AT2 but not AT1 receptor antagonism abolishes angiotensin II increase of the acquisition of conditioned avoidance responses in rats

AT2 but not AT1 receptor antagonism abolishes angiotensin II increase of the acquisition of conditioned avoidance responses in rats

Behavioural Brain Research 131 (2002) 79 – 86 www.elsevier.com/locate/bbr Research report AT2 but not AT1 receptor antagonism abolishes angiotensin ...

285KB Sizes 0 Downloads 67 Views

Behavioural Brain Research 131 (2002) 79 – 86 www.elsevier.com/locate/bbr

Research report

AT2 but not AT1 receptor antagonism abolishes angiotensin II increase of the acquisition of conditioned avoidance responses in rats Jan J. Braszko * Department of Clinical Pharmacology, Medical Academy of Bialystok, Ludwik Zamenhof Childrens Hospital, J. Waszyngtona St. 15 A, 15 -274, Bialystok, Poland Received 5 June 2001; received in revised form 7 August 2001; accepted 7 August 2001

Abstract In this study we attempted to determine behavioural, including cognitive, consequences of the brain AT1 (losartan, 2 nmol), AT2 (PD 123319, 1.5 nmol), and joint AT1/AT2 angiotensin receptors blockade. Male Wistar rats (160– 180 g) were injected into the left cerebral ventricle with the above doses of the blockers dissolved in 0.9% NaCl solution (vehicle) or with the vehicle alone. Five minutes later they received, to the right cerebral ventricle, 1 nmol of angiotensin II (Ang II) dissolved in vehicle or the vehicle alone. Ang II consistently increased rate of acquisition of conditioned avoidance respones (CARs) and facilitated recall of the passive avoidance behaviour. In one out of the three series of experiments in open field Ang II stimulated rats locomotor activity. Losartan and PD 123319, both ineffective alone, given prior to Ang II abolished all the behavioural changes produced by the peptide except for the Ang II facilitation of CARs acquisition, which was unchanged by losartan. Interestingly, joint injection of losartan and PD 123319 significantly decreased the rate of CARs acquisition both in control and Ang II treated animals. In conclusion, the present data suggest significant though different involvement of both AT1 and AT2 angiotensin receptors in cognitive processes. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Angiotensin II; Angiotensin receptors; Avoidance learning; Exploratory behaviour

1. Introduction It is becoming increasingly clear that the brain angiotensins participate in cognitive processing [2,6,7,29,36]. Baranowska et al. [3] found that angiotensin II (Ang II) facilitates acquisition of conditioned avoidance responses (CARs) and enhances retention of passive avoidance. Subsequently, several reports described similar effects of the intracerebroventricular (ICV) administration of Ang II (2 – 8) (Ang III) [13], Ang II (3–8) (Ang IV) [9,38,39] and Ang II (3–7) [10]. In addition to an enhancement of the aversively motivated learning, increased efficiency of food finding * Tel.: +48-85-745-0591; fax: +48-85-742-1838. E-mail address: [email protected] (J.J. Braszko).

in T-maze [11] as well as an improved discrimination between unfamiliar and the previously seen objects were observed after the ICV administration of Ang II and Ang II (3–7) [8]. Introduction of the selective antagonists of AT1 (losartan; 2-n-butyl-4-chloro-5-hydroksymethyl-1-[2%(1H-tetrazol-5-yl) biphenyl-4-yl) methyl] imidazole) [17], AT2 (PD 123319; (1-[[4-(dimethylamino)-3-methylphenyl]methyl] - 5 - (diphenylacetyl) - 4,5,6,7 - tetrahydro1H-imidazo [4,5-c] pyridine-6-carboxylic acid) [34] and AT4 (divalinal; Val c Tyr Val c His-Pro-Phe) [24] angiotensin receptors made it possible to assess relative involvement of these Ang II receptor subtypes in the various aspects of cognitive behaviour. Wright et al. [37] tends to ascribe all the cognitive effects of angiotensins to the recently discovered [38] AT4 angiotensin receptors. However, considerable evi-

0166-4328/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 6 - 4 3 2 8 ( 0 1 ) 0 0 3 4 9 - 7

