layer of dentate gyrus. These results suggest that NPY metabolism in the limbic brain contributes to the seizure susceptibility in this model of epilepsy.

Abnormal expression of SNS/PN3 sodium channel in cerebellar Purkinje cells following loss of myelin in the taiep rat.

Using in situ hybridization and immunochemical methods, we have observed an increase in the expression of SNS/PN3 sodium channel mRNA and protein in cerebellar Purkinje cells of the taiep rat. These changes are present in taiep rats at 12 months of age, following loss of myelin, but not at one month, prior to loss of myelin. Increased SNS/PN3 expression is not associated with aging per se, because it was not observed in control rats at 12 months of age. These results suggest that altered sodium channel expression in Purkinje cells may contribute to the ataxia that occurs in taiep rats.