Subjective, psychomotor, and physiological effects of cumulative doses of opioid mu agonists in healthy volunteers

The subjective, psychomotor, and physiological effects of three opioid mu-receptor agonists were studied in healthy volunteers using a cumulative-dosing procedure. Sixteen volunteers with no history of drug abuse received i.v. injections of saline (SAL), morphine (MOR), hydromorphone (HM), or meperidine (MEP) in a randomized double-blind crossover design. Subjects received 1 injection/h for the first 4 h, and a 3-h recovery period followed. SAL was injected first during each session, then SAL or increasing doses of each drug were administered every hour for the next 3 h. The absolute doses per injection were MOR: 2.5, 5, and 10 mg/70 kg; HM: 0.33, 0.65, and 1.3 mg/70 kg; and MEP: 17.5, 35, and 70 mg/70 kg. These injections resulted in cumulative doses of MOR: 2.5, 7.5, and 17.5; HM: 0.33, 0.98, and 2.28; and MEP: 17.5, 52.5, and 122.5 mg/70 kg. Subjects completed mood forms and psychomotor tests, and physiological measures were recorded at various times after each injection and during recovery. MEP tended to produce the most intense effects immediately after drug injection, which dissipated rapidly. MOR produced the mildest effects but was associated with unpleasant side effects during recovery and after the session. HM's effects were stronger than MOR's, and the recovery from HM was slower than with MEP. None of the opioids produced consistent effects that are typically associated with abuse liability. Orderly dose-response functions suggested that our cumulative-dosing procedure is an efficient way of determining dose-response functions for multiple opioids within the same subjects within the same study.

Augmented methamphetamine-induced overflow of striatal dopamine 1 day after GDNF administration

Glial cell line-derived neurotrophic factor (GDNF) can attenuate the dopamine (DA)-depleting effects of neurotoxic doses of methamphetamine (METH) when given 1 day prior to the METH. The neurotoxic effects of METH may be due, in part, to sustained increases in extracellular levels of DA. It is therefore possible that GDNF may be altering the effects of METH by influencing extracellular levels of DA during the METH treatment. The purpose of the present study was to determine if GDNF has effects on extracellular levels of DA in the striatum by 24-h post-administration. GDNF (10 microgram in 2 microliter vehicle) or vehicle was injected into the right striatum or substantia nigra of anesthetized male rats. The next day the animals were anesthetized again and dialysis probes were positioned in both the right and left striata and perfused with artificial cerebrospinal fluid. Following the collection of baseline samples the rats were administered METH (5 mg/kg, s.c.). The METH injections dramatically increased extracellular DA levels on both sides of the brain. However, levels on the GDNF injected side were significantly greater than levels on the contralateral side. Basal levels of DA were not significantly different between the two sides, but levels of DA metabolites were elevated on the GDNF side. Post-mortem tissue levels of DA metabolites, but not DA, were also elevated in the striatum and substantia nigra. These results indicate that GDNF has significant effects on DA neuron functioning within 24 h of administration and that GDNF can augment DA overflow while inhibiting the neurotoxic effects of METH.

Attenuation of cocaine-induced response-rate increases during repeated administration despite increases in rate of reinforcement

Repeated administration of cocaine often results in tolerance to its effects on operant behavior. The tolerance is often associated with an initial drug effect that results in loss of reinforcement. Cocaine can also produce effects that result in a gain of reinforcement, and it is not known if tolerance will be observed in such a circumstance. The present experiments investigated whether tolerance would develop when cocaine was administered repeatedly to subjects who experienced an increase in the frequency of reinforcement when cocaine was administered acutely. Pigeons were trained to peck a response key under fixed-ratio schedules of food presentation. The ratio value for each pigeon was chosen such that performance indicated that the ratio was relatively large, and produced "ratio strain.". Cocaine was administered acutely (once per week), and then subsequently a dose was chosen and administered before each session. Once performance under the daily drug regimen was stable, other doses occasionally were substituted for the usual daily dose. Acute administration of cocaine (0.3-10.0 mg/kg) revealed substantial increases of 100% or more in response rate, and therefore equivalent increases in rate of food presentation, at some doses. That finding permitted examination of the role of drug-induced increases in rate of reinforcement during repeated administration of a response-rate-increasing dose. Repeated, daily administration of a rate-increasing dose resulted in attenuation of the effects of that dose, and subsequent administration of other doses that previously had increased response rates revealed that these doses, too, had lost their ability to increase rates. That is, "tolerance" developed to the rate-increasing effects, even though the rate increases were associated with more frequent access to food. These findings suggest that "reinforcement gain" may not be sufficient to prevent tolerance from developing to effects of cocaine on operant behavior.

