TOXICOLOGYANDAPPLIEDPHARMACOLOGY
42,339-344(1977)
Fluctuating Dental Asymmetry as an Indicator Stressful Prenatal Effects of d9-Tetrahydrocannabinol Laboratory Rat P.SIEGEL,' M. I.SIEGEL,'*' Anthropology Medicine;
E. C. KRIMMER?,~ W.J. DOYLE,' AND H. BARRY, III’,3-5
Department, Faculty of Arts and Sciences; Anat0m.v and Pharmacology Department, School of Pharmacy, Pennsylvania 15260 Received
of the in the
January
13, 1977; accepted
and Cell Biology Department, School University of Pittsburgh, Pittsburgh,
May
of
24,1977
Fluctuating Dental Asymmetry as an Indicator of the Stressful Prenatal Effects of dyTetrahydrocannabinol in the Laboratory Rat. SIEGEL, P.. SIEGEL. M. I., KRIMMER, E. C., DOYLE. W. J.. AND BARRY III, H. (1977). Toxicol. Appl. Pharmacol. 42, 1399344. Different groups of pregnant laboratory rats were given oral doses of &tetrahydrocannabinol (THC) (5 or 20 mgikg) or its vehicle (propyleneglycol). Additional nondosed groups were pair-fed with the high-dose group or were allowed continuous access to food. A previously tested technique was used to assess the stressful effects on the offspring. Increased fluctuating dental asymmetry was found in the mandibular dentition of the offspring of THC treated animals. As the experimental design was controlled for route of administration, drug vehicle, and drug-induced dietary variation, we concluded that THC was stressful. An alternative to placental transfer, behavioral stress is a possible explanation for this effect.
For bilaterally symmetric organisms, antimeric (e.g., mirror image left and right) structures may exhibit at least two different types of asymmetry. If, for a group or population, the mean dimensions for left and right are significantly different, they are said to exhibit directional asymmetry (i.e., left larger than right). If, on the other hand, these means are not significantly different and the dimensions fluctuate (per individual), left larger in some and right larger in others, it is fluctuating asymmetry (Van Valen, 1962). Stress has been defined as any alteration in the normal environment of an organism which disrupts the “steady state” of that organism (Selye, 1956). The relationship between stress and fluctuating asymmetry has been the focus of recent research (Siegel and Smookler, 1973; Siegel and Doyle 1975a,b,c). Various stressing agents (noise, cold) were found to produce significant increases in the magnitude of fluctuating dental asymmetry in the laboratory rat and mouse. This method of assessing the effects of stress applied both prenatally and postnatally permits the detection of such subtle effects in the absence of obvious teratology. ’ Anthropology ? Anatomy and ’ Pharmacology 1 Supported by ’ Supported by 13595 from NIMH.
Department, Faculty of Arts and Sciences. Cell Biology Department, School of Medicine. Department, School of Pharmacy. USPH Postdoctoral Fellowship DA 2376 from NIDA. USPH Research Scientist Development Award KZ-MH-5921
and Research
Grant
MH-
339 ISSN
004
I -008X
340
SIEGEL
ET .4L
There is abundant literature on the behavioral effects of A9-tetrahydrocannabinol (THC) in animals, including humans, and this work has been well reviewed by Miller and Drew (1974). Studies on the physiological and teratological effects of THC are also abundant; however, the conclusions of many such studies are difficult to compare. Toxicity of oral doses of AS-tetrahydrocannabinol was established by Thompson et al. (1973), and postmortem examination showed an increase in adrenal weight, an indicator of stress (Selye, 1973). Harbison and Mantilla-Plata (1972) found that placental transfer of THC in pregnant rodents given high (ip) doses (200 mg/kg) resulted in resorption and fetal deaths. Previous to this work, Borgen et al. (1971) had reported no resorptions and no significant malformations in the young of females treated with varying (SC) doses (O.Ol200 mg/kg) of THC. Doses larger than 50 mg/kg did produce significant increases in postnatal mortality. Uyeno ( 1973) found no significant increase in the number of abnormal pregnancies in rats treated with up to 120-mg/kg (SC) doses of THC. Neonatal mortality was not significantly increased. The lack of concordance of the results of these studies indicates the need for a more sensitive measure of the teratogenic effects of THC. The present study was designed to determine if the young of pregnant female rats treated with THC were “stressed.” The indication of such a stress would be an increase in fluctuating dental asymmetry. METHODS
