Progress in neurobiology
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Progress in neurobiology · Jun 1997
ReviewThe neurobiology of placebo analgesia: from endogenous opioids to cholecystokinin.
Placebo is a widespread phenomenon in medicine and biology and its mechanisms are understood only partially. Most of our understanding of placebo comes from studies on pain. In particular, placebo analgesia represents a situation where the administration of a substance known to be non-analgesic produces an analgesic response when the subject is told that it is a pain killer. ⋯ This claim comes from the observation that the opioid antagonist naloxone can reverse placebo analgesia. On the basis of the discovery of the anti-opioid action of the neuropeptide cholecystokinin, recent studies demonstrate that the blockade of cholecystokinin receptors potentiates the placebo analgesic response, thus suggesting an inhibitory role of cholecystokinin in placebo analgesia. Thus, by antagonizing the anti-opioid action of cholecystokinin during a placebo procedure, a potentiation of the endogenous opioid systems can be obtained.
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Progress in neurobiology · Sep 1996
ReviewThe organization and function of endogenous antinociceptive systems.
Much progress has been made the understanding of endogenous pain-controlling systems. Recently, new concepts and ideas which are derived from neurobiology, chaos research and from research on learning and memory have been introduced into pain research and shed further light on the organization and function of endogenous antinociception. ⋯ Results demonstrate that characteristic activity patterns result within and outside the PAG when stimulating at its various subdivisions. The descending systems may not only depress mean discharge rates of nociceptive spinal dorsal horn neurons, but also may modify harmonic oscillations and nonlinear dynamics (dimensionality) of discharges. (2) Propriospinal, heterosegmental inhibition: antinociceptive, heterosegmental interneurons exist which may be activated by noxious stimulation or by supraspinal descending pathways. (3) Segmental spinal inhibition: a robust long-term depression of primary afferent neurotransmission in A delta fibers has been identified in superficial spinal dorsal horn which may underlie long-lasting antinociception by afferent stimulation, e.g. by physical therapy or acupuncture.
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It is established that astrocytes are the intimate partner of neurons throughout their lifespan. However, astrocytes play different roles at different stages of the lifespan. During neurogenesis and early development, glial cells provide a scaffold for the correct migration of neurons and growth cones. ⋯ Thus, astrocytes can be expected to modify the expression of endogenous neurotoxins and thus contribute to synaptic plasticity in ageing. Synaptic plasticity continues to be a homeostatic relationship between neurons and glial cells. The possibility of signaling from astrocytes to neurons has opened new horizons for glial cell function and new challenges of research for gliobiologists.
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Progress in neurobiology · Jun 1993
ReviewAntinociception induced by alpha-2-adrenoceptor agonists, with special emphasis on medetomidine studies.
Alpha-2-adrenoceptor agonists can activate varying antinociceptive mechanisms depending on the dose and the route of administration, although the main site for their antinociceptive effect in physiological pain conditions seems to be the spinal dorsal horn. In this paper the investigations on the underlying mechanisms are reviewed, with particular emphasis on novel studies using a highly selective and potent alpha-2-adrenoceptor agonist medetomidine. In behavioral studies alpha-2-adrenoceptor agonists, including medetomidine, produce antinociception following systemic administration or local application to the spinal cord. ⋯ Thus, the higher sensitivity of supraspinal neuronal responses and their behavioral correlates to the antinoceptive effect of medetomidine obviously reflects the cumulative effect of medetomidine at several areas along the polysynaptic pathway to the rostral parts of the brain. Paradoxically, the response of immediate early genes in the medial thalamic neurons is only slightly, influenced by antinociceptive doses of medetomidine. Alpha-2-adrenoceptors have significant interactions with other receptors (e.g. opioid, serotonin and muscarine) in producing antinociception at the spinal cord level.