Complete genome structure of the nitrogen-fixing symbiotic bacterium Mesorhizobium loti

The complete nucleotide sequence of the genome of a symbiotic bacterium Mesorhizobium loti strain MAFF303099 was determined. The genome of M. loti consisted of a single chromosome (7,036,071 bp) and two plasmids, designated as pMLa (351,911 bp) and pMLb (208, 315 bp). The chromosome comprises 6752 potential protein-coding genes, two sets of rRNA genes and 50 tRNA genes representing 47 tRNA species. Fifty-four percent of the potential protein genes showed sequence similarity to genes of known function, 21% to hypothetical genes, and the remaining 25% had no apparent similarity to reported genes. A 611-kb DNA segment, a highly probable candidate of a symbiotic island, was identified, and 30 genes for nitrogen fixation and 24 genes for nodulation were assigned in this region. Codon usage analysis suggested that the symbiotic island as well as the plasmids originated and were transmitted from other genetic systems. The genomes of two plasmids, pMLa and pMLb, contained 320 and 209 potential protein-coding genes, respectively, for a variety of biological functions. These include genes for the ABC-transporter system, phosphate assimilation, two-component system, DNA replication and conjugation, but only one gene for nodulation was identified.

Sequence and analysis of chromosome 3 of the plant Arabidopsis thaliana

Arabidopsis thaliana is an important model system for plant biologists. In 1996 an international collaboration (the Arabidopsis Genome Initiative) was formed to sequence the whole genome of Arabidopsis and in 1999 the sequence of the first two chromosomes was reported. The sequence of the last three chromosomes and an analysis of the whole genome are reported in this issue. Here we present the sequence of chromosome 3, organized into four sequence segments (contigs). The two largest (13.5 and 9.2 Mb) correspond to the top (long) and the bottom (short) arms of chromosome 3, and the two small contigs are located in the genetically defined centromere. This chromosome encodes 5,220 of the roughly 25,500 predicted protein-coding genes in the genome. About 20% of the predicted proteins have significant homology to proteins in eukaryotic genomes for which the complete sequence is available, pointing to important conserved cellular functions among eukaryotes.

Sequence and analysis of chromosome 5 of the plant Arabidopsis thaliana

The genome of the model plant Arabidopsis thaliana has been sequenced by an international collaboration, The Arabidopsis Genome Initiative. Here we report the complete sequence of chromosome 5. This chromosome is 26 megabases long; it is the second largest Arabidopsis chromosome and represents 21% of the sequenced regions of the genome. The sequence of chromosomes 2 and 4 have been reported previously and that of chromosomes 1 and 3, together with an analysis of the complete genome sequence, are reported in this issue. Analysis of the sequence of chromosome 5 yields further insights into centromere structure and the sequence determinants of heterochromatin condensation. The 5,874 genes encoded on chromosome 5 reveal several new functions in plants, and the patterns of gene organization provide insights into the mechanisms and extent of genome evolution in plants.

Involvement of phosphoinositide-3-kinase and p70 S6 kinase in regulation of proliferation of rat lactotrophs in culture

Phosphoinositide-3-kinase (PI-3K) and p70 S6 kinase (p70S6k) are suggested as important molecules for mediating mitogenic actions of growth factors and cytokines in a variety of cell types. The purpose of the present study was to investigate whether these kinases were involved in mediation of the mitogenic actions of not only the growth factor insulin but also cyclic adenosine monophosphate (cAMP) and estrogen on rat cultured lactotrophs. Treatment with wortmannin or LY294002, a PI-3K inhibitor, or rapamycin, a p70S6k inhibitor, decreased basal levels of 5-bromo-2-deoxyuridine (BrdU)-labeling indices of lactotrophs in a dose-dependent manner. These inhibitors were effective in blocking an increase in BrdU-labeling indices induced by insulin. LY294002 and rapamycin also suppressed an increase in BrdU-labeling indices induced by forskolin, an adenylate cyclase activator, or dibutyryl cAMP, a membrane-permeable cAMP analog, as well as that induced by estradiol, a physiologic extracellular activator of lactotroph proliferation. However, the dibutyryl cAMP-, but not insulin-induced proliferation, acquired a resistance to LY294002 and rapamycin by pretreatment with bromocriptine, a dopaminergic agonist that is able to suppress lactotroph proliferation. These results suggest that the mitogenic actions of cAMP and estradiol on rat lactotrophs are mediated by PI-3K and p70S6k, and that dopaminergic inhibition modifies the PI-3K and p70S6k dependence of the regulation of lactotroph proliferation.

