Progesterone stimulates in vitro release of prolactin and thyrotropin involving cAMP production in rat pituitary

Effects of progesterone administration in vivo or in vitro on the release of pituitary prolactin (PRL) and thyroid stimulating hormone (TSH) in vitro, as well as the generation of pituitary cyclic adenosine 3', 5'-monophosphate (cAMP) were studied in ovariectomized (Ovx) rats. Ovx rats were either decapitated or injected subcutaneously with progesterone, or oil for 3 days before decapitation. The anterior pituitary glands (APs) of progesterone treated Ovx rats were incubated with Locke's medium containing thyrotropin-releasing hormone (TRH, 10 nM) and/or 3-isobutyl-1-methylxanthine (IBMX, 1 mM) at 37 degrees C for 30 min. The APs of untreated Ovx rats were incubated in vitro with IBMX and progesterone (0, 0.1, 1, 10 nM). Progesterone increased spontaneous and TRH-induced release of PRL and TSH in vitro. Administration of progesterone, either in vivo or in vitro, increased the production of pituitary cAMP following incubation of IBMX. These results suggest that progesterone increases the release of PRL and TSH through a mechanism associated with an increase of cAMP production in rat APs.

Mediastinal liposarcoma with local recurrence: a case report

Liposarcoma is a rare mediastinal tumor. The treatment of choice is surgical resection. However, recurrence is not uncommon. In this report, recurrence of liposarcoma with local extension to chest wall is described in a 70-year-old Chinese male who had liposarcoma located in the anterior mediastinum and underwent tumor resection 5 years before. Long-term follow-up is indicated in patients with mediastinal liposarcoma because there may be an interval of several years between resection and recurrence.

Membrane transport mechanisms probed by capacitance measurements with megahertz voltage clamp

We have used capacitance measurements with a 1-microsecond voltage clamp technique to probe electrogenic ion-transporter interactions in giant excised membrane patches. The hydrophobic ion dipicrylamine was used to test model predictions for a simple charge-moving reaction. The voltage and frequency dependencies of the apparent dipicrylamine-induced capacitance, monitored by 1-mV sinusoidal perturbations, correspond to single charges moving across 76% of the membrane field at a rate of 9500 s-1 at 0 mV. For the cardiac Na,K pump, the combined presence of cytoplasmic ATP and sodium induces an increase of apparent membrane capacitance which requires the presence of extracellular sodium. The dependencies of capacitance changes on frequency, voltage, ATP, and sodium verify that phosphorylation enables a slow, 300- to 900-s-1, pump transition (the E1-E2 conformational change), which in turn enables fast, electrogenic, extracellular sodium binding reactions. For the GAT1 (gamma-aminobutyric acid,Na,Cl) cotransporter, expressed in Xenopus oocyte membrane, we find that chloride binding from the cytoplasmic side, and probably sodium binding from the extracellular side, results in a decrease of membrane capacitance monitored with 1- to 50-kHz perturbation frequencies. Evidently, ion binding by the GAT1 transporter suppresses an intrinsic fast charge movement which may originate from a mobility of charged residues of the transporter binding sites. The results demonstrate that fast capacitance measurements can provide new insight into electrogenic processes closely associated with ion binding by membrane transporters.

Dynamic evaluation of swallowing in patients with cerebrovascular accident

To determine the specific effects of cerebrovascular accident (CVA) on deglutition, especially relative to the site of CVA, we studied videotapes of barium swallow examinations in 74 patients who had had a CVA. Although there was no distinct correlation between the prevalence of oral and pharyngeal dysfunction and the site of CVA, left CVA was prone to impair only the oral phase, and right CVA tended to impair both phases.

MELAS syndrome associated with diabetes mellitus and hyperthyroidism: a case report from Taiwan

