Characteristic Features of the Transcriptome in a Rat Strain with Audiogenic Epilepsy

Audiogenic epilepsy (AE), developing in rodent strains in response to sound, is widely used as the model of generalized convulsive epilepsy, while the molecular mechanisms determining AE are currently poorly understood. The brain region that is crucial for AE development isthe inferior and superior colliculi (IC, SC). We compared IC-SC gene expression profiles in rats with different AE susceptibility using transcriptome analysis.The transcriptomes were obtained from the IC-SC of Wistar rats (with no AE), Krushinsky-Molodkina (KM) strain rats (100% AE susceptible), and ”0” strain rats (with no AE) selected from F2 KM x Wistar hybrids for AE absence. KM gene expression displayed characteristic differences inboth of the strains that were not susceptible to AE. There was increased expression of a number of genes responsible for positive regulation of the MAPK signaling cascade, as well as of genes responsible for the production of interferon and several other cytokines. An increase in the expression levels of theTTR gene was found in KM rats, as well as significantly lower expression of the Msh3 gene (involved in post-replicative DNA repair systems). AE was also describedin the 101/HY mouse strain with a mutation in the locus controlling DNA repair. The DNA repair system defects could be the primary factor leading to the accumulation of mutations, which, in turn, promote AE. Keywords: udiogenic seizure, KM strain, transcriptome, TTR gene, Msh3 gene, DNA repair

The Role of Trait Impulsivity and Novelty-Seeking as Predisposing Factors to the Acquisition and Reinstatement of MDMA Self-Administration

<p>It has been suggested that the response to novelty and impulsivity predict the latency to acquisition and maintenance of drug self-administration, respectively. The aim of this thesis was to examine the relationship between these two traits and (1) the latency to acquisition and (2) maintenance (drug seeking) of 3,4-methylenedioxymethamphetamine (MDMA) self–administration. Impulsivity, measured as premature responding on the 5-choice serial reaction time task (5-CSRTT), and novelty seeking, measured as the locomotor response in a novel environment, were measured prior to self-administration. Due to characteristics of the rat strain and test equipment the 5-CSRTT was configurated in the first part of this study and modified from the standard version. Following training in this task animals were implanted with a siliastic catheter and were subsequently screened for their response to a novel environment prior to MDMA self-administration. Latency to acquisition was determined as the number of test sessions required to self-administer an initial criterion of 90 infusions of 1.0 mg/kg/infusion as well as an additional 150 infusions of 0.5 mg/kg/infusion MDMA. For some rats, the ability of MDMA (0, 5.0 or 10.0 mg/kg, IP) to produce drug seeking was subsequently measured and for others, impulsivity was again measured following self-administration. Novelty seeking predicted cocaine self-administration but was not significantly correlated with either the acquisition or drug-seeking measures of MDMA self-administration. Impulsivity was not significantly correlated with the latency to acquire self-administration of MDMA but was significantly and positively correlated with the magnitude of MDMA produced drug-seeking. Furthermore, MDMA self-administration produced a number of notable, but transient, deficits in the 5-CSRTT; there was an increase in omission rate and a delayed increase in premature responses in particular. These findings suggest that impulsivity, but not sensation seeking, might be a risk factor for the development of compulsive drug-seeking following withdrawal from MDMA self-administration. A surprising finding from this study was a high acquisition rate amongst rats that acquired the 5-CSRTT prior to self-administration. This difference was examined in a separate set of experiments. This effect could not be explained by an effect of handling, food restriction, or exposure to sweetened condensed milk and might possibly be due to differences in instrumental learning.</p>

The Role of Trait Impulsivity and Novelty-Seeking as Predisposing Factors to the Acquisition and Reinstatement of MDMA Self-Administration

<p>It has been suggested that the response to novelty and impulsivity predict the latency to acquisition and maintenance of drug self-administration, respectively. The aim of this thesis was to examine the relationship between these two traits and (1) the latency to acquisition and (2) maintenance (drug seeking) of 3,4-methylenedioxymethamphetamine (MDMA) self–administration. Impulsivity, measured as premature responding on the 5-choice serial reaction time task (5-CSRTT), and novelty seeking, measured as the locomotor response in a novel environment, were measured prior to self-administration. Due to characteristics of the rat strain and test equipment the 5-CSRTT was configurated in the first part of this study and modified from the standard version. Following training in this task animals were implanted with a siliastic catheter and were subsequently screened for their response to a novel environment prior to MDMA self-administration. Latency to acquisition was determined as the number of test sessions required to self-administer an initial criterion of 90 infusions of 1.0 mg/kg/infusion as well as an additional 150 infusions of 0.5 mg/kg/infusion MDMA. For some rats, the ability of MDMA (0, 5.0 or 10.0 mg/kg, IP) to produce drug seeking was subsequently measured and for others, impulsivity was again measured following self-administration. Novelty seeking predicted cocaine self-administration but was not significantly correlated with either the acquisition or drug-seeking measures of MDMA self-administration. Impulsivity was not significantly correlated with the latency to acquire self-administration of MDMA but was significantly and positively correlated with the magnitude of MDMA produced drug-seeking. Furthermore, MDMA self-administration produced a number of notable, but transient, deficits in the 5-CSRTT; there was an increase in omission rate and a delayed increase in premature responses in particular. These findings suggest that impulsivity, but not sensation seeking, might be a risk factor for the development of compulsive drug-seeking following withdrawal from MDMA self-administration. A surprising finding from this study was a high acquisition rate amongst rats that acquired the 5-CSRTT prior to self-administration. This difference was examined in a separate set of experiments. This effect could not be explained by an effect of handling, food restriction, or exposure to sweetened condensed milk and might possibly be due to differences in instrumental learning.</p>