80

J.J. Braszko / Beha6ioural Brain Research 131 (2002) 79–86

dence has recently accumulated showing that AT1 [25] and particularly AT2 [22,29] receptor subpopulations might be involved as well. The question of whether or not AT1 and AT2 angiotensin receptors are involved in cognitive processes needs to be clearly answered at least because of the wide clinical use of AT1 receptor blockade in the treatment of hypertension. Moreover, angiotensin converting enzyme inhibitors (ACEIs) are frequently used in the range of cardiovascular diseases [40]. To further our understanding of angiotensins’ role in the cognitive processing this study attempts to answer two specific questions: (i) how AT1 and AT2 angiotensin receptors blockade affects learning facilitated by Ang II and; (ii) can unopposed angiotensin receptor subtypes influenced by the presumed high levels of endogenous Ang II make an apparent behavioural change. We used acquisition of CARs and recall of a passive avoidance behaviour as cognitive tests and locomotor exploratory activity in open field to assess the rats’ motor performance. Losartan and PD 123319, given separately or jointly, were used to antagonize, respectively AT1 and AT2 angiotensin receptors.

2. Materials and methods

2.1. Subjects Male Wistar rats weighing 160– 180 g at the time of testing, i.e. about 8-weeks old, were used. The animals were housed in groups of eight in the plastic cages (55 ×40× 20 cm) (length×width × height) in a temperature controlled room with a constant 12 h light/ dark cycle (lights on at 7:00 h) and with free access to standard lab chow and tap water up to the time of experimentation. The experiments were conducted between 10:00 and 15:00 A. Thirty minutes habituation period to the experimental room preceded all the behavioural experiments. The experimental procedures were carried out in accordance with the National Institutes of Health Guide for Care and Use of Laboratory Animals (publication No. 85-23, revised 1985) and were approved by the Local Ethics Commission for the Animal Experimentation. A preliminary account of the present results has been published in abstract form [6].

2.2. Surgery Under light ether anaesthesia, a round piece of skin, 7 mm in diameter, was cut off the rat’s head and the underlying skull surface was cleaned from the soft tissue. A burr holes, 0.5 mm in diameter, were drilled in

the skull 2.5 mm laterally and 1 mm caudally from the point of intersection of the bregma and the superior saggital suture on the right and left side of the head. The operation took about 2 min and, after 48 h recovery, the wound was completely dry and the animal behaved normally. On the following day (i.e. 3 days after surgery) the ICV injections were made freehand into the lateral cerebral ventricles with a 10 ml Hamilton syringe, using a removable KF 730 needle cut 4.5 mm from its base. This procedure allowed lowering the tip of the needle about 0.5 mm below the ceiling of the lateral cerebral ventricle. It was relatively nontraumatic as the animal, gently fixed by the left hand of the experimenter, was usually quiet and no vocalization occurred. The injection volume was 2 ml administered over 3 s. Upon completion of each experiment all rats were sacrificed and the sites of injections were verified microscopically after brain sectioning.

2.3. Experimental procedure CARs were studied in a shuttle box (60× 28×24 cm) divided in two equal parts by a wall having 6 cm wide and 8 cm high opening in the middle of its length [10]. A buzzer (45 dB, 2000 Hz, conditioned stimulus, CS) was sounded for 3 s. If the rat did not make a positive (+)CAR, i.e. move to the other compartment within 3 s, a 0.1 mA scrambled electric shock (unconditioned stimulus, US) was delivered through the box floor which was made of stainless steel rods 4 mm in diameter and spaced at 18 mm intervals. The US was terminated when the animal escaped to the other compartment of the box. CARs acquisition training consisted of the five daily 20-trial sessions and the second ICV injection (Ang II or saline) was made 15 min before the first session. The number of (+)CARs (avoidance responses) was recorded every day and expressed as percent of the total number of trials. The intertrial interval was 10 s. The gird floor was kept clean throughout training sessions. Passive avoidance behaviour was studied in a one trial learning, step-through situation, which utilizes the natural preference of rats for dark environment [1]. After 2 min habituation to the dark compartment the rat was placed on the illuminated platform and allowed to enter the dark compartment. Two more approach trials were given on the following day with a 2 min interval. At the end of the second trial unavoidable scrambled electric footshock (0.25 mA, AC, 2 s) was delivered through the gird floor of the dark compartment (learning trial). The second ICV injection was made 24 h later and retention of the passive avoidance responses was tested after additional 15 min by placing the animal on the platform and measuring latency to re-enter the dark compartment to a maximum of 300 s.

J.J. Braszko / Beha6ioural Brain Research 131 (2002) 79–86

Locomotor and exploratory activity was measured in an open field which was a square 100 cm× 100 cm white floor divided by eight lines into 25 equal squares and surrounded by 47 cm high wall [10]. Four plastic bars, 20 cm high, were designed as objects of possible animals’ interest and fixed perpendicularly, parallel to each other, in four line crossings in the central area of the floor. Fifteen minutes after the second injection rat was placed in the center of the floor and, following 1 min of adaptation, crossings, rearings and bar approaches were counted manually for 5 min. Bar approach was considered when the rat directed its head toward the bar, approached and touched it with its nose.

