- Email: [email protected]
Response to open commentary, “Validity and Utility of Geotaxis” by Motz and Alberts
Neurotoxicology and Teratology 27 (2005) 539 – 540 www.elsevier.com/locate/neutera
Open peer commentary
Response to open commentary, ‘‘Validity and Utility of Geotaxis’’ by Motz and AlbertsB Virginia C. Moser * Neurotoxicology Division (MD B105-04), National Health and Environmental Effects Research Laboratory, US Environmental Protection Agency, Research Triangle Park, NC 27711, United States Received 17 February 2005; accepted 18 March 2005 Available online 19 July 2005
The thesis of this commentary by Motz and Alberts is that ‘‘infant rats do not display negative geotaxis’’. They provide an interesting historical perspective of how this test was developed and made popular. (It is always surprising to see how little some things change in so many decades.) The authors state that this test does not represent a true negative geotaxis behavior. While I agree with much that is presented, it is my opinion that the authors misstate some facts as well as misstating the use and interpretation of negative geotaxis as a behavioral endpoint in developing rodents. The authors misrepresent the use of negative geotaxis in some toxicity tests. They state that it ‘‘is part of the Functional Observational Battery’’, which is simply not true. The functional observational battery (FOB) was developed for adult rodents, whereas negative geotaxis has always been used only in a developmental context. Furthermore, the papers cited [9,10] do not mention geotaxis at all. I have also published on a modification of the FOB for developing rats [11], but negative geotaxis was not mentioned in that paper, either. Over the past several decades, negative geotaxis has often been used in behavioral teratology and developmental toxicity tests, specifically for pharmaceutical safety assessment. Surveys of industrial testing laborato-
i This response has been reviewed by the National Health and Environmental Effects Research Laboratory and approved for publication. Approval does not signify that the contents reflect the views of the Agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. * Tel.: +1 919 541 5075. E-mail address: [email protected].
0892-0362/$ - see front matter D 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.ntt.2005.06.004
ries have reported that this test is used in about a quarter to half of the studies [6,8]. Indeed, the respondents in the Lochry survey [6] rated it between acceptable and good in terms of overall utility in a test battery. The test remains popular in academic laboratories as well, and with a quick literature search I could find as many as 36 studies with it published in the last five years (for example, [3 – 5,7]). Interestingly, this test is not mentioned in the Developmental Neurotoxicity Test Guidelines promulgated by the US Environmental Protection Agency [13]. It has therefore not been used in studies conducted for regulatory purposes on pesticides and environmental agents. Regardless of its widespread use, Motz and Alberts appear to be more concerned with what this behavior actually is, i.e., the construct validity of the test. The authors describe how developing rats actually perform on this test. Having tested many rats and mice myself, I have a similar mental image. Perhaps the rats really are moving upward just so that their claws can ‘‘hook’’, or catch, the wire mesh. Even so, neuromotor and vestibular function are required to make that movement. If they do not move as well on a smooth surface, then why use one? The recent paper by Alberts et al. [2], using small angles of inclination, may be irrelevant to the current discussion since such an almost-flat surface is not a challenge to the pup. The finding that the wall-contact was the initiating event seems to support that. Motz and Alberts warn against over-interpreting data obtained using negative geotaxis, but I feel that this has not been the case, at least not for behavioral testing. They state that it has been ‘‘considered diagnostic of vestibular and/or proprioceptive function’’ (emphasis added). I could
540
V.C. Moser / Neurotoxicology and Teratology 27 (2005) 539 – 540
find no source that made such a bold claim. For example, its use in the Collaborative Behavioral Teratology Study was justified by it being a ‘‘vestibular and postural reflex requiring neuromotor coordination’’ [1]. Some authors consider it a developmental landmark or a ‘‘movement enforced by direct manipulation’’ [14]. Clearly vestibular function is necessary to maintain balance, especially on the more challenging steep inclines. Neuromotor coordination is required for the subject to move into the end position (facing upwards). Note that it should really be considered a ‘‘reaction’’, or ‘‘response’’, since there is not a simple neural circuit governing the movement, as there is in a reflex [12]. In addition, it is an apical measure since it reflects the integration of several neural systems. Such apical tests may be preferable for screening batteries, since endpoints that are too complex or too specific may not be altered by the test chemical [12]. Furthermore the goal of an apical test is not to identify underlying mechanisms, but rather to determine whether a normal, adaptive, developmentally relevant and highly predictable behavior has been disrupted by chemical exposure. A possible compromise, as suggested by the authors, is for this behavioral assay to be renamed in a way that avoids the implication that gravity is the only stimulus eliciting the response, and that movement away from gravity is the only relevant aspect of the response. A simple name like ‘‘incline test’’ would convey what the test is, not what it might measure. The benefits of such a name change, however, must be weighed against the potential confusion that might ensue, given the hundreds of published articles that use the currently accepted terminology. The main question seems to be whether this is indeed a response to gravity, or a vestibular/neuromotor reaction that occurs when the pup is placed in an unstable position and that improves as the pup develops. Perhaps the former is of interest to physiological psychologists who strive to understand the neural circuitry underlying behavior. But for those of us who are interested in finding apical behaviors that can be used as indicators of chemical-induced dysfunction, the
negative geotaxis assay has a firm place in our testing repertoire.