Twenty-five Wistar-derived Sprague-Dawley-timed pregnancy rats were randomly placed into five groups of equal size and were housed individually. From a stock solution of THC in propylene glycol (20 mg/ml), a dilution of 1 : 3 with propylene glycol was prepared. yielding a concentration of 5 mg/ml. Effects of THC have been compared with different vehicles (Sofia et a/., 1971) and also with different routes of administration (Sofia et al., 1974) in mice. One group served as a standard control and was maintained under normal laboratory conditions without drug or vehicle treatment. A high-dose group received orally the stock solution at a volume of 1 ml/kg (20 mg/kg of THC). The third, or low-dose group, received the dilute solution (5 mg/ml) in a volume of 1 ml/kg (5 mg/kg of THC). A fourth group was given only the propylene glycol (vehicle group) in a volume of 1 ml/kg. The animals in each of these four groups had continuous access to food and water. Since THC may decrease food intake (Sofia and Barry, 1974), the animals in the fifth group were pair-fed with the animals in the high-dose group to determine if such a dietary change could affect our measure of stress. Oral administration began on Day 9 of gestation and continued until the birth of the pups. At this time. all animals were allowed food and water ad lib&m and were maintained with their litters until the sacrifice of the pups at 21 days postpartum. The crown dimensions of the rat’s first molar tooth are established between Day 1Oof gestation and Day 10 postpartum. In the present study. then, we are only able to assess the prenatal effects of treatment.
THE
STRESS-DENTAL
ASYMMETRY
IN
THE
RAT
341
Specimens were cleaned by the use of dermestid beetles. Measurements of mandibular (lower) and maxillary (upper) mesiodistal (length) and buccolingual (width) diameters were taken for antimeric (left and right) first molars for all litters from all groups. All measurements were made using a Wild stereomicroscope with a camera lucida drawing attachment (9.4 x magnification). Jaws and skulls were oriented under the microscope so as to place the occlusal surface of a given tooth row parallel to the surface of the lens. Dots representing maximal mesiodistal and buccolingual diameters were drawn, and these dimensions were then measured to the nearest 0.05 cm. RESULTS
The mean antimeric difference (left dimensions minus right dimension) in tooth dimensionsfor each group of pups is presented in Table 1, for the length and width measurementsof maxillary and mandibular first molars. From Table 1 it can be seen that the mean differences (L - R) for each group and all dimensionsdo not differ significantly from zero. The paired f-test was used, dividing the meandifference (L - R) by the SD as shown in Table 1. Therefore, no dimension exhibits directional asymmetry. Fluctuating asymmetry is measuredby the magnitude of the variance (S’), which is the square of the SD.This term (variance) may be calculated by the following equation: Var (L - R) = Var (L) + Var (R) - 2 Cov (LR), as described by Suarez (1974) and Doyle and Johnston (1976). It can be seenthat there are no significant differences in the magnitude of fluctuating dental asymmetry for maxillary mesiodistal dimensions between any of the experimental groups and control animals measuredby the F ratio for the two S2 values (designatedgroup divided by the control group). For the buccolingual diameters, however, both the low dose and the vehicle groups exhibit significantly greater (p < 0.05) fluctuating asymmetry than the controls. Since the difference was obtained for the vehicle group also, the F ratio was calculated between low dose and vehicle group S’ values (2.25/1.83), and this difference is not significant. For the mandibular dentition the mesiodistal diameters showed significantly (p < 0.05) increasedfluctuating asymmetry for the high-dosegroup, as did the buccolingual diametersfor the low-dosegroup. For these samegroups there were no significant differences in litter size or weight of pups at sacrifice. Food intake and body weight gain during gestation were found to be lower for the high-dosefemalesand their pair-fed group than for the other groups. DISCUSSION
Siegel and Smookler (1973) have reported a significant increase in the magnitude of fluctuating dental asymmetry for a population of laboratory rats exposedto intermittent audiogenic stress. Recent studieshave verified this conclusion and have demonstrated similar effects resulting from other stressingconditions, for example, cold (Siegel and Doyle 1975a,b,c). These investigators have proposed that the observed increase in the magnitude of fluctuating dental asymmetry is a responseof the organism to general
342
SIEGEL
ETAL.
