Yasumasa Arai

Distribution and possible roles of the highly polysialylated neural cell adhesion molecule (NCAM-H) in the developing and adult central nervous system

The neural cell adhesion molecule (NCAM) is a cell surface glycoprotein which is thought to mediate cell adhesion and recognition. During developmental stages, NCAM is highly polysialylated (NCAM-H) by a unique alpha-2,8-linked polysialic acid chain (PSA), and this PSA portion of NCAM-H has been found to be closely associated with various developmental processes of the nervous system. Further, recent immunohistochemical investigations have revealed that even in the adult nervous system, a persistent PSA expression has been found confined to several regions: the olfactory bulb, the piriform cortex, the hippocampal dentate gyrus, the hypothalamus, some nuclei of the medulla and the dorsal horn of the spinal cord, which are related directly or indirectly to sensory systems. Moreover, in the dentate gyrus and olfactory bulb the expression is connected with adult neurogenesis that may add new neuronal circuits to the adult neural tissue. Therefore, the possible role of NCAM-H in the central nervous system may be associated not only with neural development, but also with adult functions, such as the processing system of sensory information and neuronal plasticity.

Expression of highly polysialylated NCAM in the neocortex and piriform cortex of the developing and the adult rat

SummaryThe expression of a highly polysialylated form of the neural cell adhesion molecule (NCAM-H) has been investigated in the neocortex and piriform cortex of the developing and the adult rat by using a monoclonal antibody 12E3, which has been found to recognize the polysialic acid portion of NCAM-H. Immunoblot analysis of the cortical homogenates showed that NCAM-H was temporarily expressed during the late embryonic and early postnatal stages. Further, immunohistochemical observations revealed that NCAM-H appeared at embryonic day 13 (E13) in the plexiform primordium in horizontally-oriented cells, probably Cajal-Retzius cells, which are the first neurons to differentiate. During the late embryonic stage, the marginal zone, subplate, and intermediate zone strongly stained, whereas the ventricular zone stained weakly. After birth, the NCAM-H expression was progressively attenuated from a week onwards, and almost vanished in the adult neocortex. In the primordium of the piriform cortex, NCAM-H immunoreactivity also became positive at E13. The time sequences of the NCAM-H expression in these neurons were similar to those of the neurons in the neocortical area. In the piriform cortex, however, the expression remained in a number of neurons in the layer II, which receives a large number of olfactory fibers from the olfactory bulb, where prolonged neurogenesis and construction of neural circuits take place in adulthood. These results suggest that NCAM-H not only plays an important role in the developing rat cortex, but also may be involved in some functions related to reorganization in the adult piriform cortex.

Sexual dimorphism in synaptic organization in the amygdala and its dependence on neonatal hormone environment.

Abstract Electron microscopic observation was made on coronal sections from the middle part of the medial amygdaloid nucleus (AMN) of the rats. According to postsynaptic elements, shaft synapses (SHS) terminating on dendritic shafts, spine synapses (SPS) made on dendritic spines and somatic synapses (SOS) made on neuronal cell bodies were differentially counted on a field of 10,000 sq. μm in a single section of the identical level of the nucleus in each brain. The total number of SHS, SPS, and SOS per 10,000 sq. μm in normal adult male rats was significantly larger than in normal female rats. This sex difference in synaptic number was due to a significant increase in number of SHS in normal male rats, while the incidences of SPS and SOS in normal males were not significantly different from those in normal females. A single injection of 1.25 mg testosterone propionate (TP) to day 5 females caused a marked increase in the number of SHS, compared to normal females. The incidence of SHS in androgenized females was almost the same as that in normal males. However, the other two components of synaptic population (SPS and SOS) were not influenced by neonatal treatment with TP. On the other hand, neonatal orchidectomy resulted in a significant decrease in the number of SHS to the level comparable to that of normal females. These results clearly indicate the existence of sexual dimorphism in the synaptic pattern in the AMN. Furthermore, this sex difference was highly dependent on the neonatal presence of androgen, which effectively stimulated shaft synaptogenesis during early postnatal period. The modification of synaptic patterns caused by neonatal exposure to androgen in the amygdala may participate in the possible process of sexual differentiation of neuroendocrine and behavioral parameters of the amygdaloid function.