Sequence polymorphisms in the Pneumocystis carinii cytochrome b gene and their association with atovaquone prophylaxis failure

Atovaquone (Mepron, 566c80) is an effective agent against Pneumocystis carinii, which probably acts by binding to cytochrome b and inhibiting electron transport. To assess the possibility that atovaquone resistance might be developing, the genes for the cytochrome b from P. carinii sp. f. carinii and P. carinii sp. f. hominis were partially sequenced. Eight of 10 patient isolates had cytochrome b genes with the same amino acid sequence. The P. carinii cytochrome b genes from 2 of 4 patients who had atovaquone prophylaxis failure contained mutations resulting in amino acid changes in one of the ubiquinone (coenzyme Q) binding sites (Qo). These mutations are homologous to mutations in other microorganisms that confer resistance to similar inhibitors. Variations in the sequence of the P. carinii cytochrome b gene suggest but do not prove the development of drug resistance.

Subjective, psychomotor, and analgesic effects of oral codeine and morphine in healthy volunteers

The subjective, psychomotor, and physiological effects of analgesic doses of oral codeine and morphine were examined in 12 healthy volunteers. Subjects ingested placebo, morphine 20 or 40 mg, or codeine 60 or 120 mg in a randomized, double-blind, crossover design. The smaller and larger doses of each drug were putatively equianalgesic, and the cold-pressor test was included to test this assumption. Codeine and morphine increased ratings of "feel drug effect" but had little effect on other subjective measures, including the Addiction Research Center Inventory, visual analog scales, and adjective checklists. The few subjective effects that were observed were modest and were dose-related for morphine but not for codeine. The drugs did not affect performance on Maddox-Wing, digit-symbol substitution, coordination, auditory reaction, reasoning, and memory tests. Dose-related decreases in pupil size (miosis) were observed following codeine and morphine. Ratings of pain intensity decreased in a dose-related manner for morphine but not for codeine. Plasma codeine and morphine levels varied as an orderly function of dose. These results suggest that oral codeine and morphine are appropriate drugs for outpatient pain relief because they are effective analgesics at doses that have only modest effects on mood, produce few side effects, and do not impair performance. The results also suggest a possible ceiling effect of codeine on analgesia and subjective effects.

Metabolic transition in the development of Hymenolepis diminuta (Cestoda)

Cysticercoids as well as 6-, 10-, and 14-day Hymenolepis diminuta were evaluated in terms of enzymatic activities related to phosphoenolpyruvate (PEP) utilization and mitochondrial succinate accumulation. The data obtained support a transition toward anaerobic electron-transport-dependent succinate accumulation, characteristic of adult H. diminuta, with development from cysticercoid to adult. This transition was reflected most prominently in the increasing activities of PEP carboxykinase (PEPCK), malate dehydrogenase, NADPH-->NAD+ transhydrogenase, and fumarate reductase. Developmental increases in PEPCK/pyruvate kinase (PK), fumarate reductase (FR)/NADH oxidase (NO), and FR/succinate dehydrogenase (SDH) activity ratios were also apparent. Evaluations of "egg-free" immature, mature, and pregravid-gravid segments of adult H. diminuta revealed that in general the greater levels of activity were associated with the immature and mature segments. Whereas FR/NO and FR/SDH ratios remained relatively constant in segment comparisons, the greatest PEPCK/PK ratio was associated with the pregravid-gravid segment.

