Biomedical subjects

I K Ho

Publications and source records attributed to I K Ho.

At least 55 records · Page 3Linked to original sources

PubMed1998

The role of glutamate in the locus coeruleus during opioid withdrawal and effects of H-7, a protein kinase inhibitor, on the action of glutamate in rats.

To investigate the role of glutamate in the locus coeruleus (LC) during opioid withdrawal, rats were continuously infused with morphine (a mu-opioid receptor agonist, 26 nmol/microl/h) or butorphanol (a mu/delta/kappa-mixed opioid receptor agonist, 26 nmol/microl/h) intracerebroventricularly (i.c.v.) via osmotic minipumps for 3 days. A direct LC injection of glutamate (1 or 10 nmol/5 microl) or naloxone (an opioid receptor antagonist, 24 nmol/5 microl) induced withdrawal signs in morphine- or butorphanol-dependent animals. However, these agents failed to precipitate any withdrawal signs in saline-treated control animals. On the other hand, the expression of withdrawal signs precipitated by the administration of glutamate or naloxone in opioid-dependent animals was completely blocked by concomitant infusion with 1 or 10 nmol/microl/h of an inhibitor of adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase and protein kinase C, H-7 [1-(5-isoquinolinesulfonyl)-2-methylpiperazine]. In animals that had been infused with opioids in the same manner, i.c.v. injection of naloxone (48 nmol/5 microl) precipitated withdrawal signs and increased extracellular fluid levels of glutamate in the LC of morphine- or butorphanol-dependent rats measured by in vivo microdialysis method. However, concomitant infusion with H-7 inhibited the increases of glutamate levels in the LC. These results strongly suggest that an expeditious release of glutamate in the LC region plays an important role in the expression of physical dependence on opioids. Furthermore, the action on glutamate release might be increased by the enhancement of cAMP-dependent protein kinase and/or protein kinase C activity.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1998

Visceral analgesic tolerance to intrathecal butorphanol in rats.

PURPOSE: Recent experimental data suggest that intrathecal (it) kappa-opioid agonists produce profound visceral analgesia. This study investigated the development of visceral analgesic tolerance to it butorphanol, a potent kappa-agonist that has fewer side effects than commonly used it opioids. Understanding of this tolerance could make it butorphanol more effective in treating chronic visceral pain. METHODS: This was a randomized, controlled animal study involving 80 Sprague-Dawley rats. Rats implanted with lumbar it catheters were infused either with it saline or butorphanol (52 nmol.hr-1) for 96 hr. Six hours afterwards, each rat was challenged once with one of the differing it butorphanol doses to construct dose-response curves. Visceral analgesia was evaluated by the abdominal writhing responses to the acetic acid injected intraperitoneally. The time of the first writhe and the total number of writhes were recorded. RESULTS: For both the saline- and butorphanol-infused groups, a higher challenge dose of it butorphanol produced longer time for the first writhe to occur (P < 0.01, one-way ANOVA), and fewer writhes occurring within 30 min (P < 0.01, one-way ANOVA). However, the dose response curves of the butorphanol-infused groups were shifted rightward (P < 0.001, partial F test). CONCLUSION: The challenge doses of it butorphanol produced dose-dependent visceral analgesia in both the saline- and butorphanol-infused groups, confirming its efficacy. The butorphanol-infused groups showed dose-response shifts, demonstrating the development of tolerance to this visceral analgesia.

Acetic Acid↗

PubMed1998

Supersensitivity of spinal opioid receptors to antagonists in intrathecal butorphanol and morphine dependence.

The purpose of this investigation was to evaluate changes in the sensitivity of spinal opioid receptors to selective antagonists in rats rendered dependent on intrathecal (i.t.) butorphanol and morphine. Using quantitative autoradiography, competitive binding assays with selective opioid antagonists were performed in the spinal cord sections of i.t. butorphanol- and morphine-dependent rats in which withdrawal was precipitated by i.t. naloxone. In butorphanol-dependent rats, the spinal kappa-opioid receptor developed a greater degree of antagonist supersensitivity than the spinal delta- and mu-opioid receptors did. In contrast, the spinal mu-opioid receptor became more sensitive than the delta-opioid receptor in morphine-dependent rats. These results indicate that differential supersensitivity of spinal opioid receptors was induced after chronic i.t. infusions of butorphanol and morphine.