2.4. Experimental design All behavioural tests were preceded by the ICV injections of the angiotensin receptor antagonist dissolved in 2 ml of saline (0.9% NaCl solution) (2 nmol of losartan, 1.5 nmol of PD 123319 or both) or the saline alone given to the left cerebral ventricle followed 5 min later by 1 nmol of Ang II dissolved in saline or saline alone given to the right cerebral ventricle. Behavioural effects of each blocker alone as well as the effects of a joint administration of the two blockers followed or not by Ang II were tested in a separate experiments each comprising of the four groups injected ICV (left+ right) as follows: (1) Saline+Saline; (2) Losartan or PD 123319 or both+Saline; (3) Saline+ Ang II; (4) Losartan or PD 123319 or both+Ang II.

81

passive avoidance situation were assessed with Mann– Whitney ranking test. Crossings, rearings and bar approaches in open field were analysed with one-way ANOVA followed by Newman-Keuls test. Levels were deemed significant at P B 0.05.

3. Results

3.1. Effects of angiotensin II, losartan, and PD 123319 on the acquisition of conditioned a6oidance responses [(+) CARs] 3.1.1. Losartan Fig. 1 presents the mean (9 SE) percentages of the daily (+ ) CARs in rats pretreated with the selective AT1 receptor blocker losartan followed by Ang II as compared with those given each drug alone or saline. Both groups receiving Ang II acquired (+ ) CARs at the similar rates across the whole 5 day training period which were markedly higher than these of the remaining two groups i.e. treated with losartan or control. The statistical analyses to support these conclusions indicated significant differences among the groups (F3,37 = 12.93, PB 0.0001), a days effect over the 5 day acquisition period (F4,148 = 122.39, PB 0.0001) and significant groups× days interaction (F12,148 = 3.49, PB

2.5. Drugs Ang II (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe) was obtained from Sigma-Aldrich (Steinheim, Germany). Losartan (2-n-butyl-4-chloro-5-hydroksymethyl-1-[2%(1H-tetrazol-5-yl) biphenyl-4-yl) methyl] imidazole, potassium salt) was a gift from Dr Ronald Smith of Du Pont Merck (New Jersey, USA). PD 123319 (1-[[4-(dimethylamino)-3-methylphenyl]methyl] - 5 - (diphenylacetyl) - 4,5,6,7 - tetrahydro - 1Himidazo[4,5-c]pyridine-6-carboxylic acid, ditrifluoroacetate, monohydrate) was purchased from RBI (Natick, USA). All drugs were dissolved in saline and given intracerebroventricularly (ICV) at the volume of 2 ml per one lateral cerebral ventricle.

2.6. Statistics The daily percentages of (+ ) CARs were analysed using treatments×days two-way analysis of variance (ANOVA) with repeated measures on the factor 1; post-hoc multiple comparisons were made using Bonferroni test. The re-entry latencies obtained in the

Fig. 1. Effect of 1 nmol of angiotensin II (Ang II) given to the right cerebral ventricle 15 min before the learning session on day 1, 2 nmol of losartan given to the left cerebral ventricle 20 min before the learning session on day 1, or both in combination given at the same routes and times, on the acquisition of ( + ) CARs over 5 days. Control injections were made of 0.9% NaCl (Saline) at the appropriate routes and times. Points represent means 9 SE of the values obtained from 9 to 11 animals. *P B 0.05 vs (Saline +Saline) and (Losartan +Saline) groups.

82

J.J. Braszko / Beha6ioural Brain Research 131 (2002) 79–86

with PD 123319 followed or not by Ang II, and the saline control group which on the other hand acquired (+ ) CARs at the similar to each other rate.

Fig. 2. Effect of 1 nmol of angiotensin II (Ang II) given to the right cerebral ventricle 15 min before the learning session on day 1, 1.5 nmol of PD 123319 given to the left cerebral ventricle 20 min before the learning session on day 1, or both in combination given at the same routes and times, on the acquisition of ( + ) CARs over 5 days. Control injections were made of 0.9% NaCl (Saline) at the appropriate routes and times. Points represent means + SE of the values obtained from 10 animals. *PB0.05 vs each of the remaining three groups.