MELAS syndrome is a form of mitochondrial myopathy with manifestations of seizure, stroke-like syndrome, lactic acidosis, ragged red muscle fibres and mitochondrial encephalopathy. The syndrome has been reported in association with a variety of endocrine and metabolic disorders including diabetes mellitus (DM), hypothalamo-pituitary hypofunction, hypothalamic growth hormone deficiency and delayed puberty. Mitochondrial DNA (mtDNA) point mutation may be the major pathological defect. However, association of MELAS syndrome with hyperthyroidism has not previously been reported. A case is reported from Taiwan of a 32-year-old woman suffering from MELAS syndrome with associated DM and hyperthyroidism. When the latter was diagnosed in April 1988, the patient underwent subtotal thyroidectomy. There was no family history of thyroid disease. Because of repeated seizures, she had computed tomography (CT) and magnetic resonance imaging (MRI) of the brain which showed focal, low-density lesions over the cerebral hemispheres. Both serum and cerebral spinal fluid lactic acid levels were elevated. Mild elevations of serum T4 and T3 and a high titre of TSH receptor antibody were still present. Hyperglycaemia was noted during hospitalization and DM confirmed by oral glucose tolerance test. Muscle biopsy showed ragged red fibres. DNA analysis showed an A-to-G transition at the 3243rd nucleotide position of the tRNA(Leu(UUR)) gene of the mtDNA from the patient. Quantitative polymerase chain reaction (PCR) and restriction analysis revealed that about 60% of the blood mtDNA was of mutant type. The patient received antithyroid drugs for hyperthyroidism, diet control for DM and anti-epileptic drugs for seizure.

Diminished actin polymerization of neonatal neutrophils determined by a microvolume whole blood method

To investigate the actin response to chemotactic stimulation of neonatal neutrophils, we developed a new procedure to measure neutrophil F-actin content directly in microvolume whole blood (100 microliters sample each test). Using this procedure, we compared neutrophil actin response to N-formyl-methyonyl-leucyl-phenylalanine (FMLP) between groups of normal neonate and adult volunteers. Relative F-actin content (FMLP/control ratio) of neonatal neutrophils is significantly lower than those of adult volunteers' neutrophils both at 30 sec (1.94 +/- 0.34 vs. 2.25 +/- 0.31; n = 16, p < 0.05, t test) and 60 sec (2.23 +/- 0.19 vs. 2.40 +/- 0.27; n = 16, p < 0.05, t test) after FMLP stimulation. These results provide new evidence of impairment of neutrophil actin response in the neonate, which may partially explain the observed chemotactic defect in neonatal neutrophils.

Key role of a CCAAT element in regulating hepatitis B virus surface protein expression

Two separate promoters, the upstream preS1 and the downstream S promoters, give rise to transcripts encoding three forms of the hepatitis B virus surface protein. Overproduction of large surface protein because of increased preS1 transcripts leads to a block in secretion of all forms of the surface protein and of virion particles. We show here that a CCAAT element in the S promoter not only increases the amount of S transcripts, but also decreases the amount of preS1 transcripts by up to fivefold. Consequently, mutations in this element cause intracellular accumulation of surface proteins because of the secretory block. Therefore, this CCAAT element appears to be critical for maintaining the high ratio of S versus preS1 transcripts that is necessary for the viral life cycle.

Gastric inhibitory polypeptide and gastric acid secretion in pregnant rats

The effects of pregnancy on the basal and pentagastrin-stimulated gastric acid secretion and the level of plasma gastric inhibitory polypeptide (GIP) in rats were studied on pentobarbital-anaesthetized non-pregnant rats and rats in the 1st, 2nd, or 3rd week of gestation. Acid output was determined by titration of the gastric perfusate. Basal secretion was collected for 45 min before a 30 min infusion of pentagastrin (8 micrograms/ml/300 g body weight). Concentration of plasma GIP was measured by a radioimmunoassay (RIA). The immunoreactivity of GIP-like substance in the extract of the rat placenta collected from the rat at day 21 of gestation was examined by RIA. The biological activity of GIP-like substance in the rat placenta extract was tested by the reduction of pentagastrin-stimulated gastric acid secretion in male rats. The basal level of gastric secretion was higher in late pregnancy as compared with the non-pregnant rats. Pentagastrin induced a greater increase of gastric acid secretion in early but not late pregnant rats as compared with the non-pregnant animals. The basal and post-pentagastrin level of plasma GIP was higher in rats in late pregnancy. Both immunoreactivity and biological activity of GIP exist in the rat placenta extract. These results suggest that the normalization of gastric acid secretion in late pregnant rats is at least in part due to the production of GIP-like substance from placenta.