References [1] J. Adams, J. Buelke-Sam, C.A. Kimmel, C.J. Nelson, L.W. Reiter, T.J. Sobotka, H.A. Tilson, B.K. Nelson, Collaborative behavioral teratology study: protocol design and testing procedures, Neurobehav. Toxicol. Teratol. 7 (1985) 579 – 586. [2] J.R. Alberts, B.A. Motz, J.C. Schank, Positive geotaxis in infant rats (Rattus norvegicus): a natural behavior and a historical correction, J. Comp. Psychol. 118 (2004) 123 – 132. [3] V. Boue¨t, R.J. Wubbels, H.A.A. deJong, A. Gramsbergen, Behavioural consequences of hypergravity in developing rats, Dev. Brain Res. 153 (2004) 69 – 78. [4] W.J. Bowers, J.S. Nakai, I. Chu, M.G. Wade, D. Moir, A. Yagminas, S. Gill, O. Pulido, R. Meuller, Early developmental neurotoxicity of a PCB/organochlorine mixture in rodents after gestational and lactational exposure, Toxicol. Sci. 77 (2004) 51 – 62. [5] C.A. Lazarini, R.Y. Lima, A.P. Guedes, M.M. Bernardi, Prenatal exposure to dichlorvos: physical and behavioral effects on rat offspring, Neurotoxicol. Teratol. 26 (2004) 607 – 614. [6] E.A. Lochry, C. Johnson, P.J. Wier, Behavioral evaluations in developmental toxicity testing: MARTA survey results, Neurotoxicol. Teratol. 16 (1994) 55 – 63. [7] A. Lubics, D. Reglo¨di, A. Tama´s, P. Kiss, M. Szalai, L. Szalontay, I. Lengva´ri, Neurological reflexes and early motor behavior in rats subjected to neonatal hypoxic – ischemic injury, Behav. Brain. Res. 157 (2005) 157 – 165. [8] L.D. Middaugh, D. Dow-Edwards, A.A. Li, J.D. Sandler, J. Seed, L.P. Sheets, D.L. Shuey, W. Slikker Jr., W.P. Weisenburger, L.D. Wise, M.R. Selwyn, Neurobehavioral assessment: a survey of use and value in safety assessment studies, Toxicol. Sci. 76 (2003) 250 – 261. [9] V.C. Moser, Screening approaches to neurotoxicity: a functional observational battery, J. Amer. Coll. Toxicol. 8 (1989) 85 – 93. [10] V.C. Moser, Approaches for assessing the validity of a functional observational battery, Neurotoxicol. Teratol. 12 (1990) 483 – 488. [11] V.C. Moser, The functional observational battery in adult and developing rats, Neurotoxicol 21 (2000) 989 – 996. [12] B. Ulbrich, A.K. Palmer, Neurobehavioral aspects of developmental toxicity testing, Environ. Health Perspect. 104 (suppl 2) (1996) 407 – 412. [13] U.S. Environmental Protection Agency, Developmental neurotoxicity study, Health Effects Test Guidelines, 1998 (OPPTS 870.6300, EPA 712-C-98-239, http://www.epa.gov/epahome/resource.htm). [14] G. Zbinden, Experimental methods in behavioral teratology, Arch. Toxicol. 48 (1981) 69 – 88.
