Neuroendocrine Asymmetry

Abstract

The information available at present clearly indicates that asymmetry exists from the level of elementary particles to the human cerebral cortex, the latest stage of evolution. Cerebral lateralization is one of the well-known asymmetries. This paper summarizes the data published in the past decades on the asymmetry of the neuroendocrine system. The information on the sided-differences between the gonads, adrenals, and thyroid lobes and that on the lateralization of hypothalamic, limbic, and other brain structures participating in the control of the endocrine glands as well as relevant clinical observations are reviewed here. The innervation of the peripheral endocrine glands is also briefly summarized because the afferent and efferent fibers of these glands may represent one part of the pathway involved in neuroendocrine asymmetry. The data reviewed clearly indicate that some kind of asymmetry (morphological, biochemical, physiological, pathological) is evident at different levels of the neuroendocrine system (at limbic, hypothalamic, peripheral endocrine glands and their innervation) and there are species, sex, and age differences. Most of the information accumulated deals with the CNS-gonadal system. A majority of the observations suggest that in both male and female rats there is a predominance of the right half of brain structures controlling gonadal function. The asymmetry, however, is not restricted to CNS structures: it also exists at the level of the gonads, including their innervation. It appears that the characteristic pattern of the CNS-gonadal system becomes fixed only after sexual maturation. Very few reports are available suggesting some kind of asymmetry of the CNS-adrenal cortex and the CNS-thyroid system. There are convincing findings consistent with the view that in addition to the hypothalamo-adenohypophyseal system acting via the general circulation on the peripheral endocrine glands, there is also a pure neural link between the CNS and the gonads, the CNS and the adrenal gland, and also between the CNS and the thyroid. This link contains afferent and efferent pathways and is able to modulate the functional activity or the responsiveness of the gland. It may also serve as a neural reflex arc. It is assumed that the neuroendocrine asymmetry expresses itself through (i) hypophysiotrophic neurohormones and hormones of the peripheral endocrine glands, (ii) neural pathways, or (iii) a combination of (i) and (ii). The authors hope that this publication, in addition to providing an overview, will also stimulate research, both basic and clinical, in this exciting area of neuroendocrinology.

Sexually Dimorphic Synaptic Organization of the Medial Amygdala

“…We evaluated both excitatory and inhibitory synaptic physiology in MeApd slices from 25-to 29-dold male and female rats. Previous reports that the MeA is lateralized (Gerendai and Halász, 1997;Cooke et al, 2003) led us to examine the left and right MeApd slices separately.…”

Local variation in endoparasite intensities of bank voles (Clethrionomys glareolus) from ecologically similar sites: morphometric and endocrine correlates

“…Our prediction is that animals showing greater fluctuating asymmetry and/or with larger adrenal glands, testes and seminal vesicles relative to body size will show greater intensities. We also included right -left asymmetry in adrenal gland weight as an independent variable because studies have suggested an association between directional (left-biased) asymmetry in adrenal gland size and dysfunction of the hypothalamic -pituitary -adrenal hormone axis (Szigethy et al, 1994;Abramov et al, 1996;Gerendai & Halasz, 1997), with greater asymmetry being associated with reduced production of glucocorticoids (Abramov et al, 1996;M. Moshkin, personal communication).…”

Asymmetry of Thyroid Lobe Volume in Normal Chinese Subjects: Association with Handedness and Position of Esophagus

“…It has been reported that unilateral posterior deafferentation of the hypothalamus on the left side induces a significant decrease in the basal mitosis of the thyroid follicular cells in the left and right lobes and prevents the hemithyroidectomy-induced increase in mitotic activity of follicular cells in the remaining lobe (Lewinski et al, 1982;Gerendai and Halasz, 1997). Therefore, pathways to and from the hypothalamus may exhibit a functional asymmetry in the control of the proliferation of thyroid follicular cells, which affects the thyroid size (Gerendai and Halasz, 1997). The actual reason for the association of handedness with thyroid asymmetry is still unclear.…”

“…Various kinds of asymmetry, including morphological, biochemical, functional, and pathological, exist in the central nervous system (CNS)-target endocrine gland system (Gerendai and Halasz, 1997). In humans, the right testis is heavier and has a higher position than the left testis (Cholst, 1947).…”

“…It has been suggested that thyroid asymmetry is related to the unilateral deafferentation of the hypothalamus on the thyroid gland (Lewinski et al, 1982;Gerendai and Halasz, 1997). However, besides the association of the CNS and thyroid gland asymmetry, the asymmetry of paired organs may also be associated with the presence and the size of their adjacent organs.…”