Insulin autoimmune syndrome in a patient with methimazole and carbimazole-treated Graves' disease: a case report

Insulin autoimmune syndrome (IAS) includes fasting or reactive hypoglycemia, hyperinsulinemia and the presence of insulin-binding antibodies in patients who have never been exposed to exogenous insulin. The report concerns a 34-year-old male patient with Graves' disease who had history of having taken methimazole for two months, without any consequence, 4 years previously. However, when methimazole was again administered for three weeks followed by a week of carbimazole, the patient suffered hypoglycemia 4 times during the next 4 weeks. He denied history of diabetes mellitus (DM), of taking any oral hypoglycemic agent or of having received insulin injection. Laboratory data showed total serum insulin level > 320 microU/mL, free insulin 55 microU/mL and insulin antibody 88.3%. Oral glucose tolerance test (OGTT) revealed DM pattern. Since the patient had history of allergy to anti-thyroid drugs before this event, so he was treated with radioiodine (131I). There was no episode of hypoglycemic attack during 15 months of follow-up.

Ancient origin of the vacuolar H(+)-ATPase 69-kilodalton catalytic subunit superfamily

Recently, two distinct cDNA clones encoding the catalytic subunit of the vacuolar H(+)-ATPase (V-ATPase) were isolated from the allotetraploid cotton species Gossypium hirsutum L. cv 'Acala SJ-2' (Wilkins 1992, 1993). Differences in the nucleotide sequence of these clones were used as molecular markers to explore the organization and structure of the V-ATPase catalytic subunit genes in the A and D genomes of diploid and allotetraploid cotton species. Nucleotide sequencing of polymerase chain reaction (PCR) products amplified from G. arboreum (A2, 2n=26), G. raimondii (D5, 2n=26), and G. hirsutum cv 'Acala SJ-2' [(AD)1, 2n=4x=52] revealed a V-ATPase catalytic subunit organization more complex than indicated hitherto in any species, including higher plants. In the genus Gossypium, the V-ATPase catalytic subunit genes are organized as a superfamily comprising two diverse but closely related multigene families, designated as vat69A and vat69B, present in both diploid and allotetraploid species. As expected, each vat69 subfamily is correspondingly more complex in the allotetraploid species due to the presence of both A and D alloalleles. Because of this, about one-half of the complex organization of V-ATPase catalytic subunit genes predates polyploidization and speciation of New World tetraploid species. Comparison of plant and fungal V-ATPase catalytic subunit gene structure indicates that introns accrued in the plant homologs following the bifurcation of plant and fungi but prior to the gene duplication event that gave rise to the vat69A and vat69B genes approximately 45 million years ago. The structural complexity of plant V-ATPase catalytic subunit genes is highly conserved, indicating the presence of at least ten introns dispersed throughout the coding region.

Calcitonin inhibits testosterone and luteinizing hormone secretion through a mechanism involving an increase in cAMP production in rats

Effects of calcitonin peptides, including human calcitonin (hCT), salmon calcitonin (sCT), and calcitonin gene-related peptide (CGRP), on the secretion of testosterone and luteinizing hormone (LH) in male rats were studied. Male rats were injected intravenously with human chorionic gonadotropin (hCG), calcitonin peptides, or hCG plus calcitonin peptides. Blood samples were collected at several intervals following hormone challenge. In an in vitro experiment, testis blocks were incubated with hCG (0, 0.05, 0.5, or 5 IU/ml) or hCG (0.5 IU/ml) plus calcitonin peptides (0-10(-9) or 10(-6) M) at 34 degrees C for 30 minutes. Both medium and plasma samples were extracted by ether and analyzed for testosterone by radioimmunoassay (RIA). The concentration of calcium in each plasma sample was measured by an automatic calcium analyzer. The anterior pituitary gland (AP) was incubated with or without calcitonin peptides (0-10 nM) at 37 degrees C for 30 minutes. They were then incubated with gonadotropin releasing hormone (GnRH, 10 nM) for a further 30 minutes. The concentration of LH in AP medium was measured by RIA. The accumulation of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) in both testicular tissues and APs were measured by RIA. A single intravenous injection of calcitonin peptides decreased the basal and hCG-stimulated levels of plasma testosterone gradually from 60 to 180 or 360 minutes after challenge. The plasma calcium was not altered by the injection of calcitonin peptides and/or hCG. Administration of calcitonin peptides in vitro resulted in a dose-dependent inhibition of both basal and hCG-stimulated release of testosterone.(ABSTRACT TRUNCATED AT 250 WORDS)

Ectopic gastric mucosa in the upper esophagus: detection and radiographic findings

PURPOSE

To detect and characterize the appearance of islands of ectopic gastric mucosa in the upper esophagus at routine examination of the upper gastrointestinal (GI) tract.

