Biomedical subjects

D K Lim

Publications and source records attributed to D K Lim.

36 records · Page 2Linked to original sources

PubMed1989

Comparative studies of muscarinic and dopamine receptors in three strains of rat.

Cholinesterase activities and characteristics of muscarinic and dopamine receptors from 9 week old male Sprague-Dawley (SD), Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) were studied. Plasma cholinesterase activity in WKY was significantly lower (50%) than activity in the other strains. In studies of muscarinic receptors, the number of [3H]QNB binding sites in striata from SD rats was lower (18%) than those from WKY and SHR. However, muscarinic receptor properties (Kd and Bmax) were the same in hypothalami. Studies of dopamine receptors revealed that the densities of both D-1 and D-2 receptors in both striata and hypothalami were significantly higher in SHR than in other strains. However, there were no differences in the affinity constant (Kd). The higher densities in hypothalami from SHR were mainly due to the high population of D-1 and D-2 receptors in the posterior hypothalamus. In the anterior hypothalamus, there was no difference in the population of D-2 receptors. These results provide a substantive basis, i.e. demonstration of alterations in drug metabolizing enzymes and receptor populations, on which to build an understanding of the genetic predisposition to the actions of xenobiotic agents.

Acetylcholinesterase↗

PubMed1989

Effects of picrotoxin treatment on GABAA receptor supramolecular complexes in rat brain.

The effects of acute and chronic administration of a subconvulsive dose of picrotoxin on t-[35S]butylbicyclophosphorothionate ([3S]TBPS), [3H]muscimol, and [3H]flunitrazepam binding characteristics in various regions and on the convulsant potency of picrotoxin in Sprague-Dawley rats were examined. Acute administration of a subconvulsive dose of picrotoxin (3 mg/kg, i.p.) significantly increased [35S]TBPS and [3H]muscimol binding in cerebellum (CB) with no change in frontal cortex (FC). In rats treated chronically with picrotoxin (3 mg/kg, i.p., daily for 10 days), the Bmax of [35S]TBPS binding site was significantly decreased in the FC, striatum (ST), and CB with no change in KD values. Neither [3H]muscimol binding in the FC and CB nor [3H]flunitrazepam binding in the FC was affected in these rats. In addition, the potency of pentobarbital to inhibit [35S]TBPS binding in vitro was not altered following acute or chronic treatment of picrotoxin. Chronic administration of picrotoxin did not affect convulsive ED50 or LD50 of picrotoxin; however, it delayed the onset of convulsions and increased the time to death. These results suggest that treatment with picrotoxin at a subconvulsive dose for 10 days causes down-regulation of [35S]TBPS binding sites and that this down-regulation might be related, at least in part, to the decreased extent of convulsant potency of picrotoxin. In addition, the results indicate possible interaction between convulsant binding sites and GABAA receptor sites in the CB following picrotoxin treatment.

Animals↗

PubMed1989

Binding characteristics of t-[35S]butylbicyclophosphorothionate in discrete brain regions of rats made tolerant to and dependent on pentobarbital.

The effects of acute and continuous pentobarbital administration by pellet implantation on binding characteristics of t-[35S]butylbicyclophosphorothionate ([35S]TBPS) in discrete regions of rat brains were examined. Acute administration of pentobarbital (60 mg/kg, s.c.) affected neither the KD nor the Bmax values of [35S]TBPS binding in any of the regions studied. The cerebella of pentobarbital-tolerant rats had an increased density of [35S]TBPS binding sites with no change in their apparent affinity. There were no significant changes in the binding characteristics in the frontal cortex (FC), the striatum (ST), and the substantia nigra (SN) of these animals. Twenty-four hours after removal of the pentobarbital pellets, a significant decrease in the latency of onset of first twitch response induced by pentylenetetrazol (PTZ) (50 mg/kg, i.p.) was observed. In addition, the density of [35S]TBPS binding sites was significantly increased in the FC, the SN, and the cerebellum but not in the ST. In all brain regions studied, placebo pellet implantation and pentobarbital tolerance and dependence caused no changes in the apparent affinity of [35S]TBPS binding or the IC50 of pentobarbital for the inhibition of [35S]TBPS binding. These results suggest that [35S]TBPS binding was significantly increased following the withdrawal of the pentobarbital pellets without altering intrinsic coupling activity of barbiturate recognition sites and convulsant binding sites and that these increases in [35S]TBPS binding are related to the increased susceptibility to seizures induced by PTZ in rats made dependent on pentobarbital.

