PubMed Health⌕ Search

Biomedical subjects

K F Shen

Publications and source records attributed to K F Shen.

At least 19 recordsLinked to original sources
PubMed1995

Ultra-low concentrations of naloxone selectively antagonize excitatory effects of morphine on sensory neurons, thereby increasing its antinociceptive potency and attenuating tolerance/dependence during chronic cotreatment.

Ultra-low picomolar concentrations of the opioid antagonists naloxone (NLX) and naltrexone (NTX) have remarkably potent antagonist actions on excitatory opioid receptor functions in mouse dorsal root ganglion (DRG) neurons, whereas higher nanomolar concentrations antagonize excitatory and inhibitory opioid functions. Pretreatment of naive nociceptive types of DRG neurons with picomolar concentrations of either antagonist blocks excitatory prolongation of the Ca(2+)-dependent component of the action potential duration (APD) elicited by picomolar-nanomolar morphine and unmasks inhibitory APD shortening. The present study provides a cellular mechanism to account for previous reports that low doses of NLX and NTX paradoxically enhance, instead of attenuate, the analgesic effects of morphine and other opioid agonists. Furthermore, chronic cotreatment of DRG neurons with micromolar morphine plus picomolar NLX or NTX prevents the development of (i) tolerance to the inhibitory APD-shortening effects of high concentrations of morphine and (ii) supersensitivity to the excitatory APD-prolonging effects of nanomolar NLX as well as of ultra-low (femtomolar-picomolar) concentrations of morphine and other opioid agonists. These in vitro studies suggested that ultra-low doses of NLX or NTX that selectively block the excitatory effects of morphine may not only enhance the analgesic potency of morphine and other bimodally acting opioid agonists but also markedly attenuate their dependence liability. Subsequent correlative studies have now demonstrated that cotreatment of mice with morphine plus ultra-low-dose NTX does, in fact, enhance the antinociceptive potency of morphine in tail-flick assays and attenuate development of withdrawal symptoms in chronic, as well as acute, physical dependence assays.

Analgesia↗
PubMed1995

Specific N- or C-terminus modified dynorphin and beta-endorphin peptides can selectively block excitatory opioid receptor functions in sensory neurons and unmask potent inhibitory effects of opioid agonists.

We recently showed that the opioid alkaloids, etorphine, dihydroetorphine and diprenorphine, have remarkably potent antagonist actions on excitatory opioid receptor functions in mouse sensory dorsal root ganglion (DRG) neurons. Pretreatment of naive nociceptive types of neurons with pM concentrations of these antagonists blocks excitatory prolongation of the calcium-dependent component of the action potential duration (APD) elicited by pM-nM morphine or other bimodally acting mu, delta and kappa opioid agonists and unmasks inhibitory APD shortening which usually requires much higher (ca. microM) concentrations. The present study demonstrates that pM concentrations of [des-Tyr1] fragments of dynorphin and beta-endorphin, as well as beta-endorphin-(1-27), can also selectively block excitatory opioid receptor functions in DRG neurons and unmask potent inhibitory effects of low concentrations of bimodally acting mu, delta and kappa opioid peptides and alkaloid agonists. These N- or C-terminus modified dynorphin or beta-endorphin peptides can be readily formed in neurons by specific peptidase activities. Since sustained activation of excitatory opioid receptor functions is essential for the development of tolerance/dependence in chronic morphine-treated DRG neurons in culture, the present in vitro study may help to account for the unexplained efficacy of [des-Tyr1] dynorphin fragments, as well as the endogenous opioids dynorphin A and beta-endorphin, in suppressing development and expression of naloxone-precipitated withdrawal and morphine tolerance in vivo.

Action Potentials↗
PubMed1994

Antagonists at excitatory opioid receptors on sensory neurons in culture increase potency and specificity of opiate analgesics and attenuate development of tolerance/dependence.

