Opioid defined

In addition to the weU-defined opioid systems in the central nervous system, the three opioid peptides and their precursor mRNA have also been identified in peripheral tissues. ( -Endorphin is most abundant in the pituitary, where it exists in corticotroph cells with ACTH in the anterior lobe and in melanotroph cells with MSH in the intermediate lobe (59). Enkephalin and pre-pro-enkephalin mRNA have been identified in the adrenal medulla (60) and this has been the source of material for many studies of pro-enkephalin synthesis and regulation. Pre-pro-enkephalin mRNA has also been identified in the anterior and posterior lobes of the pituitary (61). mRNA for all three opioid precursors has been identified in the reproductive system (62—64). POMC... 

Such an approach should include an initial comprehensive medical history and physical examination, firm documentation that nonopioid therapy has failed, clearly defined treatment goals, an understanding between the provider and the patient of the true benefits and pitfalls of long-term opioids, use of a single provider and pharmacy whenever possible, and comprehensive follow-up. 

Hypoventilation is defined as a reduction in the rate and depth of breathing. Inadequate ventilation results in hypoxemia, or a decrease in the concentration of oxygen in the arterial blood. Hypoventilation may be induced inadvertently by various pharmacological agents, including opioid analgesics such as morphine. These medications cause hypoventilation by way of their effects on the respiratory centers in the brainstem. Doses of... 

Another research group has applied gold particle tracking to measure movements of the p-opioid GPCR on the surface of GPCR-transfected fibroblasts [30], They describe the pattern observed in Fig. 2-11 as a walking defined diffusion mode . More than 90% of the observed particles displayed this pattern, which consists of rapid... 

Opioids create their effects by acting at opioid receptors (table 8.3). These are, namely, p, k, and 5. Each is further divided into subtypes, which are differentially distributed throughout the nervous system pi, pi, 51, 52, k1, and k3. A k2 receptor was defined pharmacologically, but no one to date has cloned a receptor that resembles it (Zukin et al. 1998). Selective agonists have been developed for the receptor subtypes (see table 8.3). Naloxone is a general antagonist for all classical opioid receptors. All opioid receptors create cellular effects through G-protein-... 

The behavioral effects of nicotine have been defined as both stimulant and depressant, effects that are influenced by the present mental status and expectations of the smoker. Smokers may feel alert and relaxed. Nicotine produces myriad effects on the central nervous system (CNS), almost all of which appear to be mediated through nicotinic receptors. Additionally, nicotine influences multiple neuronal systems. One of its most prominent effects is stimulated release of dopamine, particularly in the nucleus accumbens, which is a major component of the reward system. Nicotine also stimulates the release of endogenous opioids and glucocorticoids. 

In the U.S., all opioids are controlled substances. Section 802 of the Controlled Substances Act defines an opiate as ... 

Portenoy and Payne (1997) insist upon a distinction between physical dependence and addiction. What they mean by physical dependence is roughly what 1 mean, but they define addiction as a condition in which one is unable to abstain "Use of the term addiction to describe patients who are merely physically dependent reinforces the stigma associated with opioid therapy and should be abandoned. If the clinician wishes to describe a patient who is believed to have the capacity for abstinence, the term physical dependency must be used (564). Since my second level of dependency, which I consider to be addiction proper, need not involve this inability, Portenoy and Payne are marking a different distinction. 

Physical dependence is usually defined as the onset of withdrawal symptoms when the drug is abruptly removed. Withdrawal syndrome from opioid dependence is associated with a number of obvious and unpleasant symptoms (Table 14—3). In severe dependence, withdrawal symptoms become evident within 6 to 10 hours after the last dose of the drug, and symptoms reach their peak in the second or third day after the drug has been stopped. Withdrawal symptoms last approximately 5 days. This does not necessarily mean that the individual no longer desires the drug, only that the physical symptoms of withdrawal have ceased. Indeed, an addict may continue to crave the drug after months or years of abstinence. 

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