Male-female difference in synaptic organization of the ventromedial nucleus of the hypothalamus in the rat.

The ventromedial nucleus of the hypothalamus (VMN) of male and female rats was examined ultrastructurally at 100 days of age. Axodendritic shaft and spine synapses were counted in two subdivisions of the nucleus, the dorsomedial part (DM-VMN), which contains only a few sex steroid-concentrating neurons, and the ventrolateral part (VL-VMN), which is abundant in such neurons. In normal males, the numbers of shaft and spine synapses were significantly greater in the VL-VMN than in the DM-VMN. In normal females, however, there was no significant difference in the numbers of shaft and spine synapses between the DM-VMN and the VL-VMN. Moreover, the numbers of shaft and spine synapses in the VL-VMN were significantly greater in normal males than in normal females. Castration of males on day 1 significantly reduced the numbers of shaft and spine synapses in the VL-VMN to the level comparable to those of normal females. In contrast, neonatal treatment of females with 1.25 mg testosterone propionate (TP) on day 5 significantly increased the numbers of shaft and spine synapses to the levels comparable to those of normal males. In the DM-VMN, there were no significant differences in the numbers of shaft and spine synapses among normal and experimental animals. These results suggest that the synaptic organization in the VMN is sexually dimorphic but the occurrence of this structural difference is limited to the VL-VMN which is abundant in sex steroid receptors, and is modified by neonatal sex steroid environment.

Sexual difference in nuclear volume and its ontogeny in the rat amygdala

Nuclear volume of the medial and lateral nuclei of the amygdala was investigated in male and female rats. The volume of the medial nucleus in the adult male rat was significantly greater than that of the female rat. Treatment of female rats with estrogen for the first 30 days of postnatal life increased the nuclear size, and the volume became comparable to that of the males. Although there was no significant difference in volume of this nucleus between male and female rats from days 1 (day of birth) to 11, the difference became evident at day 21, and thereafter it persisted. In contrast, the nuclear volume of the lateral nucleus was not different between the two sexes. Estrogen treatment did not influence the volume of the lateral nucleus in the female animals. These data indicate that the nuclear volume is sexually different in the medial nucleus of the amygdala, and its differentiation occurs during the early postnatal period under the influence of the organizational action of sex steroids.

Estrogen and apoptosis in the developing sexually dimorphic preoptic area in female rats

Effect of estrogen on apoptotic cell death was studied in the two sexually dimorphic neuronal groups in the developing rat preoptic area (POA): the anteroventral periventricular nucleus of the POA (AVPvN-POA); and the sexually dimorphic nucleus of the POA (SDN-POA). A specific labelling of nuclear fragmentation was performed by terminal deoxynucleotydyl transferase(TdT)-mediated dUTP-biotin nick end-labeling method (TUNEL method) to demonstrate apoptosis. In the AVPvN-POA whose size is larger in females than in males, the number of TUNEL-positive cells was not significantly different between day 5 control and female pups sacrificed 10 h after 25 micrograms estradiol benzoate (EB) injection. However, TUNEL-positive cells showed a significant increase in the female pups sacrificed 24 h after EB injection, compared to that shown in the control female pups. In the SDN-POA whose size is larger in males than in females, EB injection significantly decreased TUNEL-positive cells in the female pups sacrificed 24 h after EB injection, compared to that in controls. These results suggest that estrogen regulates the neuronal number by facilitating apoptotic cell death in the developing AVPvN-POA or by inhibiting it in the developing SDN-POA.

Long-term effects of perinatal exposure to sex steroids and diethylstilbestrol on the reproductive system of male mammals.

