Monday, 16 December 2013

The Effects of Hormone Catecholamines - Norepinephrine(2)

 Catecholamines, derived from the amino acid tyrosine, produced by the adrenal glands, which are found on top of the kidneys. are epinephrine (adrenaline), norepinephrine (noradrenaline) and dopamine. The hormone are released into the blood during times of physical or emotional stress.
9. Relationship between locus coeruleus discharge rates and rates of norepinephrine release within neocortex
In the study to examine the relationship between discharge rates of locus coeruleus noradrenergic neurons and rates of norepinephrine release, found that  In general, neither activation nor suppression of locus coeruleus neuronal discharge rates appeared to alter the relationship between discharge activity and norepinephrine efflux during subsequent epochs. The one exception to this was observed during recovery from relatively high-magnitude locus coeruleus activation. In two out of three cases in which locus coeruleus discharge rates were increased greater than 450%, a recovery of norepinephrine concentrations to basal levels occurred more quickly than the recovery of locus coeruleus neuronal discharge rates to basal levels. Although limited, these latter observations suggest that dysregulation of norepinephrine release may occur following sustained activation of locus coeruleus at the highest rates examined, which may mimic those associated with intense arousal or stress.(9).

10. Norepinephrine facilitates inhibitory transmission in substantia gelatinosa of adult rat spinal cord
. The activation of descending norepinephrine-containing fibers from the brain stem inhibits nociceptive transmission at the spinal level.In the study to evaluate  the descending noradrenergic pathways exert the analgesic effect, found that norepinephrine enhances inhibitory synaptic transmission in the substantia gelatinosa through activation of presynaptic alpha1 receptors, thus providing a mechanism underlying the clinical use of alpha1 agonists with local anesthetics in spinal anesthesia(10).

11. Olanzapine and dopamine and norepinephrine release in rat prefrontal cortex, nucleus accumbens and striatum
The in vivo effects of olanzapine on the extracellular monoamine levels in rat prefrontal cortex (Pfc), nucleus accumbens (Acb) and striatum (Cpu) were investigated by means of microdialysis. In the study of the effect of Sequential doses of olanzapine at 0.5, 3 and 10 mg/kg (s.c.) dose-dependently in the extracellular dopamine (DA) and norepinephrine (NE) levels in all three brain areas, found that in the case of sequential dosing olanzapine more effectively enhances DA and NE release in the Pfc than in the subcortical areas, which may have an impact on its atypical antipsychotic actions(11).

12. Actions of norepinephrine in the cerebral cortex and thalamus
Norepinephrine (NE) has potent and long-lasting ionic effects on cortical and thalamic neurons. In the study by Yale University School of Medicine, indicated that  In cortical pyramidal cells, activation of beta-adrenergic receptors results in an enhanced excitability and responsiveness to depolarizing inputs. This enhanced excitability is expressed as a reduction in spike frequency adaptation and is mediated by a marked suppression of a slow Ca(++)-activated potassium current known as IAHP. In the thalamus, application of NE results in the suppression of ongoing rhythmic burst activity and a switch to the single spike firing mode of action potential generation. This effect is mediated through an alpha 1-adrenergic suppression of a resting leak potassium current, IKL, and through a beta-adrenoceptor-mediated enhancement of the hyperpolarization activated cation current Ih(12).

13. Peripheral hormone epinephrine (EPI) and brainstem nuclei
The peripheral hormone epinephrine (EPI) is known to modulate memory for arousing experiences. In the study to test the hypothesis of the actions of EPI on the LC suggest that its mnemonic properties may also be mediated by influencing NE output in the HIPP, dialysate levels of NE were collected from the HIPP of male rats given an i.p. injection of saline that was followed 100 min later by i.p. EPI (0.3 mg/kg). NE levels sampled 20 min after EPI injection were significantly larger than baseline and continued to show significant peaks for 60 min found that the mnemonic effects of EPI reported in a wide range of learning conditions may not be mediated solely by NE release in the amygdala, but may also involve coactivation of the HIPP NE system, according to the study by The University of Virginia(13).

14. Norepinephrine and Cerebellum
Presynaptic modulation of synaptic transmission is the primary function of central nicotinic acetylcholine receptors (nAChRs) in developing and adult brain. nAChR activation regulates release of various neurotransmitters, including norepinephrine (NA). In the study of to determine whether nAChRs modulate NA release in developing cerebellum. In vitro experiments using cerebellar slices examined the effects of nAChR stimulation on release of radiolabeled NA ([3H]NA), showed that these data support recent findings of a possible functional role of nAChRs in regulating cerebellar ontogeny, and provides further support for the role of NA as a neurotrophic factor during development(14).
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