stress. The mechanism, although as yet only incompletely understood, appears to involve a stress-induceddisruption of developmental synchronization. Thus, the degree of fluctuating dental asymmetry appears to be a sensitive indicator of the relative amount of stress inflicted on a population. Therefore, it is possible to determine the relative stressful effects of a suspected teratogenic agent by comparing the degree of
EFFECTSOF A9-THC
N
TABLE 1 ONFLUCTUATINGDENTALASYMMETRYINTHE
Control
Vehicle
31
32
Low-dose 20
RAT"
High-dose 31
Pair-fed 22
Maxillary mesiodistal Mean (L - R) SD s2 F Significance
0.018 0.149 0.022
0.074 0.163 0.027 1.23
0.011 0.171 0.029 1.32 -
0.05 1 0.151 0.023 1.05 -
0.033 0.151 0.023 1.05
Maxillary buccohngual Mean (L - R) SD S2 F Significance
0.094 0.111 0.012
0.040 0.147 0.022 1.83 p < 0.05
0.059 0.164 0.027 2.25 p < 0.05
0.00 1 0.123 0.015 1.25
0.026 0.144 0.02 1 1.75
Mandibular mesiodistal Mean (L-R) SD S2 F Significance
0.054 0.157 0.025
0.015 0.177 0.03 1 1.24
0.069 0.126 0.016
0.017 0.262 0.069 2.76 p < 0.05
Mandibular buccolingual Mean (L - R) SD S’ F Significance
0.057 0.156 0.024
(a Number measurement, nated group control.
0.121 0.178 0.032 1.33
< 1.00 -
0.042 0.230 0.053 2.21 p < 0.05
0.050 0.170 0.029 1.21 -
0.05 1 0.185
0.034 1.36
0.046 0.126 0.016 cl.00
of pups (N) in each of the five treatment groups, and, for each designated dimension of the mean antimeric differences (L - R). SD. variance (S’). F ratio for the S’ of the desigcompared to the control group, and level of statistical significance of this comparison vs
dental asymmetry between a standardized control population and a population exposed to such an agent (Siegel and Doyle 1975b). In the present study, the effect of prenatal &THC administration on the fluctuating dental asymmetry of newborn laboratory rats was determined. Combining the results of this study with the consideration presentedabove allows us to extrapolate to an analysis of the stressfuleffects of THC. The increase observed for the fluctuating asymmetry of mandibular mesiodistal(high dose) and buccolingual (low dose) diameters is not attributable to drug-induced food fluctuating
THE
STRESS-DENTAL
ASYMMETRY
IN
THE
RAT
343
deprivation, sinceno significant increasescould be demonstrated for pair-fed groups. As evidenced by the increases in fluctuating asymmetry for these two dimensions, we conclude that LPTHC constitutes a stressingsubstance. The vehicle groups exhibited significant differences in the magnitude of fluctuating dental asymmetry only for the maxillary buccolingual diameter, when compared to the standard control population. This effect was not observed for any other dimension. The apparent effect of low-dose treatment for this dimensionis most likely a combined effect of drug and vehicle. The apparent discrepancy involving dose-dependent effects deserves, at least. a speculative comment. One would expect that if the low dose significantly increased the fluctuating asymmetry of the mandibular buccolingual dimensions,a high dose would produce similar effects. Our only possible explanation, other than chance variation between the two dosage groups, is to suggestthat the high dose may in fact have a stress-reducingeffect with regard to this dimension. This explanation is consonant with the results of previous studies(Siegeland Doyle 1975a,b,c)where the effects of stressare not uniformly exhibited for all teeth and dimensions,but the underlying mechanismis not understood. Stress is defined as any alteration in the normal environment of an organism which disrupts the steady state of that organism (Selye, 1956). Therefore, a possible alternative to a direct physiological effect is stress induced through behavioral modifications, the importance of which has recently been emphasizedby Mason (197 1). Since THC can alter the behavior of the mother, this may be translated into an alteration of the fetal environment which could be stressfulto the young. ACKNOWLEDGMENTS The Btetrahydrocannabinol was received through the courtesy of Dr. Monique National Institute on Drug Abuse.