Effects of variable-interval value and amount of training on stimulus generalization

In Experiment 1 pigeons pecked a key that was illuminated with a 501-nm light and obtained food by doing so according to a variable-interval (VI) schedule of reinforcement, the mean value of which differed across groups: either 30 s, 120 s, or 240 s. The pigeons in all three groups were trained for 10 50-min sessions. Generalization testing was conducted in extinction with different wavelengths of light. Absolute and relative generalization gradients were similar in shape for the three groups. Experiment 2 was a systematic replication of Experiment 1 using line orientation as the stimulus dimension and a mean VI value of either 30 s or 240 s. Again, gradients of generalization were similar for the two groups. In Experiment 3 pigeons pecked a key that was illuminated with a 501-nm light and obtained food reinforcers according to either a VI 30-s or a 240-s schedule. Training continued until response rates stabilized (> 30 sessions). For subjects trained with the 30-s schedule, generalization gradients were virtually identical regardless of whether training was for 10 sessions (Experiment 1) or until response rates stabilized. For subjects trained with the VI 240-s schedule, absolute generalization gradients for subjects trained to stability were displaced upward relative to gradients for subjects trained for only 10 sessions (Experiment 1), and relative generalization gradients were slightly flatter. These results indicate that the shape of a generalization gradient does not necessarily depend on the rate of reinforcement during 10-session single-stimulus training but that the effects of prolonged training on stimulus generalization may be schedule dependent.

Spontaneous ambulatory activity as a quantifiable outcome measure for osteoarthritis of the knee

OBJECTIVE

Quantifiable outcome measures for disabling diseases such as osteoarthritis (OA) of the knee are necessary in order to compare the impact of different interventions competing for financial resources. Current subjective and questionnaire data are not satisfactory for such study. In this study, we examine the potential of the direct measurement of ambulatory activity as such a measure.

POPULATION

Patients with X-ray evidence of OA of the knee recruited to studies of anti-inflammatory agents (n = 29). Patients with OA of the knee awaiting knee replacement surgery (n = 28).

METHODS

Comparison of various standard measures with total energy output data from an activity monitor.

RESULTS

Spearman rho correlations of ambulatory energy output (number of steps x average amplitude of steps) correlated with other measures. Correlation with physician's opinion was greater than with patient's opinion (r = 0.4 and 0.2, respectively). There was no correlation with visual analogue pain scale or OA severity index. Correlation with scales of the Nottingham Health Profile questionnaire were not significant either for mobility (r = - 0.15) or for pain (r = - 0.13). There was, however, a significant correlation between poor sleep and increased activity (r = 0.34, P < 0.05). Correlation with Kellgren X-ray grade was significant (r = - 0.45, P = 0.01). Patients recruited to anti-inflammatory studies were 69% more active than those awaiting replacement surgery.

CONCLUSION

The monitoring of ambulatory activity shows some construct and discriminant validity, and is worthy of further study.

Thermal grating velocimetry

A method is reported for time- and space-resolved nonintrusive velocimetry of high-speed gas flows by measurement of the Doppler shift of light scattered from a laser-induced thermal grating. The principle is demonstrated by use of a pulsed frequency-doubled Nd:YAG laser to induce a thermal grating in NO(2) seeded into an argon flow. Signals are generated by Bragg scattering of probe beams at the fundamental frequency of the same Nd:YAG laser. Flow velocities in the range 30-180 ms(-1) are measured, in agreement with values obtained with a Pitot tube. The measurement uncertainties obtained indicate that a precision of 1% is feasible for flows at Mach 1.

