A genotype-dependent hippocampal dynorphinergic mechanism controls mouse exploration

Revealing potential lipid biomarkers in clear cell renal cell carcinoma using targeted quantitative lipidomics

BACKGROUND

The high drug resistance and metabolic reprogramming of clear cell renal cell carcinoma (ccRCC) are considered responsible for poor prognosis. In-depth research at multiple levels is urgently warranted to illustrate the lipid composition, distribution, and metabolic pathways of clinical ccRCC specimens.

METHODS

In this project, a leading-edge targeted quantitative lipidomic study was conducted using 10 pairs of cancerous and adjacent normal tissues obtained from ccRCC patients. Accurate lipid quantification was performed according to a linear equation calculated using internal standards. Qualitative and quantitative analyses of lipids were performed with multiple reaction monitoring analysis based on ultra-performance liquid chromatography (UPLC) and mass spectrometry (MS). Additionally, a multivariate statistical analysis was performed using data obtained on lipids.

RESULTS

A total of 28 lipid classes were identified. Among them, the most abundant were triacylglycerol (TG), diacylglycerol (DG), phosphatidylcholine (PC), and phosphatidylethanolamine (PE). Cholesteryl ester (CE) was the lipid exhibiting the most considerable difference between normal samples and tumor samples. Lipid content, chain length, and chain unsaturation of acylcarnitine (CAR), CE, and DG were found to be significantly increased. Based on screening for variable importance in projection scores ≥1, as well as fold change limits between 0.5 and 2, 160 differentially expressed lipids were identified. CE was found to be the most significantly upregulated lipid, while TG was observed to be the most significantly downregulated lipid.

CONCLUSION

Based on the absolute quantitative analysis of lipids in ccRCC specimens, it was observed that the content and change trends varied in different lipid classes. Upregulation of CAR, CE, and DG was observed, and analysis of changes in the distribution helped clarify the causes of lipid accumulation in ccRCC and possible carcinogenic molecular mechanisms. The results and methods described herein provide a comprehensive analysis of ccRCC lipid metabolism and lay a theoretical foundation for cancer treatment.

Criteria for validating mouse models of psychiatric diseases

Animal models of human diseases are in widespread use for biomedical research. Mouse models with a mutation in a single gene or multiple genes are excellent research tools for understanding the role of a specific gene in the etiology of a human genetic disease. Ideally, the mouse phenotypes will recapitulate the human phenotypes exactly. However, exact matches are rare, particularly in mouse models of neuropsychiatric disorders. This article summarizes the current strategies for optimizing the validity of a mouse model of a human brain dysfunction. We address the common question raised by molecular geneticists and clinical researchers in psychiatry, "what is a 'good enough' mouse model"?

Behavioural and physiological characterization of inbred mouse strains: prospects for elucidating the molecular mechanisms of mammalian learning and memory

With the advent of recombinant DNA methodology, it has become possible to dissect the molecular mechanisms of complex traits, including brain function and behaviour. The increasing amount of available information on the genomes of mammalian organisms, including our own, has facilitated this research. The present review focuses on a somewhat neglected area of genetics, one that involves the study of inbred mouse strains. It is argued that the use of inbred mice is complementary to transgenic approaches in the analysis of molecular mechanisms of complex traits. Whereas transgenic technology allows one to manipulate a single gene and investigate the in vivo effects of highly specific, artificially induced mutations, the study of inbred mouse strains should shed light on the roles of naturally occurring allelic variants in brain function and behaviour. Systematic characterization of the behavioural, electrophysiological, neurochemical, and neuroanatomical properties of a large number of inbred strains is required to elucidate mechanisms of mammalian brain function and behaviour. In essence, a 'mouse phenome' project is needed, entailing the construction of databases to investigate possible causal relationships amongst the phenotypical characteristics. This review focuses on electrophysiological and behavioural characterization of mouse strains. Nevertheless, it is emphasized that the full potential of the analysis of inbred mouse strains may be attained if techniques of numerous disciplines, including gene expression profiling, biochemical analysis, and quantitative trait loci (QTL) mapping, to name but a few, are also included.

Basal levels and alcohol-induced changes in nociceptin/orphanin FQ, dynorphin, and enkephalin levels in C57BL/6J mice

