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Reply to: Improving Research Standards to Restore Trust in Intranasal Oxytocin
Correspondence Reply to: Improving Research Standards to Restore Trust in Intranasal Oxytocin To the Editor: In their thoughtful commentary, Carson et al. (1) point out that animal studies often show the same weaknesses that confuse the literature on intranasal oxytocin, and they make some important constructive comments on how research practice can and should be improved. We agree with many of their points. In our recent review (2), we expressed concern about publication bias, questionable statistical analysis, and methodologic weaknesses in the literature on intranasal oxytocin and noted that there “are similar concerns about basic biological research.” Carson et al. (1) expand on this, quoting a commentary by Freedman et al. (3), who estimated the prevalence of irreproducible research in animal science generally as .50%. Freedman et al. used a very wide definition of irreproducibility, including the absence of sufficient methodologic detail to allow replication, the unavailability of key materials, inappropriate statistics, and the lack of transparency in reporting data, all of which are likely to contribute to the excess of false-positive results not only in studies of intranasal oxytocin but also in published biological research generally (4). We fully agree that these are cause for serious concern. There is a need for much more openness about original data and how they are analyzed, and, as Carson et al. (1) state, preclinical scientists have been notoriously protective of their data sets. We raised this issue in a recent editorial (5), and, following our own advice, our most recent research paper (on the olfactory bulb) is accompanied by 11 workbooks of supplementary material of raw data and analyses (6). We are intimately aware of the burden on researchers that can be involved in making large data sets openly available in a form that is transparent and usable by others, but we see no reason why the (relatively) small data sets from behavioral studies should not routinely be published in full. Some key data from influential articles on intranasal oxytocin are now unavailable for reanalysis after being “discarded within old computers,” and this is unfortunate (7). Carson et al. (1) draw attention to an article by Calcagnoli et al. (8) that showed antiaggressive and prosocial effects in rats after intranasal delivery of oxytocin that were similar to the effects seen earlier with central administration of oxytocin. This study used an extremely high dose of intranasal oxytocin (20 mg; 20 times the total pituitary content of oxytocin and a dose that is proportionately far higher than any used in human studies), and it had similar effects to the effects that occurred with central infusion at a rate of 10 ng/hour. The lowest dose of oxytocin administered by the intracerebroventricular route that has been shown to have clear physiologic effects after acute bolus administration in rats (2) is 1 ng. This dose is just .005% of the dose that Calcagnoli et al. (8) administered intranasally, and this seems in accord with the observed very low level of entry into the brain from either the intranasal route or the intravenous route. It seems to us that the effects
Biological Psychiatry
reported by Calcagnoli et al. (8) do not imply any privileged route of entry into the brain from the nose. Carson et al. (1) subsequently draw attention to the studies of intranasal oxytocin that have used functional neuroimaging. It has been suggested by other authors that the field of functional neuroimaging “may be particularly vulnerable to false positives” (9), but, this aside, we note that observing effects of intranasal oxytocin with functional magnetic resonance imaging says nothing about the site of action of oxytocin. An action on, for example, the gut or penis would certainly produce effects in the brain. Carson et al. (1) suggest that intranasal oxytocin might influence the brain by passage along olfactory and trigeminal extracellular pathways, quoting a study of radiolabeled insulinlike growth factor-I given intranasally (10). Two points should be noted. First, in contrast to oxytocin, insulin-like growth factor-I can cross the blood-brain barrier by a saturable transport mechanism (11). Second, the cited study measured the radiolabel but did not establish that the label was associated with intact peptide. Such an association may be important, for when Ang and Jenkins (12) gave radiolabeled vasopressin to dogs, they could detect label in the cerebrospinal fluid, but they found by high-performance liquid chromatography that none of it was associated with intact vasopressin. Nevertheless, the possibility that oxytocin and vasopressin might enter the brain via the olfactory nerves is one that we have addressed ourselves. After characterizing the effect of locally applied vasopressin on olfactory neurons in vivo (13), we looked for similar effects after intranasal application, but we found none (14). We also found activation of Fos expression in the olfactory bulbs after central administration of 2 ng of either oxytocin or vasopressin, but we found no such activation after intranasal application. We may not have given enough oxytocin or vasopressin—we gave only 1 mg intranasally in rats, thinking that giving the equivalent of one pituitary content as a bolus should be enough for access to the brain via a privileged entry route. Finally, in their title, Carson et al. (1) indicate the need to “restore trust in intranasal oxytocin.” Studies with intranasal oxytocin have produced some interesting effects that are likely to be real and worth pursuing, even if, as we suspect, these may be mediated by peripheral actions. However, on the issue of trust, a recent review of psychological research on oxytocin concluded that “cumulative evidence does not provide robust convergent evidence that human trust is reliably associated with oxytocin” (15). Gareth Leng Mike Ludwig
Acknowledgments and Disclosures This work was supported by the Biotechnology and Biological Sciences Research Council (Grant No. BB/J004723), the Edinburgh Patrick Wild Centre, and the European Union Seventh Framework Programme for research, technological development and demonstration (Grant Nos. 245009 [NeuroFAST] and 607310 [Nudge-it]).
