The effect of hypothalamic stimulation on food choice with rats maintained on different water-salt rations]

Electrical stimulation of the lateral hypothalamus in rats induces an increase of water intake and decrease of thresholds of eaten salty food. These effects are displayed in control animals and under salt diet and water deprivation. The hypothalamus stimulation relaxes the effects of "psychic distillation" of food which occur during spatial coincidence of conditioned signal of insipid food with salty reinforcement. Besides, the trans-switching of signal significance of conditioned stimuli connected with insipid and salty reinforcements is accelerated. The electrostimulation of the hypothalamus accelerates the elaboration of conditioned aversion of salty food inhibition of conditioned runnings toward corresponding food-box, and intensifies the existent state of thirst transforming it in the dominant motivation.     

The effect of dopaminergic nigrostriatal system on sleep deprivation in rats

The analysis of the electrophysiological features of sleep-wakefulness cycle in Wistar rats for 9h after a 6h sleep deprivation was carried out. The delay of sleep rebound (since 2.5-3 h after deprivation) was found in the form of moderate increasing of slow-wave sleep and fast-wave sleep phases. According to these sleep-wakefulness cycle changes, a quantitative immunohistochemical study of tyrosine hydroxylase: a key enzyme of dopamine synthesis--and D1 and D2 receptors in nigro-striatal projections has been performed. After sleep, an elevation of D1 receptors immunoreactivity in caudate nucleus and reduction of tyrosine hydroxylase immunoreactivity in compact part of substancia nigra was found. After postdeprivation sleep, a decrease of D1 receptors immunoreactivity and increase of D2 receptors immunoreactivity in caudate nucleus together some increase of tyrosine hydroxilase immunoreactivity in substancia nigra compacta has been observed. These data can testify about active role of dopaminergic nigrostriatal system which provide at the same time with another neurotransmitters of the central nervous system the telencephalo-diencephalic interaction in sleep-wakefulness-sleep cycle.     

Propranolol induces acute natriuresis by beta blockade and dopaminergic stimulation.

dl-Propranolol (0.8-1.6 mg/kg - h for 1 h) produced a transient two- to three-fold increase in sodium excretion in nondiuretic rats infused with Pitressin and aldosterone and in water diuretic rats. Sodium excretion increased more in rats depleted of renin by chronic Doca and salt administration than in rats maintained on a low salt diet. An angiotensin inhibitor (1,sarcosine-8,valine angiotensin II) decreased sodium excretion. Therefore the natriuresis was not mediated by antidiuretic hormone, aldosterone, or renin-angiotensin. d-Propranolol did not produce a natriuresis. Prior treatment with phenoxybenzamine did not prevent the natriuretic response but chlorisondamine pretreatment did. The natriuresis is produced by beta blockade and requires post ganglionic nerve function but is independent of alpha receptors. dl-Propranolol decreased heart rate and cardiac output but systemic pressure did not fall and renal blood flow increased. This suggests a dopamine-mediated renal vasodilation and natriuresis. Haloperidol and pimozide, both dopamine blocking agents with minimal beta blocking effects, prevented the natriuretic response. We conclude that propranolol may increase sodium excretion directly by blocking beta receptors in the distal nephron and indirectly by dopamine-mediated renal vasodilation.     

Influence of imidazole on behavioral effects induced by dopaminergic agonists in rats

Imidazole (IMI) (from 18.7 to 300 mg/Kg) i.p. injected in adult rats induced shaking, which was antagonized by both morphine (MOR) and haloperidol (HALO) but not by methysergide (MET). I.p. IMI pretreatment inhibited the penile erections (PE) and stretching and yawning (SY) typically elicited by N-n-propylnorapomorphine (NPA), a well-known CNS dopamine (DA) receptor stimulant, injected either i.p. or i.c.v., whereas it enhanced stereotyped behavior (SB). IMI had similar effects on the same parameters considered when injected before lisuride, an ergot derivative also active as a central DA receptor agonist. In this case not only SB but also and above all aggressiveness were markedly potentiated, both the signs appearing at doses of lisuride which were "per se" ineffective. Aggressiveness, like SB, was not sex linked and was antagonized by HALO and MOR, but not by MET. IMI alone potentiated the fighting induced by electrical shock, an effect which was abolished by HALO pretreatment. Considering the results obtained as a whole it is submitted that IMI antagonizes PE and SY through a selective blockade of a class of DA receptors, presumably DA presynaptic autoinhibitors, thus potentiating SB and aggressiveness, which involve stimulation of DA postsynaptic receptors.     