MATERIALS AND METHODS

Well-distended upper esophagus was documented with spot radiographs obtained with routine double-contrast examination performed after administration of high-density barium in nine patients. Detected lesions were confirmed by means of endoscopy and biopsy.

RESULTS

Twelve lesions were detected. Radiographic findings were characterized by either a discrete, shallow depression surrounded by a subtle, rimlike elevation on double-contrast images or by a pair of small indentations on the same wall on full-column, single-contrast images at the level of the thoracic inlet. Endoscopic examination revealed well-circumscribed areas of reddish mucosa located 15-26 cm from the incisors.

CONCLUSION

Ectopic gastric mucosa in the upper esophagus is easily demonstrated at routine examination of the upper GI tract. Diagnosis can be based on location and characteristic radiographic appearance.

CT findings of plexiform neurofibromatosis involving the ileum and its mesentery

We present a case of plexiform neurofibromatosis involving the ileum and its mesentery. Computed tomography (CT) scans showed a cluster of small soft-tissue density nodules, which represented a cross-sectional image of the enlarged peripheral nerves and wall thickening of the distal ileum. Trapped fat tissue was demonstrated between these enlarged nerves. Histopathologic studies of the resected specimen correlated well with CT findings.

Molecular characterization of glucose-6-phosphate dehydrogenase deficiency in Chinese infants with or without severe neonatal hyperbilirubinaemia

To characterize mutations in the glucose-6-phosphate dehydrogenase (G6PD) gene in Chinese infants, we studied 213 G6PD-deficient infants without blood exchange transfusion (BET) therapy, and 34 patients who required BET therapy for their severe hyperbilirubinaemia after birth. Nine different point mutations were characterized in all infants. Of these mutations, the G to T substitution at cDNA nucleotide (nt) 1376, which accounts for the mutations in 131 (53.0%) neonates, followed by G to A substitution at nt 1388 in 18 (10.5%) infants, A to G substitution at nt 493 in 17 (6.9%) infants, A to G substitution at nt 95 in 10 (4.1%) infants, C to T substitution at nt 1024 in six (2.4%) infants, and G to T substitution at nt 392 in three (1.2%) infants, G to A substitution at nt 487 in two (0.8%) infants, C to T substitution at nt 1360 in two (0.8%) infants and C to T substitution at nt 592 in two (0.8%) infants. Mutations in 48 (19.5%) G6PD-deficient infants were not characterized. Most (64.7%) mutations in the G6PD-deficient infants who required BET therapy after birth result from a G to T substitution at nt 1376. The enzyme activity of G6PD deficient infants who required BET therapy is significantly lower than for those who did not, even in a group with the same variant (as in 1376 mutation). Severe neonatal jaundice requiring BET therapy can take place with the majority of variants encountered in this area.

Does a normal small-bowel enteroclysis exclude small-bowel disease? A long-term follow-up of consecutive normal studies

The purpose of our study was to determine if a normal small-bowel enteroclysis excludes small-bowel disease in adult patients, using long-term follow-up as the major reference standard. We reviewed 193 consecutive small-bowel enteroclysis (SBE) studies completed during a period from January 1987 to February 1989, of which 83 were judged to be normal at the time of the study. Eight of these latter patients were excluded due to inadequate follow-up. The indications included detection of gastrointestinal bleeding, small-bowel obstruction, Crohn's disease, nonspecific abdominal pain, chronic diarrhea, and a miscellaneous group. Each patient was followed for at least 3 years by chart review or until a definite diagnosis was established. Six of the 75 patients whose SBE was originally interpreted as normal were eventually judged to have small-bowel disease. The remaining 69 patients were judged to be free of small-bowel disease by autopsy, surgical laparotomy, endoscopic observation or biopsy, or long-term follow-up for at least 3 years. Therefore, a normal SBE correctly excluded small-bowel disease in 69 of our 75 patients (true negatives) and failed to diagnose disease in six patients (false negatives), for a specificity of .92 +/- .03 (SE). In this experience, SBE was sufficiently specific in most patients to exclude small-bowel disease.