SEE COMMENTARY ON PAGE
http://dx.doi.org/10.1016/j.biopsych.2015.08.030 ISSN: 0006-3223
e1 & 2015 Society of Biological Psychiatry Biological Psychiatry ]]], 2015; ]:]]]–]]] www.sobp.org/journal
Biological Psychiatry
Correspondence
The authors report no biomedical financial interests or potential conflicts of interest.
Article Information From the Centre for Integrative Physiology, University of Edinburgh, Edinburgh, Scotland, United Kingdom. Address correspondence to Gareth Leng, Ph.D., Centre for Integrative Physiology, University of Edinburgh, Hugh Robson Building, George Square, Edinburgh, Scotland EH9 8XD, United Kingdom; E-mail: Gareth. [email protected]. See also associated correspondence, http://dx.doi.org/10.1016/j.biop sych.2015.08.031.
References 1.
2. 3. 4.
5.
e2
Carson DS, Yuan H, Labuschagne I (2015): Commentary on Leng and Ludwig (2015): Improving research standards to restore trust in intranasal oxytocin. Biol Psychiatry. Leng G, Ludwig M (2015): Intranasal oxytocin: Myths and delusions. Biol Psychiatry. Freedman LP, Cockburn IM, Simcoe TS (2015): The economics of reproducibility in preclinical research. PloS Biol 13:e1002165. Walum H, Waldman ID, Young LJ (2015): Statistical and methodological considerations for the interpretation of intranasal oxytocin studies. Biol Psychiatry. Leng G. (2014): Publishing the data behind the data (Show me yours, I’ll show you mine) [published online ahead of print Oct 1]. Physiol Rep.
Biological Psychiatry ]]], 2015; ]:]]]–]]] www.sobp.org/journal
6.
7. 8.
9. 10.
11. 12.
13.
14.
15.
Leng G, Hashimoto H, Tsuji C, Sabatier N, Ludwig M. (2014): Discharge patterning in rat olfactory bulb mitral cells in vivo [published online ahead of print Oct 1]. Physiol Rep. Conlisk J (2011): Professor Zak’s empirical studies on trust and oxytocin. J Econ Behav Organ 78:160–166. Calcagnoli F, Kreutzmann JC, de Boer SF, Althaus M, Koolhaas JM (2015): Acute and repeated intranasal oxytocin administration exerts anti-aggressive and pro-affiliative effects in male rats. Psychoneuroendocrinology 51:112–121. Carp J (2012): The secret lives of experiments: Methods reporting in the fMRI literature. Neuroimage 63:289–300. Thorne RG, Pronk GJ, Padmanabhan V, Frey WH (2004): Delivery of insulin-like growth factor-I to the rat brain and spinal cord along olfactory and trigeminal pathways following intranasal administration. Neuroscience 127:481–496. Pan W, Kastin AJ (2000): Interactions of IGF-1 with the blood-brain barrier in vivo and in situ. Neuroendocrinology 72:171–178. Ang VT, Jenkins JS (1982): Blood-cerebrospinal fluid barrier to arginine-vasopressin, desmopressin and desglycinamide argininevasopressin in the dog. J Endocrinol 93:319–325. Tobin VA, Hashimoto H, Wacker DW, Takayanagi Y, Langnaese K, Caquineau C, et al. (2010): An intrinsic vasopressin system in the olfactory bulb is involved in social recognition. Nature 464:413–417. Ludwig M, Tobin VA, Callahan MF, Papadaki E, Becker A, Engelmann M, Leng G (2013): Intranasal application of vasopressin fails to elicit changes in brain immediate early gene expression, neural activity and behavioural performance of rats. J Neuroendocrinol 25:655–667. Nave G, Camerer C, McCullough M. (in press): Does oxytocin increase trust in humans? A critical review of research. Perspect Psychol Sci.
