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At least 955 records · Page 53Linked to original sources

PubMed1990

Neurosteroids: a new brain function?

The biosynthesis of neurosteroids proceeds through cholesterol side-chain cleavage, and gives rise to pregnenolone (P) and dehydroepiandrosterone (D). These steroids accumulate in the rat brain independently of the supply by peripheral endocrine glands. This led to the discovery of a steroid biosynthesis pathway in rat brain oligodendrocytes based on enzyme immunocytochemistry and conversion of radioactive precursors to C-21 steroids. Several biological functions have been proposed for P and D. They may serve as precursors of other steroids (such as progesterone and testosterone and their metabolites). They are implicated in the control of some behavioural activities. They have excitatory effects on neurons, and they modulate the function of GABAA-receptors. These observations may apply to all mammalian species including the human, and the physiological significance of neurosteroid synthesis needs further investigation. The relationship between steroids and cerebral function may be reconsidered in the light of a new fact: the existence of a biosynthetic pathway of these compounds from cholesterol, assured in the brain by the oligodendrocytes, glial cells which synthesize myelin.

Animals↗

PubMed2003

Astrocytes and brain function: implications for reproduction.

Recent evidence suggests that astrocytes have important neuroregulatory functions in addition to their classic functions of support and segregation of neurons. These newly revealed functions include regulation of neuron communication, neurosecretion, and synaptic plasticity. Although these actions occur throughout the brain, this review will focus on astrocyte-neuron interactions in the hypothalamus, particularly with respect to their potential contribution to the regulation of gonadotropin-releasing hormone (GnRH) secretion and reproduction. Hypothalamic astrocytes have been documented to release a variety of neuroactive factors, including transforming growth factors-alpha and -beta, insulin-like growth factor-1, prostaglandin E2, and the neurosteroid, 3 alpha-hydroxy-5 alpha-pregnane-20-one. Each of these factors has been shown to stimulate GnRH release, and receptors for each factor have been documented on GnRH neurons. Astrocytes have also been implicated in the regulation of synaptic plasticity in key areas of the hypothalamus that control GnRH release, an effect achieved by extension and retraction of glial processes (i.e., glial ensheathment). Through this mechanism, the number of synapses on GnRH neurons and GnRH regulatory neurons can potentially be modulated, thereby influencing the activation state of GnRH neurons. The steroid hormone 17beta-estradiol, which triggers the GnRH and luteinizing hormone surge, has been shown to induce the astrocyte-regulated changes in hypothalamic synaptic plasticity, as well as enhance formation and release of the astrocyte neuroactive factors, thereby providing another potential mechanistic layer for astrocyte regulation of GnRH release. As a whole, these studies provide new insights into the diversity of astrocytes and their potential role in reproductive neuroendocrine function.

Animals↗

PubMed1984

Lateral brain function in normal and disordered emotion: interpreting electroencephalographic evidence.

Given the developing awareness of the lateral specialization of the human brain for both cognitive and emotional processes, the recent findings of characteristic hemispheric asymmetries in psychopathological groups suggests a neuropsychological model may be explanatory for abnormal psychology. Since the activity of arousal systems of the brain is a primary issue in interpreting both biochemical abnormalities and thought disorders in psychopathology, electroencephalographic (EEG) measures of cortical arousal are relevant. A better understanding of the relation of EEG measures to normal emotional arousal and cognitive effort may facilitate interpretation of the functional significance of EEG asymmetries in psychopathology.

Affect↗

PubMed1996

Steroid control of higher brain function and behavior.

In higher vertebrates, many behavioral characteristics can be attributed to effects in the central nervous system, in response to gonadal hormones secreted early in development. The lipophilic properties of steroids facilitate their easy passage in free form through the blood-brain barrier. At the cerebral level, the function of many nerve cells is influenced by steroid hormones originating from the periphery (synthesis of gluco-, and mineralo-corticosteroids in the adrenal glands and of sex steroids in the gonads and the placenta from cholesterol). However, the relationship between steroids and cerebral function may need reconsidering in light of the recent discovery of a biosynthetic pathway (independently of peripheral sources) of steroidal compounds ensuring the synthesis of neurosteroids from cholesterol in certain brain cells.

Animals↗

PubMed1991

Functional brain imaging and Alzheimer-type dementia.

Alzheimer disease is a common neurodegenerative disorder consisting of memory impairment and intellectual function that produces not only profound disabilities in the patient, but a significant cost to society as well. The biochemical basis for Alzheimer disease is not completely understood, but both positron-emission tomography and single-photon-emission computed tomography provide insights into the in vivo biochemistry associated with this disease. Both techniques show characteristic brain abnormalities, which consist of reductions in temporal-parietal metabolism that progress in severity and extent as the disease itself shows clinical progression. Such noninvasive biochemical assays may ultimately prove to be of assistance in clinical management, and are clearly helpful in understanding the pathophysiologic mechanisms associated with the production of this disease.

Alzheimer Disease↗

PubMed2000

Functional brain mapping of the relaxation response and meditation.

Meditation is a conscious mental process that induces a set of integrated physiologic changes termed the relaxation response. Functional magnetic resonance imaging (fMRI) was used to identify and characterize the brain regions that are active during a simple form of meditation. Significant (p<10(-7)) signal increases were observed in the group-averaged data in the dorsolateral prefrontal and parietal cortices, hippocampus/parahippocampus, temporal lobe, pregenual anterior cingulate cortex, striatum, and pre- and post-central gyri during meditation. Global fMRI signal decreases were also noted, although these were probably secondary to cardiorespiratory changes that often accompany meditation. The results indicate that the practice of meditation activates neural structures involved in attention and control of the autonomic nervous system.

Adult↗

PubMed1979