Animals↗

PubMed1989

Effects of diisopropylfluorophosphate on brain acetylcholinesterase, butyrylcholinesterase, and neurotoxic esterase in rats.

The inhibition and the recovery of brain AChE, BuChE, and NTE activities after acute and subacute administration of DFP were studied in the rat. DFP displayed different specificities in inhibiting these enzymes; inhibition was greatest for BuChE followed by AChE and NTE. Recovery was most rapid for BuChE followed by NTE and AChE. The recovery rates of AChE and BuChE following acute and subacute treatment were similar. However, the recovery rate of NTE in subacutely treated rats was significantly faster than that in acutely treated rats. The results suggest that DFP inhibits these three enzymes and the rates of regeneration of these enzymes are significantly different.

Acetylcholinesterase↗

PubMed1988

Toxicity study of continuous administration of physostigmine salicylate.

The present study demonstrates that continuous administration with physostigmine salicylate (0.12 or 0.24 mg/kg/hr via mini-osmotic pumps) induces toxicities (e.g., body weight loss, decreased water consumption, tremors, decreased body temperatures, mortality) in guinea pigs. Both blood and brain cholinesterase activity is inhibited dose-dependently by physostigmine salicylate. The signs of toxicity in the guinea pigs which received the low dose appeared within 2 or 3 days and then the animals recovered, while toxic signs in the guinea pigs treated with the high dose of the drug persisted throughout the experiments. The study further shows that continuous administration of physostigmine salicylate also caused down-regulation of muscarinic receptors in the striata of the guinea pigs.

Acetylcholinesterase↗

PubMed1988

Prevention of soman toxicity after the continuous administration of physostigmine.

Protective effects of continuous administration of physostigmine alone, or in addition to scopolamine, against soman-induced toxicity were studied in guinea pigs. The results clearly demonstrated that treatment with physostigmine continuously via implanted mini-osmotic pumps for 4 or 7 days prior to soman exposure significantly protected from soman-induced mortality. In vehicle-infused guinea pigs, tremors, convulsions and loss of righting reflex occurred prior to their deaths induced by soman. Although all of the guinea pigs which received physostigmine pretreatment for 4 days prior to soman administration also displayed soman-induced tremors and convulsions, the onsets of these symptoms were significantly delayed. When animals continuously treated with physostigmine received injections of scopolamine 10 min prior to soman injections, there was a decreased incidence of all three toxicity symptoms as well as an increase in the latency to onset of tremors. Scopolamine was also able to reverse toxicity symptoms when soman was administered earlier. In animals which had been continuously treated with physostigmine via mini-osmotic pumps, the protective action against soman-induced toxicity was still apparent. On the contrary, acute physostigmine administration failed to protect against soman lethality. The present results suggest that the prophylactic uses of physostigmine via mini-osmotic pumps might be more useful than the acute bolus administration of physostigmine.

Acetylcholinesterase↗

PubMed1988

Effects of acute and subacute administration of bicuculline on dopamine and muscarinic receptors in rat brain.

The changes of characteristics of dopamine (D1 and D2) and muscarinic receptors after acute and subacute administration of bicuculline were examined in rat brain. The results demonstrated that in striatal region, the Bmax of D2 receptor was significantly increased with no change of affinity after subacute administration of bicuculline. However, neither Bmax nor Kd or the D2 receptor was changed after single administration. The characteristics of D1 receptor were not changed by either acute or subacute administration. The Bmax of muscarinic receptor in striatal area was significantly increased without changes of affinity after both a single and repeated administration of bicuculline. However, in hippocampus, the Bmax of muscarinic receptor was significantly decreased after subacute administration of bicuculline. The results suggest that the interactions among GABAergic, dopaminergic and cholinergic neuron exist in central nerve system.

Animals↗

PubMed1988

Bicuculline up-regulation of GABAA receptors in rat brain.