Publisher Summary This chapter reviews the experimental data concerning the effects of perinatal sex steroid and the diethylstilbestrol (DES) treatment on the central and peripheral aspects of genital structural and functional development in male mammals, in particular male rodents. The pathology of the testis of perinatally estrogenized animals is of complex origin, with several critical factors directly or indirectly involved, whose relative importance is possibly dependent on the dose, time, and duration of perinatal estrogen treatment. The chapter discusses the direct and indirect effects of sex hormones given perinatally on the male reproductive tract. The experimental data suggest the desirability of follow-up studies on the possibly higher risk of genital cancer development and gonadal dysfunction in the prenatally DES-exposed human male population.

The ontogeny of luteinizing hormone-releasing hormone (LHRH) producing neurons in the chick embryo : Possible evidence for migrating LHRH neurons from the olfactory epithelium expressing a highly polysialylated neural cell adhesion molecule

The development of neurons expressing luteinizing hormone-releasing hormone (LHRH) has been studied immunohistochemically in the chick embryo from the 3.5 embryonic day (ED) to the day of hatching. At ED-3.5, LHRH-immunoreactive neurons were first detected in the medial epithelium of the olfactory pit, but their appearance in the brain was delayed to ED-4.5. On EDs-6-7, cords of the LHRH-immunoreactive cells extended across the nasal septum towards the ventromedial forebrain with the olfactory nerve. By double staining for LHRH and, a highly polysialylated form of neural cell adhesion molecule (NCAM-H), the LHRH-positive neurons in the olfactory-forebrain system were found strongly NCAM-H-positive. At ED-8, a marked decrease in the number of LHRH-positive cells in the olfactory epithelium and a concomitant increase in the LHRH-positive cells in the forebrain area were noted. From ED-11 to the day of hatching, the majority of LHRH-positive neurons tended to move into their usual adult position, whereas the LHRH-positive cells had almost disappeared in the olfactory epithelium. No LHRH-immunoreactive neurons were found strongly positive to NCAM-H. These results suggest that LHRH neurons originate from the olfactory placode, then as they develop they migrate across the nasal septum and enter the forebrain with the olfactory nerve. The close association of NCAM-H with the developing LHRH neurons raises the possibility that NCAM-H plays some role in guiding the migrating LHRH neurons from the olfactory epithelium to the forebrain.

The origin of the luteinizing hormone-releasing hormone (LHRH) neurons in newts (Cynops pyrrhogaster): the effect of olfactory placode ablation

SummaryNeurons containing luteinizing hormone-releasing hormone (LHRH) are first detected in newt embryos (Cynops pyrrhogaster) in the olfactory epithelium and ventromedial portion of the olfactory nerve, after which they sequentially appear in the intracerebral course of the terminal nerve at prometamorphosis, and in the septo-preoptic area at postmetamorphosis. In adults, however, LHRH-immunoreactive cells are rarely seen in the nasal region, and their distribution shifts into the brain, suggesting their migration. In order to ascertain the origin and possible migration route of these neurons in newt larvae, the effect of unilateral or bilateral olfactory placodectomy on the LHRH neuronal system has been studied. Removal of the olfactory placode results in the absence of LHRH-immunoreactive cells in the nasal and brain regions of the operated side, whereas the subsequent growth and the LHRH-immunoreactive cellular distribution in the contralateral side are identical to those of normal larvae. Following bilateral placodectomy, no LHRH immunoreactivity is detected on either side of the olfactory-brain axis. These results suggest that LHRH neurons of the newt, Cynops pyrrhogaster, originate in the olfactory placode and then migrate into the brain during embryonic development.

Organizational action of estrogen on synaptic pattern in the amygdala: implications for sexual differentiation of the brain

Estrogen markedly promotes the specific formation of dendritic shaft synapses in the medial amygdaloid nucleus (AMN) of the rat when given in early postnatal days. The high incidence of this type of synapse permanently persists until sacrifice at adult ages. The data provide evidence for the synaptic plasticity of the developing amygdala to estrogen and suggest a possible morphological mechanism for sexual differentiation of the brain.