The Plasmodium falciparum translationally controlled tumor protein homolog and its reaction with the antimalarial drug artemisinin

Artemisinin and its derivatives are important new antimalarial drugs. When Plasmodium falciparum-infected erythrocytes are incubated with [10-3H]dihydroartemisinin, several malaria-specific proteins become labeled. One of these proteins is the P. falciparum translationally controlled tumor protein (TCTP) homolog. In vitro, dihydroartemisinin reacts covalently with recombinant TCTP in the presence of hemin. The association between drug and protein increases with increasing drug concentration, plateauing at approximately 1 drug/TCTP molecule. By Scatchard analysis, there appear to be 2 hemin binding sites on TCTP with dissociation constants of approximately 18 microM. When the single cysteine moiety is blocked by pretreatment with iodoacetamide, hemin binding is not affected, whereas drug binding is reduced by two-thirds. Thus, TCTP reacts with artemisinin in situ and in vitro in the presence of hemin and appears to bind to hemin. The function of the malarial TCTP and the role of this reaction in the mechanism of action of artemisinin await elucidation.

Response suppression during cumulative dosing: a role for Pavlovian conditioning

Key pecking by pigeons was maintained by a fixed-ratio 15 or a fixed-interval 15 s schedule of food presentation. Sessions consisted of six blocks that included a 4 min blackout then 2 min of schedule time or six food presentations. Cumulative dose-response curves were assessed by injecting saline at the start of the second block and increasing cocaine doses at the onset of subsequent blocks. Repeated cumulative dosing often shifted dose-response curves to the left, and these effects appeared to be due to the reliable correlation between smaller and larger doses administered early and later in the session. When saline was substituted for the larger doses later in the session, dose-response curves initially remained shifted to the left, and continued substitution eventually resulted in curves shifting to the right. Cumulative dosing was compared with two noncumulative dosing procedures: (a) pre-session dosing and (b) one cocaine injection at the block in which the same cumulative dose would be tested, with saline injections at the other blocks (except the first). Noncumulative dosing tended to produce more reliable (repeatable) results than did cumulative dosing, and at least one interpretation is the possibility of conditioning factors that may be present in cumulative-dosing but not in noncumulative-dosing procedures.

Ambulatory activity as an objective and quantifiable measure of nonsteroidal therapy

OBJECTIVE

To quantify any increase in short term spontaneous ambulatory activity resulting from the use of nonsteroidal antiinflammatory drugs (NSAID) in patients with rheumatoid arthritis (RA).

METHODS

Double blind placebo controlled crossover study of 8 women with RA using conventional assessments and the Numact activity monitor.

RESULTS

Patients' ambulatory activity was 50% greater during NSAID treatment compared to placebo treatment. Effect size calculated at 0.62, suggesting good sensitivity to change. The increased activity occurred late morning.

CONCLUSION

Spontaneous ambulatory activity is an objective and relevant measure of disability.

Developmental and tissue-specific expression of 2-methyl branched-chain enoyl CoA reductase isoforms in the parasitic nematode, Ascaris suum

The 2-methyl branched-chain enoyl CoA reductase (ECR) plays a pivotal role in the reversal of beta-oxidation operating in anaerobic mitochondria of the parasitic nematode, Ascaris suum. Two-dimensional gel electrophoresis of the purified ECR yielded multiple spots, with two distinct but overlapping N-terminal sequences. These multiple isoforms were not the result of population effects, as the pattern observed on 2-D gels of the purified ECR was identical to those on immunoblots of muscle homogenates isolated from individual worms. A full-length cDNA coding for the major ECR isoform (ECRI) has been cloned and sequenced and compared with that of the minor isoform (ECRII) which has been described previously (Duran et al. J Biol Chem 1993;268:22391-22396). ECRI contained the 22-nucleotide trans-spliced leader sequence characteristic of many nematode mRNAs, a 5' untranslated region (UTR) of 13 nucleotides, an open reading frame (ORF) of 1257 nucleotides, a 3'-UTR of 110 nucleotides that included the polyadenylation signal AATAAA downstream of the termination codon and a short poly(A) tail. The ORF predicted a 16 amino acid leader sequence not found in the native protein and a mature protein of 403 amino acids with a molecular weight of 43 698 and a predicted pI of 6.2. ECRI and ECRII were 73% identical at the predicted amino acid level and their mRNAs exhibited significant structural similarity even though they were products of separate genes. Comparison of ECRI and ECRII with the sequences of acyl CoA dehydrogenases from a variety of different sources revealed a high degree of interspecies sequence identity, suggesting that these enzymes may have evolved from a common ancestral gene. This result is surprising since the ascarid enzymes function as reductases, not as dehydrogenases. Both ECRs were tissue-specific and developmentally regulated and were found in transitional third-stage larvae (L3) and adult muscle, but not in early, aerobic larval stages or adult testis, ovary, or intestine. The ratio of ECRII to ECRI was greater in L3 than in adult muscle. Interestingly, both ECRs also appeared to be expressed in pharyngeal muscle, suggesting that branched-chain fatty acid synthesis may not be confined exclusively to body wall muscle.