Neutrophil chemoattractant 2 beta regulates expression of the Reg gene in injured gastric mucosa in rats

BACKGROUND & AIMS

Regenerating (Reg) protein has a trophic effect on gastric mucosal cells. We have shown that Reg gene expression is increased in enterochromaffin-like (ECL) cells during the healing of damaged gastric mucosa around mucosal erosion. This study was designed to explore the stimulants of Reg expression during the healing of gastric mucosal damage.

METHODS

Time course changes of the expression of genes for various proinflammatory cytokines and Reg were investigated after induction of gastric mucosal lesions in rats. The direct effect of proinflammatory cytokines on Reg gene expression and Reg protein production were investigated in vitro using counterflow elutriation-enriched rat ECL cells. CXC receptor 2 (CXCR-2) expression was investigated in ECL cells by reverse-transcription polymerase chain reaction. Reg gene expression was also investigated in rats treated by the neutralizing antibody of cytokine-induced neutrophil chemoattractant (CINC-2 beta).

RESULTS

During healing, the gene expression of several proinflammatory cytokines and Reg was markedly augmented. Among the proinflammatory cytokines, CINC-2 beta is the only cytokine in which augmented expression preceded the increase of Reg gene expression. In rats treated with CINC-2 beta neutralizing antibody, the augmentation of Reg gene expression was significantly inhibited. When ECL cells were incubated with these proinflammatory cytokines, CINC-2 beta dose-dependently increased Reg messenger RNA and Reg protein in ECL cells. CXCR-2 was identified in isolated ECL cells.

CONCLUSIONS

CINC-2 beta, expressed in damaged gastric mucosa, stimulates the production of Reg protein in ECL cells via CXCR-2 and may be involved in the accelerated healing of injured gastric mucosa.

Molecular phylogeographic studies on Paragonimus westermani in Asia

The lung fluke, Paragonimus westermani (Kerbert, 1878), is widely distributed in Asia, and exhibits much variation in its biological properties. Previous phylogenetic studies using DNA sequences have demonstrated that samples from north-east Asia form a tight group distinct from samples from south Asia (Philippines, Thailand, Malaysia). Among countries from the latter region, considerable molecular diversity was observed. This was investigated further using additional DNA sequences (partial mitochondrial cytochrome c oxidase subunit 1 (COI) and the second internal transcribed spacer of the nuclear ribosomal gene repeat (ITS2)) from additional samples of P. westermani. Phylogenies inferred from these again found three or four groups within P. westermani, depending on the method of analysis. Populations of P. westermani from north-east Asia use snail hosts of the family Pleuroceridae and differ in other biological properties from populations in south Asia (that use snail hosts of the family Thiaridae). It is considered that the populations we sampled can be divided into two species, one in north-east Asia and the other in south Asia.

Expression of peroxisome proliferator-activated receptor (PPAR)gamma in gastric cancer and inhibitory effects of PPARgamma agonists

Peroxisome proliferator-activated receptor (PPAR) gamma is expressed in human colon cancer, prostate cancer and breast cancer cells, and PPARgamma activation induces growth inhibition in these cells. PPARgamma expression in human gastric cancer cells, however, has not been fully investigated. We report the PPARgamma expression in human gastric cancer, and the effect of PPARgamma ligands on proliferation of gastric carcinoma cell lines. Immunohistochemistry was used to demonstrate the presence of PPARgamma protein in surgically resected specimens from well differentiated, moderately differentiated and poorly differentiated adenocarcinoma. We used reverse transcription-polymerase chain reaction and Northern and Western blot analyses to demonstrate PPARgamma expression in four human gastric cancer cell lines. PPARgamma agonists (troglitazone and 15-deoxy-Delta(12,14)-prostaglandin J2) showed dose-dependent inhibitory effects on the proliferation of the gastric cancer cells, and their effect was augmented by the simultaneous addition of 9- cis retinoic acid, a ligand of RXRalpha. Flow cytometry demonstrated G1 cell cycle arrest and a significant increase of annexin V-positive cells after treatment with troglitazone. These results suggest that induction of apoptosis together with G1 cell cycle arrest may be one of the mechanisms of the antiproliferative effect of PPARgamma activation in human gastric cancer cells.

