Dopaminergic processes in the striatum mediating corticoliberin effect on behavior of active and passive rats

The action of intranasal corticotropin-releasing hormone (CRH) administration on open field behavior and striatal and hypothalamic levels of dopamine, noradrenaline and their metabolites has been studied in rats with different behavior strategies (KHA and KLA strains). In KLA rats, CRH administration resulted in increased locomotor and exploratory activity, while KHA rats demonstrated decreased that. The analysis of catecholamine levels did not detect any strain differences in hypothalamus, but in striatum the dopamine levels have been twice higher, while the metabolite levels (DOPAC and HVA) were significantly lower in KLA rats as compared to KHA rats. The CRH administration led to increased dopamine and noradrenaline levels in hypothalamus and decreased those in striatum in rats of both strains, but in KLA the decrease was more evident. It is probably a result of intensified mediator turnover induced by the neurohormone in KLA rats, as supported by a fact of increased dopamine metabolite levels in this structure.     

The open-field behavior of neuroticized rats]

A detailed study has been carried out of the behaviour in the open field of the lines of rats with different functional state of the nervous system after prolonged neurotization in dependence on the phase of circadian rhythm and terms after the end of the influence. Significant changes have been shown by the amplitude of circadian rhythms of emotionality and motor activity. It is established that the reaction of the rats lines to prolonged neuroticizing action depends on the phase of the circadian rhythm, the time after its termination and on genetically determined level of excitability of the nervous system.     

The effect of chronic food and water restriction on open-field behaviour and serum corticosterone levels in rats

In operant conditioning experiments, two methods are commonly used to motivate laboratory rats to perform designated tasks. The first is restricting food so that rats are forced to lose 20% of body weight within one week, followed by maintenance at 80% of the baseline weight for the remainder of the experiment. The second is restricting access to water to 15 min in each 24 h period. These methods are effective in motivating the animals. There is, however, little information available on the effects on performance in tests of behaviour that are not related to operant conditioning. In addition, it is not clear if these commonly used methods of food and water restriction will lead to physiological stress as indicated by an elevation of serum corticosterone. Male rats were either food-restricted to reduce and maintain their weight at 80% of baseline weight, or were restricted to 15 min access to water every 24 h. Activity in the open field was significantly greater in food-restricted rats than in water-restricted or control rats, but freezing behaviour was similar in all experimental groups. Food-restricted rats had a higher mean serum corticosterone level than water-restricted and control rats 37 days after the start of the experimental period. These data suggested that chronically restricting food and maintenance of body weight at 80% of baseline body weight led to significant behavioural changes and physiological stress. In contrast, water restriction did not lead to changes in behaviour or corticosterone levels. A second experiment was conducted to compare the effects of food restriction to 80% of baseline body weight, as described above, with a less stringent protocol in which test rats were initially reduced to 80% of baseline weight, but were then maintained at 80% of an ad libitum fed control rat's weight. Serum corticosterone levels and adrenal gland weights were measured after the initial week of forced weight loss and after maintenance for 21 days. Forced loss of 20% of body weight in the first week led to significantly increased serum corticosterone levels and adrenal gland weights compared to ad libitum fed controls. Serum corticosterone levels and adrenal gland weights in rats maintained at 80% of their initial body weight for 21 days remained higher than ad libitum fed control rats. However, rats maintained at 80% of an ad libitum fed control rat's weight did not differ from control rats in serum corticosterone levels or adrenal gland weights at the end of the 21-day study period. Adjustment of the feeding regimen in this manner eliminated physiological evidence of chronic stress.     

The morphochemical characteristics of the brain in Wistar rats that differ by open-field motor activity]

By cytochemical and biochemical methods it is established that in rats with low motor activity the increased content of proteins of cytoplasma and nuclei of neurones of the sensorimotor cortex, caudate nucleus and n. accumbens, the increased activity of a number enzymes of oxidizing and protein metabolism in them are combined with a low activity of enzymes of mediator exchange. In the studied formations in rats with high motor activity an increased activity of synaptic and membrane forms of acetylcholinesterase appears at the same level of activity of cholineacetyltransferase in these subcortical formations and at high monoamineoxidase activity in cellular structures of the cortex and in subcortical formations. It is shown that in animals of the same line but differing by the behaviour in the open field, brain formations such as the sensorimotor cortex, caudate nucleus and n. accumbens have their own biochemical properties of the studied characteristics.     