In order to investigate the involvement of the opioid and nociceptin/orphanin FQ (N/OFQ) system in alcohol drinking behaviour, N/OFQ and the opioid peptides dynorphin B (DYNB) and Met-enkephalin-Arg(6) Phe(7) (MEAP) were examined in the alcohol-preferring C57BL/6J mice. Basal peptide levels were compared in the brain and the pituitary gland with basal levels in the alcohol-avoiding DBA/2J mice. Furthermore, the effects of chronic alcohol self-administration on peptides were studied in the C57BL/6J mice. Compared to the DBA/2J mice, C57BL/6J mice had low immunoreactive (ir) levels of DYNB and MEAP in the nucleus accumbens, the hippocampus, and the substantia nigra, low ir-DYNB levels in the striatum and low ir-MEAP levels in the frontal cortex. Higher ir-DYNB levels in the pituitary gland and in the periaqueductal gray (PAG) and higher ir-N/OFQ levels in the frontal cortex and in the hippocampus were detected in C57BL/6J mice compared to the DBA/2J mice. After 4 weeks of voluntary alcohol consumption, only minor changes in steady-state peptide levels were identified. However, 5 days after the alcohol-drinking period, lower levels of all peptides were detected in the ventral tegmental area and ir-DYNB levels were also lower in the amygdala and in the substantia nigra. Twenty-one days after cessation of alcohol self-administration, the opioid peptides in alcohol-consuming C57BL/6J mice were lower in the PAG, the N/OFQ was lower in the frontal cortex and DYNB was higher in the amygdala and substantia nigra as compared to control C57BL/6J mice. This study demonstrates strain differences between C57BL/6J mice and DBA/2J mice that could contribute to divergent drug-taking behaviour, and it also demonstrates time- and structure-specific changes in neuropeptide levels after alcohol self-administration in the C57BL/6J mice.

Variation in hippocampal dynorphin b-immunoreactive mossy fiber terminal fields of apomorphine-(un)susceptible rats

The size of distinct hippocampal sub-fields were measured in the apomorphine-susceptible and apomorphine-unsusceptible rat lines. Mossy fiber terminal fields were delineated using dynorphin B immunoreactivity and area measurements were taken from (1) the supra-pyramidal mossy fiber terminal field; (2) the intra- and infra-pyramidal mossy fiber terminal field; (3) the hilus of the fascia dentata (4) the non dynorphin B immunoreactive area of the regio inferior and fascia dentata and (5) the total area of regio inferior and fascia dentata. The data indicate that statistically significant differences in the morphometry of the hippocampal subfields of the apomorphine susceptible and unsusceptible rats are confined to the intra- and infra terminal field: the relative size of the left and right intra- and infra terminal field of apomorphine unsusceptible rats are significantly larger than those of the apomorphine susceptible rats. These data explain at least in part the differential response of these rats to novelty.

Genetic analysis of anxiety-related behaviors and responses to benzodiazepine-related drugs in AXB and BXA recombinant inbred mouse strains

Recombinant inbred (RI) strains derived from the C57BL/6J and A/J mouse strains were used for behavioral studies designed to estimate the number and location of chromosomal loci responsible for anxiety-related behaviors and differential sensitivity to agonists and inverse agonists of the gamma-aminobutyric acidA (GABAA)/benzodiazepine receptor complex. The phenotypes of the parental inbred strains and of 28 RI strains were characterized for the number of transitions in the light<-->dark exploratory model, anxiolytic response to diazepam, vertical and ambulatory activities in an open field, and sensitivity to the convulsant properties of methyl-beta-carboline-3-carboxylate (beta-CCM). The strain distribution patterns and estimates of the minimal number of loci obtained for each trait suggest that multiple chromosomal loci contribute to differences in anxiety-related behavioral phenotypes and the behavioral responses to diazepam and beta-CCM between C57BL/6J and A/J mice. The best probabilities of linkage were found between the variables characterizing response to diazepam and loci on chromosomes 1 (Xmv-41) and 10 (D10Mit2) and between the sensitivity to the convulsant actions of beta-CCM and locus D15Mit5 on chromosome 15.

Effects of adrenal steroid manipulations and repeated restraint stress on dynorphin mRNA levels and excitatory amino acid receptor binding in hippocampus

Adrenal steroid and stress effects were determined in hippocampus on levels of dynorphin (DYN) mRNA, expressed in dentate gyrus, and excitatory amino acid receptors, measured in Ammon's horn and dentate gyrus. Adrenalectomy (ADX) decreased DYN mRNA levels in dentate gyrus and replacement with aldosterone (ALDO), a specific type I adrenal steroid receptor agonist, prevented the decrease. Ru28362, a specific type II receptor agonist, had no effect. Likewise, kainate receptor binding to the stratum lucidum and hilus region of dorsal hippocampus was decreased after ADX and this decrease was prevented by ALDO but not by Ru28362 treatment. Similar though smaller effects were found for CNQX binding to AMPA receptors but only in the dentate gyrus molecular or infra- and supragranular layers. Although corticosterone (CORT) treatment of intact rats (40 mg/kg for 3 weeks) elevated DYN mRNA levels in dentate gyrus, up to 14 days of daily restraint stress (1 or 6 h/day) had no significant effect. Neither CORT treatment nor repeated restraint stress altered NMDA and non-NMDA glutamate receptors in hippocampus. The results of this study showing ADX-induced decreases of DYN mRNA and CNQX binding in dentate gyrus and decreased kainate binding in mossy fiber terminal regions are consistent with morphological evidence showing that adrenal steroids maintain normal integrity and structure of dentate gyrus neurons and do so via type I adrenal steroid receptors. These same parameters are apparently not sensitive to chronic restraint stress although the effects of other stressors must be examined.