Calcium signaling and c-Fos gene expression via M3 muscarinic acetylcholine receptors in human T- and B-cells

We previously showed that blood acetylcholine (ACh) originates mainly from T-lymphocytes, and that stimulation of muscarinic ACh receptors (mAChRs) induces Ca2+ oscillations and up-regulates c-fos gene expression in both T- and B-lymphocytes. In the present study, we investigated which mAChR subtypes are involved in Ca2+ signaling and c-fos gene expression in human T- (CEM) and B- (Daudi) cells. Stimulation of mAChRs with 100 microM oxotremorine-M, an M1/M3 agonist, increased levels of intracellular free Ca2+ ([Ca2+]i) and c-fos mRNA expression in both cell lines. 4-DAMP, an M3 antagonist, more effectively blocked the oxotremorine-M-induced increase in [Ca2+]i than pirenzepine and telenzepine, M1-receptor antagonists; AF-DX 116, an M2 antagonist; hexahydrosiladifenidol, a weak M3 antagonist; or hexamethonium and d-tubocurarine, nicotinic receptor antagonists. McN-A-343 (100 microM), a partial M1-receptor agonist, had no apparent effect on [Ca2+]i in either cell line. The oxotremorine-M-induced up-regulation of c-fos transcription was inhibited by 4-DAMP, but not by pirenzepine or AF-DX 116. Our findings thus suggest that ACh released from T-lymphocytes acts as an autocrine/paracrine factor, transmitting a Ca2+-dependent signal to the nuclei of T- and B-lymphocytes via M3 receptors.

Bidirectional effects of hypergravity on the cell growth and differentiated functions of osteoblast-like ROS17/2.8 cells

A low level of hypergravity (1.5-2.0 G) stimulated the proliferation of ROS17/2.8 cells, whereas it inhibited the differentiated functions of alkaline phosphatase activity and osteocalcin synthesis. These results were just the opposite of our results obtained when the cells were exposed to a high level of hypergravity (40-80 G): inhibition of cell growth and the stimulation of the differentiated functions. The direction of change in the cAMP contents of the cells was also reversed, with a low level of hypergravity causing a decrease in the cAMP content and a high level of hypergravity an increase in it. Therefore, bidirectional effects of hypergravity on the growth and differentiated functions exist in ROS17/2.8 cells according to the magnitude of the hypergravity.

Comparative immunohistopathology in pigs infected with highly virulent or less virulent strains of hog cholera virus

Eight pigs were inoculated subcutaneously with a highly virulent hog cholera virus (HCV) strain ALD. The infected pigs developed severe illness and became moribund on postinoculation day (PID) 7 or PID 10. Histologic lesions were characterized by severe generalized vasculitis, necrosis of lymphocytes, and encephalitis. HCV antigen was detected in crypt tonsilar epithelial cells, macrophages, and reticular endothelial cells of lymphoid tissues. Antigen localization corresponded well with histologic lesions. Five pigs were inoculated with less virulent HCV Kanagawa/74 strain and were euthanatized on PID 30. All five infected pigs recovered from the illness but became stunted. They also had a slight follicular depletion of lymphocytes, histiocytic hyperplasia, and hematopoiesis in the spleen. Less virulent HCV antigen was observed in the tonsils, kidneys, pancreas, adrenal glands, and lungs. Although antigen localization was less associated with histologic lesions, immunoreactivity was stronger than that in the pigs infected with the ALD strain of HCV. An almost complete loss of B lymphocytes was recognized in pigs infected with the ALD strain and was correlated with follicular necrosis in lymphoid tissues. Loss of B lymphocytes was not prominent in the pigs infected with Kanagawa/74 strain. The number of CD4+ and CD8+ T lymphocytes was significantly higher than that in the noninfected control pigs.

Effects of physostigmine and calcium on acetylcholine efflux from the hippocampus of freely moving rats as determined by in vivo microdialysis and a radioimmunoassay

The effects varying the concentration of Ca2+ in perfused artificial cerebrospinal fluid ([Ca2+]csf) on basal acetylcholine (ACh) efflux from the hippocampus of freely moving rats, in the presence and absence of the cholinesterase (ChE) inhibitor physostigmine, were investigated using in vivo microdialysis and a highly specific radioimmunoassay for ACh. In the absence of physostigmine, basal ACh efflux was 3.4+/-0.7 pg/30 min (mean +/- SEM) at [Ca2+]csf = 1.26 mM. Stepwise increases in [Ca2+]csf elicited a gradual increase in ACh efflux that was significant at [Ca2+]csf = 5.04 mM. Inhibition of ChE by addition of 10 microM physostigmine to the perfusate increased the efflux of ACh to 103.2+/-21.1 pg/30 min ([Ca2+]csf = 1.26 mM), and the efflux was augmented still further by increasing [Ca2+]csf, a change that became significant at [Ca2+]csf = 3.78. These results illustrate the sensitivity of basal ACh efflux from the hippocampus to changes in the extracellular Ca2+ concentration, and suggest that a more accurate picture of hippocampal cholinergic activity is obtained by microdialysis using normal artificial cerebrospinal fluid, under physiological conditions, rather than in the presence of a ChE inhibitor.