Braude,
REFERENCES BORGEN, L. A., DAVIS. W. M., AND PACE, H. B. (1971). Effects of synthetic Aytetrahydrocannabinol on pregnancy and offspring in the rat. Toxicol. Appl. Pharmacol. 20. 480-486. DOYLE, W. J.. AND JOHNSTON, 0. (1976). On the meaning of increased fluctuating dental asymmetry: A cross populational study. Amer. J. Phys. Anthropol.. in press. HARBISON, R. D., AND MANTILLA-PLATA, B. (1972). Prenatal toxicity, maternal distribution and placental transfer of tetrahydrocannabinol. J. Pharmacol. Exp. Ther. 180,446-453. MASON, J. W. (1971). A re-evaluation of the concept of “nonspecificity” in stress theory. J. Psychiatr. Res. 8, 323-333. MILLER, L. L., AND DREW. W. G. (1974). Cannabis: Review of behavioral effects in animals. Psycho/. Bull. 81,401417. SELYE, H. (1956). The Stress of Life. McGraw-Hill, New York. SELYE, H. (1973). The evolution of the stress concept. Amer. Sci. 61 (61, 692-699 SIEGEL, M. I., AND SMOOKLER, H. H. (1973). Fluctuating dental asymmetry and audiogenic stress. Growth 37, 35-39. SIEGEL, M. I., AND DOYLE, W. J. (1975a). The differential effects of prenatal and postnatal audiogenic stress on fluctuating dental asymmetry. J. Exp. Zool. 191. 21 l-214. SIEGEL. M. I., AND DOYLE, W. J. (1975b). The effects of cold stress on fluctuating asymmetry in the dentition of the mouse. J. Exp. Zool. 193, 385-389.
344
SIEGEL
ET AL.
SIEGEL, M. I., AND DOYLE, W. J. (1975~). Stress and fluctuating limb asymmetry in various species of rodents. Growth 39,363-369. SOFIA, D. R., AND BARRY III, H. (1974). Acute and chronic effects of &tetrahydrocannabinol on food intake by rats. Psychopharmacologia (Berlin) 39, 2 13-222. SOFIA, D. R.. KUBENA, R. K., AND BARRY III, H. (1971). Comparison of four vehicles of intraperitoneal administration of d’-tetrahydrocannabinol. .I. Pharm. Pharmacol. 23. 889891. SOFIA, D. R.. KUBENA, R. K., AND BARRY III, H. (1974). Comparison among four vehicles and four routes for administering dQetrahydrocannabino1. J. Pharmac. Sci. 63, 939-94 1. SUAREZ, B. T. (1974). Neanderthal dental asymmetry and the probable mutation effect. Amer. J. Phw Anthropol. 41.41 l-416. THOMPSON, G. R., MASON, M. M., ROSENKRANTZ, A., AND BRAUDE, M. C. (1973). Chronic oral toxicity of cannabinoids in rats. Toxicol. Appl. Pharmacol. 25, 373-390. UYENO. E. T. (1973). d9-tetrahydrocannabinol administration during pregnancy of the rat. Proc. West. Pharmacol. Sot. 16, 64-67. VAN VALEN. L. (1962). A study of fluctuating asymmetry. Evolution 16, 125-142.
42,339-344(1977)
Fluctuating Dental Asymmetry as an Indicator Stressful Prenatal Effects of d9-Tetrahydrocannabinol Laboratory Rat P.SIEGEL,' M. I.SIEGEL,'*' Anthropology Medicine;
E. C. KRIMMER?,~ W.J. DOYLE,' AND H. BARRY, III’,3-5
Department, Faculty of Arts and Sciences; Anat0m.v and Pharmacology Department, School of Pharmacy, Pennsylvania 15260 Received
of the in the
January
13, 1977; accepted
and Cell Biology Department, School University of Pittsburgh, Pittsburgh,
May
of
24,1977
Fluctuating Dental Asymmetry as an Indicator of the Stressful Prenatal Effects of dyTetrahydrocannabinol in the Laboratory Rat. SIEGEL, P.. SIEGEL. M. I., KRIMMER, E. C., DOYLE. W. J.. AND BARRY III, H. (1977). Toxicol. Appl. Pharmacol. 42, 1399344. Different groups of pregnant laboratory rats were given oral doses of &tetrahydrocannabinol (THC) (5 or 20 mgikg) or its vehicle (propyleneglycol). Additional nondosed groups were pair-fed with the high-dose group or were allowed continuous access to food. A previously tested technique was used to assess the stressful effects on the offspring. Increased fluctuating dental asymmetry was found in the mandibular dentition of the offspring of THC treated animals. As the experimental design was controlled for route of administration, drug vehicle, and drug-induced dietary variation, we concluded that THC was stressful. An alternative to placental transfer, behavioral stress is a possible explanation for this effect.
