Hyperalgesia induced by naloxone follows diurnal rhythm in responsivity to painful stimuli.

A diurnal rhythm was observed in the responsiveness of mice to nociceptive stimuli and in the hyperalgesic activity of endogenous opioid peptides and may partly account for previous controversy over the direct action of naloxone in opiate-naive animals.

Enkephalin-induced depression of single neurons in brain areas with opiate receptors--antagonism by naloxone.

Enkephalin, applied microiontophoretically, depressed spontaneous and glutamate-induced firing of single neurons in frontal cortex, caudate nucleus, and periaqueductal gray matter, where enkephalin and high concentrations of opiate receptors are found. Many of the depressions were blocked by the specific narcotic antagonist naloxone. The data are compatible with a neurotransmitter or neuromodulator role for this new brain pentapeptide.

Metkephamid, a systemically active analog of methionine enkephalin with potent opioid alpha-receptor activity.

Metkephamid is an analog of methionine enkephalin that retains high affinity for the delta receptor and is a systemically active analgesic. Since it is at least 100 times more potent than morphine as an analgesic when placed directly into the lateral ventricles, and is 30 to 100 times more potent on the delta receptor and yet is roughly equipotent on the mu receptor in vitro, it is concluded that it probably produces analgesia by action on delta receptors as well as, or rather than, on mu receptors. It has less tendency to produce respiratory depression, tolerance, and physical dependence than standard analgesics, and it is presently undergoing clinical trial.

Dual actions of substance P on nociception: possible role of endogenous opioids.

Substance P produces analgesia when administered to mice in very small doses by the intraventricular route (1.25 to 5 nanograms per mouse). The analgesic effect can be blocked by naloxone. At higher doses (greater than 50 nanograms per mouse), this activity is lost. At these higher doses, however, substance P produced hyperalgesia when combined with naloxone and analgesia when combined with baclofen [beta-(4-chlorophenyl)-gamma-aminobutyric acid]. Substance P may have dual actions in brain, releasing endorphins at very low doses and directly exciting neuronal activity in nociceptive pathways at higher doses.

Astroglia in Alzheimer's disease.

Amyloid deposits are characteristic of Alzheimer's Disease (AD) and there is growing evidence that amyloid may play an important role in the genesis of this neurodegenerative disease. This review discusses data which suggests that reactive astrocytes and microglia may be a necessary concomitant with amyloid to produce the neuropathology which manifests as AD. Several hypotheses and supporting data for mechanisms by which reactive astrocytes may mediate this neuropathology are presented. These include the possibility that amyloid induces excitotoxicity by interferring with astrocytic glutamate uptake, the possibility that amyloid has this effect via an action on a tachykinin-related receptor and the possibility that proteoglycans released by astrocytes may facilitate the deposition of amyloid plaques. Both symptomatic treatment to enhance cognitive function and treatment to stop the progression of AD are needed. It is hoped that answers to some of the unique questions raised here may provide new insight into the etiology and treatment of AD.

Neuroglial-mediated immunoinflammatory responses in Alzheimer's disease: complement activation and therapeutic approaches.

Increasing evidence points to A beta-containing senile plaques as primary etiological agents in Alzheimer's disease (AD). The mechanism by which these deposits cause neurotoxicity is unresolved, but there are compelling data suggesting that the activated glia found associated with senile plaques contribute to the pathology of AD. These cells appear to release a variety of immunoinflammatory molecules, including complement proteins whose activation products colocalize with senile plaques and dystrophic neurites. Previous studies showed that A beta can bind and activate complement protein C1q, providing a plausible explanation for the initiation of the complement cascade in AD. Data presented here further define the nature of A beta-C1q association, revealing key aspects of the C1q domain involved in binding the amyloid peptide. Moreover, we show that it is possible to inhibit A beta-induced complement activation without affecting the normal immunoglobulin-mediated complement pathway. This indicates that it should be feasible to develop drugs to reduce complement damage in AD without compromising this important immune-defense mechanism throughout the body.

Deposits of A beta fibrils are not toxic to cortical and hippocampal neurons in vitro.