3.1.3. Losartan and PD 123319 Fig. 3 presents the mean (9SE) percent values of the daily (+ ) CARs in rats pretreated before Ang II with both, losartan and PD 123319 compared to those receiving Ang II, the receptor antagonists, or saline. Ang II treated group learned CARs faster than all the other groups i.e. losartan/PD 123319 treated, losartan/PD 123319 followed by Ang II treated or the saline control group. Interestingly, both groups receiving the receptor antagonists i.e. these subsequently treated with Ang II or with saline presented on days 3 and 4 significantly less (+ ) CARs than the control group thus showing an adverse effect of the joint AT1/AT2 angiotensin receptor antagonism on this type of learning. The statistical analyses to support these conclusions indicated significant differences among the groups (F3,44 = 10.36, PB 0.001) a days effect over 5 day period (F4,176 = 42.08, PB0.0001) and a significant groups×days interaction (F12,176 = 3.04, PB0.001). Post hoc analyses indicated that the Ang II treated rats achieved significantly greater percentages of (+ ) CARs on days 3–5 compared to the remaining three groups.

0.01). Pairwise comparisons indicated that the rate of improvement in acquisition performance was during all 5 day substantially greater in rats receiving Ang II no matter whether they were or were not pretreated with losartan in comparison with the losartan alone and saline control groups.

3.1.2. PD 123319 Fig. 2 shows the mean (9SE) percent values of the daily (+ ) CARs in rats pretreated before Ang II with PD 123319, a selective AT2 receptor blocker, compared with those receiving the peptide, the blocker, or only saline. The group receiving Ang II alone learned (+) CARs much faster than the remaining three groups i.e. these treated with saline, the AT2 blocker, and Ang II preceded by the blocker. This showed that PD 123319 completely prevented the Ang II effect. Statistical analysis indicated a significant differences among the groups (F3,36 =30.219, P B0.0001), a days effect over the 5 d acquisition period (F4,144 =167.39, PB 0.0001), and a significant groups×days interaction (F12,144 =7.90, PB 0.001). Post hoc analyses indicated that the rates of (+) CARs acquisition were on days 2–5, significantly greater in Ang II treated rats compared to each of the remaining three groups i.e. treated

Fig. 3. Effect of 1 nmol of angiotensin II (Ang II) given to the right cerebral ventricle 15 min before the learning session on day 1, 2 nmol of losartan and 1.5 nmol of PD 123319 given to the left cerebral ventricle 20 min before the learning session on day 1, or both in combination given at the same routes and times, on the acquisition of ( +) CARs over 5 days. Control injections were made of 0.9% NaCl (Saline) at the appropriate routes and times. Points represent means9SE of the values obtained from 11 to 13 animals. *PB 0.05 vs control (Saline +Saline).

J.J. Braszko / Beha6ioural Brain Research 131 (2002) 79–86

83

Table 1 Effect of angiotensin II and losartan on re-entry latencies in the passive avoidance situation

Table 3 Effect of angiotensin II, losartan and PD 123319 on re-entry latencies in the passive avoidance situation

Treatment

n

Re-entry latency (s)

Treatment

n

Re-entry latency (s)

Saline+Saline Losartan+Saline Saline+Ang II Losartan+Ang II

11 14 18 11

30 30.5 135 27

Saline+Saline Losartan/PD 123319+Saline Saline+Ang II Losartan/PD 123319+Ang II

9 11 10 9

42 (25–45) 60 (19–67) 183.5 (126–293)* 59 (14–113)**

(20–50) (15–35) (15–180)* (20–30)**

All rats were injected into the lateral cerebral ventricle (ICV, 2 ml) first on the left side followed, 5 min later, by the right side (left+ right). The second injection was made 15 min before the retention trial. The dose of losartan was 2 nmol and Ang II 1 nmol. * Median latencies are given, with the 25–75 percentiles in parentheses; PB0.05, ** PB0.01 for the differences, respectively from the Saline only and Saline+Ang II treated groups (Mann–Whitney ranking test).

Also, rats receiving jointly losartan and PD 123319 followed or not by Ang II were, on days 3 and 4, significantly inferior in the number of (+ ) CARs to the control rats.