Animals↗

PubMed1998

Differential involvement of opioid receptors in intrathecal butorphanol-induced analgesia: compared to morphine.

The present experiments were performed to investigate the differential involvement of the opioid receptor subtypes in the antinociception of intrathecal (IT) butorphanol compared to IT morphine. A single dose (26 nmol) of IT nor-binaltorphimine (nor-BNI), beta-funaltrexamine (beta-FNA), and naltrindole (NTI) demonstrated a significant attenuation in the overall antinociception of IT butorphanol (52 nmol) or IT morphine (26 nmol). However, IT butorphanol elicits thermal antinociceptive effect through kappa > delta > or = mu, whereas morphine acts on mu >delta >> kappa. These results indicate that the antinociceptive effect of both IT butorphanol and IT morphine are mediated through mu, delta, and kappa opioid receptors in different relative orders.

Analgesics, Opioid↗

PubMed1998

Relative involvement of spinal opioid receptors in physical dependence on intrathecal butorphanol and morphine.

The present study was carried out to investigate the relative involvement of spinal opioid receptors in the development of physical dependence on intrathecal (i.t.) butorphanol in comparison with i.t. morphine. Dependence was induced by continuous i.t. infusion of butorphanol (52 nmol/h) and morphine (26 nmol/h) for 4 days in male Sprague-Dawley rats. Naloxone, CTOP, naltrindole, and nor-binaltorphimine (nor-BNI) were administered i.t. to precipitate behavioral signs of withdrawal. Administration of i.t. naloxone produced a significantly greater increase in the profile of withdrawal signs in i.t. morphine dependence than that in i.t. butorphanol dependence. An i.t. nor-BNI challenge elicits behavioral signs of withdrawal only in rats dependent on i.t. butorphanol, but not in rats dependent on i.t. morphine. CTOP administered i.t. precipitated withdrawal signs in i.t. morphine dependence that were greater than that in i.t. butorphanol dependence. An i.t. treatment with naltrindole produced equivalent signs of withdrawal in both i.t. butorphanol- and morphine-dependent rats. These results suggest that continuous i.t. butorphanol results in the development of less physical dependence than that of i.t. morphine. Spinal kappa- rather than delta- and mu-opioid receptors play a major role in the development of i.t. butorphanol dependence, whereas spinal mu-opioid receptors play a more important role than delta-opioid receptors in i.t. morphine dependence.

Animals↗

PubMed1998

Changes in NMDAR2 subunit mRNA levels during pentobarbital tolerance/withdrawal in the rat brain: an in situ hybridization study.

Little is known about the functional modulation of NMDA receptor subunits at the molecular level. Therefore, a series of experiments were conducted to elucidate more fully the role of NMDA receptor subtypes in pentobarbital tolerance and withdrawal. We investigated the influence of centrally administered pentobarbital on the regulation of mRNA levels of the family of NMDA receptor 2 (NR2) subtypes (NR2A, NR2B, and NR2C) by in situ hybridization histochemistry in rat brain. Animals were rendered tolerant by continuous intracerebroventricular (i.c.v.) infusion with pentobarbital (300 microg/10 microl/hr for 6 days) through pre-implanted cannulae connected to osmotic mini-pumps, and dependent, by abrupt withdrawal from pentobarbital. The NR2A subunit mRNA was increased in cortical areas in pentobarbital tolerant and withdrawal rats. In contrast, the NR2B mRNA was decreased in parietal cortex and hippocampus in both tolerance and withdrawal rats. The level of NR2C mRNA was increased in withdrawal rats, while there was no change in tolerant rats. These results indicate that continuous i.c.v. infusion with pentobarbital alters NR2 subunit mRNA expression in the rat brain, suggesting that NR2 subunits may play an important role in the development of tolerance to and withdrawal from pentobarbital.

Animals↗

PubMed1998

Changes in [3H]forskolin binding to adenylate cyclase and [3H]phorbol dibutyrate binding to protein kinase C in pentobarbital tolerant/dependent rats.

