Opioid peptides and receptors

Neuroendocrine regulation of thyrotropin-releasing hormone (TRH) in the tuberoinfundibular system

[...] It is now required to list each part needed for mucous excretion. They are two ducts in the brain substance, then a thin portion of membrane shaped as the infundibulum, then the gland that receives the tip of this infundibulum and the ducts that drive the mucus (pituita) from this gland to the palate and nares. [...] and I said that one (duct) [...] from the middle of the common cavity (third ventricle) descends [...] into the brain substance, and the end of this duct is [...] the sinus of the gland where the brain mucus is collected [...].

Heroin addiction: neurobiology, pharmacology, and policy

The neurobiology of drug addiction is being clarified. Research is revealing the anatomic pathways of primary drug reinforcement (reward) in the brain and the molecular architecture of the receptors on which addictive drugs act. All addictive drugs mimic (or occasionally block) the actions of some neurotransmitter; in the case of heroin or methadone an endogenous opioid, probably beta-endorphin. The groundwork is being laid for understanding Dole and Nyswander's "metabolic disease" concept as a concrete neurochemical abnormality of the endogenous opioid system. Thus, a stronger basis is developing for regarding methadone maintenance as a means of replacing a neurohormonal deficiency. Three practical conclusions that can be drawn from this model are: (1) methadone dosage must be adequate (never less than 50-80 mg); (2) it should be more widely accepted that some patients may require lifelong methadone maintenance; and (3) longer-acting, better stabilizing methadone congeners, such as LAAM and its metabolites, should be brought into general use.

State-dependent variation in the inhibitory effect of [D-Ala2, D-Leu5]-enkephalin on hippocampal serotonin release in ground squirrels

Accumulated evidence has suggested that increased endogenous opioid activities may facilitate the onset of hibernation either directly or possibly through modulation of other neurotransmitter systems. The seasonal change of [D-Ala2, D-Leu5]-enkephalin (DADLE), a delta receptor agonist, in modulating K+ (35 mM)-induced [3H]-5-hydroxytryptamine (5-HT) release from the hippocampal and hypothalamic slices of euthermic and hibernating Richardsons' ground squirrels was therefore investigated. DADLE (0.1-10 microM) had no effect on 5-HT release in the hypothalamic slices but elicited a dose-related inhibition on [3H]-5-HT release from the hippocampal slices of the euthermic ground squirrel. The inhibitory effect of DADLE was completely reversed by naloxone (10 microM), but not by tetrodotoxin (1 microM). In contrast, DADLE failed to alter the K(+)-induced 5-HT release from the hippocampal slices of the hibernating ground squirrel. This state-dependent reduction in responsiveness to an opioid is consistent with the hypothesis that enhanced endogenous opioid activity in the hibernating phase could lead to down regulation of the opioid receptors and minimize its inhibition on hippocampal serotonergic activity. A high 5-HT activity would inhibit midbrain reticular activating system indirectly through non-serotonergic fibers, which in turn facilitate the onset or maintenance of hibernation.