3.2. Effects of angiotensin II, losartan, and PD 123319 on retrie6al of the passi6e a6oidance beha6iour Rats which were treated with Ang II before the retention trial re-entered the dark chamber of the apparatus significantly later than did the control, losartan, and losartan followed by Ang II treated animals (Table 1). The median re-entry latency of the later group was more than four-fold greater than the median latency of each of the remaining three groups. It means that losartan, alone failed to influence conditioning in the passive avoidance task, but when given prior to Ang II, blocked the Ang II facilitation. In the experiment summarized in Table 2 Ang II increased median re-entry latency also about four-fold above the latency observed in the control animals. Again, this increase was almost completely abolished by Table 2 Effect of angiotensin II and PD 123319 on re-entry latencies in the passive avoidance situation Treatment

n

Re-entry latency (s)

Saline+Saline PD 123319+Saline Saline+Ang II PD 123319+Ang II

10 10 10 10

35 (23–63) 50 (28–73) 150 (124–300)* 39.5 (31–82)**

All rats were injected into the lateral cerebral ventricle (ICV, 2 ml) first on the left side followed, 5 min later, by the right side (left+ right). The second injection was made 15 min before the retention trial. The dose of PD 123319 was 1.5 nmol and Ang II 1 nmol. * Median latencies are given, with the 25–75 percentiles in parentheses; PB0.05, ** PB0.01 for the differences. respectively from the Saline only and Saline+Ang II treated groups (Mann–Whitney ranking test).

All rats were injected into the lateral cerebral ventricle (ICV, 2 ml) first on the left side followed, 5 min later, by the right side (left+ right). The second injection was made 15 min before of the retention trial. The doses were losartan was 2 nmol, PD 123319 1.5 nmol and Ang II 1 nmol. * Median latencies are given, with the 25–75 percentiles in parentheses; PB0.05, ** PB0.01 for the differences, respectively from the Saline only and Saline+Ang II treated groups (Mann–Whitney ranking test).

the pretreatment with PD 123319 at the dose ineffective on its own. Also, in the third series of the experiments testing recall of the passive avoidance behaviour summarized in Table 3 Ang II increased median re-entry latency more than four-fold above the latency seen in the control animals. Joint ICV injection of rats with losartan and PD 123319, ineffective on its own, made Ang II given 5 min later unable to exert its re-entry latency prolonging effect rendering median latency of this group significantly lower than that in the group treated with Ang II preceded by saline.

3.3. Effects of angiotensin II, losartan, and PD 123319 on exploratory motor beha6iuor in open field No significant differences were found in the numbers of crossings, rearings and bar approaches counted in the open field after pretreatment of rats wich losartan, Ang II or losartan followed by Ang II (Fig. 4). Although the animals receiving Ang II preceded or not by losartan tended to make more crossings and rearings than did control or losartan treated rats the differences were not statistically significant. Nevertheless, in the experiment testing effects of PD 123319 followed or not by Ang II as well these of the peptide alone treated and saline control rats ANOVA of the numbers of crossings in four groups yielded F3,44 = 6.04, PB 0.002 showing the significant group effect (Fig. 5). Post-hoc pair-wise comparisons revealed Ang II treated group to be significantly different from both control and PD 123319 followed by Ang II treated groups. This showed marked increase of crossings by the Ang II treatment which was abolished by the PD 123319 given before Ang II. However, no statistically significant changes of the remaining two parameters of locomotor exploratory activity measured in the open field, i.e. rearings and bar approaches, were observed.

84

J.J. Braszko / Beha6ioural Brain Research 131 (2002) 79–86

The experiment employing joint injection of losartan and PD 123319 followed or not by Ang II, as well as Ang II alone and saline alone, showed similar numbers of crossings, rearings and bar approaches in the four groups and there were no statistically significant differences (data not shown).

4. Discussion The results of this study confirm and extend our original observation that both AT1 and AT2 angiotensin receptors are involved in the memory enhancing effects of Ang II [5,6,25]. Presently, we were able to show a considerable differences in modifying cognitive effects of Ang II by the AT1 (losartan) and AT2 (PD 123319) selective receptor antagonists. The AT1 receptor inhibition by losartan rendered Ang II, injected ICV 5 min later, behaviourally inactive in all but one instances. Namely, the drug did not influence Ang II facilitation of CARs acquisition. The AT1 blocker pretreated, and then Ang II injected rats acquired CARs as well as these given vehicle followed by Ang II. Similar results have recently been obtained with valsartan, another selective AT1 receptors antagonist [5]. The simplest explanation of this apparent lack of effectiveness of an AT1 angiotensin receptor inhibition on the Ang II action would be a relative unimportance of the AT1 receptors in such type of learning. This however would be difficult to renconcile with the AT1 mediated stimulation of brain dopaminergic [14,23] and noradrenergic neurotransmission [19,30,32] that in turn appear indispensable in an Ang II increase of CARs acquisition [12,35]. Alternatively, an apparent lack of influence of losartan on the Ang II facilitation of CARs acquisition