Proceedings of the 2021 National Toxicology Program Satellite Symposium

The 2021 annual National Toxicology Program (NTP) Satellite Symposium, entitled “Pathology Potpourri,” was the 20th anniversary of the symposia and held virtually on June 25th, in advance of the Society of Toxicologic Pathology’s 40th annual meeting. The goal of this symposium was to present and discuss challenging diagnostic pathology and/or nomenclature issues. This article presents summaries of the speakers’ talks along with select images that were presented to the audience for voting and discussion. Various lesions and topics covered during the symposium included differentiation of canine oligodendroglioma, astrocytoma, and undefined glioma with presentation of the National Cancer Institute’s updated diagnostic terminology for canine glioma; differentiation of polycystic kidney, dilated tubules and cystic tubules with a discussion of human polycystic kidney disease; a review of various rodent nervous system background lesions in control animals from NTP studies with a focus on incidence rates and potential rat strain differences; vehicle/excipient-related renal lesions in cynomolgus monkeys with a discussion on the various cyclodextrins and their bioavailability, toxicity, and tumorigenicity; examples of rodent endometrial tumors including intestinal differentiation in an endometrial adenocarcinoma that has not previously been reported in rats; a review of various rodent adrenal cortex lesions including those that represented diagnostic challenges with multiple processes such as vacuolation, degeneration, necrosis, hyperplasia, and hypertrophy; and finally, a discussion of diagnostic criteria for uterine adenomyosis, atypical hyperplasia, and adenocarcinoma in the rat.

A Novel circRNA Highlights a Path to Cardiac Hypertrophy in Spontaneously Hypertensive Rats.

BackgroundCardiac hypertrophy can be considered a maladaptive response which in many cases results in heart failure and sudden death. Genetic predisposition to cardiac hypertrophy is ill-defined, but current research has given credence to a role of non-protein-coding RNAs in the development of cardiac hypertrophy.ResultsWe used microarrays, RNA-Seq and quantitative genetics with the spontaneously hypertensive, SHR (SHR/OlaIpcv) rat strain, the normotensive Brown Norway (BN-Lx/Cub) rat strain, and a recombinant inbred (RI) panel of rats (HXB/BXH) derived from these strains to examine the areas of the genome associated with cardiac hypertrophy. We identified circular (circ) RNAs coded within these areas. Of the 122 differentially expressed circRNAs in left ventricle of SHR and BN-Lx rats, three were transcribed from areas corresponding to the QTLs we identified for cardiac hypertrophy using the HXB/BXH rat panel. We then identified microRNAs which are “sponged” by the circ RNAs and the mRNAs which are destabilized by the microRNAs. 265 miRNAs could be identified as targets for the three circRNAs. We focused on the four miRNAs that were also differentially expressed between SHR and BN-Lx rats. One of the miRNAs (Mir-210-5p) was a target of the differentially expressed circ H2afy and circ H2afy was located within the QTL on Chr 17 (genome wide p-value = 0.011). Mir-210-5p has a binding site on the 3’ UTR of DR6, which is differentially expressed and in turn controls the expression level of NFκB. NFκB is an important component of the oxidative stress response leading to hypertrophy.ConclusionsOur work identified a novel circRNA that may be the mediator of a cascade of events that influence a cardiac hypertrophy phenotype. The circRNA and miRNA which we identified may become useful as markers of the risk for cardiac hypertrophy.

New homozygous gpt delta transgenic rat strain improves an efficiency of the in vivo mutagenicity assay

Background Gene mutation assays in transgenic rodents are useful tools to investigate in vivo mutagenicity in a target tissue. Using a lambda EG10 transgene containing reporter genes, gpt delta transgenic mice and rats have been developed to detect point mutations and deletions. The transgene is integrated in the genome and can be rescued through an in vitro packaging reaction. However, the packaging efficiency is lower in gpt delta rats than in mice, because of the transgene in gpt delta rats being heterozygous and in low copy number. To improve the packaging efficiency, we herein describe a newly developed homozygous gpt delta rat strain. Results The new gpt delta rat has a Wistar Hannover background and has been successfully maintained as homozygous for the transgene. The packaging efficiency in the liver was 4 to 8 times higher than that of existing heterozygous F344 gpt delta rats. The frequency of gpt point mutations significantly increased in the liver and bone marrow of N-nitroso-N-ethylurea (ENU)- and benzo[a]pyrene (BaP)-treated rats. Spi− deletion frequencies significantly increased in the liver and bone marrow of BaP-treated rats but not in ENU-treated rats. Whole genome sequencing analysis identified ≥ 30 copies of lambda EG10 transgenes integrated in rat chromosome 1. Conclusions The new homozygous gpt delta rat strain showed a higher packaging efficiency, and could be useful for in vivo gene mutation assays in rats.

