Angiotensins in the central mechanisms of drinking instrumental activity of rats with different manifestations of risk behavior

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 According to an outstanding Russian physiologist academician P.K. Anokhin, a system-forming factor of a functional system of any level is a useful adaptive result of the activity which can be evaluated quantitatively [1]. The risk permits to predict the outcome of a situation, it is measurable [2] and performs several functions: stimu-lating, analytic, regulatory and protective [3, 4]. A situation of uncertainty stimulates an individual to actions in the situation of choice, on the other hand – risk permits to evaluate usefulness (danger) of this choice. Trying to eliminate a risky situation, an individual makes a choice and realizes the aim in a behavioral act with subsequent emotional evaluation of the achieved result [5-7]. A.P. Algin [6] defines risk «…as an activity associated with overcoming of uncertainty in the situation of unavoidable choice in which it is possible to quantitatively and qualitatively evaluate the probabil-ity of achievement of the expected result, failure and deviation from the aim».

In our work a comparative analysis was carried out of individual-typological peculiarities of behavior of rats before and after intracerebral introduction of equally effective dipsogenic doses of angiotensins. A key criterion which served the basis of individual-typological classification of peculiarities of rats’ behavior was the initial intensity of their behavior in the experiment determined by a quantity of instrumental acts terminated by intake of water.

Materials and Methods

The work was conducted on 19 male rats of Wistar line with 250-300 g mass. All manipulations with animals were performed in accordance with the international ethic recommendations on medico-biomedical research with use of animals. Scalping, implantation of cannula into the lateral ventricle were performed under ether anesthesia according to the coordinates of stereotaxic atlas for rats (L.D. Pellegrino at al., 1979) (AP = +1.0; L= 2; H= 2.5). Intraventricular microinjections of angiotensins («Sigma», the USA) were made to non-narcotized animals using a microsyringe of 5 μL volume («Hamilton», the USA).

Rats were taught instrumental skills on an automated setup – АУ (A.V. Shvad-chenko, A.P. Shcherbina et al., 1992) that permitted objective evaluation of successive fulfilment of stages of behavioral acts aimed at getting portions of water.

Training began with placing an animal into the start box where the rat occasionally found access to the treadbahn bloсked by a mobile shutter. Then the rat per-formed a runway, he reached a rotating disk and had to turn it at a certain angle to move a water cup closer. After intake of water the rat was to return into the start box and again repeat purposeful act. The principal scheme of АУ is given in Figure 1.  

     

 

Fig. 1. General view and scheme of setup: А – start box; B – «treadbahn» block; C – «manipulation» box; D – rotating disk; E – water cup with a signal lamp; F – mobile curtain

 

 During training period rats were kept on a fixed supporting regime that is they were given water within 15 minutes once a day after daily manipulations in the set-up. Food was given without limitations. Temporal parameters of behavioral acts in rats were determined: dT-1 – latent period of coming onto the treadbahn; dT-2 – period from appearance on the treadbahn to taking the «manipulation» posture; dT-3 – time from start of «manipulation» to start of intake of water; dT-4 – time of intake of water; dT-5 – time from cessation of intake of water to withdrawal from «manipulation» posture; dT-6 – time of returning to the treadbahn; dT-7 – time of passage from the treadbahn to the start box. For evaluation of periods of the behavioral act (from dT-1 to dT-7) their absolute values were determined in sec. The time of testing of animals in АУ was 10 minutes. Besides, there were also registered the number of pro-ductive instrumental acts, initiation of grooming acts and vertical upright postures, and the number of attempts to overcome obstacles on the way to water. The obtained data of behavioral experiments were processed using parametric Student’s t-test for sampling with normal distribution.

After that animals with different manifestations of risk behavior receiving water and food ad libitum, were introduced doses of angiotensins equally effective in water intake: angiotensin-II(А-II) – 300 ng, angiotensin-III(A-III) – 350 ng and [des-Asp1] angiotensin-I ([des-Asp1]-A-I) – 400 ng («Sigma», the USA) into the lateral cerebral ventricles. «Equally-effective» doses of angiotensins that, being introduced into the lateral cerebral ventricles, initiated intake of equal amounts of water, were selected earlier in our research [8]. A solvent was normal saline solution (0.9 % NaCl), the volume of each microinjection was 3µL. Injection of saline with dissolved substances was made slowly within 15-20 sec.

Results and Discussion

By the results of experiment all rats were divided into 3 groups. The 1st group included animals (n=2, m=34 – number of runways in АУ), whose behavior was initially inactive and was characterized by performing not more than 2 instrumental acts, by delay on the treadbahn (dT-7) when returning to the start box, and by a high level of species-specific activity (grooming, upright postures). After introduction of «equally-effective» dose of A-II the animals reproduced the same quantity of full-scale drinking acts, with reduction of the time of passage from the treadbahn to the start box (dT-7¯), prolongation of the time of intake of water (dT-4 ); the time of ex-it of the animals from the start box to treadbahn (dT-1) did not change. Taking into account peculiarities of the given individuals it can be stated that A-II not only repro-duced the characteristic features of the instrumental pattern of drinking behavior, but also promoted fulfilment by the animals of the optimal algorithm of achievement of the useful result of their activity (intake of water, p>0.05 – compared to the initial level). According to the established strategy and effectiveness of the purposive drinking behavior, rats of the 1st group were classified as «non-risk-taking».