Effects of acute and subacute administration of bicuculline on [3H]muscimol, [3H]flunitrazepam, and t-[35S]butylbicyclophosphorothionate ([35S]TBPS) binding to various brain regions were studied in Sprague-Dawley rats. Acute administration of bicuculline affected neither the KD nor the Bmax of the three receptor sites. In rats treated subacutely with bicuculline (2 mg/kg, i.p., daily for 10 days), [3H]muscimol binding was increased in the frontal cortex, cerebellum, striatum, and substantia nigra. Scatchard analysis revealed that subacute treatment of rats with bicuculline resulted in a significantly lower KD of high-affinity sites in the striatum and in a significantly lower KD of high- and low-affinity sites in the frontal cortex. In the cerebellum, two binding sites were apparent in controls and acutely treated animals; however, only the high-affinity site was defined in subacutely treated animals, with an increase in the Bmax value. Triton X-100 treatment of frontal cortical membranes eliminated the difference in [3H]muscimol binding between control and subacute bicuculline treatments. On the other hand, [3H]muscimol binding was significantly increased in the cerebellum from bicuculline-treated animals even after Triton X-100 treatment. The apparent Ki of bicuculline for the GABAA receptor was also decreased in the frontal cortex and the striatum following the treatment. However, subacute administration of bicuculline affected neither the KD nor the Bmax of [3H]flunitrazepam and [35S]TBPS binding in the frontal cortex and the cerebellum. These results suggest that GABAA receptors are up-regulated after subacute administration of bicuculline, with no change in benzodiazepine and picrotoxin binding sites.

Animals↗

PubMed1987

Evidence for the involvement of presynaptic cholinergic functions in tolerance to diisopropylfluorophosphate.

Rats were treated with diisopropylfluorophosphate (DFP) acutely or daily for 14 days. The involvement of various presynaptic and postsynaptic functions of the cholinergic system in the development of tolerance to DFP was studied. Receptor density and affinity of both muscarinic and nicotinic receptors, high-affinity choline uptake, and [K+]-evoked release of acetylcholine (ACh) by atropine were not changed after acute administration of 2 mg/kg DFP. Both muscarinic and nicotinic receptors were down-regulated to the same extent (40-50%) after subacute administration of DFP (1 mg/kg) without changes in their affinities. Binding sites of muscarinic receptors were maximally decreased after 7 days of DFP administration. Thereafter, they remained constant throughout 14 days of administration. One hour after the last injection of 2 mg/kg DFP to subacutely treated rats, the maximum velocity of high-affinity choline uptake was significantly decreased in the striatum (33%) and hippocampus (53%) without changes in Km values. Twenty-four hours after the last injection of DFP, only a higher dose of DFP (2 mg/kg) significantly inhibited choline uptake. Potassium-evoked release of ACh by slices of striatum was not different between acutely and subacutely treated rats. However, the release of ACh by slices of striatum and hippocampus was significantly increased by atropine in subacutely treated rats. It is suggested that along with the down-regulation of the postsynaptic receptors, subsensitivity of presynaptic functions of the cholinergic synapse also develops during subacute administration of DFP.

Acetylcholine↗

PubMed1987

Changes in ACh levels in the rat brain during subacute administration of diisopropylfluorophosphate.

Rats were treated with diisopropylfluorophosphate (DFP) acutely and daily for 14 days. The total, free, and bound acetylcholine (ACh) levels were monitored in striatum, hippocampus, and frontal cortex after DFP administration. Thirty minutes after daily administration of DFP, the total and free ACh levels were significantly increased and remained constant after each successive dose. The bound ACh levels in striatum and frontal cortex were also significantly increased; however, they were comparable to control levels after the 14th injection of DFP. The total ACh levels 30 min after a challenge dose of 2 mg/kg DFP in saline and DFP subacutely treated rats were significantly increased in hippocampus (34 and 76%) and frontal cortex (49 and 64%) and were not significantly different between the two groups. However, the level of total ACh in striatum was increased less in the tolerant rats (10%) than in the acutely treated rats (36%). The levels of free and bound ACh after acute administration of 2 mg/kg DFP were markedly increased in three brain regions. After subacute administration, the levels of bound ACh were significantly increased in hippocampus (84%) and frontal cortex (40%); however, that in striatum did not change. The increase in the bound ACh level in the subacute treatment group was less than that in acutely treated rats in all three brain regions; however, the duration of the elevation of the free ACh in striatum was shorter in subacutely treated rats. These results suggest that the presynaptic cholinergic storage sites for ACh might be changed during subacute administration of DFP.

