- Email: [email protected]
Comments on “The process of spermatogenesis liberates significant heat and the scrotum has a role in body thermoregulation”
Correspondence out of data; data alone do not generate ideas’’ [1]. However, the hypothesis that epidural anaesthesia improves surgical care [2] has a long history of being tested, and whether the overall answer is for support or rejection is uncertain. There are many published papers on this topic. A cursory search of MedLine, just of papers published in 2006, turned up three in which levobupivacaine had been used for major surgery. But there are other issues. In 1999, an editorial [3] commented that epidurals improve physiological variables, but with still no certainty of ‘better’ outcome, and the editorialists made the important point that we need to think carefully about what better outcome means, and to take notice of what patients want and feel. Postoperative care is a lot more than just one or other technique. As Holte and Kehlet [4] wrote, ‘‘the evolving concept of fast-track surgery and multimodal postoperative rehabilitation programmes with demonstrated improved outcomes and reduction of postoperative hospital stay indicates that previous efforts to show an improvement in postoperative outcome after major operations by continuous epidural analgesia may have had a faulty design. . .’’.
699 Just because you think of a good idea does not mean that someone else has not already thought of it. This one has not only already been thought of; it has been tested many times. It is not enough simply to make suggestions, but provide no data, just because of a new local anaesthetic.
References [1] Huszagh VA, Infante JP. The hypothetical way of progress. Nature 1989;338:109. [2] Yoldas O, Yoldas S, Tez M, Gocmen E. Epidural anaesthesia with levobupivacaine in patients undergoing major abdominal surgery. Med Hypoth 2007;69:468–9. [3] Buggy DJ, Smith G. Epidural anaesthesia and analgesia: better outcome after major surgery? BMJ 1999;319:530–1. [4] Holte K, Kehlet H. 14: Postoperative epidural analgesia and outcome – a research agenda. In: Trame `r MR, editor. Evidence-based resource in anaesthesia and analgesia. 2nd ed. London: BMJ Books; 2003. p. 175–83.
Neville W. Goodman Southmead Hospital, Bristol BS10 5NB, United Kingdom E-mail address: [email protected]
doi:10.1016/j.mehy.2007.07.014
Comments on ‘‘The process of spermatogenesis liberates significant heat and the scrotum has a role in body thermoregulation’’ The authors of this paper have presented an interesting hypothesis to the age old question pertaining to the evolutionary significance of development of the scrotum [1]. However, the authors have not mentioned or critically reviewed the following points in rationalizing their hypothesis: Firstly, the authors question the role of the pampiniform plexus in functioning as an efficient countercurrent mechanism. It is important to understand that the plexus merely helps in maintaining the temperature gradient between the testes and core body temperature and hence will not function intra abdominally, where presumably no gradients exist. All ascrotal mammals probably have other mechanisms of maintaining testicular
temperature below core body temperature if required for efficient spermatogenesis. Phylogenetic analysis of scrotal evolution in mammals has shown that scrotum has primarily evolved to maintain a lower temperature for effective spermatogenesis and species are progressing towards testicondia if alternative ways of maintaining euspermia are established [2,3]. The authors further state that on exposure to cold temperatures the scrotal muscle contract and bring the testes closer to the abdomen and hence contributes to body temperature regulation. The authors have not stated how heat transfer could take place in such situations and mechanisms of body thermoregulation being intrinsically
700 different between sexual members of a species are highly implausible. Moreover, quantitative aspects of the relative contributions of spermatogenesis and the muscular system of the body in maintaining core body temperature has not been brought to light. Since the muscles are in a state of constant tonic and contractile activity to maintain body posture, they are probably far more important in maintaining body temperature. Moreover, the surface area of the skin of scrotum is much less in comparison to that of the total body surface area. The phenomenon of non-shivering thermogenesis due to presence of excess brown fat in hibernating animals to maintain body temperature has not been commented upon. Nevertheless the authors’ hypothesis does find weightage in the previous report of Zorgniotti et al. [4] in showing differences in tympanic membrane temperature in patients affected with varicocele compared to healthy controls and requires further exploration.
