Brain pain perception

The pathophysiologic mechanisms of TTH are not clearly understood. The pain is thought to originate in the myofascial tissues of the head, but central brain processing is believed to be an important modulator of pain perception.14... 

Dorsal raphe Main serotonin (5-HT)-containing neurons that project through the brain. Other raphe neurons project down the spinal cord where they act as a gating mechanism for pain perception from the periphery. Main activity is in the regulation of mood, anxiety, sexual behaviour, sleep. 

Effects of opioids (B). The analgesic effect results from actions at the level of the spinal cord (inhibition of nociceptive impulse transmission) and the brain (attenuation of impulse spread, inhibition of pain perception). Attention Ltillmann, Color Atlas of Pharmacology 2000 Thieme All rights reserved. Usage subject to terms and conditions of license. 

Most of the serotonin in the brain is in the brainstem, specifically in the raphe nuclei considerable amounts also are present in areas of the hypothalamus, the limbic system, and the pituitary gland. Current evidence indicates that serotonin is involved in the regulation of several aspects of behavior, including sleep, pain perception, depression, sexual activity, and aggressiveness. Some of the most important antidepressant agents are believed to prevent the reuptake of serotonin (see Chapter 33). Serotonin also may be involved in temperature regulation and in the hypothalamic control of the release of pituitary hormones. 

A THC tetrahydrocannabinol is the major psychoactive ingredient in the Cannabisplant. A THC is responsible for both the psychiahic and therapeutic effects obtained from marijuana. Its receptor, the cannabinoid receptor, is located mainly tat the presynaptic gap. The areas of the brain most affected are the basal ganglia, cerebellum, cerebral cortex, and the hippocampus. The acute effects consist of degradation in short term memory, changes in sensory perception, reduced concenhation, disturbances in motor abilities, hypothermia, increased blood pressure and heart rate, and reduced pain perception. 

Opiates, such as opium and morphine, have been known for centuries as substances that relieve pain and suffering. Neuropharmacologists have theorized that opiates interact with receptors in the brain that are affected by endogenous substances that function as regulators of pain perception. The important breakthrough came in 197S. with the isolation of two peptides with opiatc-iike activity from pig brains. These related pentapeptides. called methionine-enkephalin (metenkephalin) and leucine-enkephalin (leuenkephalin). are abundant in certain nerve terminals and have been found in the pituitary gland. 

Neuronal projections from the hypothalamus to other regions of the brain relay important output information that influence blood pressure, appetite, thirst, circadian rhythm, behavior, nociception (pain perception), and others factors. Although many of these neurons release neurotransmitter amines at synapses, some of them are known to release neurotransmitter peptides. These include, among others, peptides that closely resemble hormones formed in the gastrointestinal system as well as the endogenous opiates (Table 31-3). 

Opioid neurotransmitters in the brain are peptides that modulate pain perception and/or the reaction to perceived pain they include the enkephalins, endorphins, dynorphins, and neoendorphins. All exert their effects by binding to specific types of opiate receptors that are located in various parts of the CNS, but particularly in those regions... 

The above discrepancies seem to be due mainly to the stringencies of the end-points in each test. However, one can also doubt the applicability of these tests for cannabinoids. These tests were developed for opiates and may not necessarily parallel and be fully relevant to THC activity in man. Indeed, recent work on electrodes implanted into several distinct brain areas of the rat led to the conclusion that the apparent analgesia produced by the cannabinoids is more related to their disruption of discharge in response to some synthetic impact rather than to a depression of pain pathways [130]. The question whether cannabinoids cause analgesia by interference with pain reception or with pain perception is still unresolved. 

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