might really be a net effect of the two opposite actions. One would be attenuating action of losartan occupying AT1 receptors and preventing AT1 mediated stimulation of dopaminergic [14,23] and noradrenergic [30] systems function which in turn are necesary for the Ang II facilitation of CARs acquisition [12,35] in particular, as well as for normal cognition in general [15]. And the other would be augmenting action of endogenous Ang II, released in response to the AT1 receptor blockade [16,27], via AT2 angiotensin receptors. Such an explanation is supported by the fact that after joint AT1/AT2 receptor inhibition the rate of CARs learning was significantly lower than that in the control group, no matter whether the blocked animals were or were not subsequently treated with Ang II. Their rates of CARs learning were lower than these in both, losartan and PD 123319 treated groups which acquired CARs at least as well as the saline treated controls, probably because of the additional stimulation of unopposed, respectively AT2 or AT1, receptors by the increased amounts of the endogenous Ang II. Hence, cognitive effects mediated by the AT1 and AT2 angiotensin receptors appear to be in the same direction rather, similiar to these on the baroreceptor reflex inhibition for example [4,26] than opposite, like those on apoptosis or drinking behaviour [18]. This reasoning appears to be in line with the recent findings of Gelband et al. [20] suggesting that both subtypes of angiotensin receptors, often occurring on the same nerve ending, are usually activated jointly in proportion adequate to local tissue conditions and the desired functional state. In contrast to the CARs acquisition, Ang II facilitation of recall of the behaviour allowing rats to avoid previously experienced foot shock in the one trial learning step-through paradigm was abolished by losartan as

Fig. 4. Effect of 1 nmol of angiotensin II (Ang II) given to the right cerebral ventricle 15 min before testing, 2 nmol of losartan given to the left cerebral ventricle 20 min before testing or both in combination given at the same routes and times, on the number of crossing, rearings, and bar approaches in the open field. Columns represent means + SE of the values obtained from 9 to 12 rats. The control injections were made of 0.9% NaCl (Saline) at the appropriate times and routes.

J.J. Braszko / Beha6ioural Brain Research 131 (2002) 79–86

85

Fig. 5. Effect of 1 nmol of angiotensin II (Ang II) given to the right cerebral ventricle 15 min before testing, 1.5 nmol of PD 123319 given to the left cerebral ventricle 20 min before testing or both in combination given at the same routes and times, on the number of crossing, rearings, and bar approaches in the open field. Columns represent means +SE of the values obtained from 12 rats. The control injections were made of 0.9% NaCl (Saline) at the appropriate times and routes. *P B 0.05 vs (Saline + Saline) and (Saline + Ang II) group.

well as by PD 123319. There are at last two reasons which could account for that difference. First, in the testing of CARs acquisition drugs were given before the first learning trial whereas in the passive avoidance situation they were injected before the test trial, i.e. acquisition and retrieval of the relevant information, respectively, were affected by our treatments. In our earlier studies [12,35] using similar experimental protocols different effects of the inhibition of various monoaminergic receptors on the learning of active vs. recall of passive avoidance behaviour were observed. Second, acquisition of CARs requires unimpaired motor performance of the animals which, on the other hand, appears to be less necessary for the expression of the passive behaviour. In the latter, rats which upon the test trial remember that they should not enter the dark part of the apparatus had to merely stay on the elevated platform and not move. The animals, however, which were to express improved after Ang II acquisition of CARs had to enter the other part of the shuttle-box and, therefore, were more dependent on their motor performance. Recent evidence [21,22,28] suggest that the AT2 receptors, abundantly occurring in the inferior olivary nuclei [2,31,33], are engaged in the execution of the voluntary movements and hence their blockade may impair rats’ motor skills rendering PD 123319 pretreated animals less fit to acquire CARs. Such a notion is supported by the present observation that the AT2 angiotensin receptor blockade by PD 123319 effectively diminished number of crossings in the open field. In conclusion, this study showed an involvement of AT2 and, to a minor degree, AT1 angiotensin receptors in the Ang II enhancement of acquisition and recall of avoidance behaviours in rats.

Acknowledgements The skilful technical assistance of Agata Purzecka and Edyta Sitko and secretarial help of the former are gratefully acknowledged. This study was supported by the Medical Academy of Bialystok (3-66 713).