The lung contents of endothelin are altered by thyroid hormone status in rat

Endothelin-1 (ET-1) is a 21-residue peptide isolated from the conditioned medium of cultured porcine endothelial cells and is widely distributed throughout the body, with relatively high levels in the kidney and lung. Animal studies have revealed that the lung appears to have the largest capacity for ET-1 removal from the blood stream. In this study we have examined the possible influence of thyroid status on immunoreactive endothelin (IR-ET) levels in the plasma and lung of the male rats. 3 weeks after the surgical removal of the thyroid gland from male rats, the IR-ET levels in the lung were reduced by 39%. Similarly, IR-ET levels were decreased 46% in the lung of rats rendered hypothyroid by treatment with 0.1% (w/w) PTU in the drinking water for 30 days, and replacement with daily L-thyroxine (T4) injections (5 micrograms/100 g) prevented this decrease. However, thyrotoxicosis induced by daily L-T4 injections (10 micrograms/100 g) also caused a decrease of the lung IR-ET levels by 49%. Nevertheless, the plasma IR-ET levels are similar in each group. Fast protein liquid chromatography study verified the presence of ET-1 immunoreactivity in both rat plasma and lung tissue extracts. This study demonstrates that euthyroid status is required for the maintenance of physiological concentrations of IR-ET in the lung of male rats.

Purification and amplification of DNA from Penaeus monodon-type baculovirus (MBV)

The purpose of this paper was to purify and amplify the DNA fragment of Penaeus monodon-type baculovirus (MBV). Using 30-50% caesium chloride gradients, MBV virions and occlusion bodies with density parameters of 1.28-1.29 and 1.32-1.33 g/ml, respectively, were purified. Two oligonucleotide primers have been successfully designed and utilized for the amplification of a DNA fragment of MBV. After 35 amplification cycles of the MBV DNA fragment, a large amount of amplified product with an approximate molecular weight of 600 bp was obtained. This is the first successfully published work on the amplification of MBV using the polymerase chain reaction (PCR). Using the same primers, DNA extracted from MBV noninfected P. monodon, P. japonicus, and P. orientalis had a negative PCR response. However, a positive PCR response was obtained from DNA extracted from MBV-infected postlarval P. monodon. DIG-dot blot hybridization technique using PCR product obtained from the present study as a probe further confirmed that the product is originated from a portion of MBV polyhedrin gene. It is also suggested that PCR product may be beneficial for an accurate and early diagnosis of MBV infection in larval shrimp.

Signal fidelity requirements for deriving impedance cardiographic measures of cardiac function over a broad heart rate range

Our findings indicate that the impedance cardiogram spectrum extends from DC to 50 Hz. Any amplifier with an upper band limit less than 50 Hz can be expected to produce attenuation and distortion of the impedance cardiogram. This signal attenuation may be systematically enhanced under conditions of high heart rate when a greater proportion of signal energy will be in the upper frequency range of the impedance cardiogram spectrum. Therefore, the present study was designed to assess the influence of amplifier bandwidth on dZ/dtmax, stroke volume, and systolic time intervals (LVET, PEP, QZ, QX). Simultaneously measured delta Z and dZ/dt signals from two impedance cardiographs, with corner frequencies of 120 and 60 Hz for the delta Z and 50 and 15 Hz for dZ/dt channels, were contrasted over a broad range of heart rate (70-150 bpm). In addition to the analog dZ/dt signals obtained from the instruments, the delta Z signals were digitally converted to dZ/dt by off-line digital differentiation with a 50 Hz corner frequency. The results demonstrated that the measurements with the 15 Hz corner frequency, when compared with the 50 Hz corner frequency measurements, systematically attenuated the dZ/dtmax amplitude and stroke volume measurements as heart rate increased. The attenuation of dZ/dtmax and stroke volume ranged from about 13% to 26% as heart rate increased from 70 to 150 bpm. When the upper bandlimit was 50 Hz, the dZ/dt signal had greater resolution of waveform events and produced less prolonged systolic time intervals. The 15 Hz amplifier differentially influenced the B point, Z-peak and X minimum, having no apparent effect on the temporal location of the B point, but delaying the Z-peak about 21.7 ms and the X minimum about 7.4 ms. These findings indicate that impedance cardiographs with insufficient upper bandlimits will differentially influence ICG-derived measurements as heart rate varies.

[Applied anatomy of the second dorsal metacarpal artery island flap]

50 specimens of the adult hand were dissected to study the origin, course, anastomosis and supplying area of the second dorsal metacarpal artery. The island fasciocutaneous flap of dorsum of the hand, based on second dorsal metacarpal artery, has been designed for the repair of soft tissue defects in the hand. We have successfully used four neurovascular flaps. The anatomy and clinical use of the axial pattern flap based on the second dorsal metacarpal artery are described.