YM905, a novel M3 antagonist, inhibits Ca2+ signaling and c-fos gene expression mediated via muscarinic receptors in human T cells

Our earlier observations suggest that M3 muscarinic acetylcholine (ACh) receptors (mAChRs) are involved in Ca2+ signaling and regulation of c-fos gene expression in T lymphocytes. Here, we describe the effects of YM905, a novel M3 antagonist, on evoked Ca2+ signaling and c-fos gene expression in CEM human leukemic T cells. YM905 significantly inhibited increases in intracellular free Ca2+ evoked by 10 microM oxotremorine-M, an M1/M3 agonist (IC50=100 nM), and also inhibited 10 microM oxotremorine-M-induced upregulation of c-fos gene expression at 1 microM. These findings demonstrate that YM905 antagonizes the intracellular responses in T cells induced via mAChRs, possibly M3 receptors.

[PSA doubling time in prostate cancer relapsed after endocrine therapy]

PURPOSE

The PSA level of prostate cancer patients generally declines after endocrine therapy, but elevates when the cancer relapses in most cases. However, the rate of elevation differs with the case. We investigated the PSA doubling time (PSA-DT) of the prostate cancer patients whose PSA declined after endocrine therapy and later re-elevated, and investigated the relationship with other parameters.

PATIENTS AND METHODS

We investigated 55 prostate cancer patients who underwent endocrine therapy between 1991 and 1998. Their PSA re-elevated continuously after their PSA fell below 10 ng/ml after the endocrine therapy as the first line treatment. First, the correlation coefficients with time and PSA were calculated in order to decide whether their PSA elevation was exponential or linear. PSA-DT was calculated thereafter, and compared with the clinical stage, pathological differentiation, clinical relapse style, time from the beginning of the therapy to PSA relapse, pre-treatment PSA value, and prognosis. The relationship between PSA-DT and each clinical parameter was tested using the Kruskal-Wallis test. Differences in survival rates and PSA-DT were calculated using the log-rank test.

RESULTS

PSA elevated exponentially after cancer relapsed. PSA-DT in all cases ranged from 0.5 to 26.3 months, with an average of 4.4 +/- 4.8 (S.D.) months and the median was 2.5 months. PSA-DT was significantly (p < 0.01) short when the pre-treatment clinical stage was high, the time from the beginning of the therapy to PSA relapse was short, or the pre-treatment PSA value was high. PSA-DT tended to be short when the pre-treatment pathological differentiation was low, but not significantly. PSA-DT tended to be short when the cancer relapsed as distant metastasis rather than regional relapse, but not significantly. Prognosis from the initial treatment and PSA relapse was significantly poor when the PSA-DT was short.

CONCLUSIONS

PSA elevated exponentially in the relapsed prostate cancer patients after the endocrine therapy. PSA-DT was distributed in a very wide range, and this value was considered to reflect the malignant potential and prognosis of the cancer. PSA-DT may be useful for determining the strategy after relapse.

Evaluation of the pharmacological activity of extracts from amomi semen on the gastrointestinal tracts

We have investigated the effects of methanolic and alcoholic extracts from Amomi Semen on gastric secretion, as well as gastrointestinal propulsion or the prokinetic activities. The methanolic extract from Amomi Semen dose dependently decreased the volume output, acid output, and pepsin output in rat's gastric juice with increasing pH value, while the alcoholic extract had no influence on basal gastric acid secretion. Furthermore, the alcoholic extract improved the L-dopa to induce a delay of gastrointestinal transit in mice, while the methanolic extract did not improve it. However, both extracts had no influence on gastrointestinal transit in intact mice. These results suggest that Amomi Semen has an inhibitory effect on gastric acid secretion and that it has effects as the gastrointestinal prokinetics rather than propulsion. The present study pharmacologically elucidates a belief that Amomi Semen has been used in Chinese medicine for the treatment of gastrointestinal dyspepsia, which includes hyperchlorhydria, stomachache, abdominal distention, anorexia, gastric atony, etc.