At low (< nM) concentrations, mu, delta or kappa opioid peptides as well as morphine and other opioid alkaloids elicit dose-dependent excitatory prolongation of the calcium-dependent component of the action potential duration (APD) of many mouse sensory dorsal root ganglion (DRG) neurons, whereas application of the same opioids at higher (uM) concentrations results in inhibitory shortening of the APD. These bimodal opioid excitatory/inhibitory effects on DRG neurons are blocked by naloxone. In contrast to bimodally acting opioids, the opioid alkaloids, etorphine and dihydroetorphine (thebaine-oripavine derivatives) uniquely elicited only dose-dependent, naloxone-reversible inhibitory effects on sensory neurons in DRG-spinal cord explants, even at concentrations as low as 1 pM, and showed no excitatory effects at lower concentrations. These remarkably potent inhibitory opioid receptor agonists also act as antagonists at excitatory opioid receptors since pretreatment of DRG neurons with subthreshold concentrations (< pM) blocked excitatory APD prolongation by nM morphine (or other opioids) and unmasked inhibitory APD shortening which generally requires much higher concentrations. Furthermore, acute application of pM-nM etorphine to chronic microM morphine- or D-Ala2-D-Leu5 enkephalin (DADLE)-treated DRG neurons blocked the nM naloxone-precipitated APD prolongation that generally occurs in DRG cells sensitized by bimodally acting opioids. In the presence of pM etorphine, chronic treatment of DRG neurons with microM morphine or DADLE no longer resulted in development of tolerance/dependence effects, as previously observed after similar chronic opioid treatment in the presence of cholera toxin-B subunit. These in vitro studies may clarify the mechanisms underlying the potent analgesic effects of etorphine and dihydroetorphine in vivo and to guide the use of these and other excitatory opioid receptor antagonists in attenuating development of opiate dependence/addiction.

Analgesics↗
PubMed1994

Nerve growth factor rapidly prolongs the action potential of mature sensory ganglion neurons in culture, and this effect requires activation of Gs-coupled excitatory kappa-opioid receptors on these cells.

Application of low concentrations (pM-nM) of NGF to mouse dorsal root ganglion (DRG)-spinal cord explants in long-term organotypic cultures rapidly prolongs the duration of the Ca(2+)-dependent component of the action potential (APD) in a major subset of DRG neurons that were previously shown to have characteristic responsiveness to exogenous opioids. These NGF-elicited excitatory modulating effects are blocked by pretreatment of the DRG neurons with monoclonal antibodies to rodent NGF receptors. NGF-induced APD prolongation is also prevented by the opioid receptor antagonist naloxone and the specific kappa-opioid antagonist nor-binaltorphimine (but not by specific mu- and delta-opioid antagonists). The results suggest that NGF stimulates the release of endogenous opioids (e.g., dynorphin) from DRG neurons and that prolongation of the APD occurs secondarily by activation of excitatory kappa-opioid receptor functions on these same or nearby cells. NGF-induced release of small quantities of opioids by DRG neurons would be expected to prolong the APD in view of the remarkable sensitivity of these neurons to the excitatory effects of extremely low (fM-nM) concentrations of exogenous opioid agonists. NGF-induced APD prolongation is blocked by the same cholera toxin A or B subunit treatments previously shown to block Gs coupling and GM1 ganglioside regulation of excitatory opioid receptors, respectively. These in vitro studies suggest that excitatory opioid receptor-mediated functions may play a role in mediating some types of rapid NGF-induced hyperalgesic and other physiologic effects on the nervous system.

Action Potentials↗
PubMed1992

Chronic selective activation of excitatory opioid receptor functions in sensory neurons results in opioid 'dependence' without tolerance.