The effect of linear somatostatin on the active avoidance behaviour and open-field activity on haloperidol, phenoxybenzamine and atropine pretreated rats

Somatostatin administered intracerebroventricularly inhibited the extinction of active avoidance behaviour. The dopamine receptor blocking agent haloperidol, the alpha 1-receptor blocker phenoxybenzamine and the muscarinic anticholinergic agent atropine inhibited the behavioural effect of the peptide. Furthermore, somatostatin increased the locomotor activity of the animals. Neither of these drugs influenced the effect of the peptide exerted on locomotor activity. The peptide was ineffective on other parameters of the open-field test while phenoxybenzamine decreased the defecation rate of the animals and this effect was not influenced by somatostatin. The results suggest that the catecholaminergic and the cholinergic system play an important role in the inhibition of extinction produced by somatostatin but these mechanisms to not have a role in the locomotor activity induced by the peptide.     

Study on the optimum number of trials and intensity of unconditioned stimulants and strain difference in the two-way shuttle-box avoidance test using rats

In order to determine the optimun conditions suitable for a number of trials and the intensity of unconditioned stimulant (US) in the two-way shuttle-box avoidance test in Sprague-Dawley strain rats, which are used most frequently in reproduction studies, conditioned avoidance response was observed under various conditions for 30 and 60 trials and the low and high US levels. Investigation was also conducted in Wistar rats under a high US level with 30 and 60 trials. Latency time of the escape response in Sprague-Dawley rats was shortened with increasing trials. Body weight gains of both strains of rats in the high US level with the 60-trial group decreased during the observation period. These findings suggest that the high US level with the 60-trial group is not suitable for the two-way shuttle-box avoidance test. The rate and latency time of the avoidance response were lower in Wistar rats than in Sprague-Dawley rats, although those of the escape response were higher. Significant changes in the following were observed, mainly from first to third sessions: the avoidance rate of all groups in strains of rats, escape rate of 60-trial group in Sprague-Dawley rats, avoidance and escape latency time of the 60-trial groups in both strains of rats and escape latency time of the 30-trial group in Sprague-Dawley strain rats.     

Cholinergic effect on the dopamine turnover in the rat corpus striatum]

The peripheral administration of oxotremorine caused a significant increase in dihydroxyphenylacetic acid (DOPAC) in the striatum of rats, dopamine (DA) level was unaffected. Injection of oxotremorine into the substantia nigra failed to change the content of dopamine and its acid metabolites homovanillic acid (HVA) and DOPAC in striatum. Injection of oxotremorine or carbachol into the substantia nigra or into the caudate nucleus did not significantly influence the DA-turnover. The partly inconsistent results are discussed in connection with literature data in regard to the existence of excitatory as well as inhibitory cholinergic systems, which are located differently and are involved in the regulation of DA-turnover.     

The effect of substance P on the individual and group behaviors of rhesus monkeys]

The tendencies in the substance P influence on the expression of individual and group behaviour of adult males of rhesus macaques have been studied on the background of cardiopathogenic emotional stress (CES) and without it. CES stimulated the general activity of rhesus macaques in the individual cages, while the substance P injection without CES increased the frequency and duration of pathologic behavioral patterns. The maximal influence of substance P was expressed on the 3-4 day of experiments. On the 5th day the intensification of locomotion and social activity was found during the settling of all individuals in the large cage. The definite regularity of connection between the value of arterial pressure before and after experiments and the individual's social ranks is found. The injection of substance P on the CES background and without it the second-ranking individuals stood more hard, the leader and the most subordinated individuals stood easier.     

The effect of estrogens on the development of rats solitary tract nucleus neutrons transplanted into the anterior eye chamber]

By means of some autoradiografic, light and electron microscopic methods were investigated estrogen effects on synaptogenesis and neural synthetic activity in nucleus tractus solitarii grafts developed in anterior eye chamber. Estrogen increased the RNA-polymerase activity in some neurons of the grafts and also affected synaptogenesis in the neurophil of the graft tissue.     