Ca2+ oscillation and c-fos gene expression induced via muscarinic acetylcholine receptor in human T- and B-cell lines

We previously reported that blood acetylcholine (ACh) mainly originates from T-lymphocytes and that muscarinic (Ms) ACh receptor mRNA is expressed in both T- and B-lymphocytes. In the present study, we used confocal laser scanning microscopy and fluo-3, a calcium-sensitive indicator, to investigate the effects of Ms-ACh receptor agonists on the intracellular free Ca2+ concentration ([Ca2+]i) in single cells from human T-cell (CEM) and B-cell (Daudi) lines, which we used as models of lymphocytes. In both cell lines, stimulation of Ms-ACh receptors with ACh (0.1-100 microM), bethanechol (100 microM), car-bachol (100 microM) or oxotremorine-M (Oxo-M; 0.1-100 microM) induced [Ca2+]i-dependent increases in fluo-3 fluorescence, which in the presence of extracellular Ca2+ were followed by oscillations in [Ca2+]i that persisted for at least 10 min. All effects were completely blocked by atropine (1 microM), an Ms-ACh receptor antagonist. In both cell lines Oxo-M (100 microM) up-regulated expression of c-fos mRNA in an extracellular Ca2+-dependent manner. Again, the effect was blocked by 1 microM atropine. These results provide the first evidence that stimulation of Ms-ACh receptors induces Ca2+ oscillations and up-regulates c-fos gene expression in T- and B-lymphocytes, which is consistent with the notion that ACh released from T-lymphocytes triggers nuclear signaling via Ms-ACh receptors.

Urodynamics in acetone-induced cystitis of anesthetized rats

We examined the bladder function of cystitis models induced by intravesical acetone instillation in urethane-anesthetized rats. Acetone (0.35 ml) at 10, 30, or 50% concentration or deionized water (sham-treatment) was instilled into the bladder via the cannula which was inserted into the lumen. Acetone was withdrawn 90 sec after instillation and the bladder lumen was washed with saline after 15 min. One hour later, the cystometrogram induced by transvesical infusion of saline (3.3 ml/hr) was measured. During cystometrography of normal (non-treated) or sham-treated group, the time required to cause micturition, reflecting bladder capacity, was 9.6 +/- 0.9 (n = 7) or 10.0 +/- 0.8 min (n = 6), respectively. In the 10% acetone-treated group, the bladder capacity was similar to that in the normal or sham group. In the 30% acetone group, the time to micturition was 4.4 +/- 0.4 min (n = 7), indicating decreased bladder capacity, although the micturition pressure and the threshold pressure were not significantly different from those in the normal or sham group. However, in the 50% acetone group, the micturition reflex disappeared. In isolated rat bladder strips, contractile responses to carbachol or electrical field stimulation in the sham and 30% acetone group were similar. While, both responses in isolated strips from the 50% acetone group were reduced. The degree of damage from degeneration and desquamation of epithelium and hemorrhage in the bladder tissue from the 30% acetone group was less prominent than in the 50% acetone group. Additionally, some tissue from the 50% acetone group showed degeneration of muscle layer. The effects of three drugs were investigated in the 30% acetone group which showed increased urinary frequency. Baclofen (100 microg/kg, i.v.) and morphine (100 microg/kg, i.v.) increased significantly the bladder capacity and the threshold pressure. Atropine (10 microg/kg, i.v.) decreased the micturition pressure. These results suggest that cystitis models induced by intravesical instillation of 30% acetone may be valuable for evaluating drugs for the treatment of urinary frequency.

[Clinical features of multiple primary cancers including prostate cancer]

We analyzed the clinical features of multiple primary cancers (MPCs) that included prostate cancer. MPCs were observed in 93 (15.2%) of the patients suffering from prostate cancer. In the MPC group, the organ most commonly involved was the stomach, followed by bladder, colon and lungs. The median age at diagnosis of the first, second and third cancers was 72, 74, and 75 years old, respectively, and the duration between the first and second cancers (median: 20 months) was longer than that between the second and third cancers (median: 8 months). In the 37 MPC patients whose cause of death was obvious, 29 (78.4%) died of a cancer; prostate cancer was not so common (6 patients) as the cause of death. Age at diagnosis and grade distribution of prostate cancer were not significantly different between the MPC and single primary cancer (SPC) groups. However, the proportion of earlier stage was significantly (p < 0.01) higher in the MPC group than in the SPC group, and this trend was more obvious in patients whose prostate cancer was diagnosed as the second cancer. The prostate cancer-specific survival rates were significantly higher in the patients with MPC, and this trend was more obvious in the patients with stage D or moderately differentiated cancer. It is important in the follow up of prostate cancer patients to be aware of the possibility of the occurrence of a second cancer.