We previously showed that mouse sensory dorsal root ganglion (DRG) neurons chronically exposed to 1 microM D-ala2-D-leu5-enkephalin (DADLE) or morphine for > 2-3 days in culture become tolerant to the usual opioid inhibitory receptor-mediated effects, i.e. shortening of the duration of the calcium-dependent component of the action potential (APD), and supersensitive to opioid excitatory APD-prolonging effects elicited by low opioid concentrations. Whereas nanomolar concentrations of dynorphin(1-13) or morphine are generally required to prolong the APD of naive DRG neurons (by activating excitatory opioid receptors), femtomolar levels become effective after chronic opioid treatment. Whereas 1-30 nM naloxone or diprenorphine prevent both excitatory and inhibitory opioid effects but do not alter the APD of native DRG neurons, both opioid antagonists unexpectedly prolong the APD of most of the chronic opioid-treated cells. In the present study, chronic exposure of DRG neurons to 1 microM DADLE together with cholera toxin-B subunit (which selectively blocks GM1 ganglioside-regulated opioid excitatory, but not inhibitory, receptor functions) prevented the development of opioid excitatory supersensitivity and markedly attenuated tolerance to opioid inhibitory effects. Conversely, sustained exposure of DRG neurons to 1 nM DADLE, which selectively activates excitatory opioid receptor functions, resulted in characteristic opioid excitatory supersensitivity but no tolerance. These results suggest that 'dependence'-like properties can be induced in chronic opioid-treated sensory neurons in the absence of tolerance. On the other hand, development of some components of tolerance in these cells may require sustained activation of both excitatory, as well as inhibitory, opioid receptor functions.

Animals↗
PubMed1992

F11 neuroblastoma x DRG neuron hybrid cells express inhibitory mu- and delta-opioid receptors which increase voltage-dependent K+ currents upon activation.

The F11 cell line is a fusion product of cells of mouse neuroblastoma cell line N18TG-2 with embryonic rat dorsal-root ganglion (DRG) neurons. Previous biochemical results suggest that they express mu- and delta-opioid receptors that are negatively coupled to adenylate cyclase. The present study provides direct agonist-binding and electrophysiologic evidence of mu and delta, but not kappa, receptor expression in F11 cells. Radioligand binding assays show that F11 cell membranes bind the mu- and delta-opioid receptor agonists, DAGO and DPDPE with Kd = 4.5 and 4.9 nM and Bmax = 111 and 195 fmol/mg, respectively. Tight-seal patch-clamp recordings of F11 cells after several days in a differentiating culture medium (low serum, cyclic AMP and nerve growth factor) showed that: (i) the outward K+ current during pulsed depolarization in most of these cells was increased by either DAGO or DPDPE, but none were responsive to both opioids or to the kappa-opioid receptor agonist, U-50,488H. The response was blocked by relevant receptor antagonists, naloxone, beta-funaltrexamine or naltrindole; (ii) cells without processes responded neither to DAGO nor to DPDPE; (iii) treatment with pertussis toxin blocked all opioid-induced increases in outward K+ current. The opioid-induced increase in voltage-dependent membrane K+ current in F11 cells resembles the inhibitory effect elicited by mu- and delta-opioid agonists in primary cultures of mouse DRG neurons.

Animals↗
PubMed1992

After chronic opioid exposure sensory neurons become supersensitive to the excitatory effects of opioid agonists and antagonists as occurs after acute elevation of GM1 ganglioside.

Mouse sensory dorsal-root ganglion (DRG) neurons chronically exposed to 1 microM D-Ala2-D-Leu5-enkephalin (DADLE) for greater than 1 week in culture become tolerant to opioid inhibitory effects, i.e. shortening of the duration of the calcium-dependent component of the action potential (APD). Acute application of higher concentrations of DADLE (ca. 10 microM) to these treated neurons not only fails to shorten the APD but, instead, generally elicits excitatory effects, i.e. prolongation of the APD. The present study shows that chronic DADLE- or morphine-treated DRG neurons also become supersensitive to the excitatory effects of opioids. Whereas nM concentrations of dynorphin(1-13) are generally required to prolong the APD of naive DRG neurons, fM levels become effective after chronic opioid treatment. Whereas 1-30 nM naloxone or diprenorphine do not alter the APD of naive DRG neurons, both opioid antagonists unexpectedly prolong the APD of most of the treated cells. Similar supersensitivity to the excitatory effects of opioid agonists and antagonists was previously observed after acute treatment of naive DRG neurons with GM1 ganglioside. Our results suggest that both chronic opioid and acute GM1 treatments of DRG neurons greatly enhance the efficacy of opioid excitatory receptor functions so that even the extremely weak agonist properties of naloxone and diprenorphine become effective in prolonging the APD of these treated cells when tested at low concentrations, whereas their antagonist properties at inhibitory opioid receptors do not appear to be altered. Furthermore, whereas cholera toxin-B subunit (CTX-B; 1-10 nM) blocks opioid-induced APD prolongation in naive DRG neurons (presumably by interfering with endogenous GM1 modulation of excitatory opioid receptors functions), even much higher concentrations of CTX-B were ineffective in chronic opioid-treated as well as acute GM1-elevated neurons. These and related data suggest that opioid excitatory supersensitivity in chronic opioid-treated DRG neurons may be due to a cyclic AMP-dependent increase in GM1 ganglioside levels. Our results may clarify mechanisms of opioid dependence and the paradoxical supersensitivity to naloxone which triggers withdrawal symptoms after opiate addiction.