Acetylcholine↗

PubMed1987

Quantitative assessment of tolerance development to diisopropylfluorophosphate.

Rats were treated with diisopropylfluorophosphate (DFP) acutely or daily for 14 days. The quantitative assessment of tolerance development after a challenge dose of DFP, 2 mg/kg, was studied. The subacutely-treated rats developed tolerance to DFP-induced tremors. However, the severity of tremors in DFP-tolerant animals was not significantly different from that of the controls after the challenge dose of DFP was administered. Hind-limb abduction was significantly lower in the subacutely-treated group than in the acutely-treated group. The recovery of body weights in subacutely-treated rats (3.5%/day) was significantly higher than that in acutely-treated rats (2.0%/day). The consummatory behaviors (food and water consumption) recovered faster in subacutely-treated rats than in the acutely-treated group. Body temperatures were decreased to the same extent in both groups, but the subacutely-treated group recovered faster. The total mortality was significantly lower in subacutely-treated rats (10%) than in acutely-treated rats (35%). The results further substantiate the finding that tolerance develops to various DFP-induced signs of toxicity.

Animals↗

PubMed1986

Correlation of muscarinic receptor density and acetylcholinesterase activity in repeated DFP-treated rats after the termination of DFP administration.

Following chronic exposure to DFP, both AChE activity and muscarinic receptor density were markedly depressed in the rat striatum. The rate of recovery of AChE activity was 5.2% per day within 7 days, while the density of muscarinic receptor recovered at the rate of 1.94% per day. The correlation between 2 parameters was very high (R = 0.99). Thus, it is suggested that the muscarinic receptor density was intimately related to AChE activity.

Acetylcholinesterase↗

PubMed1986

Relationship between the neurotoxicities of Soman, Sarin and Tabun, and acetylcholinesterase inhibition.

Acetylcholinesterase (AChE)-induced chewing movements, tremors, convulsions and hind limb abduction at doses of 50-85% LD50 in rats were monitored in order to determine whether the severity of these different signs would correlate with brain AChE levels and the time course of such a relationship. 30 min after subcutaneous (s.c.) injection of Soman, the intensities of toxic signs were significantly correlated with the degree of striatal AChE inhibition. In the case of Sarin, the corresponding r-values were not significant except for tremors. For Tabun-induced chewing, tremor and hind-limb abduction, the r-values were significant. The neurotoxicity was most intense between 15 min to 2 h after treatment, but at 2 or 6 h, the r-values were well below 0.5. The inhibition of brain AChE was maximal by 30 min and was still high at 24 h.

Animals↗

PubMed1985

Variability of neurotoxicity of and lack of tolerance to the anticholinesterases soman and sarin in the rat.

The neurotoxicity and lethality of Soman and Sarin, after single and repeated treatment at 50-60% of their LD50 doses in rats were investigated. Single treatment with Soman (100 micrograms/kg) and Sarin (120 micrograms/kg) produced severe tremors, convulsions and hypothermia, in some rats only, while the others did not show toxicity, i.e. an all or none effect. Soman and Sarin (100-120 micrograms/kg) caused, respectively, 89-93% and 26-48% inhibition of AChE at 6 hr and 56-68% and 17-39% inhibition at 24 h after single injections. Repeated treatment with Soman (90 micrograms/kg) and Sarin (100 micrograms/kg) at 4 day intervals caused variable incidences of neurotoxicity and increasing mortalities, and after ten injections the survival rates were 31 and 54%, and AChE inhibition was 86 and 75%, respectively. It is suggested, that the variable neurotoxicity of and the low tolerance to of these compounds are partly related to peripheral dispositional mechanisms. Furthermore, the profile of toxicity of these anticholinesterase agents should be differentiated from, but not generalized with, that of the other anticholinesterase organophosphates.

Animals↗

PubMed1984

Effects of diisopropylfluorophosphate (DFP) on renal function in the rat.