These studies were designed to examine the effect of chronic administration of pentobarbital on activity of adenylate cyclase (AC) and protein kinase C (PKC) in the rat brain by autoradiography. Recently, it has been suggested that the phosphorylation of specific proteins may be involved in the development of physical dependence. An experimental model of barbiturate tolerance and dependence was developed using i.c.v. infusion of pentobarbital (300 microg/10 microl/hr for 7 days) by osmotic minipumps and abrupt withdrawal from pentobarbital. The levels of [3H]forskolin binding were elevated (28-67%) in cortex, thalamus, dentate gyrus, hippocampal CA3 and cerebellum of the pentobarbital withdrawal animals, while these changes were not observed in tolerant rats. The levels of [3H]phorbol dibutyrate binding were highly elevated (38-65%) in the region of cortex, caudate putamen, septum, thalamus, dentate gyrus, and cerebellum of rats withdrawal from pentobarbital. These results show that the levels of AC and PKC were significantly elevated in pentobarbital withdrawal rats, and suggest that the levels of AC and PKC are altered in a region-specific manner during pentobarbital withdrawal.

Adenylyl Cyclases↗

PubMed1998

Competitive inhibition of delta8-tetrahydrocannabinol and its active metabolites for cannabinoid receptor binding.

In vitro binding characteristics of delta8-tetrahydrocannabinol (delta8-THC) and its metabolites, 11-hydroxy-delta8-THC (11-OH-delta8-THC) and 11-oxo-delta8-THC, as well as an inactive metabolite, delta8-THC-11-oic acid, as a cannabinoid receptor site from bovine cortex were examined using the specific agonist [3H]CP-55940. 11-OH-delta8-THC and 11-oxo-delta8-THC strongly inhibited the specific binding of [3H]CP-55940. The Ki values of 11-OH-delta8-THC and 11-oxo-delta8-THC for the specific binding of [3H]CP-55940 were 52 and 143 nM, respectively, whereas that of delta8-THC-11-oic acid was 917 nM. Scatchard plot analyses indicated that 11-OH-delta8-THC and 11-oxo-delta8-THC caused a significant increase in the apparent KD value without changing the apparent Bmax. These results reveal that active metabolites of delta8-THC also competitively bind to the cannabinoid receptor as agonists.

Animals↗

PubMed1998

Synthesis and sedative-hypnotic effects of N3-allyl- and N1-allyl-5,6-substituted 2-thiouracil derivatives in mice.

Twenty four thiouracil derivatives, including N3-allyl- (19) and N1-allyl-2-thiouracil (20) were synthesized and their pharmacological effects [sedative-hypnotic activity (loss of righting reflex and spontaneous activity), convulsant activity, effect on pentobarbital (PB)-induced sleep and mortality] were evaluated in mice at doses of 320 mg/kg, i.p. and 2 mumol/mouse by intracerebroventricular (i.c.v.) injections, respectively. N3-Allyl-6-propyl-2-thiouracil (3), N3-allyl-5,6-dimethyl-2-thiouracil (10), N3-allyl-1,2,3,4,5,6,7,8,9-nonahydro-4-oxo-2-thiocyclohepta [d]pyrimidine (16) and N3-allyl-5-methyl-2-thiouracil (18) exhibited sedative-hypnotic activity, whereas N3-allyl-6-ethyl-5-methyl-2-thiouracil (11), N1-allyl-5-methyl-2-thiouracil (21), N1-allyl-1,2,3,4,5,6,7,8,9-nonahydro-4-oxo-2-thiocyclohepta[ d]pyrimidine (23) and N1-allyl-5,6-dimethyl-2-thiouracil (24) conversely displayed clonic- and/or tonic-convulsant seizures. N3-Allyl-6-propyl-2-thiouracil (3) and N3-allyl-5-methyl-2-thiouracil (18) decreased spontaneous activity. Other compounds examined were inactive, or only slightly active in the sedative-hypnotic assay even at high doses. Fifteen compounds (1-4, 7, 10, 11, 14-16, 18-21, and 23) significantly prolonged the PB-induced sleeping time. Interestingly, only N1-allyl-5,6-dimethyl-2-thiouracil (24) shortened the PB-induced sleeping time. These results showed that these thiouracils possessed many different effects such as sedative-hypnotic, anticonvulsant and/or convulsant, and that N3-allyl-5-methyl-2-thiouracil (18) and N1-allyl-5,6-dimethyl-2-thiouracil (24) had the most potent hypnotic activity and antagonistic effect against PB, respectively.

