Managing bile duct injury during and after laparoscopic cholecystectomy

Laparoscopic cholecystectomy is now the treatment of choice for gallstones, but there has been concern that bile leakage after a laparoscopic cholecystectomy is more frequent than after an open cholecystectomy. We have experienced 16 patients with bile duct injury after a laparoscopic cholecystectomy. Five patients had a circumferential injury to the major bile duct, and we employed a converted open technique for biliary reconstruction. The other 11 patients had partial injury to the major bile duct, and we performed laparoscopic restoration; all 11 of these patients received endoscopic retrograde cholangiography (ERC) on the day after the operation and stenting for biliary decompression and drainage. No complications were identified and the duration of hospitalization in these patients was significantly shorter than in those who had the converted procedure. If intraoperative cholangiography is performed routinely, the presence and form of bile duct injury can be clearly identified, and the decision to restore the site of injury or to convert to the open technique for biliary reconstruction can be made immediately.

A novel conception for liver preservation at a temperature just above freezing point

BACKGROUND

It is generally accepted that 0 to 4 degreesC is a suitable temperature for organ preservation. The reason for this is based on the premise that at temperatures below 0 degreesC, intracellular ice is likely to form, with subsequent damage to cellular structures. However, it cannot be assumed that subzero temperatures will freeze the cell. In this study, we attempted to confirm the specific freezing point of rat liver and to preserve it at a temperature just above that point.

METHODS

Rat livers were stored for 24, 48, 72, and 96 h either at 4 degreesC (Group N) or at -0.8 degreesC (just above the temperature ascertained to be the specific freezing point of rat liver; Group H). After cold storage, the livers were perfused for 60 min using an isolated perfused liver model for assessment of liver function.

RESULTS

ATP and TAN (total adenine nucleotides) in reperfused liver tissues were significantly higher in Group H than in Group N for all preservation periods. ADP was significantly higher in Group H than in Group N for 24-, 72-, and 96-h preservation periods. Energy charge was significantly higher in Group H than in Group N for 24-, 48-, and 96-h preservation periods.

CONCLUSIONS

Regarding the content of ATP, ADP, and TAN and the adenylate energy charge, our results indicate that preservation at -0.8 degreesC is advantageous. This novel preservation technique seems to prolong the period that organs can be stored.

Ex vivo liver perfusion with arterial blood from a pig with ischemic liver failure

To simplify liver support using an ex vivo perfused liver, an isolated pig liver was perfused with arterial blood from the recipient pig while monitoring the metabolic capacity of the ex vivo perfused liver. It was possible to perfuse the isolated liver for more than 24 h using arterial blood from a pig with ischemic liver failure. The viability of the isolated liver during support from the liver failure pig was well maintained as evidenced by the high adenylate energy charge (0.815) and a constant ketone body ratio (KBR) of over 1.0 sampled from the hepatic vein. Oxygen consumption (mean, 29.0 microl/min/g of liver) and bile production (mean, 24.2 microl/h/g of liver) were significantly higher in the isolated liver connected to the liver failure pig than in the organ connected to the pig without liver failure (15.5 microl/min/g and 7.3 microl/h/g, respectively). These findings suggest that this liver support system has sufficient metabolic capacity to support a failed liver. Further studies may provide the experimental basis necessary for the clinical application of this device in treatment of patients with acute liver failure.

[Significance of percutaneous endoscopic gastrostomy (PEG) in home medical care]

In recent years, reflecting our aging society, the importance of home medical care has been recognized in view of medical economic and patients' needs. We are actively responding to this trend by positioning home medical care as a "new comprehensive medical care" and by organizing home medical care team. Percutaneous endoscopic gastrostomy (PEG) was developed by Ponsky et al. in 1980. While it has been widespread in Europe and America, it has not been much used in Japan yet. PEG does not require complicated hand skills. It is less invasive and sufficiently applicable to severe cases. Also, since the nursing management is easy, it can be carried out at home. It is an enteral feeding method with superb features as described earlier, in view of home medical care that attaches importance to the quality of life (QOL). In this research, we investigated hand skills for PEG and problems with PEG nutrition. Also, we referred to new possibilities for PEG in home medical care. The success of home medical care will depend on the introduction of PEG, which plays a key role in home medical care.

