NEUROENDOCRINE ASYMMETRY

The information available at present clearly indicates that asymmetry exists from the level of elementary particles to the human cerebral co rtex, 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, an d thyroid lobes and that on the lateralization of hypothalamic, limbic , and other brain structures participating in the control of the endoc rine glands as well as relevant clinical observations are reviewed her e. The innervation of the peripheral endocrine glands is also briefly summarized because the afferent and efferent fibers of these glands ma y represent one part of the pathway involved in neuroendocrine asymmet ry. The data reviewed clearly indicate that some kind of asymmetry (mo rphological, biochemical, physiological, pathological) is evident at d ifferent levels of the neuroendocrine system (at limbic, hypothalamic, peripheral endocrine glands and their innervation) and there are spec ies, sex, and age differences. Most of the information accumulated dea ls with the CNS-gonadal system. A majority of the observations suggest that in both male and female rats there is a predominance of the righ t 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 af ter 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 addit ion to the hypothalamo-adenohypophyseal system acting via the general circulation on the peripheral endocrine glands, there is also a pure n eural link between the CNS and the gonads, the CNS and the adrenal gla nd, and also between the CNS and the thyroid. This link contains affer ent and efferent pathways and is able to modulate the functional activ ity or the responsiveness of the gland. It may also serve as a neural reflex are. 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 combina tion of (i) and (ii). The authors hope that this publication, in addit ion to providing an overview, will also stimulate research, both basic and clinical, in this exciting area of neuroendocrinology. (C) 1997 A cademic Press.