Animals↗

PubMed1998

The role of glutamate in physical dependence on opioids.

The present review will evaluate the interactions between kappa-opioid receptors and glutamate within the locus coeruleus (LC) during the development of opioid dependence and on expression of withdrawal from dependence on opioids. Hyperactivity of noradrenergic neurons in the LC has been proposed to play a critical role in the physiological and behavioral responses that comprise opioid withdrawal. Several studies indicate that the excitatory amino acid system, in particular, glutamate and its receptors, participate in both the withdrawal-associated increase in LC neuronal activity and the expression of opioid withdrawal behaviors. Most studies on opioid dependence have focused on the prototypical opioid morphine, which produces its physical dependence through agonist actions at the mu-opioid receptor. Butorphanol (Stadol), which exhibits a markedly different profile of opioid receptor activity than does morphine, produces its physical dependence primarily through actions at the kappa-opioid receptor. Studies from our laboratories using a rodent model in which butorphanol administration induces dependence indicate further that the kappa-opioid receptor is an important regulator of glutamate release within the LC. Glutamate exerts actions within the LC that mediate expression of behavioral symptoms of butorphanol withdrawal.

Analgesics, Opioid↗

PubMed1998

Excitatory amino acids and lead-induced neurotoxicity.

The NMDA receptor non-competitive antagonist, [3H]MK-801, was used as a ligand for an autoradiographic study to determine the effects of lead on NMDA receptor in rat brain. Adult male rats were given lead acetate, 100 mg/kg, or sodium acetate, 36 mg/kg (control), by i.p. for 7 days. Lead levels were detected in blood (41.1 micrograms/dl) and brain (16.7-29.4 micrograms/g). Concentrations of lead in various brain regions did not differ. [3H]MK-801 binding was heterogeneous throughout the brain with the following order of binding densities: hippocampal formation > cortex > caudate-putamen > thalamus > brainstem. Lead exposure caused a decrease in [3H]MK-801 binding to NMDA receptors in the hippocampal formation including CA2 stratum radiatum, CA3 stratum radiatum and presubiculum, and in the agranular insular, cingulate, entorhinal, orbital, parietal and perirhinal areas of cerebral cortex. In another experiment, female rats were exposed pre- and post-natally from the 4th +/- 1 post conception day with 1,000 ppm lead in their drinking water. This treatment continued after weaning. No effects of lead on [3H]MK-801 binding were found at postnatal day (PM) 28. However, lead caused a significant increase in [3H]MK-801 binding in the hippocampus including CA1 and CA2, and in the occipital and temporal cortical areas at PN 56 and at PN 112. Increases in [3H]MK-801 binding were also found in entorhinal cortex and dentate gyrus at PN 112. The hippocampal formation is a critical neural structure for learning and memory processes, whereas cortical and subcortical regions are involved in the modulation of complex behavioral processes. NMDA receptors have been shown to play a key role in synaptic plasticity underlying learning and memory. Therefore, lead-induced alterations of ligand binding to NMDA receptors in the hippocampal formation and cortical areas may play a role in lead-induced neurotoxicity.

Animals↗

PubMed1998

Responses to N-methyl-D-aspartate and kainic acid in cerebellar granule cells of lead-exposed rat pups.

To determine changes in response to N-methyl-D-aspartate (NMDA) and kainic acid (KA) in cerebellar granule cells of offspring of lead-exposed mothers, pregnant rats received 0.25% lead acetate in their drinking water 2 days after mating. The control animals were given sodium acetate (0.125%) in their drinking water. The cerebellar granule cells were cultured from 8-day old pups. Changes in the levels of cytosolic Ca++ and cGMP and the release of glutamic acid were measured using fura-2 spectrofluorometer, radio-immunoassay, and HPLC, respectively. Increases in cytosolic Ca++ in response to 50 microM of NMDA and KA were less responsive (77%) in the lead exposed group as compared to that of the control group. However, the maximum responses to KA were not different. The NMDA- and KA-stimulated release of glutamate from cerebellar granule cells prepared from lead-exposed pups were also significantly reduced. While the NMDA-induced elevation of cGMP was not affected in the lead-exposed pups, the normal KA-induced increases in cGMP level in cerebellar granule cells of lead-exposed pups was not observed. The specific binding of [3H]MK-801 was significantly lower in cerebellar granule cells of the lead-exposed pups. These results indicate that lead exposure to the mother affects excitatory amino acid systems during the development of the offspring.