Action Potentials↗
PubMed1992

After GM1 ganglioside treatment of sensory neurons naloxone paradoxically prolongs the action potential but still antagonizes opioid inhibition.

Low (nanomolar) concentrations of opioid agonists prolong the calcium-dependent component of the action potential duration (APD) of many dorsal root ganglion (DRG) neurons, whereas higher (micromolar) levels shorten the APD. Both effects are blocked by naloxone (1-10 nM). Opioid-induced APD prolongation appears to be mediated by excitatory opioid receptors that are positively coupled via a cholera toxin-A-sensitive Gs protein to adenylate cyclase/cyclic AMP-dependent ion conductances, whereas opioid-induced APD shortening is mediated by inhibitory receptors linked via pertussis toxin-sensitive Gi/Go proteins. Cholera toxin-B subunit, which binds to GM1 ganglioside, also selectively blocks opioid-induced APD prolongation. After brief treatment with GM1 ganglioside, the opioid agonists, dynorphin (1-13) or morphine, prolong the APD at femtomolar vs. the usual nanomolar concentrations, whereas no significant alterations were observed in the sensitivity of these GM1-treated cells to opioid inhibitory effects elicited by higher opioid concentrations. The present study shows that the opioid antagonists, naloxone or diprenorphine (1-30 nM), did not alter the APD of naive DRG neurons. In contrast, after GM1 treatment (1 microM, greater than 10 min), both opioid antagonists (but not (+)naloxone) unexpectedly prolonged the APD of most of the GM1-treated cells, but still continued to antagonize opioid-induced APD shortening. These results suggest that the supersensitivity of GM1-treated DRG neurons to the excitatory effects of opioid agonists and antagonists is due primarily to a remarkably increased efficacy of excitatory Gs-coupled opioid receptor functions, similar to the opioid excitatory supersensitivity that we have recently observed in chronic opioid-treated DRG neurons.

Action Potentials↗
PubMed1991

Brief treatment of sensory ganglion neurons with GM1 ganglioside enhances the efficacy of opioid excitatory effects on the action potential.

In previous studies, we showed that low (nM) concentrations of opioid prolong the action potential duration (APD) of many mouse dorsal root ganglion (DRG) neurons via Gs-linked excitatory opioid receptors, whereas micromolar opioid levels shorten the APD via Gi/Go-linked inhibitory receptors. In addition, cholera toxin-B subunit (CTX-B) selectively blocks opioid- but not forskolin-induced prolongation of the APD in DRG neurons. Since CTX-B binds with selective high affinity to GM1 ganglioside located on the cell surface, the results suggest that GM1 plays an essential role in regulating excitatory opioid receptor functions. This hypothesis was tested by treating DRG neurons in mouse DRG-cord explants with exogenous gangliosides and determining whether the efficacy of opioid agonists in prolonging the APD is enhanced. The threshold concentration of the opioids, dynorphin(1-13) and morphine required to prolong the APD in many DRG neurons was markedly decreased from nM to fM levels after bath exposure to 10 nM to 1 microM GM1 ganglioside for less than 5 min. In contrast, GM2 and GM3 gangliosides and asialo-GM1 ganglioside were ineffective, even when DRG neurons were exposed to high concentrations (1-10 microM) for periods greater than 1 h. Although GD1a, GD1b and GQ1b gangliosides appeared to be as effective as GM1 when tested at microM concentrations for 15 min, tests at lower concentrations, shorter periods, and/or at lower temperature (24 degrees vs 34 degrees C), showed that they were significantly less effective than GM1.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1991

Opioids at low concentration decrease openings of K+ channels in sensory ganglion neurons.