Numerous studies have suggested a role for the nervous system in renal function. Several cholinergic agents have been examined for effects in vivo and in renal slices. Effects mediated through the vascular system and also direct effects have been reported. In this study an irreversible cholinesterase inhibitor, diisopropylfluorophosphate (DFP) in doses of 1-4 mg/kg, was tested on renal function. A single dose of DFP (2, 3 or 4 mg/kg) caused an increased flow of urine of low osmolality over the 6 h after the administration of the drug with essentially a return to control status by 24 h after either of the lower doses. Twenty-four hours after 4 mg/kg, urine volume was less and urine osmolality greater than control. Renal and brain cholinesterases remained depressed 24 h after DFP. In acute experiments on anesthetized animals, inulin clearance was increased by the lower doses and decreased by the highest dose of DFP. Renal blood flow measured with an electromagnetic flow meter showed a similar dose-response relationship. However, urine flow increased at all doses. The increased urine flow associated with decreased inulin clearance (4 mg/kg) and renal blood flow (3 or 4 mg/kg) suggest a direct effect of DFP on renal tubular function. These effects do not appear to be related to inhibition of cholinesterase.

Animals↗

PubMed1983

Effect of acute and chronic cholinesterase inhibition with diisopropylfluorophosphate on muscarinic, dopamine, and GABA receptors of the rat striatum.

The effects of acute and chronic administration of diisopropylfluorophosphate (DFP) to rats on acetylcholinesterase (AChE) activity (in striatum, medulla, diencephalon, cortex, and medulla) and muscarinic, dopamine (DA), and gamma-aminobutyric acid (GABA) receptor characteristics (in striatum) were investigated. After a single injection of (acute exposure to) DFP, striatal region was found to have the highest degree of AChE inhibition. After daily DFP injections (chronic treatment), all brain regions had the same degree of AChE inhibition, which remained at a steady level despite the regression of the DFP-induced cholinergic overactivity. Acute administration of DFP increased the number of DA and GABA receptors without affecting the muscarinic receptor characteristics. Whereas chronic administration of DFP for either 4 or 14 days reduced the number of muscarinic sites without affecting their affinity, the DFP treatment caused increase in the number of DA and GABA receptors only after 14 days of treatment; however, the increase was considerably lower than that observed after the acute treatment. The in vitro addition of DFP to striatal membranes did not affect DA, GABA, or muscarinic receptors. The results indicate an involvement of GABAergic and dopaminergic systems in the actions of DFP. It is suggested that the GABAergic and dopaminergic involvement may be a part of a compensatory inhibitory process to counteract the excessive cholinergic activity produced by DFP.

Acetylcholinesterase↗

PubMed1983

Diisopropylfluorophosphate and GABA synaptic function: effect on levels, enzymes, release and uptake in the rat striatum.

The present study revealed that diisopropylfluorophosphate increased the GABA and glutamate levels, decreased the uptake of GABA, decreased the spontaneous release of GABA and did not exhibit its effects on the metabolic enzymes of GABA, glutamic acid decarboxylase and GABA-transaminase. These results, together with our previous finding that the postsynaptic GABA receptor population is increased by DFP treatment, indicate that GABA transmission is affected by DFP. An overall enhancement of GABA function appears to be involved in DFP poisoning; it is suggested that this may be a compensatory mechanism to counteract the cholinergic hyperactivity.

4-Aminobutyrate Transaminase↗

PubMed1983

Assessment of diisopropylfluorophosphate (DFP) toxicity and tolerance in rats.

Single s.c. injection of 1, 2, 3 or 4 mg/kg of DFP in saline was given to male rats. Control rats received saline. Beginning 24 hr after injections, body weights and food and water consumption were measured at 24 hr intervals. The 1 and 2 mg/kg DFP-treated group maintained these parameters at levels equal to those of the controls. The other DFP-treatment groups showed significant depressions in body weights and in food and water consumption, but these groups recovered 48 and 72 hrs after DFP administration of 3 mg/kg or 4 mg/kg, respectively. Daily injections of 2, 3 or 4 mg/kg of DFP, s.c., caused significant depressions of all three parameters, with only 75% of the 2 mg/kg group showing recovery over the 14 day treatment period. Of the 2 mg/kg group, 25% died following the 6th injection, 100% of the 3 mg/kg group were dead following the 4th injection and 100% of the 4 mg/kg group were dead following the 3rd injection. Prior to deaths in all DFP-treatment groups, the decreases in body weights and in food and water consumption were progressive and dose-dependent. The data show dose-dependency of general toxicity during acute and subacute exposure to DFP and of tolerance during subacute exposure.

Animals↗