Compound heterozygosity for the shared epitope and the risk and severity of rheumatoid arthritis in extended pedigrees

The objective was to explore the role of HLA-DRB1 genes in determining disease severity in rheumatoid arthritis (RA). The population comprised extended pedigrees of 17 multicase RA families. Family members were genotyped for both HLA-DRB1 alleles using restriction fragment length polymorphism (RFLP). Identification of HLA-DRB1*04 variants was performed using the Multiplex ARMS-RFLP technique. Compound heterozygote individuals carrying two different alleles containing the shared epitope (SE) were at greatest risk of developing RA (odds ratio = 36, 95% CI 9.1-143). A synergistic or additive effect of these alleles is suggested. Individuals carrying no SE alleles expressed milder disease, as measured by the Spread Severity (SS) index, compared to compound heterozygotes (P = 0.045). Compound heterozygosity was not invariably associated with severe disease with six (50%) having clinically mild disease at a median age of 57.5 yr and median disease duration of 16 yr. Inheriting two different SE-bearing alleles results in an increased risk of RA and, on average, greater disease severity. This is not, however, invariably associated with severe disease, making it of limited use as a predictor of prognosis.

A continuous patient activity monitor: validation and relation to disability

The measurement of patient activity over prolonged periods has been attempted with accelerometer-based devices, but these summate total acceleration and deceleration over time periods, are difficult to relate to recognizable activities and are influenced by passive movement. We describe the development of a portable monitor of ambulation. This logs posture (sitting, standing and lying) and number and vigour of steps in real time over prolonged periods, usually 24 h. This is based on a system of position sensors and an accelerometer which is sampled when the subject is standing. Data are processed through an interface and stored on a Psion Series 3 'palm top' computer. The system has been validated against observation, and the relationship of activity to disability in rheumatoid arthritis explored.

Hymenolepis diminuta: mitochondrial NADH --> NAD transhydrogenation and the lipoamide dehydrogenase system

The occurrence of NADH --> NAD transhydrogenation and lipoamide dehydrogenase activities was demonstrated for cysticercoids of the intestinal cestode, Hymenolepis diminuta. In addition, both activities were catalyzed by the mitochondria of 6-, 10-, and 14-day H. diminuta and by the mitochondria from immature, mature, and pregravid/gravid regions of the adult cestode. A developmentally related increase in NADH --> NAD activity was suggested and the levels of both activities in the immature region of the helminth were consistent with it being a region of high metabolic activity. Adult H. diminuta mitochondrial lipoamide dehydrogenase was purified to homogeneity. The native enzyme was a homodimer with a monomeric and dimeric molecular mass of 47 and 93 kDa, respectively. Spectral analyses revealed that the enzyme contained flavin. More importantly, the purified enzyme catalyzed appreciable NADH --> NAD transhydrogenation activity, a premier finding for the phylum Platyhelminthes. The ratio of NADH --> NAD transhydrogenation to lipoamide reduction was 1:5. Both activities were inhibited by Cu2+ and Cd2+ with the NADH --> NAD activity being more resistant to inhibition. Interestingly, aside from NADH diaphorase activity, the cestode enzyme displayed NADH-ferricyanide reductase and, to a lesser degree, NADPH --> NAD transhydrogenation activities. The partial amino acid sequence of H. diminuta lipoamide dehydrogenase indicated that this enzyme was most similar to the corresponding enzymes of other parasitic helminths. Moreover, the phenylalanine for leucine substitution found in the redox-active disulfide site of the lipoamide dehydrogenases of some anaerobic systems was noted for the H. diminuta enzyme.