Administration, Oral↗

PubMed1998

Developmental lead exposure alters the distribution of protein kinase C activity in the rat hippocampus.

Chronic low-level lead (Pb) exposure in children is known to cause a deficit in learning and memory. In vitro studies have demonstrated that Pb altered protein kinase C (PKC) activity. Especially, hippocampal PKC has been correlated with performance in several learning tasks. The effects of Pb exposure on hippocampal PKC were investigated during development at various postnatal ages: postnatal day (PN) 7, 14, 28, and 56. Two-tenth % Pb acetate was administered to pregnant and lactating dams and then administered to weanling rats in drinking water. PKC activity was measured in both membrane and cytosolic fractions from the hippocampi of the controls and Pb-exposed animals. Pb-induced increase in PKC activity in the cytosolic fraction was observed in the PN56 rats. In contrast, PKC activity was decreased by Pb at PN7 in the membrane fraction. Furthermore, a significant decrease in the ratio of membrane to cytosolic PKC activity which is representative of PKC distribution was observed in the PN28 and PN56 Pb-exposed rats relative to the same-age controls. This study indicates that chronic Pb exposure during development influences hippocampal PKC activity and distribution. These changes may be involved in the subclinical neurotoxicity of chronic Pb exposure in young children.

Animals↗

PubMed1997

Effects of subacute lead exposure on [3H]MK-801 binding in hippocampus and cerebral cortex in the adult rat.

We used the NMDA receptor non-competitive antagonist, [3H]MK-801, as a ligand for an autoradiographic study to determine the effects of lead on NMDA receptor in the rat brain. Adult male rats were administered lead acetate, 100 mg/kg, or sodium acetate, 36 mg/kg (control), by i.p. for 7 days. High lead levels were detected in blood (41.1 microg/dl) and in brain (16.7-29.4 microg/g). Concentrations of lead in brain regions were not significantly different. The [3H]MK-801 binding was heterogeneously distributed throughout the rat brain with the following order of binding densities: hippocampal formation > cortex > caudate-putamen > thalamus > brainstem. Lead exposure produced a significant decrease in [3H]MK-801 binding to the NMDA receptor in the hippocampal formation including CA2 stratum radiatum, CA3 stratum radiatum, hilus dentate gyrus and presubiculum, and in the cerebral cortex including agranular insular, cingulate, entorhinal, orbital, parietal and perirhinal areas. The hippocampal formation is known as a critical neural structure for learning and memory processes, whereas, cortical and subcortical regions have been demonstrated to be involved in the modulation of complex behavioral processes. The NMDA receptor has been demonstrated to play a key role in synaptic plasticity underlying learning and memory. Lead-induced alterations of NMDA receptors in the hippocampal formation and cortical areas may play a role in lead-induced neurotoxicity.

Animals↗

PubMed1997

Effects of chronic lead exposure on [3H]MK-801 binding in the brain of rat.

We have used quantitative autoradiographic methods to determine the effects of chronic lead exposure on N-methyl-D-aspartate (NMDA) receptors in the brain of female rat. Rats were exposed pre- and post-natally from day 4 +/- 1 post conception with 1000 ppm lead in their drinking water. This treatment continued after weaning. No effects of lead on [3H]MK-801 binding were found at PN 28. However, lead caused a significant increase in [3H]MK-801 binding in the hippocampus including CA1 and CA2, and in the occipital and temporal cortical areas at PN 56 and at PN 112. An increase in binding was also found in the entorhinal cortex and the dentate gyrus at PN 112. Because the NMDA receptor is involved in learning and memory, the lead-induced disruption of NMDA receptors in the hippocampus and cortex may be associated with the cation-induced cognition deficits.

Animals↗

PubMed1997

Increased release of excitatory amino acids in rat locus coeruleus in kappa-opioid agonist dependent rats precipitated by nor-binaltorphimine.

