Opioid inhibition of rapid eye movement sleep by a specific mu receptor agonist

Structural and compositional determinants of cortistatin activity

Cortistatin-14 (CST-14) is a putative novel neuropeptide that shares 11 of its 14 residues with somatostatin-14 (SRIF-14), yet its effects on sleep physiology, locomotor behavior and hippocampal function are different from those of somatostatin. We studied the structural basis for cortistatin's distinct biological activities. As with SRIF-14, CST-14 does not show any preferred conformation in solution, as determined by circular dichroism and nuclear magnetic resonance. Synthetic cortistatin analogs were designed and synthesized based on the cyclic structure of octreotide. Biological assays were carried out to determine their binding affinities to five somatostatin receptors (sstl-5) and their ability to produce changes in locomotor activity and to modulate hippocampal physiology and sleep. The results show that the compound with N-terminal proline and C-terminal lysine amide exhibits cortistatin-like biological activities, including reduction of population spike amplitudes in the hippocampal CA1 region, decrease in locomotor activity and enhancement of slow-wave sleep 2. These findings suggest that both proline and lysine are necessary for cortistatin binding to its specific receptor.

cAMP and protein kinase A modulate cholinergic rapid eye movement sleep generation

Cholinergic neurotransmission in the medial pontine reticular formation (mPRF) modulates rapid eye movement (REM) sleep generation. Microinjection of cholinergic agonists and acetylcholinesterase inhibitors into the mPRF induces a REM sleep-like state, and microdialysis data reveal increased mPRF levels of acetylcholine during REM sleep. Muscarinic cholinergic receptors (mAChRs) participate in REM sleep generation, and data suggest that mAChRs of a non-M1 subtype modulate REM sleep generation. The signal transduction pathway activated by m2 and m4 mAChRs involves a pertussis toxin-sensitive G protein, adenylate cyclase (AC), adenosine 3',5'-cyclic monophosphate (cAMP), and protein kinase A (PKA). Therefore, the present study tested the hypothesis that cAMP and PKA within the mPRF modulate the carbachol-induced REM sleep-like state. To test this hypothesis, the mPRF was microinjected with compounds known to facilitate the effects of cAMP (dibutyryl cAMP and 8-bromo-cAMP), stimulate PKA (Sp-cAMP[S]), and inhibit PKA (Rp-cAMP[S]). The results showed that compounds that fostered the intracellular effects of cAMP significantly decreased cholinergic REM sleep, while having no effect on spontaneously occurring REM sleep. These data are consistent with the recent finding that within the mPRF, AC and a pertussis toxin-sensitive G protein modulate cholinergic REM sleep generation. These new data suggest a modulatory role for pontine cAMP and PKA in cholinergic REM sleep regulation.

Postoperative opioid analgesia: time for a reconsideration?

Postoperative pain relief has improved in recent years with the development of new analgesics, additional routes of administration and the appearance of the hypothesis of preemptive as well as balanced analgesia (Kehlet H; Postoperative pain relief-what is the issue? Br J Anaesth 1994;72:375-8). Many initial improvements simply involved the administration of opioid analgesics in new ways, such as continuous or on demand intravenous (i.v.) or epidural infusion. These methods allow lower total opioid dosages, provide a more stable concentration of opioid at the receptor and correspondingly better analgesic effects, and also fewer unwanted side effects. Although opioids have played a prominent role in postoperative analgesia for centuries and are still often administered as a matter of routine, their frequent minor side effects and the increasing availability of suitable alternatives may limit their future use in some situations. Thus, the recent emphasis on ambulatory surgery and accelerated surgical stay programs, both with a focus on early recovery of organ function and provision of functional analgesia [i.e., pain relief that allows normal function (Kehlet H: Postoperative pain relief-what is the issue? Br J Anaesth 1994;72:375-8)] provide an opportunity for a reappraisal of opioid use in these settings. For this debate, controlled clinical studies on the opioid-sparing effect of different analgesic techniques are mentioned, and preferably studies with multiple dosing of analgesics and/or a reasonably large patient sample size. These data do not allow a proper meta-analysis to be performed because of the large variability in surgical procedures, dosing regimens, assessment criteria, among others.

Endogenous opiates: 1995

This article is the eighteenth installment of our annual review of research concerning the opiate system. It includes articles published during 1995 reporting the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects. The specific topics covered this year include stress: tolerance and dependence; eating; drinking; gastrointestinal, renal, and hepatic function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.