Therapeutic significance of palliative operations for gastric cancer for survival and quality of life

BACKGROUND AND OBJECTIVES

There have been few reports on the objective assessment of quality of life (QOL) in patients with gastric cancer following palliative operations. The benefit of a palliative operation for survival and QOL of patients with gastric cancer is not clear.

METHODS

Survival and hospital-free survival (HFS), which is considered to be one objective indicator of QOL, were studied in 95 patients undergoing palliative operations for gastric cancer. Univariate and multivariate analyses were used to determine the clinicopathologic factors potentially related to survival of patients.

RESULTS

In univariate analysis, palliative gastrectomy and absence of peritoneal dissemination were significantly correlated with better survival. The significance of palliative gastrectomy for survival was, therefore, evaluated for various degrees of peritoneal dissemination: P0 no dissemination; P1, metastasis to the adjacent peritoneum; P2, a few scattered metastases to the distant peritoneum; and P3, numerous metastases. Survival and achievement of HFS for 3 months or longer were higher following palliative gastrectomy than gastrojejunostomy. Among gastrectomies, however, total gastrectomy performed in patients with P2 or P3 showed a poorer outcome for survival and HFS than total gastrectomy performed with P0 or P1 and distal gastrectomy.

CONCLUSIONS

As a palliative measure, gastrojejunostomy and total gastrectomy performed with P2 or P3 peritoneal dissemination had no beneficial effect on the prolongation of survival or improvement of QOL of patients with gastric cancer.

Seroma with fibrous capsule formation requiring a surgical resection after a modified radical mastectomy: report of a case

Seroma formation is the most common complication of a modified radical mastectomy for breast cancer. Although various management or risk factors for seroma formation have been previously reported, little has been published concerning seromas with fibrous capsule formation which ultimately require a surgical resection. We herein present a case who developed a seroma with a fibrous capsule after a modified radical mastectomy for breast cancer, in spite of an uneventful intraoperative and postoperative course. The seroma was refractory to all conventional treatments, and thus finally required a surgical resection.

A strategy for organ allografts without using immunosuppressants or irradiation

A strategy to achieve regular and long lasting organ and tissue allografts without using immunosuppressants and/or irradiation has been established for mice. One hundred percent of skin allografts can be induced to survive >350 days after transplantation if spleen cells from the same donors are first injected into the portal vein of the recipients. The mechanisms underlying this long-term tolerance induction can be described as follows: (i) donor T cells from the spleen of the donor facilitate the acceptance of the allogeneic engraftment, (ii) donor-specific anergy is induced in the cytotoxic T-lymphocytes of the recipients, (iii) T helper type 2 cells become the dominant T cells in the recipients that are accepting the skin transplants, and (iv) a lasting chimerism (microchimerism) is established in these recipients. This strategy, perhaps with minor modifications, might permit one also to overcome major barriers to organ allografting in humans. If this were the case, it could represent production of long lasting immunologic tolerance without need for irradiation or cytotoxic chemo-preparative regimen and as such could greatly facilitate allotransplantation free of episodes of chronic or acute rejection or toxic and damaging preparatory regimens.

[A clinical study of superficial bladder cancer with grade 3 components]

A retrospective study was done on 33 patients treated for superficial bladder cancer, pTa and pT1, with grade 3 components between 1986 and 1995. All patients had undergone transurethral resection of the tumor (TUR-Bt), which was followed by total cystectomy in 7 patients. Three patients died of pulmonary diseases or heart attack and 6 patients subsequently died of bladder cancer. The 2-year and 5-year disease-specific survival rates of these patients were 83% and 75%, respectively, and the mean duration of follow-up was 50 months. Comparison of the disease-specific survival rates for several factors revealed that the configuration and size of the tumors were significantly predictable factors for prognosis. In well-selected patients with grade 3 superficial bladder cancer, bladder preservation seems to be possible by TUR with or without adjuvant therapies. Hence further studies on a larger series are needed to elucidate more feasible and reliable prognostic factors to avoid unnecessary cystectomy and improve the quality of life of the patients.

[Clinical studies on the quality of life in patients with ileal conduit]

Between August, 1985 and December. 1995 ileal conduit was performed in 36 cases of bladder cancer (30 males, 6 females). A survey based on a questionnaire was carried out on 15 patients to assess their quality of life (QOL) after the surgery. The questionnaire dealt with the working situation, appetite, sleep, defecation, bathing, travel, general health condition, satisfaction, sexual life and erection. Although only 64.0% of the patients returned to work, appetite, hours of sleep and bathing frequency showed only a slight decrease. We performed total cystectomy without using the nerve sparing method. After the operation, three patients could have an erection and enjoy sexual life. Because the ileal conduit resulted in few complications and only a slight reduction in QOL, it was considered an appropriate operation.