Extracellular fluid levels of glutamate and aspartate in the locus coeruleus (LC) during nor-binaltorphimine (nor-BNI)-precipitated withdrawal from butorphanol, (5alpha,7alpha,8beta)-(+)-N-methyl-N-[7-(1-pyrrolidiny l)-1-oxaspiro [4,5] dec-8-yl]-benzeneacetamide (U-69,593), or morphine were measured in rats. When the microdialysis probe was located in the core of the LC, increases in glutamate and aspartate were noted after nor-BNI (48 nmol/50 microl, LC)-precipitated withdrawal in rats that had been intracerebroventricularly infused with butorphanol (26 nmol/1 microl/h) or U-69,593 (26 nmol/10 microl/h) for 3 days. The glutamate and aspartate levels in the LC markedly increased in the butorphanol- or U-69,593-dependent rats within 60 min following administration of nor-BNI. However, there was no significant increase in levels of glutamate, and only a slight increase in levels of aspartate, after nor-BNI treatment of the morphine (26 nmol/1 microl/h)-infused rats. Behavioral signs of withdrawal (teeth-chattering, wet-dog shakes, etc.) were observed following nor-BNI challenge in the butorphanol- or U-69,593-infused rats, with only minimal signs in the morphine-infused rats, and none in the saline-infused controls. These results directly suggest that kappa-opioid receptors and excitatory amino acids within the LC mediate withdrawal in animals dependent on butorphanol or U-69,593, but not on morphine.

Animals↗

PubMed1997

Role of NMDA receptors in pentobarbital tolerance/dependence.

Effects of continuous pentobarbital administration on binding characteristics of [3H]MK-801 in the rat brain were examined by autoradiography. Animals were rendered tolerant to pentobarbital using i.c.v. infusion of pentobarbital (300 micrograms/10 microliters/hr for 7 days) by osmotic minipumps and dependent by abrupt withdrawal from pentobarbital. The levels of [3H]MK-801 binding were elevated in rats 24-hr after withdrawal from pentobarbital while there were no changes except in septum and anterior ventral nuclei in tolerant rats. For assessing the role of NMDA receptor in barbiturate action, an NMDA receptor antagonist (MK-801, 2.7 femto g/10 microliters/hr) was co-infused with pentobarbital. The pentobarbital-infused group had a shorter duration of pentobarbital-induced loss of righting reflex (sleeping time) than that of the control group, and MK-801 alone did not affect the righting reflex. However, co-infusion of MK-801 blocked hyperthermia, and prolonged the onset of convulsions induced by t-butylbicyclophosphorothionate (TBPS) in pentobarbital withdrawal rats. In addition, elevated [35S]TBPS binding was significantly attenuated by co-infusion with MK-801. These results suggest the involvement of NMDA receptor up-regulation in pentobarbital withdrawal and that the development of dependence can be attenuated by the treatment of subtoxic dose of MK-801.

Animals↗

PubMed1997

Developmental lead exposure and two-way active avoidance training alter the distribution of protein kinase C activity in the rat hippocampus.

Long-term exposure to a low level of lead is associated with learning deficits. Several types of learning have been correlated to hippocampal protein kinase C (PKC) activation. This study was designed to determine if there is a correlation between the effects of lead on hippocampal PKC activation and those on learning performance. Rats were exposed to 0.2% (w/v) lead acetate at different developmental stages including a maternally exposed group, a postweaning exposed group, and a continuously exposed group. The continuously lead exposed rats tended to avoid less frequently and not respond more frequently in two-way active avoidance training than did controls. This training process was associated with translocation of hippocampal PKC activity from cytosol to membrane. Two-way analysis of variance of data indicates that there is a significant training and lead treatment interaction in the ratio of membrane to cytosolic PKC activity (F3,32 = 3.013; p = 0.044). The interaction is attributable to the absence of the training-induced PKC translocation in the continuously lead exposed rats. In addition, no significant changes were observed in learning performance and training-induced hippocampal PKC activation after maternal and postweaning lead exposure. Continuous and longer duration of lead exposure appears to affect the learning performance and hippocampal PKC activation. These data suggest that a change in the activation of hippocampal PKC may be involved in the lead-induced deficit in learning.

Analysis of Variance↗