Amyloid beta peptide (A beta), which is deposited as insoluble fibrils in senile plaques, is thought to play a role in the neuropathology of Alzheimer's disease. We have developed a model in which rat embryonic cerebral cortical or hippocampal neurons are seeded onto culture dishes containing deposits of substrate-bound, fibrillar A beta. The neurons attached rapidly to A beta 1-40 and A beta 1-42 substrates and extended long, branching neurites. Quantitative assessment demonstrated that survival of neurons on the A beta matrices was equivalent to or better than on control substrates of poly L-lysine or poly L-ornithine. In contrast, preparations of A beta fibrils added directly to the culture medium caused neuronal death as previously reported in the literature. These results reveal that the response of neurons to deposited A beta 1-40 and A beta 1-42 is substantially different from that observed with suspensions of the amyloid peptides, with the former serving as growth-promoting substrates for cortical and hippocampal neurons. This may thus imply that fibrillar A beta of senile plaques is not sufficient by itself to cause the plaque-associated neuronal degeneration characteristic of AD.

Amyloid beta protein (A beta) removal by neuroglial cells in culture.

Because the mechanisms of A beta degradation in normal and Alzheimer's disease brain are poorly understood, we have examined whether various cortical cells are capable of processing this peptide. Rat microglia and astrocytes, as well as the human THP-1 monocyte cell line, degraded A beta 1-42 added to culture medium. In contrast, neither rat cortical neurons or meningeal fibroblasts effectively catabolized this peptide. When A beta fibrils were immobilized as plaque-like deposits on culture dishes, both microglia and THP-1 cells removed the peptide. Astrocytes were incapable of processing the A beta deposits, but these cells released glycosaminoglycase-sensitive molecules that inhibited the subsequent removal of A beta by microglia. This implied that astrocyte-derived proteoglycans associated with the amyloid peptide and slowed its degradation. The addition of purified proteoglycan to A beta that was in medium or focally deposited also resulted in significant inhibition of peptide removal by microglia. These data suggest that A beta can be catabolized by microglia and proteoglycans which co-localize with senile plaques may slow the degradation of A beta within these pathologic bodies.

Endorphins and parturition.

Endorphins and beta-lipotropin have been implicated as the modulators of pain during the labor process. To investigate their possible role during parturition, the present study was undertaken to determine the levels of beta-endorphin, beta-endorphinlike immunoactivity, and beta-lipotropin during labor and delivery. Fourteen patients were evaluated at 4 cm dilatation, complete dilatation, at the time of delivery, and immediately postpartum. In addition, samples were obtained from nine nonpregnant control subjects. The venous levels of beta-endorphinlike immunoactivity and beta-lipotropin were determined, and the beta-endorphin level was calculated. The maternal cerebrospinal fluid (CSF) levels and the newborn umbilical venous level also were determined in the delivery room. A gradual rise was noted in the beta-endorphin, beta-lipotropin, and beta-endorphinlike immunoactivity values up to the time of delivery. There was noted to be a modest decrease in their levels in the immediate postpartum period. These levels were significantly elevated over control samples for both beta-endorphinlike immunoactivity and beta-lipotropin (P less than .05). Values for beta-endorphin were not significantly different from control levels. In addition, maternal CSF levels were found to show modest elevations above the simultaneously drawn venous specimens. The umbilical cord venous samples drawn at delivery were also higher than the simultaneous maternal venous levels. These values, although elevated over control values, were not statistically different from simultaneously drawn maternal venous levels.

Metkephamid (Tyr-D-ala-Gly-Phe-N(Me)Met-NH2), a potent opioid peptide: receptor binding and analgesic properties.

The interaction of metkephamid (Tyr-D-Ala-Gly-Phe-N(Me)Met-NH2) with 3H-dihydromorphine and 3H-D-Ala2-D-Leu5-enkephalin binding has been examined in rat brain homogenates. Displacements of both 3H-ligands by metkephamid indicate that metkephamid interacts competitively with greatest potency to the high affinity binding component for both ligands (mu1 site). Unlike most enkephalins and opiates, metkephamid binds equipotently to both morphine-selective (mu2) and enkephalin-selective (delta) binding sites. Metkephamid is differentiated from morphine by its better than 12-fold higher affinity for the delta receptor. Blockade of the high affinity (mu1) binding in vivo with high doses of naloxazone dramatically reduces metkephamid's analgesic potency.

A fragment of substance P with specific central activity: SP(1-7).