The striatum and the organization of forced swimming in rats

Prolonged repeated electric stimulation of rats striatum causes stable behavioural depression and reorganization of temporal dynamics of forced swimming. Simultaneously increases the depression index offered by us as ratio of the number of immobilization cycles shorter than 6 s to the total number of active swimming cycles. Striatectomy and amphetamine administration (1 mg/kg) uniformly change the rhythmic structure of swimming with an increase of animals general motor activity without change of the depression index. It is suggested to use striatal inactivation as a model of depression state.     

The effect of the intestinal phase of Trichinella spiralis on the open-field behavior of mice

The study assessed the impact of the adult phase of Trichinella spiralis on the open-field behavior of mice. Thiabendazole treatment was used to chemosterilize adult worms in vivo. Untreated mice exhibited a marked decline in their ambulatory and exploratory activities (from day 14 post-infection until the end of the experiment). In contrast, infected mice treated with thiabendazole did not exhibit any behavioral alterations. This suggested that the adult phase of T. spiralis did not contribute to behavioral pathology in the mouse host.     

Effects of acidic-astressin and ovine-CRF microinfusions into the ventral hippocampus on defensive behaviors in rats

This study investigated a possible role for ventral hippocampal corticotropin-releasing factor (CRF) in modulating both unconditioned and conditioned defensive behaviors by examining the effects of pre-training ventral hippocampal ovine-CRF (oCRF) or acidic-astressin ([Glu^11,16]Ast) microinfusions in male Long-Evans hooded rats exposed to various threat stimuli including the elevated plus-maze (EPM) (oCRF), cat odor (oCRF and [Glu^11,16]Ast) and a live cat ([Glu^11,16]Ast). Unconditioned defensive behaviors were assessed during threat exposure, while conditioned defensive behaviors were assessed in each predator context 24 h after the initial threat encounter. Pre-training infusions of the CRF₁ and CRF₂ receptor agonist oCRF significantly increased defensive behaviors during both the unconditioned and conditioned components of the cat odor test, as well as exposure to the EPM. In contrast to the behavioral effects of oCRF microinfusions, the CRF₁ and CRF₂ receptor antagonist [Glu^11,16]Ast significantly decreased defensive behaviors during exposure to cat odor, while producing no discernible effects following a second injection in the cat exposure test. During conditioned test trials, pre-training infusions of [Glu^11,16]Ast also significantly reduced defensive behaviors during re-exposure to both predator contexts. These results suggest a specific role for ventral hippocampal CRF receptors in modulating anxiety-like behaviors in several ethologically relevant animal models of defense.     

The effect of phenamine on the avoidance reaction in intact and striatectomized rats]

Various characteristics of a conditioned avoidance reaction were recorded in rats in a Y-maze. Small doses of d,l-amphetamine (0.5 mg/kg) facilitated avoidance response while large ones (5 mg/kg) worsened it. After ablation of the rostral part of the striatum, small doses of the drug had the same effect as before, but no deteriorating action of large doses was observed. The behaviour disturbance is related to the capacity of d,l-amphetamine for activating the nigro-striatal dopaminergic transmission.     

The effect of phenamine and caffeine on the ability to extrapolate in rats]

Solution of an extrapolation problem was studied on 28 albino rats (Way strain and laboratory population) and 68 hybrids (the first generation) of wild and laboratory rats in experiments with a screen--the search of food after the disappearance of the food stimulus from the animal's sight. Administration of caffeine (20 mg/kg) and d,l-amphetamine (0.1 mg/kg), though not changing the share of correct solutions, diminishes the number of "refusals" to solve it. Increased motor activity and diminished emotionality of the rats due to administration of the drugs, recorded in an open field test, are likely to cause a decrease in the number of refusals. Administration of d,l-amphetamine facilitates the process of conditioning which contributes to the greater number of positive solutions of the repeatedly presented task.     

The effect of unsaturated fatty acids on the lipoprotein composition of rats]

Young male rats of the Long-Evans strain were fed 10% lard or corn oil diets for 4 weeks. Analysis of plasma cholesterol showed a decrease of 22%; a decrease of the same order of magnitude as also observed in the lipoproteins, particularly in the VLDL fraction, with the unsaturated diet. Plasma triglycerides were reduced by 50%; their fatty acids were found to contain a higher proportion of linoleate and arachidonate. Cholesterol ester of the HDL fraction contained mostly arachidonate which increased significantly with the substitution of corn oil to lard. Analysis of the lipoproteins indicated a reduction in VLDL and an increase in HDL with the unsaturated diet, whereas LDL remained unchanged.