Low-excitability Rats Research Articles

The influence of the long-term emotional pain stress on the methylation of histone H3 in the cells of the hippocampus and amygdala of rats with different excitability of the nervous system

We performed an immunohistochemical study of histone H3 methylation at lysine 4 (H3K4medi+ tri) in the neurons of the hippocampus (CA3 area) and basolateral amygdala in rats with different levels of nervous system excitability under normal conditions and at different time points (24 hours, 2 weeks, and 2 months) after long-term emotional pain stress (LEPS). We found higher immunoreactivity of cells in both brain structures under normal conditions in the control groups of low-excitability rats of the HT strain in comparison with high-excitability rats of the LT strain. We describe the structural and temporal patterns of the influence of long-term emotional pain stress on the level of histone H3 methylation (K4), which depend on the excitability of the nervous system of the examined strains.

Kainate Receptors in the Hippocampus of Rats of Strains Differing in Terms of the Level of Nervous System Excitability

Glutamate receptors in the CNS play an important role in mediating the mechanisms of differential adaptation to environmental conditions. Currently, kainate receptors (KR) are the best studied in terms of structural-functional characteristics, in both health and disease. Thus, the aims of the present work were: 1) to study the distribution and content of GluR 5/6/7 KR subunits; 2) to study their changes in the pyramidal layer of the hippocampus of rats of strains with genetically determined differences in levels of nervous system excitability on exposure to transient emotional-painful stressors; 3) to assess the sensitivity of hippocampal pyramidal neurons to the actions the KR agonist kainic acid. GluR 5/6/7-containing KR were found to be located predominantly in hippocampal field CA2, with higher levels in low-excitability rats than in high-excitability animals. Transient emotional-pain stress led to increases in the quantity of KR in hippocampal field CA2 in high-excitability rats only. Pyramidal neurons in various hippocampal fields were found to show selective sensitivity to the action of kainic acid, depending on the strain characteristics of the animals’ nervous system excitability.

Neuron density in the hippocampus in rat strains with contrasting nervous system excitability after prolonged emotional-pain stress

A model system consisting of two rat strains bred for nervous system excitability in response to electric shocks was used to study changes in the number density of neurons in hippocampal field CA3 at 24 h, two weeks, and two and six months after prolonged emotional-pain stress (PEPS). Neuron density in hippocampal field CA3 decreased after completion of PEPS. These changes arose at different time points in the different rat strains (one day for low-excitability rats, two months for high-excitability rats) and persisted to six months. Thus, this is the first demonstration that persistent differential effects of stress on the number density of neurons in hippocampal field CA3, which plays an important role in learning and memory processes, depend on genetically determined constitutive characteristics of the nervous system.

A classical Mendelian cross-breeding study of the Naples high and low excitability rat lines

The development of brain and behaviour is controlled by the interaction of genetic determinants and environmental factors. To study genetic determinants, model systems such as the Naples rat lines, i.e. Naples high (NHE) and low excitability (NLE), are useful. They have been selectively bred for divergent behaviour arousal to novelty. Aim of this study was to assess the extent of the genetic control of the selection trait. Thus adult albino rats of NHE and NLE lines have been used throughout. According to a classical Mendelian cross-breeding design, a first experiment was carried out with hybrids obtained from parental lines P1 (NHE) and P2 (NLE) as F1, F2 and related backcrosses B1 (F1 × P1) and B2 (F1 × P2). Young adults (60–80 days) offspring of both gender were exposed separately for two 10 min tests to a spatial novelty (Lát-maze). To verify a possible sex link of the trait, a second experiment was carried out adding to the Mendelian cross design parental gender. Behavioural variables were horizontal (corner-crossings: HA), vertical (rearings on hindlimbs: VA) or total activity (HVA: HA + VA) scores. The heritability of HVA trait was estimated across the 20 generations of selection and Mendelian cross hybrids. Quantitative-genetic analysis on this trait and its HA and VA components, was applied by the Lynch and Walsh joint-scaling test procedure to evaluate underlying genetic mechanism. The correlation between experimental data of hybrids and estimated values from different heritability models were also computed. Results indicated that (i) the activity scores by Mendelian hybrids were intermediate between the two parental lines and were also graded; (ii) there was no sex effect on the heritability of trait but only a general tendency of females to higher activity levels; (iii) the heritability of HVA trait was very high ( h 2 index = 0.824); (iv) heritability model of HVA and HA trait was polygenic with a marked epistatic control where as VA trait was fitted by simpler model with less genes and lower epistatic effect. In conclusion the Naples lines reveal strong genetic determinants for behavioural traits associated with polygenic pattern. Moreover, HA and VA activity components with prevailing cognitive and non-cognitive meaning, respectively, show differential genetic control.

The Naples High- and Low-Excitability rats: selective breeding, behavioral profile, morphometry, and molecular biology of the mesocortical dopamine system.