A rat model for retinitis pigmentosa with rapid retinal degeneration enables drug evaluation in vivo

Background Although retinitis pigmentosa (RP) is most frequently studied in mouse models, rats, rabbits, and pigs are also used as animal models of RP. However, no studies have reported postnatal photoreceptor cell loss before complete development in these models. Here, we generated a transgenic rat strain, named the P347L rat, in which proline at position 347 in the rhodopsin protein was replaced with leucine. Results A pathological analysis of photoreceptor cells in the P347L rat model was performed, and drugs with potential use as therapeutic agents against RP were investigated. The data clearly showed rapid degeneration and elimination of the outer nuclear layer even before the photoreceptor cells were fully established in P347L rats. To test the usefulness of the P347L rat in the search for new therapeutic agents against RP, the effects of rapamycin on RP were investigated in this rat strain. The findings suggest that rapamycin promotes autophagy and autophagosomal uptake of the rhodopsin that has accumulated abnormally in the cytoplasm, thereby alleviating stress and delaying photoreceptor cell death. Conclusions In this RP model, the time to onset of retinal degeneration was less than that of previously reported RP models with other rhodopsin mutations, enabling quicker in vivo evaluation of drug efficacy. Administration of rapamycin delayed the photoreceptor cell degeneration by approximately 1 day.

Abnormal neonatal sodium handling in skin precedes hypertension in the SAME rat

We discovered high Na+ and water content in the skin of newborn Sprague–Dawley rats, which reduced ~ 2.5-fold by 7 days of age, indicating rapid changes in extracellular volume (ECV). Equivalent changes in ECV post birth were also observed in C57Bl/6 J mice, with a fourfold reduction over 7 days, to approximately adult levels. This established the generality of increased ECV at birth. We investigated early sodium and water handling in neonates from a second rat strain, Fischer, and an Hsd11b2-knockout rat modelling the syndrome of apparent mineralocorticoid excess (SAME). Despite Hsd11b2−/− animals exhibiting lower skin Na+ and water levels than controls at birth, they retained ~ 30% higher Na+ content in their pelts at the expense of K+ thereafter. Hsd11b2−/− neonates exhibited incipient hypokalaemia from 15 days of age and became increasingly polydipsic and polyuric from weaning. As with adults, they excreted a high proportion of ingested Na+ through the kidney, (56.15 ± 8.21% versus control 34.15 ± 8.23%; n = 4; P < 0.0001), suggesting that changes in nephron electrolyte transporters identified in adults, by RNA-seq analysis, occur by 4 weeks of age. Our data reveal that Na+ imbalance in the Hsd11b2−/− neonate leads to excess Na+ storage in skin and incipient hypokalaemia, which, together with increased, glucocorticoid-induced Na+ uptake in the kidney, then contribute to progressive, volume contracted, salt-sensitive hypertension. Skin Na+ plays an important role in the development of SAME but, equally, may play a key physiological role at birth, supporting post-natal growth, as an innate barrier to infection or as a rudimentary kidney.

Differential Expression of Sphingolipid Metabolizing Enzymes in Spontaneously Hypertensive Rats: A Possible Substrate for Susceptibility to Brain and Kidney Damage

Alterations in the metabolism of sphingolipids, a class of biologically active molecules in cell membranes with direct effect on vascular homeostasis, are increasingly recognized as important determinant in different vascular disorders. However, it is not clear whether sphingolipids are implicated in the pathogenesis of hypertension-related cerebrovascular and renal damage. In this study, we evaluated the existence of possible abnormalities related to the sphingolipid metabolism in the brain and kidneys of two well validated spontaneously hypertensive rat strains, the stroke-prone (SHRSP) and the stroke-resistant (SHRSR) models, as compared to the normotensive Wistar Kyoto (WKY) rat strain. Our results showed a global alteration in the metabolism of sphingolipids in both cerebral and renal tissues of both hypertensive strains as compared to the normotensive rat. However, few defects, such as reduced expression of enzymes involved in the metabolism/catabolism of sphingosine-1-phosphate and in the de novo biosynthetic pathways, were exclusively detected in the SHRSP. Although further studies are necessary to fully understand the significance of these findings, they suggest that defects in specific lipid molecules and/or their related metabolic pathways may likely contribute to the pathogenesis of hypertensive target organ damage and may eventually serve as future therapeutic targets to reduce the vascular consequences of hypertension.