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Spontaneous hypertension and open-field behavior
BEHAVIORAL AND NEURAL BIOLOGY 34, 450--452 (1982)
NOTE Spontaneous Hypertensionand Open-Field Behavior RICHARD M C C A R T Y AND ROBERT F . K IR B Y
Department of Psychology, Gilmer Hall, University of Virginia, Charlottesville, Virginia 22901
Recently, several reports have appeared in this journal concerning the open-field behavior of spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) normotensive rats. Knardahl and Sagvolden (1979) observed that prehypertensive male SHRs were more active in an openfield arena after several tests as compared to WKYs. Based upon this strain difference in open-field behavior, SHRs have been characterized as hyperactive (Schaefer, 1980) or hyperreactive (Knardahl & Sagvolden, 1981). Further, the greater activity of SHRs was linked to the increased level of sympathetic-adrenal medullary activity and the development of hypertension in this strain (Knardahl & Sagvolden, 1979; Schaefer, 1980). Studies in our laboratory present a different view of the relationship between open-field behavior and spontaneous hypertension in rats (McCarty, 1982a, 1982b). In three different experiments, we have recorded the number of squares entered and the frequency of rearing by rats during a 5-min test in an open-field arena. The arena was an open plywood box (120 x 120 x 30 cm) painted fiat black and divided by lines into 25 squares of equal size. The experiments included the following comparisons: (i) male SHR and WKY rats, (ii) male New Zealand hypertensive (GH) and normotensive (N) rats originally developed by Smirk and Hall (1958), and (iii) male WKY and Brown-Norway (B-N) rats. The B - N strain is an inbred, normotensive strain that bears no direct relationship to any animal model of hypertension (McCarty & Kopin, 1978). All rats were 10-12 weeks old at the time of testing. Our results, which are summarized in Table 1, confirm the findings of others that SHRs are more active and rear more frequently during open-field testing than WKYs (p < .05). However, there were no behavioral differences between the GH and N strains (p's > .50), and the normotensive B - N rats were more active and reared more frequently 450 0163-1047/82/040450-03502.00/0 Copyright © 1982 by AcademicPress, Inc. All rights of reproduction in any form reserved.
451
LOCOMOTOR ACTIVITY OF SHR RATS
TABLE 1 Frequency of Entering Squares and Rearing during a Single 5-Min Test in an OpenField Arena by Male Normotensive and Hypertensive Rats Mean _+ SE Strain SHR WKY °
N 6 6
Squares entered
Rearing
56 _+ 12' 18 _+ 7
14 _+ 3* 3 -+ 2
GH Nb
10 10
59 _+ 6 66 -+ 6
15 - 2 16 _+ 2
WKY B-N c
10 10
28 _+ 7 90 _+ 7*
1 _+_ .5 30 +_ 3*
Note. Data from three separate experiments are presented. ° From McCarty (1982b). b From McCarty (1982a). c Unpublished data. * p < .05 (two-tailed t test).
than the WKYs (p < .05). For each of the three experiments, the strain relationships were consistent across three consecutive daily tests in the open-field arena (data not shown). These findings indicate that open-field behavior is not a consistent predictor of a genetic susceptibility for the development of hypertension or sympathetic-adrenal medullary hyperactivity. ~n addition, our data demonstrate that the WKY strain is hypoactive in the open-field test, as the measures of activity for this strain were well below the values for the other four inbred normotensive and hypertensive strains. In contrast, the behaviors of the SHR strain were well within the ranges for the other strains. To establish a causal relationship between spontaneous hypertension and behavior (or vice versa), we believe that one valuable approach is to compare specific behavioral measures in several models of experimental hypertension and their appropriate normotensive controls. In this manner, one may distinguish between behavioral and physiological characteristics that are associated with several forms of experimental hypertension vs those that are unique to the SHR strain (McCarty, 1982b; Tucker & Johnson, 1981). REFERENCES Knardahl, S., & Sagvolden, T. (1979). Open-field behavior of spontaneously hypertensive rats. Behavioral and Neural Biology, 27, 187-200. Knardahl, S., & Sagvolden, T. (1981). Regarding hyperactivity of the SHR in the openfield test. Behavioral and Neural Biology, 32, 274-275.
452
MC CARTY AND KIRBY
McCarty, R. (1982). Physiological and behavioral responses of New Zealand hypertensive and normotensive rats to stress. Physiology and Behavior, 28, 103-108. McCarty, R. (1982). Sympathetic-adrenal medullary and behavioral responses to stress: A comparative study of SHR and New Zealand hypertensive rats. In Proceedings of the Fourth International Symposium on Rats with Spontaneous Hypertension, in press.
(b) McCarty, R., & Kopin, I. J. (1978). Sympatho-adrenal medullary activity and behavior during exposure to stress: A comparison of seven rat strains. Physiology and Behavior, 21, 567-572. Schaefer, C. F. (1980). Regarding open-field behavior of the spontaneously hypertensive rat. Behavioral and Neural Biology, 29, 537-538. Smirk, F. H., & Hall, W. H. (1958). Inherited hypertension in rats. Nature (London) 182, 727-728. Tucker, D. C., & Johnson, A. K. (1981). Behavioral correlates of spontaneous hypertension. Neuroscience and Biobehavioral Reviews, 5, 463-471.
