Abstract:
:Gonadal hormones exert a critical influence over the architecture of specific brain areas affecting the formation of neuronal contacts. Cellular mechanisms mediating gonadal hormone actions on synapses have been studied extensively in the rat arcuate nucleus, a hypothalamic center involved in the feed-back regulation of gonadotropins. Gonadal steroids exert organizational and activational effects on arcuate nucleus synaptic connectivity. Perinatal testosterone induces a sexual dimorphic pattern of synaptic contacts. Furthermore, during the preovulatory and ovulatory phases of the estrous cycle there is a transient disconnection of inhibitory synaptic inputs to the somas of arcuate neurons. This synaptic remodeling is induced by estradiol, blocked by progesterone, and begins with the onset of puberty in females. Astroglia appear to play a significant role in the organizational and the activational hormone effects on neuronal connectivity by regulating the amount of neuronal membrane available for the formation of synaptic contacts and by releasing soluble factors, such as insulin-like growth factor I (IGF-I), which promote the differentiation of neural processes. Recent evidence indicates that gonadal steroids and IGF-I may interact in their trophic effects on the neuroendocrine hypothalamus. Estradiol and IGF-I promote the survival and morphological differentiation of rat hypothalamic neurons in primary cultures. The effect of estradiol depends on IGF-I, while the effects of both estradiol and IGF-I depend on estrogen receptors. Furthermore, estrogen activation of astroglia in hypothalamic tissue fragments depends on IGF-I receptors. These findings indicate that IGF-I may mediate some of the developmental and activational effects of gonadal steroids on the brain and suggest that IGF-I may activate the estrogen receptor to induce its neurotrophic effects on hypothalamic cells. In addition, IGF-I levels in the neuroendocrine hypothalamus are regulated by gonadal steroids. IGF-I levels in tanycytes, a specific astroglia cell type present in the arcuate nucleus and median eminence, increase at puberty, are affected by neonatal androgen levels, show sex differences, and fluctuate in accordance to the natural variations in plasma levels of ovarian steroids that are associated with the estrous cycle. These changes appear to be mediated by hormonal regulation of IGF-I uptake from blood or cerebrospinal fluid by tanycytes. These results suggest that tanycytes may be involved in the regulation of neuroendocrine events in adult rats by regulating the availability of IGF-I to hypothalamic neurons. In summary, IGF-I and different forms of neuron-astroglia communication are involved in the effects of estradiol on synaptic plasticity in the hypothalamic arcuate nucleus.
journal_name
Brain Res Bulljournal_title
Brain research bulletinauthors
Fernandez-Galaz MC,Morschl E,Chowen JA,Torres-Aleman I,Naftolin F,Garcia-Segura LMdoi
10.1016/s0361-9230(97)00238-4subject
Has Abstractpub_date
1997-01-01 00:00:00pages
525-31issue
4eissn
0361-9230issn
1873-2747pii
S0361-9230(97)00238-4journal_volume
44pub_type
杂志文章,评审abstract::Waxing and waning electrographic responses (augmenting) and primary evoked responses could be induced in restricted regions of hippocampus, thalamus, and skeletal muscle by bipolar, low-frequency (7-10 Hz), low-amplitude (35 mV-4V) stimulation of selected sites within the hippocampus or thalamus of rabbits. Induction ...
journal_title:Brain research bulletin
pub_type: 杂志文章
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journal_title:Brain research bulletin
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pub_type: 杂志文章
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更新日期:2000-10-01 00:00:00
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pub_type: 杂志文章,评审
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journal_title:Brain research bulletin
pub_type: 杂志文章
doi:10.1016/0361-9230(78)90003-5
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pub_type: 杂志文章
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pub_type: 杂志文章
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journal_title:Brain research bulletin
pub_type: 杂志文章
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pub_type: 杂志文章
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journal_title:Brain research bulletin
pub_type: 杂志文章
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更新日期:1983-09-01 00:00:00
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journal_title:Brain research bulletin
pub_type: 杂志文章
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更新日期:1995-01-01 00:00:00
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journal_title:Brain research bulletin
pub_type: 杂志文章
doi:10.1016/0361-9230(94)90094-9
更新日期:1994-01-01 00:00:00
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journal_title:Brain research bulletin
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pub_type: 杂志文章
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更新日期:1987-07-01 00:00:00
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journal_title:Brain research bulletin
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