Hepatocyte growth factor stimulates synthesis of lipids and secretion of lipoproteins in rat hepatocytes

We have reported that infusion of recombinant human hepatocyte growth factor (rhHGF) stimulates liver regeneration after hepatectomy in cirrhotic rats and increases the level of serum lipids and secretion of very-low density lipoprotein (VLDL). Studies were now performed to determine whether rhHGF directly influences lipid synthesis and its secretion in cultured rat hepatocytes. Isolated cells were cultured in the presence or absence of rhHGF (20 ng/mL) for 2 days. During the first 12 hours, rhHGF transiently inhibited the release of lipids (triacylglycerol, total cholesterol, and phospholipids), but stimulated their releases with maximal levels achieved at 36 hours. [3H]-glycerol experiment with the transcriptional and translational inhibitors revealed that rhHGF stimulated de novo synthesis of lipids by affecting activities of lipid metabolic gene. [35S]-Methionine experiment also revealed de novo synthesis of apolipoprotein B by rhHGF. Furthermore, lipid analysis of lipoprotein fractions in the conditioned medium showed that rhHGF enhanced levels of triacylglycerol, total cholesterol, and phospholipids by 50% to 200% in both VLDL and low-density lipoproteins (LDL)/high-density lipoprotein (HDL). Genistein, a tyrosine kinase inhibitor, blocked the secretion of VLDL, as well as synthesis of lipids and apolipoprotein B stimulated by rhHGF. These results indicate that HGF likely stimulates lipid biosynthesis and lipoprotein secretion in hepatocytes through its tyrosine kinase-associated receptor, c-met, and accelerates the progress of cell maturation in liver regeneration.

Interleukin 1beta and interleukin 6, but not tumor necrosis factor alpha, inhibit insulin-stimulated glycogen synthesis in rat hepatocytes

Recent evidence indicates that inflammatory cytokines are involved in changes of blood glucose concentrations and hepatic glucose metabolism in infectious diseases, including sepsis. However, little is known regarding how cytokines interact with glucoregulatory hormones such as insulin. The objective of the present study is to investigate if and how cytokines influence insulin-stimulated glycogen metabolism in the liver. Interleukin 1beta (IL-1beta) and interleukin 6 (IL-6) markedly inhibited the increase of glycogen deposition stimulated by insulin in primary rat hepatocyte cultures; however, tumor necrosis factor alpha had no effect. Labeling experiments revealed that both cytokines counteracted insulin action by decreasing [14C]-glucose incorporation into glycogen and by increasing [14C]-glycogen degradation. Furthermore, it was discovered that IL-1beta and IL-6 inhibited glycogen synthase activity and, in contrast, accelerated glycogen phosphorylase activity. In experiments with kinase inhibitors, serine/threonine kinase inhibitor K252a blocked IL-1beta- and IL-6-induced inhibitions of glycogen deposition, as well as glycogen synthase activity, whereas another kinase inhibitor staurosporine blocked only IL-6-induced inhibition. Tyrosine kinase inhibitor herbimycin A blocked only IL-1beta-induced inhibition. These results indicate that IL-1beta and IL-6 regulate insulin-stimulated glycogen synthesis through different pathways involving protein phosphorylation in hepatocytes. They may mediate the change of hepatic glucose metabolism under pathological and even physiological conditions by modifying insulin action in vivo.

Palliative operation for cancer of the head of the pancreas: significance of pancreaticoduodenectomy and intraoperative radiation therapy for survival and quality of life

