The effect of siblings on early development: a potential contributor to personality differences in mammals.

Although most mammals grow up in the company of same or different age sibs (or half sibs), surprisingly little attention has been given to how relations among them might influence the development of individual differences in morphology, physiology, and behavior. Here we review evidence from our work on domestic and wild European rabbits, and more recently on laboratory rats, mice, and domestic cats, supporting the proposition that in mammals early sibling relations contribute to the development of individual differences in these three domains and thereby to long-term behavioral differences of the kind we might consider part of an animal's behavioral style or personality. First we report a consistent and marked negative relation between litter size and individuals' body mass at birth and weaning, as well as marked within-litter differences in prenatal body mass and placental efficiency. We then report individual differences in preweaning behaviors associated with these morphological variables such as position occupied in the litter huddle and development of motor ability, as well as physiological differences in thermoregulation, immune parameters, and endocrine indicators of stress. Finally, we report first evidence from wild rabbits that early relations among littermates may have long-term consequences for individual differences in behavioral style. We conclude that in mammals, individual differences in early growth, physiology and behavior potentially important for the development of animal personality, are shaped to an appreciable extent by early sibling relations and that this little-researched field deserves closer attention.

Environmental medicine and its impact on human health.

No abstract present.

Beyond reproductive effects of sex steroids.

In this special issue of Minireviews in Medicinal Chemistry, called Beyond Reproductive Effects of Sex Steroids, the reader will find representative papers of the state of the art in the field of non-reproductive effects of sex steroids. For instance, Terán-Pérez and co-workers discuss the role of steroid hormones in the sleep-waking cycle. Cabrera-Muñoz et al., review the role of estradiol and progesterone in the susceptibility and disease progression of one of the most important health problems on the last decade: HIV infection. Furthermore, González-Arenas and Agramonte-Hevia make a review on the effects that sex steroid hormones have on normal and pathologic conditions of the lung. The effects of sex steroids on the maternal brain is very nicely reviewed by Kinsley et al. The role of sex steroid hormones in immunoregulation, particularly in the establishment, growth and reproduction of parasites is reviewed by Hernández-Bello et al. De Nicola et al., make an interesting contribution regarding the role of estradiol in neuroprotection during hypertensive encephalopathy. The regulation of morphological and functional characteristics of the amygdala regulated by sex steroids in the adult rat is a topic boarded by Rasia-Filho and co-workers. Finally, Bautista et al., talk about the role of sex steroid hormones in one of the most important functions of organisms: appetitive behavior. We hope that our readers will find fascinating this Special Issue devoted to the wide non-typical functions in vertebrates.

Non-reproductive effects of sex steroids: their immunoregulatory role.

In this special issue of Current Topics in Medicinal Chemistry, the reader will find reviewed some of the hottest topics in the field of the non-reproductive effects of sex steroids. Cabrera-Muñoz et al., show that progesterone participates in the regulation of human brain tumors growth. The contribution of Martocchia suggests that sex steroid receptor modulating drugs provide new therapeutic approaches to autoimmune diseases. The role of sex steroid participation in the differentiation of stem cells to neurones is discussed by I. Velasco. Pérez-Torres and collaborators demonstrate that sex steroids play an important role in the appearance and development of renal diseases and the metabolic syndrome, the new epidemics of our century. Paris and Frye hypthetize that gestational stress, have effects on cognitive performance and/or neuronal integrity in the fetus, and that exposure to variable stress during gestation can perturb cognitive performance, concomitant with dendrite development in hippocampus and diencephalon. Muñoz-Cruz et al. thoroughly review the growing body of evidence that shows reciprocal relationship between sex steroids and the immune system, and conclude that understanding the mechanisms of action of sex steroids on immune cells is important for further progress in the development of novel therapies for chronic diseases associated to immune dysregulation. Besides, the effects of sexual steroids on pancreatic function and diabetes are reviewed by Morimoto et al. Yanes et al. review some of the contradictions raised in the context of the recently proposed critical period hypothesis, which takes into account the frame-time after cessation of ovarian function. Finally, another vey intetresting aspect of the non-reproductive effects of sex-steroids, is the related to some cognition-related aspects, which is reviewed by Picazo et al.