Correspondence
References [1] Skandhan KP, Rajahariprasad A. The process of spermatogenesis liberates significant heat and the scrotum has a role in body thermoregulation. Med Hypotheses 2007;68(2): 303–7. [2] Einer-Jensen N, Hunter RHF. Counter-current transfer in reproductive biology. Reproduction 2005;129:9–18. [3] Werdelin L, Nilsonne A. The evolution of the scrotum and testicular descent in mammals: a phylogenetic view. J Theor Biol 1999;196(1):61–72. [4] Zorgniotti AW, Toth A, Macleod J. Infrared thermometry 8for testicular temperature determinations. Fertil Steril 1979;32(3):347–8.
Harish Janardhan Palleti Department of Biochemistry, Christian Medical College, Bagayam, Vellore, Tamilnadu 632 002, India Tel.: +91 9443681139 E-mail address: [email protected]
doi:10.1016/j.mehy.2007.07.013
Psychosocial factors may act via epigenetic mechanisms in the pathogenesis of mental disorders The idiopathic mental disorders like schizophrenia show complex inheritance patterns involving the interaction of genes with the environment. Psychosocial factors are thought to be important environmental factors involved in the pathogenesis of these disorders [1]. However, the precise mechanisms by which psychosocial factors interact with the underlying genes are unclear [2]. I suggest that psychosocial factors interact with the genes underlying the idiopathic mental disorders by acting via mechanisms involving epigenetics (heritable changes in gene expression that do not involve changes in DNA sequence). Epigenetics involves three interacting mechanisms: DNA methylation, modification of histones in chromatin, and RNA-mediated gene silencing [3]. This suggestion is based on the following: (1) There is evidence that the idiopathic mental disorders are epigenetic disorders [4]. (2) Environmental factors are able to modify epigenetic
mechanisms, thereby contributing to the development of abnormal phenotypes [5]. (3) A study on rats showed that maternal behaviour like increased pup licking and grooming and archedback nursing caused changes in DNA methylation at the hippocampal glucocorticoid receptor gene promoter in the pups [6]. These changes emerged during the first week of life, were reversed with cross fostering, persisted into adulthood, and were associated with altered histone acetylation. (4) In another study which used a chronic social defeat stress model of depression in mice, a robust increase in methylation of histones at the brain-derived neurotrophic factor gene promoter occurred [7].
References [1] Peedicayil J. Psychosocial factors in the pathogenesis of mental disorders. Brit J Psychiatry 2004;185:520.
699 Just because you think of a good idea does not mean that someone else has not already thought of it. This one has not only already been thought of; it has been tested many times. It is not enough simply to make suggestions, but provide no data, just because of a new local anaesthetic.
References [1] Huszagh VA, Infante JP. The hypothetical way of progress. Nature 1989;338:109. [2] Yoldas O, Yoldas S, Tez M, Gocmen E. Epidural anaesthesia with levobupivacaine in patients undergoing major abdominal surgery. Med Hypoth 2007;69:468–9. [3] Buggy DJ, Smith G. Epidural anaesthesia and analgesia: better outcome after major surgery? BMJ 1999;319:530–1. [4] Holte K, Kehlet H. 14: Postoperative epidural analgesia and outcome – a research agenda. In: Trame `r MR, editor. Evidence-based resource in anaesthesia and analgesia. 2nd ed. London: BMJ Books; 2003. p. 175–83.