Establishment of human tubal epithelial cells for coculture in an IVF program

OBJECTIVE

Our goal was to develop a coculture system from human tubal epithelial cells for use in a human IVF program.

DESIGN

Fallopian tubes were obtained from women undergoing hysterectomy for benign disease. Ampullary epithelial cells were cultured, passaged, and frozen and the karyotype and epithelial characteristics of later passages examined.

SETTING

The study took place at the Assisted Conception Clinic, Walsgrave Hospital, and the Department of Biological Sciences, University of Warwick.

RESULTS

Ampullary epithelial cells can be successfully cultured and maintained as diploid epitheliod lines until the fifth passage. Freezing does not affect subsequent culture, the cytoskeleton, or the karyotype. In excess of 12 x 10(6) cells may be obtained from a pair of Fallopian tubes.

CONCLUSIONS

The ease of establishing and maintaining human tubal epithelial cell cultures justified their use in clinical IVF for human embryo cocultures, and further investigations into their mode of action should be encouraged.

Potassium homeostasis in vacuolate plant cells

Plant cells contain two major pools of K+, one in the vacuole and one in the cytosol. The behavior of K+ concentrations in these pools is fundamental to understanding the way this nutrient affects plant growth. Triple-barreled microelectrodes have been used to obtain the first fully quantitative measurements of the changes in K+ activity (aK) in the vacuole and cytosol of barley (Hordeum vulgare L.) root cells grown in different K+ concentrations. The electrodes incorporate a pH-selective barrel allowing each measurement to be assigned to either the cytosol or vacuole. The measurements revealed that vacuolar aK declined linearly with decreases in tissue K+ concentration, whereas cytosolic aK initially remained constant in both epidermal and cortical cells but then declined at different rates in each cell type. An unexpected finding was that cytoplasmic pH declined in parallel with cytosolic aK, but acidification of the cytosol with butyrate did not reveal any short-term link between these two parameters. These measurements show the very different responses of the vacuolar and cytosolic K+ pools to changes in K+ availability and also show that cytosolic K+ homeostasis differs quantitatively in different cell types. The data have been used in thermodynamic calculations to predict the need for, and likely mechanisms of, active K+ transport into the vacuole and cytosol. The direction of active K+ transport at the vacuolar membrane changes with tissue K+ status.

Improving the efficiency and cost-effectiveness of food aid grain delivery

Grain food aid averages 13 million tons per year. Donors have a duty to deliver food aid grain in an adequate and acceptable condition at least cost. This paper reviews commodity procurement, packaging, inspection, shipping and storage with regard to overall quality assurance and cost-effectiveness. Experience at ports of loading and discharge and in food aid delivery programmes indicates that sufficient attention is rarely paid to quality assurance and loss minimisation. Grain procurement specifications that are normally appropriate for safe handling and storage in temperate climates, particularly moisture content, are commonly inappropriate for tropical climates. The technology for safe delivery of food aid grain is well established but not always implemented. Procurement of food aid grain in developing countries has increased recently, creating a need to improve operational and management aspects of tendering and quality assurance procedures. Such purchases entail potential cost savings but are associated with lengthening delivery lead times for non-urgent consignments. Although woven polypropylene sacks are cheaper to buy than jute ones, the losses associated with handling and storage problems indicate that jute sacks are preferable for food aid delivery.