Amino-terminal fragments of substance P (SP), SP(1-7) and SP(1-8), were found to produce naloxone-reversible antinociception in the mouse similar to that produced by SP. Similar to SP, these peptides produce antinociception only within a narrow dose range. They have no activity on smooth muscle or blood pressure. These results suggest that contrary to peripheral effects of SP, which are mediated by receptors which recognize the carboxy-terminal part of the SP molecule, certain central actions of SP are mediated by receptors which recognize the amino-terminal part of the SP molecule. SP may be metabolized to this active fragment prior to its action at these receptors.

A comparison of the inhibitory effects of taurine and GABA on identified Purkinje cells and other neurons in the cerebellar cortex of the rat.

The microiontophoretic application of taurine and GABA was studied in the cerebellar cortex of the rat. Both taurine and GABA produced a dose-dependent depression of spike frequency of cerebellar neurons. GABA (2-42 nA, mean 27 nA) induced an inhibition of spike discharge on all 138 cells tested, including 29 Purkinje cells. Taurine (60-200 nA, mean 108 nA) induced an inhibition of spike discharge on 93 of the 106 cerebellar neurons tested, including inhibition on 22 of 25 Purkinje cells. Iontophoretic application of bicuculline and picrotoxin antagonized the inhibitory effects of both GABA and taurine on Purkinje cells as well as on cerebellar neurons in general. Strychnine did not antagonize the inhibition of either GABA or taurine. Simultaneous application of taurine and GABA produced a synergistic inhibitory effect on the firing rate of Purkinje cells. Taurine, in contrast to GABA, appeared to be more depressant when applied in the Purkinje cell dendritic zone than when applied near the soma. The data are discussed in terms of taurine functioning as a neurotransmitter in the cerebellum of the rat and having receptor sites distinct from those for GABA.

Behavioral and electrographic effects of opioids on kindled seizures in rats.

Our laboratory previously suggested that opioid peptides are released by an amygdaloid kindled seizure and may affect the elicitation of a subsequent seizure. The present study examined the effects of morphine, naloxone, enkephalin analogues, and conditions of morphine tolerance and withdrawal on the severity and duration of a series of amygdaloid kindled seizures. The results suggest two distinct opiate/opioid actions on seizures. The first is an anticonvulsant effect on the behavioral manifestations of seizures. This effect is seen following a high dose (50 mg/kg) of morphine or a low dose (6 mg/kg) of enkephalin analogue (LY146104), and is reversed by naloxone. The second is a naloxone-reversible prolonging effect of the high dose of morphine on the electrographic components of the seizures. Receptor affinities of these various opiate/opioid drugs suggest that these two actions are mediated by different receptors which appear not to include high affinity mu receptors.

K-stimulated release of leu- and met-enkephalin from rat striatal slices: lack of effect of morphine and naloxone.

The release of leu- and met-enkephalin from rat striatal slices was determined by superfusing the slices in vitro and running the superfusates directly over columns of Amberlite XAD-2 from which the peptides were eluted with methanol and measured by radioimmunoassay. Depolarization by high K concentrations increased the release of both pentapeptides many fold; the degree of increase, however, depended in part on the length of time chosen for the stimulation period, suggesting that the stimulation effect was very short lived. The stimulated release of both peptides (but not the resting release) was at least partially dependent on Ca in the medium and was totally inhibited by high Mg concentrations. Selected concentrations of naloxone and morphine in the superfusing medium had no effect on the resting or stimulated release of the peptides. The results support the hypothesis that these peptides serve as neurotransmitters in the striatum, but autoregulation of their release by morphine and naloxone could not be demonstrated.

Excitatory effect of L-aspartate and L-glutamate on Purkinje cells in rat cerebellum.

L-aspartate and L-glutamate were microiontophoretically applied onto Purkinje cells and unidentified cerebellar neurons of urethane-anesthetized rats. Both amino acids produced a dose-dependent increase in the spontaneous firing rate of all cells tested. Fifty-three percent (8 of 15 cells) of the dose-response relationships for L-aspartate as compared to those for L-glutamate on Purkinje cells were not parallel, implying different mechanisms of action (suggesting different receptors). On these 8 Purkinje cells, L-glutamate was three times more potent than L-aspartate. Only thirty-three percent of the dose-response relationships (8 of 24 cells) for the two agents on the unidentified cerebellar cells were not parallel. There was no statistical difference in the potency of L-aspartate as compared to L-glutamate on these particular cells. Tests for antagonism on Purkinje cells revealed L-glutamic acid diethyl ester (GDEE) to be a more effective blocker of L-aspartate than of L-glutamate while DL-alpha-aminoadipic acid (DL alpha AA)) was not selective in antagonizing the action of either amino acid. These data are discussed in terms for L-aspartate functioning as a neurotransmitter in the cerebellum of rat and possessing receptor sites distinct from those for L-glutamate.