The Naples High- (NHE) and Low-Excitability (NLE) rat lines have been selected since 1976 on the basis of behavioral arousal to novelty (Làt-maze). Selective breeding has been conducted under continuous genetic pressure, with no brother-sister mating. The behavioral analyses presented here deal with (1) activity in environments of different complexity, i.e., holeboard and Làt maze; (2) maze learning in hexagonal tunnel, Olton, and Morris water mazes and; (3) two-way active avoidance and conditioned taste aversion tests. Morphometric analyses deal with central dopaminergic systems at their origin and target sites, as well as the density of dopamine transporter immunoreactivity. Molecular biology analyses are also presented, dealing with recent experiments on the prefrontal cortex (PFc), cloning and identifying differentially expressed genes using subtractive libraries and RNAase protection. The divergence between NLE and NHE rats varies as a function of the complexity level of the environment, with an impaired working and reference memory in both lines compared to random bred (NRB) controls. Moreover, data from the PFc of NHE rats show a hyperdopaminergic innervation, with overexpression of mRNA species involved in basal metabolism, and down-regulation of dopamine D1 receptors. Altogether, the evidence gathered so far supports a hyperfunctioning mesocorticolimbic system that makes NHE rats a useful tool for the study of hyperactivity and attention deficit, learning and memory disabilities, and drug abuse.

Network operations revealed by brain metabolic mapping in a genetic model of hyperactivity and attention deficit: the Naples high- and low-excitability rats

Genetic rat models are important for research on the neural networks of attention and emotionality. Naples-High Excitability (NHE) rats and Naples Low-Excitability (NLE) rats were investigated with random-bred (NRB) rats as controls. These rat lines were named for their respective behavior on spatial novelty tasks. Quantitative cytochrome oxidase (CO) histochemistry has been demonstrated to reflect long-lasting changes in tissue metabolic capacity. CO metabolic differences between the NLE and NHE were found in the granular cell layer of the outer blade of the dentate gyrus. In addition, NLE showed greater CO activity than NRB in medial frontal cortex, and lower activity in perirhinal cortex (dorsal region). NHE showed greater CO activity than NRB in entorhinal cortex (superficial layers) and lower activities in perirhinal cortex and cortical amygdala. These data support the hypothesis that NLE/NHE rats may be an appropriate model for studying genetically altered limbic regions related to impaired emotional processing. The results support the involvement of limbic circuits in attentive processes and impulsiveness, and support the use of the NLE and NHE strains as animal models of Attention Deficit Hyperactivity Disorder (ADHD) in children.

NMDA and non-NMDA sensitive [ l- 3H] glutamate receptor binding in the brain of the Naples high- and low-excitability rats: an autoradiographic study

The Naples high-excitability (NHE) and low-excitability (NLE) rat lines, selectively bred for high and low activity in a Làt maze, respectively, are used as an animal model in the study of hippocampal functions. The aim of this study was to investigate the anatomical distribution of N-methyl- d-aspartate (NMDA) and non-NMDA sensitive [ 3H]glutamate receptor binding by quantitative autoradiography in the brain of the NHE and NLE rats with a randomly bred line (NRB) as controls. Twenty-micron-thick cryostat sagittal sections were incubated at 4°C with 150 nM [ l- 3H]glutamate alone or in the presence of 100 μM NMDA or 2.5 μM quisqualate (QA). Non-specific binding was determined in the presence of 1 mM of non-labeled glutamate. The sections were exposed to tritium-sensitive films for 3 weeks at 4°C. Quantitative analysis revealed: (1) higher levels of total binding in NHE than in NRB and NLE rats in all areas but the cerebellum; (2) fewer binding sites for both NMDA and QA receptors and larger binding sites for QA receptors in the hippocampus of NLE and NHE rats, respectively; (3) a positive correlation between total binding sites and activity level in a Làt maze in all areas, except the cerebellar molecular layer with NLE < NHE, which was due to a differential contribution from NMDA and non-NMDA types. Thus, the brain of the NHE rats shows an imbalance between NMDA and non-NMDA sensitive [ l- 3H]glutamate receptors.

Immediate early genes and brain DNA remodeling in the Naples High- and Low-excitability rat lines following exposure to a spatial novelty