NOTE Spontaneous Hypertensionand Open-Field Behavior RICHARD M C C A R T Y AND ROBERT F . K IR B Y
Department of Psychology, Gilmer Hall, University of Virginia, Charlottesville, Virginia 22901
Recently, several reports have appeared in this journal concerning the open-field behavior of spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) normotensive rats. Knardahl and Sagvolden (1979) observed that prehypertensive male SHRs were more active in an openfield arena after several tests as compared to WKYs. Based upon this strain difference in open-field behavior, SHRs have been characterized as hyperactive (Schaefer, 1980) or hyperreactive (Knardahl & Sagvolden, 1981). Further, the greater activity of SHRs was linked to the increased level of sympathetic-adrenal medullary activity and the development of hypertension in this strain (Knardahl & Sagvolden, 1979; Schaefer, 1980). Studies in our laboratory present a different view of the relationship between open-field behavior and spontaneous hypertension in rats (McCarty, 1982a, 1982b). In three different experiments, we have recorded the number of squares entered and the frequency of rearing by rats during a 5-min test in an open-field arena. The arena was an open plywood box (120 x 120 x 30 cm) painted fiat black and divided by lines into 25 squares of equal size. The experiments included the following comparisons: (i) male SHR and WKY rats, (ii) male New Zealand hypertensive (GH) and normotensive (N) rats originally developed by Smirk and Hall (1958), and (iii) male WKY and Brown-Norway (B-N) rats. The B - N strain is an inbred, normotensive strain that bears no direct relationship to any animal model of hypertension (McCarty & Kopin, 1978). All rats were 10-12 weeks old at the time of testing. Our results, which are summarized in Table 1, confirm the findings of others that SHRs are more active and rear more frequently during open-field testing than WKYs (p < .05). However, there were no behavioral differences between the GH and N strains (p's > .50), and the normotensive B - N rats were more active and reared more frequently 450 0163-1047/82/040450-03502.00/0 Copyright © 1982 by AcademicPress, Inc. All rights of reproduction in any form reserved.
451
LOCOMOTOR ACTIVITY OF SHR RATS
TABLE 1 Frequency of Entering Squares and Rearing during a Single 5-Min Test in an OpenField Arena by Male Normotensive and Hypertensive Rats Mean _+ SE Strain SHR WKY °
N 6 6
Squares entered
Rearing
56 _+ 12' 18 _+ 7
14 _+ 3* 3 -+ 2
GH Nb
10 10
59 _+ 6 66 -+ 6
15 - 2 16 _+ 2
WKY B-N c
10 10
28 _+ 7 90 _+ 7*
1 _+_ .5 30 +_ 3*
Note. Data from three separate experiments are presented. ° From McCarty (1982b). b From McCarty (1982a). c Unpublished data. * p < .05 (two-tailed t test).
than the WKYs (p < .05). For each of the three experiments, the strain relationships were consistent across three consecutive daily tests in the open-field arena (data not shown). These findings indicate that open-field behavior is not a consistent predictor of a genetic susceptibility for the development of hypertension or sympathetic-adrenal medullary hyperactivity. ~n addition, our data demonstrate that the WKY strain is hypoactive in the open-field test, as the measures of activity for this strain were well below the values for the other four inbred normotensive and hypertensive strains. In contrast, the behaviors of the SHR strain were well within the ranges for the other strains. To establish a causal relationship between spontaneous hypertension and behavior (or vice versa), we believe that one valuable approach is to compare specific behavioral measures in several models of experimental hypertension and their appropriate normotensive controls. In this manner, one may distinguish between behavioral and physiological characteristics that are associated with several forms of experimental hypertension vs those that are unique to the SHR strain (McCarty, 1982b; Tucker & Johnson, 1981). REFERENCES Knardahl, S., & Sagvolden, T. (1979). Open-field behavior of spontaneously hypertensive rats. Behavioral and Neural Biology, 27, 187-200. Knardahl, S., & Sagvolden, T. (1981). Regarding hyperactivity of the SHR in the openfield test. Behavioral and Neural Biology, 32, 274-275.
452
MC CARTY AND KIRBY
McCarty, R. (1982). Physiological and behavioral responses of New Zealand hypertensive and normotensive rats to stress. Physiology and Behavior, 28, 103-108. McCarty, R. (1982). Sympathetic-adrenal medullary and behavioral responses to stress: A comparative study of SHR and New Zealand hypertensive rats. In Proceedings of the Fourth International Symposium on Rats with Spontaneous Hypertension, in press.
(b) McCarty, R., & Kopin, I. J. (1978). Sympatho-adrenal medullary activity and behavior during exposure to stress: A comparison of seven rat strains. Physiology and Behavior, 21, 567-572. Schaefer, C. F. (1980). Regarding open-field behavior of the spontaneously hypertensive rat. Behavioral and Neural Biology, 29, 537-538. Smirk, F. H., & Hall, W. H. (1958). Inherited hypertension in rats. Nature (London) 182, 727-728. Tucker, D. C., & Johnson, A. K. (1981). Behavioral correlates of spontaneous hypertension. Neuroscience and Biobehavioral Reviews, 5, 463-471.