Open peer commentary
Response to open commentary, ‘‘Validity and Utility of Geotaxis’’ by Motz and AlbertsB Virginia C. Moser * Neurotoxicology Division (MD B105-04), National Health and Environmental Effects Research Laboratory, US Environmental Protection Agency, Research Triangle Park, NC 27711, United States Received 17 February 2005; accepted 18 March 2005 Available online 19 July 2005
The thesis of this commentary by Motz and Alberts is that ‘‘infant rats do not display negative geotaxis’’. They provide an interesting historical perspective of how this test was developed and made popular. (It is always surprising to see how little some things change in so many decades.) The authors state that this test does not represent a true negative geotaxis behavior. While I agree with much that is presented, it is my opinion that the authors misstate some facts as well as misstating the use and interpretation of negative geotaxis as a behavioral endpoint in developing rodents. The authors misrepresent the use of negative geotaxis in some toxicity tests. They state that it ‘‘is part of the Functional Observational Battery’’, which is simply not true. The functional observational battery (FOB) was developed for adult rodents, whereas negative geotaxis has always been used only in a developmental context. Furthermore, the papers cited [9,10] do not mention geotaxis at all. I have also published on a modification of the FOB for developing rats [11], but negative geotaxis was not mentioned in that paper, either. Over the past several decades, negative geotaxis has often been used in behavioral teratology and developmental toxicity tests, specifically for pharmaceutical safety assessment. Surveys of industrial testing laborato-
i This response has been reviewed by the National Health and Environmental Effects Research Laboratory and approved for publication. Approval does not signify that the contents reflect the views of the Agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. * Tel.: +1 919 541 5075. E-mail address: [email protected].
0892-0362/$ - see front matter D 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.ntt.2005.06.004
ries have reported that this test is used in about a quarter to half of the studies [6,8]. Indeed, the respondents in the Lochry survey [6] rated it between acceptable and good in terms of overall utility in a test battery. The test remains popular in academic laboratories as well, and with a quick literature search I could find as many as 36 studies with it published in the last five years (for example, [3 – 5,7]). Interestingly, this test is not mentioned in the Developmental Neurotoxicity Test Guidelines promulgated by the US Environmental Protection Agency [13]. It has therefore not been used in studies conducted for regulatory purposes on pesticides and environmental agents. Regardless of its widespread use, Motz and Alberts appear to be more concerned with what this behavior actually is, i.e., the construct validity of the test. The authors describe how developing rats actually perform on this test. Having tested many rats and mice myself, I have a similar mental image. Perhaps the rats really are moving upward just so that their claws can ‘‘hook’’, or catch, the wire mesh. Even so, neuromotor and vestibular function are required to make that movement. If they do not move as well on a smooth surface, then why use one? The recent paper by Alberts et al. [2], using small angles of inclination, may be irrelevant to the current discussion since such an almost-flat surface is not a challenge to the pup. The finding that the wall-contact was the initiating event seems to support that. Motz and Alberts warn against over-interpreting data obtained using negative geotaxis, but I feel that this has not been the case, at least not for behavioral testing. They state that it has been ‘‘considered diagnostic of vestibular and/or proprioceptive function’’ (emphasis added). I could
540
V.C. Moser / Neurotoxicology and Teratology 27 (2005) 539 – 540
find no source that made such a bold claim. For example, its use in the Collaborative Behavioral Teratology Study was justified by it being a ‘‘vestibular and postural reflex requiring neuromotor coordination’’ [1]. Some authors consider it a developmental landmark or a ‘‘movement enforced by direct manipulation’’ [14]. Clearly vestibular function is necessary to maintain balance, especially on the more challenging steep inclines. Neuromotor coordination is required for the subject to move into the end position (facing upwards). Note that it should really be considered a ‘‘reaction’’, or ‘‘response’’, since there is not a simple neural circuit governing the movement, as there is in a reflex [12]. In addition, it is an apical measure since it reflects the integration of several neural systems. Such apical tests may be preferable for screening batteries, since endpoints that are too complex or too specific may not be altered by the test chemical [12]. Furthermore the goal of an apical test is not to identify underlying mechanisms, but rather to determine whether a normal, adaptive, developmentally relevant and highly predictable behavior has been disrupted by chemical exposure. A possible compromise, as suggested by the authors, is for this behavioral assay to be renamed in a way that avoids the implication that gravity is the only stimulus eliciting the response, and that movement away from gravity is the only relevant aspect of the response. A simple name like ‘‘incline test’’ would convey what the test is, not what it might measure. The benefits of such a name change, however, must be weighed against the potential confusion that might ensue, given the hundreds of published articles that use the currently accepted terminology. The main question seems to be whether this is indeed a response to gravity, or a vestibular/neuromotor reaction that occurs when the pup is placed in an unstable position and that improves as the pup develops. Perhaps the former is of interest to physiological psychologists who strive to understand the neural circuitry underlying behavior. But for those of us who are interested in finding apical behaviors that can be used as indicators of chemical-induced dysfunction, the
negative geotaxis assay has a firm place in our testing repertoire.