The 2nd group included rats (n=10, m=86 – the number of runways in АУ) with moderate activity of drinking behavior (not more than 5 acts) which were classifies as «cautious» with «pragmatic» behavioral strategy. These animals demonstrated high values of time required for stages dT-4 and dT-7. Some rats (n=5, m=43 – the number of runways in АУ) were made intracerebral microapplications of A-II. The dT-7 parameter reduced, that is, the time of passage from the treadbahn to the start box shortened in certain sessions, the time of intake of water increased (dT-4 – p< 0.05), the time of passage from the start box to the treadbahn remained unchanged (dT-1). In rats of the 2nd group the number of «references» to the empty water cup de-creased as well as the number of «references» to the shutter (p<0,05). In response to intracerebral introduction of A-II the grooming parameters unreliably increased (p>0.05 in comparison with that in the initial condition). Introduction of [des-Asp1]-A-I to the rats of this group was not accompanied by reproduction of the instrumental skill in them (duration of dT-1 period reliably increased as compared to the initial condition, p<0.05). Single non-effective runways towards the «manipulation» compartment were noted but they did not finish with manipulation with the disk and in-take of water. The number of grooming acts and upright postures reliably increased (p<0.05).

The 3d group included rats with high effectiveness (>5 acts). They (n=7, m=64 – the number of runways in АУ) demonstrated the «beneficial» behavioral strategy – «risk-taking». The animals were under the «risk» of not to complete a large number of effective runways in the setup during the limited time of test. The longest period in these animals was the period of drinking act (dT-4, p<0.05), and all the rest additional activity appeared to be insignificant in comparison with other groups of animals. In these rats there were no «references» to the shutter and to the empty drinking cup in the initial condition, and the amount of «references» to the shutter strictly corresponded to the amount of productive acts in АУ. They did not «fritter away» the energy to «empty activity» but pragmatically structured their purposive activity and achieved the useful result due to increase in the number of productive acts in АУ. Changes in behavior in «risk-taking» rats after introduction of A-II were on the whole similar to those in the preceding group of animals. The time of consuming act (dT-4) did not change with microinjections, while dT-1 and dT-7 parameters increased. So, behavior of the animals was sort of rationalized. Animals to whom [des-Asp1]-A-I was injected, did not reproduce the drinking instrumental skill. The rats did not make a single attempt to overcome the shutter, their behavior was characterized by alternation of investigatory activity and grooming. Thus, introduction of [des-Asp1]-A-I suppressed realization of the «justified risk» strategy by probable destruction of probabilistic prediction of the result of activity [4, 5, 9]. However, after testing in АУ, the dipsogenic effect of [des-Asp1]-A-I was manifested by additional drinking with free access to water, with the amount of consumed water corresponding to the effect of the equally effective dose.

Decision taking is an «intermediary, critical» and «highly condensed» process [1] that results from the afferent synthesis initiated by the dominating motivation [10]. Situation of uncertainty may be of «regular» or «occasional» character [6], in one case decision taking is associated with the conflict caused by the necessity to overcome a physical obstacle; in the other case – with the risk as a particular way of solution of the above mentioned conflict. Decision taking rids an organism of excessive «amount of degrees of freedom» and is accompanied by formation of specific «efferent excitations» having adaptive character [1, 5, 9] and reflected in the future result of behavior. An actual physiological task is evaluation and analysis of the func-tional parameter of risk-related behavior both in the process of decision taking and in the stage of realization of the behavioral act.

All components of the functional system of behavior are integrated and not ab-solutely independent and isolated. Dominating motivation, memory apparatus, deci-sion taking are integrated, and risk is a specific component of behavior whiсh appears in conditions of the uncertainty of achievement of the goal [5]. Risk is manifested as an independent characteristics of behavior of an individual, and changes in the bio-logical functions associated with risk, are of adaptive character.

Conclusion

Depending on the initial level of the intensity of instrumental activity of animals, angiotensin-II stimulates reproduction of the full-scale «behavioral pattern» or participates in the directed modulation of complicated purposive behavior by its optimization in thirst. [des-Asp1]-angiotensin-I does not participate in mechanisms of reproduction of the instrumental skill, but only induces mechanisms of initiation of the inborn forms of behavior.

About the authors

Roman Ya. Vlasenko

Novgorod State University named after Yaroslav the Wise

Author for correspondence.
Email: romex@mail.ru
ORCID iD: 0000-0002-7328-0520
SPIN-code: 9013-1219

MD, PhD, Associate Professor, Department of Normal Physiology, Institute of Medical Education

Russian Federation, 41, St.Petersburgskaya street, Veliky Novgorod, 173003

Alexander V. Kotov

Scientific Research Institute of Normal Physiology named after P.K. Anokhin

Email: romex@mail.ru
ORCID iD: 0000-0002-1810-7741
SPIN-code: 2749-4037

MD, Grand PhD, Professor, Head of the Laboratory of Physiology of Motivation

Russian Federation, P.O.B. 72, Moscow, 125315

References

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