The effect of dopaminergic blockade on thyrotrophin response to thyrotrophin-releasing hormone and somatostatin

Using a large number of animals we have been able to demonstrate that somatostatin administration (20 micrograms/100 g bw) significantly reduces both basal serum thyrotrophin (TSH) levels and the response to thyrotrophin-releasing hormone (TRH) in the normal rat. Pretreatment with the dopaminergic antagonist domperidone resulted in increased TSH levels, increased response to TRH but no modification in the response to somatostatin.     

The effect of striatal stimulation and damage in rats on the dynamics of circadian mobility]

Prolonged and repeated low-frequency stimulation (2 imp/s, 20-30 min, 3-4 times) of the striatum disorganized rat's circadian motility. Attenuation of amplitude rhythm and shift of its acrophase to early night hours were observed. Bilateral striatectomy increased the motor activity after light switching-off and rhythm splitting to ultradian components. It is suggested that the striatum as a secondary oscillatory messenger may participate in motor maintenance of circadian motility.     

Nociceptive afferent blockade by percutaneous peripheral stimulation in the cat]

Experiments have been performed in order to study the effects of percutaneous peripheral stimulation (PCPS) both on the transmission of messages elicited by recruiting sensory units of the tooth pulp at the thalamic Centrum Medianum Level and on the jaw opening reflex (JOR). Both evoked potentials and JOR were inhibited by stimuli applied to the limbs by means of percutaneous (needle) electrodes. Observed inhibitory effects were not immediate: there was a latency period and progressive induction of these phenomena. The site of the inhibition is still unknown, nevertheless, the demonstration that PCPS was able to inhibit both evoked potentials in Centrum Medianum and JOR support the hypothesis that the analgesic effects may be due to descending inhibition blocking transmission of nociceptive information through the spinal cord.     

The role of serotonin-modulated anticonsolidation protein in memory formation in rats in a shuttle box

Two series of experiments were carried out in Wistar male rats. In the first series, rats were trained to acquire conditioning in a shuttle box to 50% and 80% learning criteria. In the animals of the experimental group that achieved 50% learning criterion, a significant decrease in the levels of serotonin-modulated anticonsolidation protein (SMAP) (solid phase, indirect ELISA-test) was observed in the temporal cortex as compared to the animals of the active control group. In the animals of the experimental group that achieved 80% learning criterion, such a decrease was found in the occipital and temporal cortex. In the second series of the experiments, animals of the experimental group were injected with SMAP in saline at a concentration of 1.5 mg/ml in a volume of 10 microl through the cannula implanted into the left lateral ventricle of the brain. Control animals were administered with heating-inactivated SMAP in the same amount. The substances were injected to the animals under light ether anesthesia daily 40 min prior to learning sessions. Learning sessions were carried out in the shuttle box for several days to 50% learning criterion. The experimental rats achieved learning criterion within 7-8 days, whereas intact and control animals reached the same criterion within 4 days. Furthermore, the experimental group of animals differed in increased levels of fear, anxiety and aggression which did not decline throughout the whole learning period. The conclusion was made that SMAP participated in negative regulation of the memory trace formation.     

Delay inhibition of the active avoidance reflex and intertrial responses in rats in the shuttle box

A diminished probability of avoidance response in early phases of a warning signal was revealed with salient signals given after short intertrial intervals. The inhibition of the delay in avoidance response is due to an interaction of the safety state conditioning and the excitation elicited by onset of warning signal.     

The effect of nalorphine on analgesia induced by peripheral stimulation]

The blockade of effects induced by percutaneous peripheral stimulation were abolished by injection of an opiate antagonist as nalorphine. Our results lead to the hypothesis that central and peripheral stimulations act by the same mechanism in producing blockade of noxious impulses. One may suggest that peripheral stimulations induce release of endogenous morphine-like substances which in turn give descending inhibition.     

The characteristics of shuttle avoidance learning in spontaneously hypertensive and normotensive rats]

In spontaneously hypertensive (strain SHR) and normotensive (strain WKY) rats was studied the elaboration of conditioned reflex of active avoidance in shuttle box. In case when the shuttle box was divided by a partition the SHR rats learned worse than WKY rats. In shuttle chamber without partition the SHR rats, on the contrary, learned better that WKY ones. Such character of interlinear differences can be connected with properties of formation of the instrumental habit of deliverance from electropainful stimulus, because the presence of partition significantly hampered its fulfillment. The obtained results, compared with literature data, testify to the fact that differences of SHR and WKY rats in elaboration of conditioned reflexes are explained basically by the properties of their unconditioned activity and not of the associative processes.     