References [1] J. Adams, J. Buelke-Sam, C.A. Kimmel, C.J. Nelson, L.W. Reiter, T.J. Sobotka, H.A. Tilson, B.K. Nelson, Collaborative behavioral teratology study: protocol design and testing procedures, Neurobehav. Toxicol. Teratol. 7 (1985) 579 – 586. [2] J.R. Alberts, B.A. Motz, J.C. Schank, Positive geotaxis in infant rats (Rattus norvegicus): a natural behavior and a historical correction, J. Comp. Psychol. 118 (2004) 123 – 132. [3] V. Boue¨t, R.J. Wubbels, H.A.A. deJong, A. Gramsbergen, Behavioural consequences of hypergravity in developing rats, Dev. Brain Res. 153 (2004) 69 – 78. [4] W.J. Bowers, J.S. Nakai, I. Chu, M.G. Wade, D. Moir, A. Yagminas, S. Gill, O. Pulido, R. Meuller, Early developmental neurotoxicity of a PCB/organochlorine mixture in rodents after gestational and lactational exposure, Toxicol. Sci. 77 (2004) 51 – 62. [5] C.A. Lazarini, R.Y. Lima, A.P. Guedes, M.M. Bernardi, Prenatal exposure to dichlorvos: physical and behavioral effects on rat offspring, Neurotoxicol. Teratol. 26 (2004) 607 – 614. [6] E.A. Lochry, C. Johnson, P.J. Wier, Behavioral evaluations in developmental toxicity testing: MARTA survey results, Neurotoxicol. Teratol. 16 (1994) 55 – 63. [7] A. Lubics, D. Reglo¨di, A. Tama´s, P. Kiss, M. Szalai, L. Szalontay, I. Lengva´ri, Neurological reflexes and early motor behavior in rats subjected to neonatal hypoxic – ischemic injury, Behav. Brain. Res. 157 (2005) 157 – 165. [8] L.D. Middaugh, D. Dow-Edwards, A.A. Li, J.D. Sandler, J. Seed, L.P. Sheets, D.L. Shuey, W. Slikker Jr., W.P. Weisenburger, L.D. Wise, M.R. Selwyn, Neurobehavioral assessment: a survey of use and value in safety assessment studies, Toxicol. Sci. 76 (2003) 250 – 261. [9] V.C. Moser, Screening approaches to neurotoxicity: a functional observational battery, J. Amer. Coll. Toxicol. 8 (1989) 85 – 93. [10] V.C. Moser, Approaches for assessing the validity of a functional observational battery, Neurotoxicol. Teratol. 12 (1990) 483 – 488. [11] V.C. Moser, The functional observational battery in adult and developing rats, Neurotoxicol 21 (2000) 989 – 996. [12] B. Ulbrich, A.K. Palmer, Neurobehavioral aspects of developmental toxicity testing, Environ. Health Perspect. 104 (suppl 2) (1996) 407 – 412. [13] U.S. Environmental Protection Agency, Developmental neurotoxicity study, Health Effects Test Guidelines, 1998 (OPPTS 870.6300, EPA 712-C-98-239, http://www.epa.gov/epahome/resource.htm). [14] G. Zbinden, Experimental methods in behavioral teratology, Arch. Toxicol. 48 (1981) 69 – 88.