Previous studies showed that low concentrations of opioids prolong the calcium-dependent component of the action potential duration (APD) of dorsal root ganglion (DRG) neurons, whereas higher concentrations shorten the APD. In the present study whole-cell voltage-clamp, as well as cell-attached membrane-patch voltage-clamp, recordings demonstrate that application of picomolar to nanomolar concentrations of mu, delta or kappa opioid agonists (DAGO, DPDPE or dynorphin) to DRG neurons in dissociated cell cultures reversibly decreased the activities of voltage-sensitive K+ channels. Pretreatment of DRG neurons with the opioid receptor antagonists, naloxone (30 nM) or diprenorphine (1 nM) prevented mu/delta or kappa opioid-induced decreases in K+ channel activities, respectively. Since opioids added to the bath solution decreased the activities of K+ channels in the membrane patch sealed off by the pipette tip, our results provide strong evidence that some modes of excitatory modulation of the action potential of DRG neurons are mediated by diffusible second messengers. The data are consonant with our previous studies indicating that opioids can elicit excitatory effects on sensory neurons via cholera toxin-sensitive Gs-linked excitatory opioid receptors coupled to cyclic AMP-dependent ionic channels.

Action Potentials↗
PubMed1990

Cholera toxin-B subunit blocks excitatory effects of opioids on sensory neuron action potentials indicating that GM1 ganglioside may regulate Gs-linked opioid receptor functions.

In a previous study, we demonstrated that cholera toxin-A subunit, as well as the whole toxin, selectively blocks opioid-induced prolongation of the Ca2+ component of the action potential duration (APD) in dorsal root ganglion (DRG) neurons, indicating mediation of this excitatory effect by Gs-linked opioid receptors. The present study shows that pretreatment of DRG neurons with the B subunit of cholera toxin (1-10 ng/ml; greater than 15 min) can also block mu/delta and kappa opioid-induced APD prolongation, but not shortening. Since the B subunit binds selectively to GM1 ganglioside located on the cell surface, these results suggest that this ganglioside may regulate Gs-linked excitatory opioid receptor functions in DRG neurons. Possible contamination of purified B subunit preparations of cholera toxin with traces of the more potent A subunit was eliminated by heating the stock solution to 56 degrees C for 20 min. Exposure of DRG neurons to an affinity-purified anti-GM1 antiserum also blocked opioid-induced APD prolongation, providing further evidence that GM1 ganglioside may play an essential role in excitatory opioid modulation of the action potential of these cells. The blockade by cholera toxin-B subunit and anti-GM1 antibodies of opioid-induced APD prolongation is best accounted for by the following hypothesis: CTX-B interferes with an endogenous GM1 ganglioside component of the excitatory, but not inhibitory, opioid receptor complex on DRG neurons that may allosterically regulate coupling of the receptors via Gs to adenylate cyclase/cyclic adenosine monophosphate-dependent ionic conductances.

Action Potentials↗
PubMed1990

Cholera toxin-A subunit blocks opioid excitatory effects on sensory neuron action potentials indicating mediation by Gs-linked opioid receptors.