Biological Psychiatry
reported by Calcagnoli et al. (8) do not imply any privileged route of entry into the brain from the nose. Carson et al. (1) subsequently draw attention to the studies of intranasal oxytocin that have used functional neuroimaging. It has been suggested by other authors that the field of functional neuroimaging “may be particularly vulnerable to false positives” (9), but, this aside, we note that observing effects of intranasal oxytocin with functional magnetic resonance imaging says nothing about the site of action of oxytocin. An action on, for example, the gut or penis would certainly produce effects in the brain. Carson et al. (1) suggest that intranasal oxytocin might influence the brain by passage along olfactory and trigeminal extracellular pathways, quoting a study of radiolabeled insulinlike growth factor-I given intranasally (10). Two points should be noted. First, in contrast to oxytocin, insulin-like growth factor-I can cross the blood-brain barrier by a saturable transport mechanism (11). Second, the cited study measured the radiolabel but did not establish that the label was associated with intact peptide. Such an association may be important, for when Ang and Jenkins (12) gave radiolabeled vasopressin to dogs, they could detect label in the cerebrospinal fluid, but they found by high-performance liquid chromatography that none of it was associated with intact vasopressin. Nevertheless, the possibility that oxytocin and vasopressin might enter the brain via the olfactory nerves is one that we have addressed ourselves. After characterizing the effect of locally applied vasopressin on olfactory neurons in vivo (13), we looked for similar effects after intranasal application, but we found none (14). We also found activation of Fos expression in the olfactory bulbs after central administration of 2 ng of either oxytocin or vasopressin, but we found no such activation after intranasal application. We may not have given enough oxytocin or vasopressin—we gave only 1 mg intranasally in rats, thinking that giving the equivalent of one pituitary content as a bolus should be enough for access to the brain via a privileged entry route. Finally, in their title, Carson et al. (1) indicate the need to “restore trust in intranasal oxytocin.” Studies with intranasal oxytocin have produced some interesting effects that are likely to be real and worth pursuing, even if, as we suspect, these may be mediated by peripheral actions. However, on the issue of trust, a recent review of psychological research on oxytocin concluded that “cumulative evidence does not provide robust convergent evidence that human trust is reliably associated with oxytocin” (15). Gareth Leng Mike Ludwig
Acknowledgments and Disclosures This work was supported by the Biotechnology and Biological Sciences Research Council (Grant No. BB/J004723), the Edinburgh Patrick Wild Centre, and the European Union Seventh Framework Programme for research, technological development and demonstration (Grant Nos. 245009 [NeuroFAST] and 607310 [Nudge-it]).
SEE COMMENTARY ON PAGE
http://dx.doi.org/10.1016/j.biopsych.2015.08.030 ISSN: 0006-3223
e1 & 2015 Society of Biological Psychiatry Biological Psychiatry ]]], 2015; ]:]]]–]]] www.sobp.org/journal
Biological Psychiatry
Correspondence
The authors report no biomedical financial interests or potential conflicts of interest.
Article Information From the Centre for Integrative Physiology, University of Edinburgh, Edinburgh, Scotland, United Kingdom. Address correspondence to Gareth Leng, Ph.D., Centre for Integrative Physiology, University of Edinburgh, Hugh Robson Building, George Square, Edinburgh, Scotland EH9 8XD, United Kingdom; E-mail: Gareth. [email protected]. See also associated correspondence, http://dx.doi.org/10.1016/j.biop sych.2015.08.031.
References 1.
2. 3. 4.
5.
e2
Carson DS, Yuan H, Labuschagne I (2015): Commentary on Leng and Ludwig (2015): Improving research standards to restore trust in intranasal oxytocin. Biol Psychiatry. Leng G, Ludwig M (2015): Intranasal oxytocin: Myths and delusions. Biol Psychiatry. Freedman LP, Cockburn IM, Simcoe TS (2015): The economics of reproducibility in preclinical research. PloS Biol 13:e1002165. Walum H, Waldman ID, Young LJ (2015): Statistical and methodological considerations for the interpretation of intranasal oxytocin studies. Biol Psychiatry. Leng G. (2014): Publishing the data behind the data (Show me yours, I’ll show you mine) [published online ahead of print Oct 1]. Physiol Rep.
Biological Psychiatry ]]], 2015; ]:]]]–]]] www.sobp.org/journal
6.
7. 8.
9. 10.
11. 12.
13.
14.
15.
Leng G, Hashimoto H, Tsuji C, Sabatier N, Ludwig M. (2014): Discharge patterning in rat olfactory bulb mitral cells in vivo [published online ahead of print Oct 1]. Physiol Rep. Conlisk J (2011): Professor Zak’s empirical studies on trust and oxytocin. J Econ Behav Organ 78:160–166. Calcagnoli F, Kreutzmann JC, de Boer SF, Althaus M, Koolhaas JM (2015): Acute and repeated intranasal oxytocin administration exerts anti-aggressive and pro-affiliative effects in male rats. Psychoneuroendocrinology 51:112–121. Carp J (2012): The secret lives of experiments: Methods reporting in the fMRI literature. Neuroimage 63:289–300. Thorne RG, Pronk GJ, Padmanabhan V, Frey WH (2004): Delivery of insulin-like growth factor-I to the rat brain and spinal cord along olfactory and trigeminal pathways following intranasal administration. Neuroscience 127:481–496. Pan W, Kastin AJ (2000): Interactions of IGF-1 with the blood-brain barrier in vivo and in situ. Neuroendocrinology 72:171–178. Ang VT, Jenkins JS (1982): Blood-cerebrospinal fluid barrier to arginine-vasopressin, desmopressin and desglycinamide argininevasopressin in the dog. J Endocrinol 93:319–325. Tobin VA, Hashimoto H, Wacker DW, Takayanagi Y, Langnaese K, Caquineau C, et al. (2010): An intrinsic vasopressin system in the olfactory bulb is involved in social recognition. Nature 464:413–417. Ludwig M, Tobin VA, Callahan MF, Papadaki E, Becker A, Engelmann M, Leng G (2013): Intranasal application of vasopressin fails to elicit changes in brain immediate early gene expression, neural activity and behavioural performance of rats. J Neuroendocrinol 25:655–667. Nave G, Camerer C, McCullough M. (in press): Does oxytocin increase trust in humans? A critical review of research. Perspect Psychol Sci.