For bilaterally symmetric organisms, antimeric (e.g., mirror image left and right) structures may exhibit at least two different types of asymmetry. If, for a group or population, the mean dimensions for left and right are significantly different, they are said to exhibit directional asymmetry (i.e., left larger than right). If, on the other hand, these means are not significantly different and the dimensions fluctuate (per individual), left larger in some and right larger in others, it is fluctuating asymmetry (Van Valen, 1962). Stress has been defined as any alteration in the normal environment of an organism which disrupts the “steady state” of that organism (Selye, 1956). The relationship between stress and fluctuating asymmetry has been the focus of recent research (Siegel and Smookler, 1973; Siegel and Doyle 1975a,b,c). Various stressing agents (noise, cold) were found to produce significant increases in the magnitude of fluctuating dental asymmetry in the laboratory rat and mouse. This method of assessing the effects of stress applied both prenatally and postnatally permits the detection of such subtle effects in the absence of obvious teratology. ’ Anthropology ? Anatomy and ’ Pharmacology 1 Supported by ’ Supported by 13595 from NIMH.
Department, Faculty of Arts and Sciences. Cell Biology Department, School of Medicine. Department, School of Pharmacy. USPH Postdoctoral Fellowship DA 2376 from NIDA. USPH Research Scientist Development Award KZ-MH-5921
and Research
Grant
MH-
339 ISSN
004
I -008X
340
SIEGEL
ET .4L
There is abundant literature on the behavioral effects of A9-tetrahydrocannabinol (THC) in animals, including humans, and this work has been well reviewed by Miller and Drew (1974). Studies on the physiological and teratological effects of THC are also abundant; however, the conclusions of many such studies are difficult to compare. Toxicity of oral doses of AS-tetrahydrocannabinol was established by Thompson et al. (1973), and postmortem examination showed an increase in adrenal weight, an indicator of stress (Selye, 1973). Harbison and Mantilla-Plata (1972) found that placental transfer of THC in pregnant rodents given high (ip) doses (200 mg/kg) resulted in resorption and fetal deaths. Previous to this work, Borgen et al. (1971) had reported no resorptions and no significant malformations in the young of females treated with varying (SC) doses (O.Ol200 mg/kg) of THC. Doses larger than 50 mg/kg did produce significant increases in postnatal mortality. Uyeno ( 1973) found no significant increase in the number of abnormal pregnancies in rats treated with up to 120-mg/kg (SC) doses of THC. Neonatal mortality was not significantly increased. The lack of concordance of the results of these studies indicates the need for a more sensitive measure of the teratogenic effects of THC. The present study was designed to determine if the young of pregnant female rats treated with THC were “stressed.” The indication of such a stress would be an increase in fluctuating dental asymmetry. METHODS
Twenty-five Wistar-derived Sprague-Dawley-timed pregnancy rats were randomly placed into five groups of equal size and were housed individually. From a stock solution of THC in propylene glycol (20 mg/ml), a dilution of 1 : 3 with propylene glycol was prepared. yielding a concentration of 5 mg/ml. Effects of THC have been compared with different vehicles (Sofia et a/., 1971) and also with different routes of administration (Sofia et al., 1974) in mice. One group served as a standard control and was maintained under normal laboratory conditions without drug or vehicle treatment. A high-dose group received orally the stock solution at a volume of 1 ml/kg (20 mg/kg of THC). The third, or low-dose group, received the dilute solution (5 mg/ml) in a volume of 1 ml/kg (5 mg/kg of THC). A fourth group was given only the propylene glycol (vehicle group) in a volume of 1 ml/kg. The animals in each of these four groups had continuous access to food and water. Since THC may decrease food intake (Sofia and Barry, 1974), the animals in the fifth group were pair-fed with the animals in the high-dose group to determine if such a dietary change could affect our measure of stress. Oral administration began on Day 9 of gestation and continued until the birth of the pups. At this time. all animals were allowed food and water ad lib&m and were maintained with their litters until the sacrifice of the pups at 21 days postpartum. The crown dimensions of the rat’s first molar tooth are established between Day 1Oof gestation and Day 10 postpartum. In the present study. then, we are only able to assess the prenatal effects of treatment.