The reactivity of the hypophyseal-adrenal system in rats with different forms of adaptive behavioral pathology]

The dexamethasone suppression test (DST) was applied to male Wistar rats with different models of depression: group with the learned helplessness, group with informational neurosis provided by time-deficit conditioned avoidance training, as well as groups of rats of two strains selected for low (KLA)--and high (KHA) avoidance learning. The pre-dexamethasone basal and stress-induced corticosterone levels were similar in intact rats and those exposed to inescapable shock. The dexamethasone administration (5 mkg/kg) failed to decrease the serum corticosterone level in rats with learned helplessness. The informational neurosis increased significantly the basal corticosterone level and decreased the stress response. Serum corticosterone levels were similar in KLA and KHA rats. These results give evidence that two stress-induced rat models of depression with similar behavioural disturbances (reduction of escape/avoidance reactions) exhibit marked differences in the activity of hypothalamo-pituitary-adrenal (HPA) axis.     

Influence of blockade of the dopaminergic D1/D2 receptors on choice behaviour at different by validity reinforcements in cats

The influence of two selective antagonists of the dopaminergic receptors, raclopride (D2) and SCH 23 390 (D1) on behavior of "impulsive" and "self-controlled" cats was similar directed. A selective blockade of the dopaminergic D1/D2 receptors by use of raclopride and SCH 23 390 changed a behavioural choice strategy of two different by validity and delay reinforcements in impulsive cats, but did not change it substantially in "self-controlled" animals. Increase of doses of raclopride and SCH 23 390 led to decrease of a part of the short-latency and increase of a part of the long-latency reactions (pedal pressings) in a total number of all effective responses. This occurred only in "impulsive" animals, that indicates probably the decrease of impulsive properties of their behaviour. Both compounds did not affect the choice strategy (a low quality immediate vs. a high quality delayed reinforcements) in "self-control" animals, but elicited more errors and inhibitory responses in their behavior. The data obtained are not consistent with the "dopamine" hypothesis, which predicts increase of impulsivity under influence of dopaminergic antagonists. The reasons that might lead to the data obtained are discussed.     

The effect of noise and vibration on motor activity and behavioral tests in rats

The investigations were carried out on 80 Albino rats. It was found that a single exposure to noise alone or noise coupled with vibratio;n increase locomotor and exploratory activities of the rats. On the other hand, repeated exposures to noise and low frequency vibration failed to change the exploratory activity and behavioral tests of rats. No significant differences were found between the effects of noise alone and associated with vibration.     

Effects of L-dopa and transcranial magnetic stimulation on behavioral reactions in kindled rats

In acute experiment in rats, the chronic epileptogenesis was reproduced in the form of pharmacological kindling induced via repeated picrotoxin administrations (1.0-1.2 mg/kg, intraperitoneally). A reduction of exploratory behavior was shown in the early period of kindling (24 h as of the moment of the last epileptogen administration). The marked alleviation of these disturbances was registered in two weeks from the moment of cessation of kindled irritations. L-DOPA (100 mg/kg, intraperitoneally) and transcranial magnetic stimulation (20 impulses with an induction at the height of their development of 1.5 TI) was followed by the net increasing exploratory, sexual and eating behavior. This is in favour of regarding the activation of dopaminergic system as a mechanism of action of transcranial magnetic stimulation upon kindling-induced behavioral deterioration.     

The effect of frontal cortex lesion on the activity of the dopaminergic system in rat striatum

The experiment was carried out on male Wistar rats weighing 180-220 g with lesion in the cortex of the frontal lobe. The activity of the dopaminergic system was studied by means of behavioural tests such as determination of spontaneous motor activity, apomorphine-induced stereotypy, haloperidol-induced catalepsy. Increased intensity of stereotypy was observed reaching a maximum 14 days after frontal lobe damage. Moreover, a slight tendency was observed for inhibition of haloperidol-induced catalepsy without changes in the spontaneous motor activity of the animals. Biochemical investigations demonstrated reduced dopamine content in the striatum on the side of the lesion.