References [1] Ader R, Weijnen JAWM, Moleman P. Retention of a passive avoidance responses as a function of the intensity and duration of electric shock. Psychon Sci 1972;26:125 – 9. [2] Allen AM, Moeller I, Jenkins TA, Zhuo J, Aldred GP, Chai SY, Mendelsohn FAO. Angiotensin receptors in the nervous system. Brain Res Bull 1998;47:17 –28. [3] Baranowska D, Braszko JJ, Wis´niewski K. Effect of angiotensin II and vasopressin on acquisition and extinction of conditioned avoidance in rats. Psychopharmacology 1983;81:247 – 51. [4] Boscan P, Allen AM, Paton JFR. Baroreflex inhibition of cardiac sympathetic outflow is attenuated by angiotensin II in the nucleus of the solitary tract. Neuroscience 2001;103(1):153 –60. [5] Braszko JJ. AT1 angiotensin receptor blockade abolishes improvement of recall and recognition memory but not facilitation of the conditioned avoidance responses caused by the peptide, Behav Pharmacol 2001 (in press). [6] Braszko JJ, Kułakowska A. Selective blockade of the brain AT2 angiotensin receptors impairs acquisition of conditioned avoidance responses in rats. J Psychopharmacol 2000;14(suppl.):A49. [7] Braszko JJ, Kułakowska A, Winnicka MM, KarwowskaPolecka W. CGP 42112A abolishes facilitation of recognition caused by angiotensin II and angiotensin II (3 – 7) in rats. Acta Neurobiol Exp 1997;57:227 – 34. [8] Braszko J, Kułakowska A, Wis´niewski K. Angiotensin II and its 3 – 7 fragment improve recognition but not spatial memory in rats. Brain Res Bull 1995;37:627 – 31. [9] Braszko JJ, Kupryszewski G, Witczuk B, Wis´niewski K. Angiotensin II-(3-8)-hexsapeptide affects motor activity, performance of passive avoidance and conditioned avoidance responses in rats. Neuroscience 1988a;27:777 – 83. [10] Braszko JJ, Własienko J, Koziołkiewicz W, Janecka A, Wis´niewski K. The 3 – 7 fragment of angiotensin II is probably

86

[11]

[12]

[13]

[14]

[15]

[16]

[17]

[18]

[19]

[20]

[21]

[22]

[23]

[24]

[25]

J.J. Braszko / Beha6ioural Brain Research 131 (2002) 79–86 responsible for its psychoactive properties. Brain Res 1991;542:49 – 54. Braszko JJ, Własienko J, Kupryszewski G, Witczuk B, Wis´niewski K. Behavioral effects of angiotensin II and angiotensin II-(4-8)-pentapeptide in rats. Physiol Behav 1988b;44:327 – 32. Braszko JJ, Wis´niewski K. a1 and a2-adrenergic receptor blockade influences angiotensin II facilitation of avoidance behavior and stereotypy in rats. Psychoneuroendocrinology 1990;15:239 – 52. Braszko JJ, Wisniewski K, Kupryszewski G, Witczuk B. Psychotropic effects of angiotensin II and III in rats: locomotor and exploratory vs. cognitive behaviour. Behav Brain Res 1987;25:195 –203. Brown DCh, Steward LJ, Ge J, Barnes NM. Ability of angiotensin II to modulate striatal dopamine release via the AT1 receptor in vitro and in vivo. Br J Pharmacol 1996;118:414 – 20. Brozoski TJ, Brown RM, Rosvold HE, Goldman PS. Cognitive deficit caused by regional depletion of dopamine in prefrontal cortex of rhesus monkey. Science 1979;205:929 –32. Campbell DJ, Kladis A, Valentijn AJ. Effects of losartan on angiotensin and bradykinin peptides and angiotensin-converting enzyme. J Cardiovasc Pharmacol 1995;26:233 –40. Chiu AT, Herblin WF, McCall DE, Ardecky RJ, Carini DJ, Duncia JV, Pease LJ, Wong PC, Wexler RR, Johnson AL, Timmermans PBMWM. Identification of angiotensin II receptor subtypes. Biochem Biophys Res Commun 1989;165:196 – 203. de Gasparo M, Catt KJ, Inagami T, Wright JW, Unger Th. International Union of Pharmacology. XXIII. The angiotensin II recptors. Pharmacol Rev 2000;52:415 –72. Garcia-Sevilla JA, Dubocovich ML, Langer SZ. Angiotensin II facilitates the potassium-evoked release of 3H-noradrenaline from the rabbit hypothalamus. Eur J Pharmacol 1979;56:173 – 6. Gelband CH, Zhu M, Lu D, Reagan LP, Fluharty SJ, Posner P, Raizada MK, Sumners C. Functional interactions between neuronal AT1 and AT2 receptors. Endocrinology 1997;138:2195 – 8. Hein L, Barsh GS, Pratt RE, Dzau V, Kobilka BK. Bahavioural and cardiovascular effects of disrupting the angiotensin II type-2 receptor gene in mice. Nature 1995;377:744 –7. Ichiki T, Labosky PA, Shiota C, Okuyama S, Imagawa Y, Fogo A, Niimura F, Ichikawa I, Hogan BLM, Inagami T. Effects on blood pressure and exploratory behaviour of mice lacking angiotensin II type-2 receptor. Nature 1995;377:748 –50. Jenkins TA, Chai SY, Howells DW, Mendelsohn FAO. Intrastriatal angiotensin II induces turning behaviour in 6-hydroxydopamine lesioned rats. Brain Res 1995;691:213 –6. Krebs LT, Krama´ r EA, Hanesworth JM, Sardinia MF, Ball AE, Wright JW, Harding JW. Characterization of the binding properties and physiological action of divalinal-angiotensin IV, a putative AT4 receptor antagonist. Regul Pept 1996;67:123 – 30. Kułakowska A, Karwowska W, Wis´niewski K, Braszko JJ. Losartan influences behavioural effects of angiotensin II in rats. Pharmacol Res 1996;34:109 –15.