[Efficacy of combined chemoendocrine therapy with doxifluridine, cyclophosphamide, and fadrozole hydrochloride hydrate in a case of stage T4N3M1 breast cancer]

A 66-year-old female presented with a swollen lump in the left breast. She was diagnosed as having advanced breast cancer of stage T4N3 (supraclavicular lymph node) M1 (bone). The administration of CEF and TAM failed to improve her condition. After the treatment regimen was changed to combined chemoendocrine therapy with CPA, EPI, 5'-DFUR, and MPA, the areas of bone metastases were reduced. However, MPA caused side-effects (acute obstruction of the lower limb), and thus the treatment was discontinued after 4 months. Subsequently, the treatment combination was changed to CPA, EPI, 5'-DFUR, and fadrozole hydrochloride hydrate. After one year of the treatment, a complete response (CR) was obtained with the disappearance of the supraclavicular lymph node and bone metastases. After EPI reached the maximum administration amount, the remaining CPA, 5'-DFUR and fadrozole hydrochloride hydrate oral administrations were continued. As of 3 years and 10 months after the onset of the chemoendocrine therapy, CR has been maintained with suppression of the primary and metastatic lesions, without degrading the patient's quality of life.

Enhancement of hippocampal cholinergic neurotransmission through 5-HT1A receptor-mediated pathways by repeated lithium treatment in rats

Hippocampal cholinergic neuronal activity is reported to be regulated, at least partly, through serotonin1A (5-HT1A) receptors. Chronic lithium treatment has been shown to alter both behavioral and neurochemical responses mediated by postsynaptic 5-HT1A receptors. We investigated whether long-term lithium treatment affects central cholinergic neurotransmission through 5-HT1A receptor-mediated pathways. Changes in acetylcholine (ACh) release induced by 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), a 5-HT1A receptor agonist, in the rat hippocampus were measured using a microdialysis technique and a radioimmunoassay for ACh. Administration of lithium for 21 days resulted in a serum lithium concentration of 1.03 mM and caused little change in density or affinity of [3H]8-OH-DPAT binding sites in the hippocampus. The local application of 8-OH-DPAT into the hippocampus of lithium treated rats increased the ACh efflux in both the absence and the presence of physostigmine, a cholinesterase (ChE) inhibitor, in the perfusion fluid. The basal ACh efflux of lithium treated rats was not different from that of the control rats under normal conditions, but was significantly higher than that of the controls when ChE was inhibited. These results demonstrate that chronic lithium treatment increases spontaneous ACh release in the hippocampus under conditions of ChE inhibition, but not under normal conditions, and enhances cholinergic neurotransmission through 5-HT1A receptor-mediated pathways, and suggest that activation of 5-HT1A receptor function by lithium is related to the enhancement of hippocampal cholinergic neurotransmission.

Enhancement of cerebral cortical acetylcholine release by intraperitoneal acetic acid and its suppression by analgesics in freely moving rats

Several lines of evidence suggest that central cholinergic neurons play a key role in the perception and control of pain. We investigated the effects of analgesics on the increase in central cholinergic activity and writhing responses elicited by i.p. injection of acetic acid. ACh efflux from the rat cerebral cortex and hippocampus was measured in the absence of a cholinesterase inhibitor using an in vivo microdialysis technique and a highly sensitive and specific radioimmunoassay. ACh efflux from the cerebral cortex was significantly increased during the first 30 min after acetic acid injection and then returned to the control levels. In contrast, acetic acid-induced writhing responses, indicative of the perception of pain, persisted for almost the entire 120 min observation period. No changes in ACh efflux were observed in the hippocampus. The centrally-acting analgesic morphine and the peripherally-acting analgesic indomethacin each completely abolished the enhanced cerebral cortical ACh efflux and the writhing, whereas diazepam, a muscle relaxant, selectively suppressed only the writhing. These results demonstrate that peripheral nociceptive stimulation transiently increases cholinergic activity in the cerebral cortex, but not in the hippocampus, and that analgesics suppress both the enhanced ACh efflux and the writhing induced by acetic acid.