Characterization of benzodiazepine-sensitive behaviors in the A/J and C57BL/6J inbred strains of mice

Exploratory behaviors as well as pharmacological actions of gamma-aminobutyric acidA (GABAA)/benzodiazepine receptor agonists and inverse agonists were characterized in C57BL/6J and A/J strains of mice. C57BL/6J mice displayed higher levels of exploratory behavior than A/J mice in the light in equilibrium with dark exploration model of anxiety and in an open-field test, suggesting that C57BL/6J mice are less "emotional" and more active than A/J mice, respectively. However, C57BL/6J mice were more sensitive than A/J mice to the anxiolytic effects of diazepam in the light in equilibrium with dark exploration model. In contrast, A/J mice were more sensitive than C57BL/6J mice to the convulsant effects of methyl-beta-carboline-3-carboxylate. C57BL/6J mice showed no evidence of acquisition of a passive avoidance task, while A/J readily acquired this memory task at low levels of footshock. C57BL/6J and A/J mice should be useful parental strains in recombinant inbred lines for investigating the genetic determinants of benzodiazepine-sensitive behaviors and sensitivity to drugs acting on the GABAA/benzodiazepine receptor complex.

Repeated ethanol administration decreases prodynorphin biosynthesis in the rat hippocampus

The effect of single and repeated (19 days) intragastric ethanol administration on prodynorphin mRNA and alpha-neoendorphin levels in the hippocampus of the rat was studied using in situ hybridization and RIA methods, respectively. Single ethanol administration had no effect on either of these two parameters. Repeated ethanol administration decreased both immunoreactive (ir) alpha-neoendorphin (by ca. 37%) and prodynorphin mRNA (by ca. 57%) levels. Two days after the last dose of ethanol no changes in the ir-alpha-neoendorphin tissue content were found, whereas the level of prodynorphin mRNA remained decreased (by ca. 44%). These results suggest that repeated ethanol evokes a long-lasting decrease in the biosynthesis of hippocampal prodynorphin, this effect that may play some role in the ethanol-induced deficiency of neuronal functions.

A genetic-correlational study of hippocampal neurochemical variation and variation in exploratory activities of mice

Previously, we have demonstrated that hippocampal mossy fibers, containing the opioid peptide dynorphin B, are functionally connected with the gene-dependent exploratory behavior of mice. In order to seek further evidence of causal relationships between dynorphin B action and exploration, a quantitative-genetic method was chosen. For this purpose, mice from the inbred strains C57BL/6, DBA/2, BLN, and CPB-K were used. By means of radioimmunoassay, the hippocampal level of dynorphin B was monitored in mice that had been exposed to environmental novelty, as compared to naive animals. Clear evidence was obtained that novelty induces the release of hippocampal dynorphin B. Furthermore, low tissue content was found to be causally connected with high exploratory scores.

Genetic control of hippocampal cholinergic and dynorphinergic mechanisms regulating novelty-induced exploratory behavior in house mice

Neurobehavioral genetics endeavors to trace the pathways from genetic and environmental determinants to neuroanatomical and neurophysiological systems and, thence, to behavior. Exploiting genetic variation as a tool, the behavioral sequelae of manipulating these neuronal systems by drugs and antisera are analyzed. Apart from research in rats, this paper deals mainly with the genetically-influenced regulation in mice of exploratory behaviors that are adaptive in novel surroundings and are hippocampally-mediated. Special attention is paid to neuropeptidergic, GABAergic, and cholinergic synaptic functions in the mouse hippocampus. The behaviorally different inbred mouse strains C57BL/6 and DBA/2 show opposite reactions (reductions and increases, respectively, in exploration rates) to peripheral and intrahippocampal injections with agents that interfere with peptidergic, cholinergic, and GABAergic neurotransmission. These findings can be explained by an interdependent over-release of opioids, arrested GABA release, and excess acetylcholine in the hippocampal neuronal network of DBA/2 mice, as compared to C57BL/6 mice where these systems are functionally well balanced. Very similar results have been obtained with the lines SRH and SRL, derived from C57BL/6 and DBA/2, and genetically selected for rearing behavior. Most probably, the opioids act to disinhibit exploratory responses. An additional genetic approach is mentioned, in which four inbred mouse strains and one derived heterogeneous stock are used for estimating genetic correlations between structural properties of the hippocampal mossy fibers and levels of hippocampal dynorphin B, on the one hand, and frequencies of exploratory responses to environmental novelty, on the other.

Distribution of dynorphin B and methionine-enkephalin in the mouse hippocampus: influence of genotype

Immunohistochemical techniques were used to localize dynorphin B and methionine-enkephalin in the mouse hippocampus. Methionine-enkephalin-like immunoreactivity was found within the somata of interneurons distributed mainly in and around the CA1 stratum pyramidale and stratum granulosum as well as in the mossy fibers. Dynorphin B appeared to be confined to the mossy fiber pathway. In addition, we observed a difference between the inbred mouse strains DBA/2 and C57BL/6 with regard to the areas of the dynorphinergic mossy fiber projections: the intra- and infrapyramidal terminal fields were larger in the latter group.