[26] Lin KS, Chan SHH, Chan JYH. Tonic suppression of spontaneous baroreceptor reflex by endogenous angiotensins via AT2 subtype receptors at nucleus reticularis ventrolateralis in the rat. Synapse 2001;40:85 – 94. [27] Mizuno K, Tani M, Niimura S, Sanada H, Haga H, Hashimoto S, Watanabe H, Ohtsuki M, Fukuchi S. Losartan, a specific angiotensin II receptor antagonist, increases angiotensin I and angiotensin II release from isolated rat hind legs: evidence for locally regulated renin-angiotensin system in vascular tissue. Life Sci 1992;50:PL-209 – 14. [28] Okuyama S, Sakagawa T, Chaki S, Imagawa Y, Ichiki T, Inagami T. Anxiety-like behavior in mice lacking the angiotensin II type-2 receptor. Brain Res 1999a;821:150 – 9. [29] Okuyama S, Sakagawa T, Inagami T. Role of the angiotensin II type-2 receptor in the mouse central nervous system. Jpn J Pharmacol 1999b;81:259 – 63. [30] Richards EM, Raizada MK, Gelband CH, Sumners C. Angiotensin II type 1 receptor-modulated signaling pathways in neurons. Mol Neurobiol 1999;19:25 – 41. [31] Rowe BP, Saylor DL, Speth RC. Analysis of angiotensin II receptor subtypes in individual rat brain nuclei. Neuroendocrinology 1992;55:563 – 73. [32] Sumners C, Phillips MI. Central injection of angiotensin II alters catecholamine activity in rat brain. Am J Physiol 1983;244:R257 – 63. [33] Walters DE, Speth RC. Neuronal localization of specific angiotensin II binding sites in the rat inferior olivary nucleus. J Neurochem 1988;50:812 – 7. [34] Widdop RE, Gardiner SM, Kemp PA, Bennett T. Differential blockade of central effects of angiotensin II by AT2-receptor antagonists. Am J Physiol 1993;265:H226 – 31. [35] Wis´niewski K, Braszko JJ. The significance of central monoamine systems in the angiotensin II (AII) improvement of learning. Clin Exp Hypertension 1984;6:2127 – 31. [36] Wright JW, Harding JW. Brain angiotensin receptor subtypes in the control of physiological and behavioral responses. Neurosci Biobehav Rev 1994;18:21 – 53. [37] Wright JW, Krebs LT, Stobb JW, Harding JW. The angiotensin IV system: functional implications. Front Neuroendocrinol 1995;16:23 – 52. [38] Wright JW, Miller-Wing AV, Shaffer MJ, Higginson C, Wright DE, Hanesworth JM, Harding JW. Angiotensin II(3-8) (Ang IV) hippocampal binding: potential role in the facilitation of memory. Brain Res Bull 1993;32:497 – 502. [39] Wright JW, Stubley LA, Pederson ES, Krama´ r EA, Hanesworth JM, Harding JW. Contributions of the brain angiotensin IV-AT4 receptor subtype system to spatial learning. J Neurosci 1999;19:3952 –61. [40] Yusuf S, Lonn E, Bosh J, Gerstein H. Summary of randomized trials of angiotensin converting enzyme inhibitors. Clin Exp Hypertension 1999;21:835 – 45.