THE
STRESS-DENTAL
ASYMMETRY
IN
THE
RAT
341
Specimens were cleaned by the use of dermestid beetles. Measurements of mandibular (lower) and maxillary (upper) mesiodistal (length) and buccolingual (width) diameters were taken for antimeric (left and right) first molars for all litters from all groups. All measurements were made using a Wild stereomicroscope with a camera lucida drawing attachment (9.4 x magnification). Jaws and skulls were oriented under the microscope so as to place the occlusal surface of a given tooth row parallel to the surface of the lens. Dots representing maximal mesiodistal and buccolingual diameters were drawn, and these dimensions were then measured to the nearest 0.05 cm. RESULTS
The mean antimeric difference (left dimensions minus right dimension) in tooth dimensionsfor each group of pups is presented in Table 1, for the length and width measurementsof maxillary and mandibular first molars. From Table 1 it can be seen that the mean differences (L - R) for each group and all dimensionsdo not differ significantly from zero. The paired f-test was used, dividing the meandifference (L - R) by the SD as shown in Table 1. Therefore, no dimension exhibits directional asymmetry. Fluctuating asymmetry is measuredby the magnitude of the variance (S’), which is the square of the SD.This term (variance) may be calculated by the following equation: Var (L - R) = Var (L) + Var (R) - 2 Cov (LR), as described by Suarez (1974) and Doyle and Johnston (1976). It can be seenthat there are no significant differences in the magnitude of fluctuating dental asymmetry for maxillary mesiodistal dimensions between any of the experimental groups and control animals measuredby the F ratio for the two S2 values (designatedgroup divided by the control group). For the buccolingual diameters, however, both the low dose and the vehicle groups exhibit significantly greater (p < 0.05) fluctuating asymmetry than the controls. Since the difference was obtained for the vehicle group also, the F ratio was calculated between low dose and vehicle group S’ values (2.25/1.83), and this difference is not significant. For the mandibular dentition the mesiodistal diameters showed significantly (p < 0.05) increasedfluctuating asymmetry for the high-dosegroup, as did the buccolingual diametersfor the low-dosegroup. For these samegroups there were no significant differences in litter size or weight of pups at sacrifice. Food intake and body weight gain during gestation were found to be lower for the high-dosefemalesand their pair-fed group than for the other groups. DISCUSSION
Siegel and Smookler (1973) have reported a significant increase in the magnitude of fluctuating dental asymmetry for a population of laboratory rats exposedto intermittent audiogenic stress. Recent studieshave verified this conclusion and have demonstrated similar effects resulting from other stressingconditions, for example, cold (Siegel and Doyle 1975a,b,c). These investigators have proposed that the observed increase in the magnitude of fluctuating dental asymmetry is a responseof the organism to general
342
SIEGEL
ETAL.
stress. The mechanism, although as yet only incompletely understood, appears to involve a stress-induceddisruption of developmental synchronization. Thus, the degree of fluctuating dental asymmetry appears to be a sensitive indicator of the relative amount of stress inflicted on a population. Therefore, it is possible to determine the relative stressful effects of a suspected teratogenic agent by comparing the degree of
EFFECTSOF A9-THC
N
TABLE 1 ONFLUCTUATINGDENTALASYMMETRYINTHE
Control
Vehicle
31
32
Low-dose 20
RAT"
High-dose 31
Pair-fed 22
Maxillary mesiodistal Mean (L - R) SD s2 F Significance
0.018 0.149 0.022
0.074 0.163 0.027 1.23
0.011 0.171 0.029 1.32 -
0.05 1 0.151 0.023 1.05 -
0.033 0.151 0.023 1.05
Maxillary buccohngual Mean (L - R) SD S2 F Significance
0.094 0.111 0.012
0.040 0.147 0.022 1.83 p < 0.05
0.059 0.164 0.027 2.25 p < 0.05
0.00 1 0.123 0.015 1.25
0.026 0.144 0.02 1 1.75
Mandibular mesiodistal Mean (L-R) SD S2 F Significance
0.054 0.157 0.025
0.015 0.177 0.03 1 1.24
0.069 0.126 0.016
0.017 0.262 0.069 2.76 p < 0.05
Mandibular buccolingual Mean (L - R) SD S’ F Significance
0.057 0.156 0.024
(a Number measurement, nated group control.