Neville W. Goodman Southmead Hospital, Bristol BS10 5NB, United Kingdom E-mail address: [email protected]
doi:10.1016/j.mehy.2007.07.014
Comments on ‘‘The process of spermatogenesis liberates significant heat and the scrotum has a role in body thermoregulation’’ The authors of this paper have presented an interesting hypothesis to the age old question pertaining to the evolutionary significance of development of the scrotum [1]. However, the authors have not mentioned or critically reviewed the following points in rationalizing their hypothesis: Firstly, the authors question the role of the pampiniform plexus in functioning as an efficient countercurrent mechanism. It is important to understand that the plexus merely helps in maintaining the temperature gradient between the testes and core body temperature and hence will not function intra abdominally, where presumably no gradients exist. All ascrotal mammals probably have other mechanisms of maintaining testicular
temperature below core body temperature if required for efficient spermatogenesis. Phylogenetic analysis of scrotal evolution in mammals has shown that scrotum has primarily evolved to maintain a lower temperature for effective spermatogenesis and species are progressing towards testicondia if alternative ways of maintaining euspermia are established [2,3]. The authors further state that on exposure to cold temperatures the scrotal muscle contract and bring the testes closer to the abdomen and hence contributes to body temperature regulation. The authors have not stated how heat transfer could take place in such situations and mechanisms of body thermoregulation being intrinsically
700 different between sexual members of a species are highly implausible. Moreover, quantitative aspects of the relative contributions of spermatogenesis and the muscular system of the body in maintaining core body temperature has not been brought to light. Since the muscles are in a state of constant tonic and contractile activity to maintain body posture, they are probably far more important in maintaining body temperature. Moreover, the surface area of the skin of scrotum is much less in comparison to that of the total body surface area. The phenomenon of non-shivering thermogenesis due to presence of excess brown fat in hibernating animals to maintain body temperature has not been commented upon. Nevertheless the authors’ hypothesis does find weightage in the previous report of Zorgniotti et al. [4] in showing differences in tympanic membrane temperature in patients affected with varicocele compared to healthy controls and requires further exploration.
Correspondence
References [1] Skandhan KP, Rajahariprasad A. The process of spermatogenesis liberates significant heat and the scrotum has a role in body thermoregulation. Med Hypotheses 2007;68(2): 303–7. [2] Einer-Jensen N, Hunter RHF. Counter-current transfer in reproductive biology. Reproduction 2005;129:9–18. [3] Werdelin L, Nilsonne A. The evolution of the scrotum and testicular descent in mammals: a phylogenetic view. J Theor Biol 1999;196(1):61–72. [4] Zorgniotti AW, Toth A, Macleod J. Infrared thermometry 8for testicular temperature determinations. Fertil Steril 1979;32(3):347–8.
Harish Janardhan Palleti Department of Biochemistry, Christian Medical College, Bagayam, Vellore, Tamilnadu 632 002, India Tel.: +91 9443681139 E-mail address: [email protected]
doi:10.1016/j.mehy.2007.07.013
Psychosocial factors may act via epigenetic mechanisms in the pathogenesis of mental disorders The idiopathic mental disorders like schizophrenia show complex inheritance patterns involving the interaction of genes with the environment. Psychosocial factors are thought to be important environmental factors involved in the pathogenesis of these disorders [1]. However, the precise mechanisms by which psychosocial factors interact with the underlying genes are unclear [2]. I suggest that psychosocial factors interact with the genes underlying the idiopathic mental disorders by acting via mechanisms involving epigenetics (heritable changes in gene expression that do not involve changes in DNA sequence). Epigenetics involves three interacting mechanisms: DNA methylation, modification of histones in chromatin, and RNA-mediated gene silencing [3]. This suggestion is based on the following: (1) There is evidence that the idiopathic mental disorders are epigenetic disorders [4]. (2) Environmental factors are able to modify epigenetic
mechanisms, thereby contributing to the development of abnormal phenotypes [5]. (3) A study on rats showed that maternal behaviour like increased pup licking and grooming and archedback nursing caused changes in DNA methylation at the hippocampal glucocorticoid receptor gene promoter in the pups [6]. These changes emerged during the first week of life, were reversed with cross fostering, persisted into adulthood, and were associated with altered histone acetylation. (4) In another study which used a chronic social defeat stress model of depression in mice, a robust increase in methylation of histones at the brain-derived neurotrophic factor gene promoter occurred [7].
References [1] Peedicayil J. Psychosocial factors in the pathogenesis of mental disorders. Brit J Psychiatry 2004;185:520.