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  • 2005-2009  (1)
  • 1995-1999  (4)
  • 1
    ISSN: 1573-6830
    Keywords: hippocampus ; synaptogenesis ; neurogenesis ; dendrite ; atrophy ; stress ; glucocorticoid ; estrogen ; N-methyl-d-aspartate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. The hippocampus is an important brain structure for working and spatial memory in animals and humans, and it is also a vulnerable as well as plastic brain structure as far as sensitivity to epilepsy, ischemia, head trauma, stress, and aging. 2. The hippocampus is also a target brain area for the actions of hormones of the steroid/thyroid hormone family, which traditionally have been thought to work by regulating gene expression. “Genomic” actions of steroid hormones involve intracellular receptors, whereas “nongenomic” effects of steroids involve putative cell surface receptors. Although this distinction is valid, it does not go far enough in addressing the variety of mechanisms that steroid hormones use to produce their effects on cells. This is because cell surface receptors may signal changes in gene expression, while genomic actions sometimes affect neuronal excitability, often doing so quite rapidly. 3. Moreover, steroid hormones and neurotransmitters may operate together to produce effects, and sometimes these effects involve collaborations between groups of neurons. For example, a number of steroid actions in the hippocampus involve the coparticipation of excitatory amino acids. These interactions are evident for the regulation of synaptogenesis by estradiol in the CA1 pyramidal neurons of hippocampus and for the induction of dendritic atrophy of CA3 neurons by repeated stress as well as by glucocorticoid injections. In addition, neurogenesis in the adult and developing dentate gyrus is “contained” by adrenal steroids as well as by excitatory amino acids. In each of these three examples, NMDA receptors are involved. 4. These results not only point to a high degree of interdependency between certain neurotransmitters and the actions of steroid hormones, but also emphasize the degree to which structural plasticity is an important aspect of steroid hormone action in the adult as well as developing nervous system.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: To investigate the effects of type I (mineralocorticoid) and type II (glucocorticoid) receptor activation on striatal neuropeptide [preproenkephalin (PPE), preprotachykinin (PPT), and preprodynorphin (DYN)] mRNA and midbrain cholecystokinin (CCK) mRNA as well as striatal tyrosine hydroxylase radioimmunoreactivity (TH-RIC) levels, we administered either replacement levels of corticosterone (CORT; 0.5 mg/kg/day, s.c.) or pharmacological levels of deoxycorticosterone acetate (DOCA; a mineralocorticoid steroid with ability to bind to type I and type II receptors; 5 mg/kg, s.c.) to adrenalectomized adult male rats. After 1 week of recovery from adrenalectomy surgery, animals were injected daily with sesame oil or CORT for 1, 3, or 7 days or DOCA for 3 or 7 days and killed 16 h after the last injection. Adrenalectomy resulted in a decrease in all three striatal neuropeptide mRNA levels, compared with sham-operated rats. CORT replacement resulted in recovered PPE and PPT mRNA levels after 1 day and elevated PPE mRNA levels over those in sham-operated controls after 3 days. In contrast, DYN mRNA levels showed recovery after 7 days of CORT replacement. Results after DOCA treatment largely paralleled those after CORT replacement. There were no significant treatment effects on indirect markers of midbrain dopaminergic activity, i.e., CCK mRNA and TH-RIC. From these results we conclude that compared with striatal tachykinin and dynorphinergic neurons, enkephalinergic cells show greater sensitivity, whereas the dopaminergic system, including mesencephalic CCK, demonstrates an insensitivity to physiological CORT and to pharmacological DOCA treatment.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Rats exposed to a low-light, low-noise, novel environment exhibit differences in individual locomotor response to the novelty stressor. The categorization of rats in a locomotor screening procedure as low- (LR) or high-responders (HR), where LRs are in the low locomotor range while HRs belong to the high locomotor range, is significant in that HRs show higher activity in mesencephalic dopaminergic projection neurons, and also show a higher propensity to self-administer psychostimulants and other drugs of abuse compared with LRs. In this study, we examined the neurobiological basis of dopaminergic hyperactivity by comparing in HRs and LRs the steady-state differences in regulatory inputs to mesencephalic (substantia nigra and ventral tegmental area: VTA) dopaminergic neurons. In particular, using in situ hybridization, we studied levels of mRNA for tyrosine hydroxylase (TH) and cholecystokinin (CCK) in the mesencephalon, and for preprodynorphin (DYN), preproenkephalin (PPE), and preprotachykinin (PPT) in the striatum and nucleus accumbens (Acb). We also evaluated TH levels by radioimmunocytochemistry (TH-RIC) in striatal, accumbal and mesencephalic regions. HRs versus LRs had lower levels of neurochemicals belonging to the intrinsic inhibitory input to dopaminergic neurons in the VTA, e.g. lower TH-RIC (–25%) and CCK-mRNA (–48%). In contrast, HRs showed higher levels of parameters belonging to extrinsic facilitating inputs, e.g. higher PPE-mRNA (+ 37%). In addition, HRs had higher DYN-mRNA in Acb (+ 61%), which has been shown to be positively correlated with higher dopaminergic activity. These results enhance our knowledge of the neurobiological correlates of individual rats' propensities to develop drug-intake and provide some putative mechanisms for the dopaminergic hyperactivity that characterizes drug-prone animals.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Neuroscience 22 (1999), S. 105-122 
    ISSN: 0147-006X
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract The hippocampus is a target of stress hormones, and it is an especially plastic and vulnerable region of the brain. It also responds to gonadal, thyroid, and adrenal hormones, which modulate changes in synapse formation and dendritic structure and regulate dentate gyrus volume during development and in adult life. Two forms of structural plasticity are affected by stress: Repeated stress causes atrophy of dendrites in the CA3 region, and both acute and chronic stress suppresses neurogenesis of dentate gyrus granule neurons. Besides glucocorticoids, excitatory amino acids and N-methyl-d-aspartate (NMDA) receptors are involved in these two forms of plasticity as well as in neuronal death that is caused in pyramidal neurons by seizures and by ischemia. The two forms of hippocampal structural plasticity are relevant to the human hippocampus, which undergoes a selective atrophy in a number of disorders, accompanied by deficits in declarative, episodic, spatial, and contextual memory performance. It is important, from a therapeutic standpoint, to distinguish between a permanent loss of cells and a reversible atrophy.
    Type of Medium: Electronic Resource
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  • 5
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    London : Henry Stewart Talks
    Keywords: Hormones
    Description / Table of Contents: Contents: Estrogen regulation of female sexual behavior in the rat -- Adrenal steroids and spatial memory -- Steroid hormone metabolism in brain -- Limitation of steroid access -- Rapid non-genomic actions of steroids in brain -- Steroid regulation of signaling pathways -- Steroid hormones have widespread effects on brain structure and function -- Effects of estrogens on synapse formation in hippocampus -- Effects of stress and glucocorticoids on dendritic remodeling in hippocampus -- Sexual differentiation of the brain
    Notes: Animated audio-visual presentation with synchronized narration.
    Pages: 1 streaming video file (27 min.) : digital, mono., SWF file, sd., col.
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