The benefits of a palliative operation and intraoperative radiation therapy (IORT) for survival and quality of life (QOL) of patients with cancer of the head of the pancreas are not clear. Survival and hospital-free survival (HFS), which are considered to be objective indicators of QOL, were studied in 13 patients who underwent palliative pancreaticoduodenectomy (PD) and 32 patients who underwent surgical bypass. Although there was no significant difference in the survival of patients who underwent PD or bypass (median survivals of 9 months and 7 months, respectively), HFS for 3 months or longer was achieved in 84.6% of the patients who underwent PD, which was significantly higher than that of the 53.1% in patients who underwent surgical bypass (p < 0.05). Among TNM stage III patients, a significant difference in survival was observed between surgical bypass associated with IORT and bypass alone (p < 0.05); the median survival time of the IORT group was 10 months, whereas that of the control group was 5 months. In addition, HFS of 3 months or longer was achieved in 83.3% of patients who underwent bypass with IORT but in only 25.0% of the patients who underwent surgery alone (p < 0.01). The addition of IORT to palliative PD neither prolonged survival nor improved HFS. These results show the beneficial effect of palliative PD on QOL, and the efficacy of IORT for survival and QOL was proved in cases with stage III pancreatic cancer who underwent surgical bypass. For patients subjected to palliative PD, however, IORT is not thought to be beneficial for either survival or QOL.

Preoperative assessment for laparoscopic cholecystectomy: feasibility of using spiral computed tomography

OBJECTIVE

The authors investigated the preoperative feasibility of using spiral computed tomography (SCT) after intravenous infusion cholangiography (IVC-SCT) for laparoscopic cholecystectomy.

SUMMARY BACKGROUND DATA

In laparoscopic cholecystectomy, the aberrant or unusual anatomy of the bile duct and severe inflammation or adhesions around the gallbladder sometimes require a conversion to open surgery.

METHODS

Laparoscopic cholecystectomies (LC's) were attempted on 440 patients, and preoperative IVC-SCT also was attempted in all of these patients. Using this spiral scanning technique, the bile ducts, cystic duct, and gallbladder were assessed for contour abnormalities, relative position, and filling defects. Forty-seven patients were diagnosed with having stones in their common bile duct or common hepatic duct.

RESULTS

Three-hundred eighty-seven patients out of the 440 patients (88.0%) who were subjected to IVC-SCT had the length and course of their cystic duct successfully determined. Anomalous unions of the cystic duct were seen in 59 (15.2%) of 387 patients with respect to the operative findings, and 48 of 440 patients (10.9%) had severe adhesions to Calot's triangle and the surrounding tissues. In these 48 patients, 45 patients (94%) had a nonvisualized cystic duct on IVC-SCT. The preoperative assessment of the feasibility (dense adhesions obscuring Calot's triangle) of using IVC-SCT demonstrated that the sensitivity, specificity, and accuracy were 93%, 98%, and 94%, respectively. Five patients had to be converted to open surgery, and the overall morbidity rates for patients undergoing laparoscopic cholecystectomy was 0.9% (4 of 440).

CONCLUSIONS

The most important factor in assessing the feasibility of using laparoscopic cholecystectomy is not the nonvisualized gallbladder, but the nonvisualized cystic duct on IVC-SCT. IVC-SCT may be of benefit to those patients scheduled to undergo laparoscopic cholecystectomy.

Stimulation of nitric oxide release from rat spinal cord by prostaglandin E2

1. We recently demonstrated that intrathecal administration of prostaglandin E2 (PGE2) and PGF2alpha induced allodynia through a pathway that includes the glutamate receptor and nitric oxide (NO)-generating systems from pharmacological studies. In order to clarify the involvement of NO in prostaglandin-induced allodynia, we measured NO released from rat spinal cord slices by a chemiluminescence method. 2. PGE2 stimulated NO release from both dorsal and ventral regions all along the spinal cord. PGE2 stimulated the release within 10 min and increased it in a time-dependent manner. 3. The PGE2-induced NO release was observed at 100 nM-10 microM. PGF2alpha stimulated the release at concentrations higher than 1 microM, but PGD2 (up to 10 microM) did not enhance it. 4. 17-Phenyl-omega-trinor PGE2 (EP1 > EP3) and sulprostone (EP1 < EP3) were as potent as PGE2, but PGE1 was less potent, in stimulating NO release. While M&B 28767 (EP3) did not enhance the release, butaprost (EP2) stimulated it at 1 microM. The PGE2-evoked release was blocked by ONO-NT-012, a bifunctional EP1 antagonist/EP3 agonist. 5. The PGE2-evoked release was Ca2+-dependent and blocked by MK-801 (NMDA receptor antagonist) and L-NAME (NO synthase inhibitor). The release was also inhibited by PGD2 and dibutyryl-cyclic AMP. 6. The present study demonstrated that PGE2 stimulates NO release in the rat spinal cord by activation of NMDA receptors through the EP1 receptor, and supports our previous findings that the NO-generating system is involved in the PGE2-induced allodynia.