The aim of these studies was to map the neural consequences of exposure to a spatial novelty on the expression of immediate gene (IEG) and on unscheduled brain DNA synthesis (UbDS) in two genetic models of altered activity and hippocampal functions, i.e., the Naples High- (NHE) and Low-excitability (NLE) rats. Adult male rats of NLE and NHE lines, and of a random-bred stock (NRB) were tested in a Làt-maze, and corner crossings, rearings, and fecal boll were counted during two 10-min tests 24 h apart. For IEG expression, rats were exposed to a Làt-maze with nonexposed or repeatedly exposed rats used as controls, and were sacrificed at different time intervals thereafter. For UBDS, rats were sacrificed immediately after the first or the second exposure o a Làt-maze. IEG expression was measured by immunocytochemistry for the FOS and JUN proteins. NRB rats exposed for the first time to the maze showed extensive FOS and JUN positive cells in the reticular formation, the granular and pyramidal neurons of hippocampus, the amygdaloid nuclei, all layers of somatosensory cortex, and the granule cells of the cerebellar cortex. The positivity, stronger in rats exposed for the first time, was present between 2 and 6 h and was prevented by the NMDA receptor antagonist CPP (5 mg/kg). The positivity was very low in NHE rats, and it was stronger in NLE compared to NRB rats. UBDS was measured in ex vivo homogenates of brain areas by the incorporation into DNA of 3H-[methyl]-thymidine given intraventricularly 15 min before test trial 1 or 2 (pulse of 0.5 h). The basal level of UBDS was higher in the hippocampus and neostriata of both NLE/NHE compared to NRB rats. On test trial 1 only, there was a significant decrease in UBDS in the neocortex and hippocampus of the NLE/NHE rats, and in the hypothalamus, midbrain, and cerebellum of NLE rats only. This decrease was lower in NHE than in NLE rats. In conclusion, the differential genotype-dependent profile of FOS and JUN peptides and UBDS in the NLE/NHE rats might cast some light on the neural substrates of spatial and emotional information processing in these neurogenetic models.

Evidence for and against the Naples high- and low-excitability rats as genetic model to study hippocampal functions

The Naples high- (NHE) and low-excitability (NLE) are two rat lines, selectively bred for high and low activity levels in a Làt-maze, respectively. Because the activity level in a novel environment depends mainly on the integrity of the hippocampal formation, and NLE and NHE rats differ with a similar background of emotionality, arterial blood pressure, and learning ability, they have been proposed as animal model to study hippocampal functions. Our aim is to prove evidence in favor and against this hypothesis. The evidence in favor indicates that NLE/NHE rats have a defective spatial processing, and pertains to (a) Differential activity in a spatial novelty situation (selection trait), proportional to the stimulus complexity rats are exposed to (NHE are hyper- and NLE-rats hypoactive); and (b) Impaired working memory in a six-arm non-reinforced tunnel maze in both lines compared to random-bred rats, that was reversed by the introduction of a reinforcer. In addition, multiple evidence of (i) lower intra- + infrapyramidal mossy fiber terminals in both NLE/NHE vs. controls; (ii) increased sensitivity of hippocampal elements to microinjections of vasopressin (but not oxytocin) and of "delta" (but not "mu") opioids; (iii) lower number of high-affinity glucocorticoid receptors; (iv) lower number of alpha- but not beta-adrenergic receptors in the hippocampus and hypothalamus of NHE rats only; and (v) the genotype-dependent behavior of a DNA fraction with fast turnover, suggest that both NHE/NLE are "disintegrated" at the hippocampal interface. Further, neurobehavioral covariations among individual differences reveal nonlinear, complex relationships, an evidence apparently against the hypothesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Circadian activity, nociceptive thresholds, nigrostriatal and mesolimbic dopaminergic activity in the Naples High- and Low-Excitability rat lines

These experiments were designed to further characterize the differential phenotypic constellation of the Naples High- (NHE) and Naples Low-Excitability (NLE) lines. In order to determine possible differences between NHE and NLE rats in activity and circadian rhythms, besides reactivity to novelty (selection trait), adult male rats of both strains were tested during two 10-min exposures to a Làt-maze. They were then kept in activity cages continuously for 3 days. Moreover, nociceptive thresholds were measured with the hot-plate and the tail-flick test, to probe the possibility that these rats could be differentially sensitive to nociceptive stimuli. Further, the integrity of the nigro-striatal and mesolimbic system was investigated by measuring tyrosine-hydroxylase activity in the striatum and 3,4-dihydroxyphenylacetic acid (DOPAC) levels in the striatum as well as in the nucleus accumbens. In addition, TH activity was measured in the adrenals to probe the sympathetic section of the neurovegetative system. The results indicate that NHE and NLE rats differ by a factor of two in their phasic activity in a Làt-maze. In contrast, no differences in 24-h activity during the dark or light phase could be observed in the activity cages. However, NHE rats anticipated the light-on stimulus in the morning by reducing their activity 1 h earlier than NLE rats. Further, no difference could be found with the hot-plate and the tail-flick test. Finally, biochemical analyses revealed no difference in the NHE and NLE rats in the main terminal zone of mesolimbic system (n. accumbens) nor of nigrostriatal system (striatum) nor in the adrenal glands. In conclusion, since the only consistent difference between NHE and NLE rats appears to be reactivity to spatial novelty, an hippocampus-dependent behavioral trait (selection trait), independent of altered activity in the sympathetic system or dopaminergic activity in the major dopaminergic brain systems, the usefulness of these strains as genetic model to test current hypotheses of spatial processor device(s) in the mammalian brain is supported.