0.121 0.178 0.032 1.33
< 1.00 -
0.042 0.230 0.053 2.21 p < 0.05
0.050 0.170 0.029 1.21 -
0.05 1 0.185
0.034 1.36
0.046 0.126 0.016 cl.00
of pups (N) in each of the five treatment groups, and, for each designated dimension of the mean antimeric differences (L - R). SD. variance (S’). F ratio for the S’ of the desigcompared to the control group, and level of statistical significance of this comparison vs
dental asymmetry between a standardized control population and a population exposed to such an agent (Siegel and Doyle 1975b). In the present study, the effect of prenatal &THC administration on the fluctuating dental asymmetry of newborn laboratory rats was determined. Combining the results of this study with the consideration presentedabove allows us to extrapolate to an analysis of the stressfuleffects of THC. The increase observed for the fluctuating asymmetry of mandibular mesiodistal(high dose) and buccolingual (low dose) diameters is not attributable to drug-induced food fluctuating
THE
STRESS-DENTAL
ASYMMETRY
IN
THE
RAT
343
deprivation, sinceno significant increasescould be demonstrated for pair-fed groups. As evidenced by the increases in fluctuating asymmetry for these two dimensions, we conclude that LPTHC constitutes a stressingsubstance. The vehicle groups exhibited significant differences in the magnitude of fluctuating dental asymmetry only for the maxillary buccolingual diameter, when compared to the standard control population. This effect was not observed for any other dimension. The apparent effect of low-dose treatment for this dimensionis most likely a combined effect of drug and vehicle. The apparent discrepancy involving dose-dependent effects deserves, at least. a speculative comment. One would expect that if the low dose significantly increased the fluctuating asymmetry of the mandibular buccolingual dimensions,a high dose would produce similar effects. Our only possible explanation, other than chance variation between the two dosage groups, is to suggestthat the high dose may in fact have a stress-reducingeffect with regard to this dimension. This explanation is consonant with the results of previous studies(Siegeland Doyle 1975a,b,c)where the effects of stressare not uniformly exhibited for all teeth and dimensions,but the underlying mechanismis not understood. Stress is defined as any alteration in the normal environment of an organism which disrupts the steady state of that organism (Selye, 1956). Therefore, a possible alternative to a direct physiological effect is stress induced through behavioral modifications, the importance of which has recently been emphasizedby Mason (197 1). Since THC can alter the behavior of the mother, this may be translated into an alteration of the fetal environment which could be stressfulto the young. ACKNOWLEDGMENTS The Btetrahydrocannabinol was received through the courtesy of Dr. Monique National Institute on Drug Abuse.
Braude,
REFERENCES BORGEN, L. A., DAVIS. W. M., AND PACE, H. B. (1971). Effects of synthetic Aytetrahydrocannabinol on pregnancy and offspring in the rat. Toxicol. Appl. Pharmacol. 20. 480-486. DOYLE, W. J.. AND JOHNSTON, 0. (1976). On the meaning of increased fluctuating dental asymmetry: A cross populational study. Amer. J. Phys. Anthropol.. in press. HARBISON, R. D., AND MANTILLA-PLATA, B. (1972). Prenatal toxicity, maternal distribution and placental transfer of tetrahydrocannabinol. J. Pharmacol. Exp. Ther. 180,446-453. MASON, J. W. (1971). A re-evaluation of the concept of “nonspecificity” in stress theory. J. Psychiatr. Res. 8, 323-333. MILLER, L. L., AND DREW. W. G. (1974). Cannabis: Review of behavioral effects in animals. Psycho/. Bull. 81,401417. SELYE, H. (1956). The Stress of Life. McGraw-Hill, New York. SELYE, H. (1973). The evolution of the stress concept. Amer. Sci. 61 (61, 692-699 SIEGEL, M. I., AND SMOOKLER, H. H. (1973). Fluctuating dental asymmetry and audiogenic stress. Growth 37, 35-39. SIEGEL, M. I., AND DOYLE, W. J. (1975a). The differential effects of prenatal and postnatal audiogenic stress on fluctuating dental asymmetry. J. Exp. Zool. 191. 21 l-214. SIEGEL. M. I., AND DOYLE, W. J. (1975b). The effects of cold stress on fluctuating asymmetry in the dentition of the mouse. J. Exp. Zool. 193, 385-389.
344
SIEGEL
ET AL.
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