Prolonged decreases in plasma nitrate levels at early postoperative phase after hepato-pancreato-biliary surgery

Nitric oxide (.NO) is known to influence circulatory, neural, immunologic, and metabolic alterations. To evaluate the clinical significance of .NO production under surgical stress, serial measurements of plasma nitrite plus nitrate levels were performed in 45 surgical patients. Group A included 19 patients who underwent major surgery with uneventful postoperative courses. Group B included 18 patients who underwent laparoscopic cholecystectomy. Group C included 8 patients whose surgery was complicated by intra-abdominal abscesses. Eight healthy volunteers served as controls. Plasma nitrate levels were determined with a redox chemiluminescence .NO analyzer and coincided with measurements made by high-performance liquid chromatography (r = 0.868, p < 0.0001, 58 samples). During laparotomy, arterial nitrate levels correlated well with peripheral, portal, and hepatic venous nitrate levels (r = 0.966, 0.938, and 0.949, respectively; p < 0.0001). A significant decrease in nitrate from preoperative levels in groups A (postoperative day (POD) 1 and 3; p < 0.0005) and B (POD 1, p < 0.0001) was observed; nitrate levels in group C did not decrease for 14 days after surgery. Plasma nitrate levels in groups A and B were significantly different (POD 1 through 6, p < 0.05) and at POD 3 were significantly lower in group A (p < 0.005). Plasma nitrate levels measured before and after fasting or food intake were not significantly different. These results suggest that surgical stress leads to a decrease in the end product of .NO in the whole body, and that the greater the surgical stress the longer the duration of decreased .NO production.

A simplified model of hypoxic injury in primary cultured rat hepatocytes

The Anaeropack system for cell culture, which was originally designed for the growth of anaerobic bacteria, was used to produce a hypoxic atmosphere for cultured hepatocytes. We measured changes in the oxygen and carbon dioxide concentrations and the atmospheric temperature in an airtight jar. We also measured changes in the pH of the medium during hypoxia to assess the accuracy of this system. Moreover, we used three durations (2, 3, and 4 h) of hypoxia and 8 h of reoxygenation in cultured rat hepatocytes, and then measured the lactate dehydrogenase (LDH), ketone body concentration (acetoacetate + beta-hydroxybutyrate), and the ketone body ratio (KBR: acetoacetate/beta-hydroxybutyrate) in the medium in order to assess the suitability of this system as a model for reperfusion following liver ischemia. The oxygen concentration dropped to 1% or less within 1 h. The concentration of carbon dioxide rose to about 5% at 30 min after the induction of the hypoxic conditions, and was maintained at this level for 5 h. No effect of the reaction heat produced by the oxygen absorbent in the jar was recognized. The extent of cell injury produced by changing the hypoxic parameters was satisfactorily reflected by the KBR, the ketone body concentration, and the LDH activity released into the medium. Because this model can duplicate the conditions of the hepatocytes during revascularization following ischemic liver, and the Anaeropack system for cell culture is easy to manipulate, it seems suitable for the experimental study of hypoxic injury and revascularization in vitro.

[Imaging studies of excretory urography and computed tomography scan for patients suffering from renal colic]

Renal colic mainly due to urolithiasis is one of the most common morbid conditions in urology and commonly seen in the urology emergency clinic. Imaging studies were performed to evaluate the upper urinary tract of 29 patients suffering from renal colic in the 2 years between November, 1994 and October, 1996. After intramuscular injection of the analgesic (pentazocine, 15 mg), all 29 patients were examined by excretory urography (IVP) at the time of the first visit. In some patients abdominal plain computed tomography (CT) scan was performed consecutively even when extravasation of the contrast medium was not seen. Spontaneous peripelvic extravasation was seen in 14 patients (11 males and 3 females) with urolithiasis; 7 of them were diagnosed by IVP, 5 by IVP plus CT scan and 2 with CT scan only. IVP imaging study followed by plain abdominal CT scan is useful even when the contrast medium is not extravasated on IVP in patients suffering from renal colic.

Do intronic mutations affecting splicing of WT1 exon 9 cause Frasier syndrome?