Identification of a novel dihydrolipoyl dehydrogenase-binding protein in the pyruvate dehydrogenase complex of the anaerobic parasitic nematode, Ascaris suum

A novel dihydrolipoyl dehydrogenase-binding protein (E3BP) which lacks an amino-terminal lipoyl domain, p45, has been identified in the pyruvate dehydrogenase complex (PDC) of the adult parasitic nematode, Ascaris suum. Sequence at the amino terminus of p45 exhibited significant similarity with internal E3-binding domains of dihydrolipoyl transacetylase (E2) and E3BP. Dissociation and resolution of a pyruvate dehydrogenase-depleted adult A. suum PDC in guanidine hydrochloride resulted in two E3-depleted E2 core preparations which were either enriched or substantially depleted of p45. Following reconstitution, the p45-enriched E2 core exhibited enhanced E3 binding, whereas, the p45-depleted E2 core exhibited dramatically reduced E3 binding. Reconstitution of either the bovine kidney or A. suum PDCs with the A. suum E3 suggested that the ascarid E3 was more sensitive to NADH inhibition when bound to the bovine kidney core. The expression of p45 was developmentally regulated and p45 was most abundant in anaerobic muscle. In contrast, E3s isolated from anaerobic muscle or aerobic second-stage larvae were identical. These results suggest that during the transition to anaerobic metabolism, E3 remains unchanged, but it appears that a novel E3BP, p45, is expressed which may help to maintain the activity of the PDC in the face of the elevated intramitochondrial NADH/NAD+ ratios associated with anaerobiosis.

Effects of cocaine on briefly signaled versus completely signaled delays to reinforcement

Key pecking by 4 pigeons was maintained by a multiple schedule consisting of two variable-interval 60-s schedules wherein each food presentation followed a nonresetting 27-s delay that was either briefly signaled at its outset or completely signaled. Brief-signal duration was adjusted so that response rates maintained by the briefly and completely signaled delays of reinforcement were similar. In general, acute administration of small to intermediate doses (0.3 to 3.0 mg/kg) of cocaine produced either small increases in response rates in both components or no change, and larger doses (5.6 to 13.0 mg/kg) decreased response rates. Chronic (i.e., daily) cocaine administration (10.0 mg/kg) resulted in tolerance to the rate-decreasing effects in both components. Cocaine's effects were generally similar whether delays were completely or briefly signaled. Discontinuation of cocaine administration and subsequent removal of the delay signals also had similar effects in both components of the multiple schedule. Taken together, these results are consistent with the view that the two types of delay signals were equally effective in maintaining responding during the variable-interval schedules.

Simultaneous Measurement of Intracellular pH and K+ or NO3- in Barley Root Cells Using Triple-Barreled, Ion-Selective Microelectrodes

The manufacture and use of triple-barreled microelectrodes, which are capable of simultaneous in vivo measurement of intracellular pH and the activities of K+ or NO3- and cell membrane potential (Em), are described. Scanning electron micrographs showed that the three tips were aligned and that the overall tip diameter was approximately 0.8 [mu]m. When filled with 100 mM KCl, all three barrels simultaneously reported identical transmembrane potentials, showing that all three tips were located in the same subcellular compartment. Intracellular estimates of Em in barley (Hordeum vulgare L. cv Klaxon) root epidermal cells obtained with these triple-barreled microelectrodes were indistinguishable from those obtained using single- or double-barreled microelectrodes. Measurements made with triple-barreled K+ and pH-selective microelectrodes in root cells of 7-d-old barley plants grown in a nutrient solution containing 0.5 mM K+ yielded cytosolic and vacuolar populations having mean K+ activity values of 71.3 and 68.7 mM, respectively. The associated mean pH values ([plus or minus]SE) were 7.26 [plus or minus] 0.06 (cytosol) and 5.18 [plus or minus] 0.08 (vacuole). Analysis of whole-tissue digests confirmed the microelectrode measurements. Measurements made using triple-barreled pH- and nitrate-selective microelectrodes confirmed earlier double-barreled measurements of pH and nitrate in barley root epidermal cells growing in 10 mM nitrate.