Association between peridural scar and recurrent radicular pain after lumbar discectomy: magnetic resonance evaluation. ADCON-L European Study Group.

The purpose of this study was to investigate the presence of any correlation between recurrent radicular pain during the first six months following first surgery for herniated lumbar intervertebral disc and the amount of lumbar peridural fibrosis as defined by MR imaging. 197 patients who underwent first-time single-level unilateral discectomy for lumbar disc herniation were evaluated in a randomized, double-blind, controlled multicenter clinical trial. Clinical assessments, performed by physicians blinded to patient treatment status, were conducted preoperatively and at one and six months postoperatively. The enhanced MR images of the operative site utilized in the analysis were obtained at six months postoperatively. Radicular pain was recorded by the patient using a validated visual analog pain scale in which 0 = no pain and 10 = excruciating pain. The data obtained at the 6 month time point were analyzed for an association between amount of peridural scars as measured by MR imaging and clinical failure as defined by the recurrence of radicular pain. The results showed that the probability of recurrent pain increases when scar score increases. Patients having extensive peridural scar were 3.2 times more likely to experience recurrent radicular pain than those patients with less extensive peridural scarring. In conclusion, this prospective, controlled, randomized, blinded, multicenter study has demonstrated that there is a significant association between the presence of extensive peridural scar and the occurrence of recurrent radicular pain.

Cross-tolerance studies distinguish morphine- and metkephamid-induced analgesia.

In vitro data demonstrate that metkephamid (LY127623), an analog of methionine enkephalin, has a high affinity for the delta opioid receptor, as well as the mu-receptor. Data generated utilizing two in vivo measures of receptor selectivity, furthermore, indicate that metkephamid's analgesic activity is in part mediated by delta opioid receptors. The analgesic activity of metkephamid was investigated in the mouse writhing assay following chronic treatment with morphine, the prototypic mu agonist. Mice were treated chronically with increasing doses of morphine or saline and the inhibition of writhing measured in response to an acute injection of morphine or metkephamid. The dose response curve for morphine was shifted to the right 3- to 4-fold following chronic administration of morphine. In contrast, no such shift in the dose response curve for metkephamid was observed in these morphine-tolerant mice. In a further series of tests, a 50 mg/kg dose of naloxazone 20 hr prior to the assessment of morphine or metkephamid analgesia in the mouse hot plate test substantially shifted the dose-response curve for morphine to the right, while leaving the dose-response curve for metkephamid unchanged. These results suggest that delta-receptor activation contributes to the analgesia produced by metkephamid.

Enantiomers of [R,S]-thiorphan: dissociation of analgesia from enkephalinase A inhibition.

The [R] and [S] enantiomers of the enkephalinase A inhibitor [R,S]-thiorphan have been prepared by asymmetric synthesis. The [S] isomer is principally responsible for the angiotensin converting enzyme inhibitory activity of [R,S]-thiorphan, whereas there were only small differences in the ability of the [R] and [S] isomers to inhibit enkephalinase both in vivo and in vitro. In contrast, the in vivo analgesic activity of [R,S]-thiorphan resided principally in the [R] isomer. These data indicate a surprising dissociation of enkephalinase inhibition from analgesic activity. The fact that the two enantiomers of [R,S]-thiorphan were effective inhibitors of enkephalinase, yet the [R] isomer had substantially greater analgesic activity, indicates that factors other than enkephalinase inhibition may be important for [R, S]-thiorphan's analgesic properties.

Use of ADCON in neurosurgery: preclinical review.

ADCON-L and ADCON-T/N are two bioabsorbable adhesion barrier gels designed to inhibit post-operative fibrosis around the dura and nerve structure. Two ADCON products were evaluated in animal models emulating their use in neurosurgery. In all studies ADCON-L and ADCON-T/N were safe and effective barriers to post-operative peridural and perineural fibrosis.