Silicone fluid-induced pulmonary embolism

Silicone fluid injection for mammary augmentation is a well-known illegal procedure. It has been associated with many complications, including local tissue granulomatous reaction, chronic infection, and sclerosis, but pulmonary involvement in human beings has been documented in only six cases. We describe three more such cases of pulmonary embolism. These three patients were all female, young, and previously healthy. They received the procedures only for cosmetic reasons. Unfortunately, one of them died and another lived with the sequelae of pulmonary fibrosis. The mortality rate of the nine total patients with pulmonary embolism induced by silicone fluid, including our three cases, is 33%. Because of this high mortality rate and long-term sequelae of pulmonary fibrosis, no silicone fluid injection should be given for cosmetic reasons, especially in mammary augmentation in which a large volume of silicone fluid is more likely to be used, and the early use of corticosteroid therapy may be helpful.

Midgut volvulus as a complication of intestinal malrotation in adults

Seven adults with midgut volvulus as a complication of malrotation are presented. All patients were men with an average age of 33 years. Four presented with long histories of intermittent abdominal pain. In three patients, the twisted, corkscrew appearance of the barium column in the duodenum and proximal jejunum in an upper gastrointestinal series made the diagnosis. In the remaining patient, small-bowel follow-through performed three years before surgery showed intestinal malrotation. Three patients presented with the acute onset of severe abdominal pain. Plain films showed small-bowel obstruction and pneumatosis intestinalis in two patients and only nearly complete small-bowel obstruction in the third. Barium studies were not done in this group because of the need to proceed to exploratory laparotomy and the risk of perforation. In one patient, abdominal angiography suggested the diagnosis by showing abnormal courses of the mesenteric vessels to the volvulized segment of small bowel. All three of these patients showed ischemic segments of bowel at laparotomy.

Tissue contents of endothelin vary according to thyroid hormone status in rat

Endothelin-1 (ET-1) is a 21-residue peptide isolated from the conditioned medium of cultured porcine endothelial cells and is widely distributed throughout the body, with relatively high levels in the kidney and lung. In this study we examined the influence of thyroid hormone status on immunoreactive endothelin (ir-ET) levels in the plasma, lung, and kidney tissues of rats. Three weeks after surgical removal of the thyroid gland from male rats, the ir-ET levels in the lung and kidney were reduced by 39% and 42%, respectively. Similarly, ir-ET levels were decreased by 46% in the lung and 45% in the kidney of rats rendered hypothyroid by treatment with 0.1% (wt/wt) n-propylthiouracil (PTU) in the drinking water for 30 days. Replacement with daily L-thyroxine (T4) injections (5 micrograms/100 g) prevented this decrease. However, thyrotoxicosis induced by daily L-T4 injections (10 micrograms/100 g) also caused a decrease of the lung ir-ET levels by 49%, but had no significant effect on the renal ir-ET levels. However, the plasma ir-ET levels were similar in each group. Fast protein liquid chromatography study verified the presence of ir-ET-1 in the plasma and tissue extracts. This study demonstrates that thyroid hormone status affects tissue levels of ir-ET differently and that a euthyroid status is required for the maintenance of physiologic concentrations of ir-ET in the lung of male rats.

Role of locus coeruleus and serotonergic drug actions on schedule-induced polydipsia

Schedule-induced polydipsia (SIP) poses a general buffering property to reduce the heightened arousal produced by a schedule of intermittent feeding. It thus provides a unique opportunity to study CNS integration in stress-coping reactions. In the present study, we examined the role of the locus coeruleus (LC) and the pharmacological actions of serotonergic (5-HT2) analogs on SIP. Water intake, licking, and bar presses per minute in rats were recorded as indices of SIP activity after they had been subjected to 1-h performance of a fixed-interval 1-min operant pellet conditioning. Our results showed that SIP was progressively decreased after lesions were placed bilaterally in the LC areas and then followed by further lesioning in the bilateral ventral tegmental area. Neurotoxin DSP-4 also had an inhibitory action on the SIP potency. In addition, SIP was attenuated by 2,5-dimethoxy-4-iodoamphetamine (0.1, 0.5, or 1.0 mg/kg, IP), a 5-HT2 agonist, and activated by ritanserin (2.5 mg/kg, IP), a 5-HT2 agonist. After bilateral LC lesions, SIP was attenuated and the activating effect of RIT was abolished. Our data suggest that the LC is involved in the central integration of SIP and that the modulating effects of 5-HT2 receptors on SIP depend upon the integrity of LC function.