The WT1 gene, one of the genes responsible for Wilms tumour, is thought to play a crucial role in the development of the kidneys and gonads. This gene encodes four protein isoforms resulting from two alternative splicing sites, one of which involves inclusion or exclusion of lysine, threonine, and serine (KTS) between the third and fourth zinc finger domains. WT1 is virtually always mutationally inactivated in patients with Denys-Drash syndrome. We analysed WT1 in eight patients who had been diagnosed as having this syndrome, and identified five previously unknown mutations affecting splicing donor sites of intron 9. These mutations affect alternative splicing. The isoforms retaining KTS are not produced. The clinical features of the patients with these intronic mutations were consistent with those of Frasier syndrome, characterised by a more slowly progressive nephropathy than Denys-Drash syndrome, associated streak gonads, and no Wilms tumour development. Our results indicate that WT1 isoforms, including/excluding KTS, have different functions in tumorigenesis and organogenesis of the kidneys and gonads.

Immunohistochemical studies of proliferating cell nuclear antigen and cathepsin D in transitional cell carcinoma of the urinary bladder

Immunohistochemical staining for proliferating cell nuclear antigen (PCNA) and cathepsin D was performed on 60 transitional cell carcinoma (TCC) specimens from 60 patients with bladder cancer. The percentage of PCNA-positive cells (PCNA-labelling index) was determined by counting 500 or 1,000 cells, and cathepsin D expression was graded according to the extent of immunoreactivity to anti-cathepsin D antibody. The PCNA-labelling index was significantly higher in high-grade and high-stage tumors compared to that in low-grade and low-stage tumors. Cathepsin D was highly positive in grade-1 tumors. In contrast, 82% of grade-3 tumors and 76% of advanced tumors showed negative or low reactivity to anti-cathepsin D. Groups of high PCNA-labelling index and negative cathepsin D had significantly poorer prognoses compared to those of the low PCNA group and cathepsin D highly positive group, respectively, in univariate analyses. However, neither of these two factors were independent prognostic factors in multivariate analyses. These results suggest that the PCNA-labelling index and cathepsin D expression may indicate the malignant potential of TCC and may be able to provide additional information for predicting survival when stratifying for grade of bladder cancer.

Spiral computed tomography scanning after intravenous infusion cholangiography for biliary duct anomalies

BACKGROUND

Iatrogenic injury of the bile duct during cholecystectomy represents a failure of surgical technique, especially for laparoscopic surgery. Knowledge of the patient's individual ductal anatomy and anomalies preoperatively would be helpful in avoiding such injuries. Therefore, we investigated the anatomy of the biliary duct and any anomalies using spiral computed tomography (SCT) scanning following intravenous infusion cholangiography (IVC-SCT).

MATERIALS

Laparoscopic cholecystectomies (LC) were attempted on 437 patients at the Kansai Medical University. Preoperative IVC-SCT and laparoscopic cholangiography were attempted in all of the patients.

RESULTS

An overall anomalous union of the cystic duct was seen in 71 (16.2%) out of the 437 patients subjected to IVC-SCT. The following anomalies were observed: right hepatic duct entry in 7 cases (1.6%), parallel low entry in 17 cases (3.9%), posterior spiral entry in 35 cases (8.0%), anterior spiral entry in 7 cases (1.6%), and accessory duct entry in 5 cases (1.1%). The success rate for the LC was 99.5% (435/437). Three patients were switched to open surgery owing to advanced gallbladder cancer and severe adhesions. The success rate for the laparoscopic cholangiography was 97.2% (423 of 435). Intraoperative right hepatic duct injury occurred in only 1 patient with a bile duct anomaly, and it was repaired with laparoscopic T-tube drainage.

CONCLUSIONS

The preoperative examination of the biliary tract by IVC-SCT was technically simple, less invasive, and may helpful in avoiding damage to the bile duct, especially in patients with biliary duct anomalies.

Desensitization of the GABAA receptor shifts the dynamic range of retinal horizontal cells due to light and dark adaptation

The effects of the GABAergic pathway on the dynamic range of the light response of cone-driven horizontal cells (HCs) in the carp retina were investigated using conventional intracellular recordings and computer simulations. The amplitude of the HC responses to repetitive test flashes was altered by background illumination in control Ringer's solution, but was not changed following the application of picrotoxin or bicuculline, which suggests that GABAA receptors mediate the subsequent change in light response. This phenomenon was simulated by introducing the desensitization mechanism of the GABAA receptor into a cone-HC network model. These results suggest that desensitization of the GABAA receptor shifts the dynamic range of the HCs due to light and dark adaptation.