Our previous studies indicated that opioid-induced prolongation of the Ca2+ component of the action potential duration (APD) in dorsal root ganglion (DRG) neurons is mediated by excitatory opioid receptors that are coupled to cyclic AMP-dependent voltage-sensitive ionic conductances. In the present study, DRG neurons were treated with cholera toxin (CTX), or with the A subunit of CTX, in order to determine if these excitatory opioid receptors are positively coupled via the GTP-binding protein Gs to the adenylate cyclase/cyclic AMP system. In contrast, inhibitory opioid receptors have been shown to be linked to pertussis toxin-sensitive Gi/Go regulatory proteins that mediate APD shortening responses. After pretreatment of DRG-spinal cord explants with remarkably low concentrations of CTX-A (1 pg/ml-1 ng/ml; greater than 15 min) or whole toxin (1 pg/ml-1 microgram/ml) the APD prolongation elicited in DRG neurons by 1-10 nM delta/mu (DADLE) or kappa (U-50,488H) opioids was blocked (29 out of 30 cells), whereas APD shortening by microM opioid concentrations was unaffected. Opioid-induced APD prolongation was blocked even when the initial treatment with CTX or CTX-A alone did not prolong the APD. The blocking effects of CTX and CTX-A were reversed in tests made 2 h after return to control medium. The mechanisms underlying the unusually potent blocking effects of CTX and CTX-A on opioid excitatory modulation of the APD of DRG neurons require correlative biochemical analyses.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1990

Opioids can evoke direct receptor-mediated excitatory effects on sensory neurons.

Activation of opioid receptors has generally been considered to produce inhibitory effects on neuronal activity. However, recent studies indicate that specific mu-, delta- and kappa-opioid receptor agonists can elicit excitatory, as well as inhibitory, modulation of the action potentials of sensory neurons isolated in culture. Stanley Crain and Ke-Fei Shen review the evidence for mediation of these direct excitatory effects by naloxone-reversible opioid receptors. They propose that this dual modulatory mechanism may help to account for previously unexplained enhancement by opioids of transmitter release, paradoxical hyperalgesic and aversive effects of opioids, and some aspects of opioid tolerance and addiction.

Humans↗
PubMed1990

Dynorphin prolongs the action potential of mouse sensory ganglion neurons by decreasing a potassium conductance whereas another specific kappa opioid does so by increasing a calcium conductance.

Previous studies have reported that large (microM) concentrations of kappa opioids, e.g. dynorphin and 3,4 dichloro-N-methyl-N-(2-[1-pyrrolidinyl]-cyclohexyl)benzene-acetamide (U-50,488H), shorten the duration of the calcium component of the action potential of dorsal root ganglion neurons by decreasing a voltage-sensitive Ca2+ conductance. The present study showed that, in addition to these inhibitory modulatory effects, small (nM) concentrations of dynorphin, as well as U-50,488H, prolonged the action potential in about 75% of the neurons of dorsal root ganglia in ganglion spinal cord explants of mouse (tested in 5 mM Ba2+). Both the excitatory and inhibitory effects of these kappa opioids were prevented by perfusion together with the opioid antagonist, diprenorphine (10 nM). However, when responsivity tests with opioids were carried out in the presence of multiple K+ channel blockers [Ba2+, Cs+ and tetraethylammonium (TEA)], 1 nM dynorphin prolonged the action potential in only 7% of the neurons (n = 28), whereas 1 nM U-50,488H still elicited the prolongation of the action potential in 60% of the cells (n = 39). These data suggest that dynorphin prolongs the action potential of neurons of dorsal root ganglion by activating a kappa subtype of receptor that decreases a voltage-sensitive K+ conductance, whereas U-50,488H produces similar excitatory modulation of the action potential by activating another kappa subtype of receptor that increases a voltage-sensitive Ca2+ conductance. Thus, U-50,488H-induced prolongation of the action potential appears to be mediated by a kappa subtype of receptor that produces the opposite effect on Ca2+ channels to that which occurs during kappa opioid-induced shortening of the action potential.(ABSTRACT TRUNCATED AT 250 WORDS)

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed1989

Dual opioid modulation of the action potential duration of mouse dorsal root ganglion neurons in culture.

Multiple modulatory effects of opioids on the duration of the calcium component of the action potential (APD) of dorsal-root ganglion (DRG) neurons of mouse spinal cord-ganglion explants were studied. The APD of DRG neuron perikarya has been previously shown to be shortened by exposure to high concentrations of opioids (ca. 0.1-1 microM) in about 1/2 of the cells tested. The present study demonstrates that in addition to these inhibitory modulatory effects of opioids, lower concentrations (1-10 nM) of present study demonstrates that in addition to these inhibitory modulatory effects of opioids, lower concentration (1-10 nM) of delta- mu, and kappa-opioid agonists elicit excitatory modulatory effects, i.e. prolongation of the APD, in about 2/3 of the sensory neurons tested. APD prolongation as well as shortening elicited by delta, mu, and kappa agonists were prevented by coperfusion with the opioid antagonists, naloxone or diprenorphine (10 nM). APD prolongation induced by the delta-agonist [D-Ala2-D-Leu5]enkephalin (DADLE) was prevented in the presence of multiple K+ channel blockers, whereas excitatory modulation by the specific kappa-agonist, U-50,488H was not attenuated under these conditions. After treatment of DRG neurons with pertussis toxin (1 micrograms/ml for several days) or forskolin (50 muM for less than 15 min), a much smaller fraction of cells showed opioid-induced APD shortening; moreover, a much larger fraction of cells showed opioid-induced APD prolongation, even when tested with high concentrations of DADLE (1-10 muM). These data indicate that opioid-induced APD prolongation is not mediated by pertussis toxin-sensitive G proteins (which have been shown to regulate opioid inhibitory effects) and suggest that elevation of cyclic AMP levels may enhance opioid excitatory responsiveness. Furthermore, our analyses indicate that mu-, delta- and kappa-subtypes of excitatory as well as inhibitory opioid receptors may be expressed on the same DRG neuron perikaryon under in vitro conditions. If dual opioid modulation of the APD of DRG perikarya also occurs in central DRG terminals this may play a significant role both in nociceptive signal transmission as well as tolerance to opioid analgesia.

Action Potentials↗
PubMed1988

Effects of temperature alterations on population and cellular activities in hippocampal slices from mature and immature rabbit.

Effects of temperature on population spike and cellular activities have been assessed in the CA1 region of hippocampal slices from mature and immature rabbit. In field potential recordings, population spike amplitude was maximal at near 30 degrees C for both mature and immature tissue, and fell off as temperature was either raised (to a maximum of 44 degrees C) or lowered (to a minimum of 20 degrees C). With cooling below 30 degrees C, population spikes decreased in amplitude and became broader; stimuli always elicited some response, and changes due to cooling were reversible. With increases in temperature, however, irreversible decrease and/or loss of population spikes occurred when tissue was warmed beyond 43 degrees C. Input-output curves established for mature and immature slices indicated that, at all temperatures, population spike amplitude grew more rapidly with small increases in stimulus intensity in immature slices as compared to mature slices. Intracellular recordings were made from CA1 pyramidal cells in mature and immature hippocampal slices. For both mature and immature tissues, moderate warming (to 40 degrees C) produced membrane hyperpolarizations in many cells, especially in the mature hippocampus. Increasing temperature beyond 40 degrees C led to marked depolarizations in a number of cells, a depolarization that was irreversible, particularly in mature neurons. Cooling generally produced a depolarizing shift in membrane potential and an accompanying increase in input resistance; these effects, however, were reversible. Temperature changes in both warming and cooling directions had effects on repetitive firing patterns in both mature and immature neurons. In particular, spike trains elicited by a constant current pulse at a given membrane potential became shorter. The effects of cooling on this cell parameter were reversible, but warming-induced changes were usually permanent. Irreversibility of the warming effects was more pronounced in cells from mature than from immature hippocampus. As reported previously, cooling produced marked spike broadening and changes in synaptic potentials in both mature and immature neurons. These studies confirm previously reported temperature sensitivities of neuronal properties in hippocampal slices. On the basis of these data, and reports from other laboratories, it is clear that relatively small changes in temperature can have rather dramatic effects on properties of single cells and cell populations. Such temperature sensitivity is critical in evaluating data obtained from in vitro slice preparations.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