Mutant oocytic low density lipoprotein receptor gene family member causes atherosclerosis and female sterility

The so-called very low density lipoprotein receptors (VLDLRs) are related to the LDLR gene family. So far, naturally occurring mutations have only been described for the prototype LDLR; in humans, they cause familial hypercholesterolemia. Here we describe a naturally occurring mutation in a VLDLR that causes a dramatic abnormal phenotype. Hens of the mutant restricted-ovulator chicken strain carry a single mutation, lack functional oocyte receptors, are sterile, and display severe hyperlipidemia with associated premature atherosclerosis. The mutation converts a cysteine residue into a serine, resulting in an unpaired cysteine and greatly reduced expression of the mutant avian VLDLR on the oocyte surface. Extraoocytic cells in the mutant produce higher than normal amounts of a differentially spliced form of the receptor that is characteristic for somatic cells but absent from germ cells.

Possible role of protein kinase C in the regulation of intracellular stability of focal adhesion kinase in mouse 3T3 cells

Effects of various types of protein kinase inhibitor on the adhesion and spreading of BALB/c mouse 3T3 cells and on the phosphorylation and stability of focal adhesion kinase (FAK) in the cells were studied. Inhibitors of protein tyrosine kinases, methyl 2,5-dihydroxycinnamate and herbimycin A, inhibited tyrosine-phosphorylation of FAK and the adhesion of 3T3 cells to fibronectin. Among inhibitors of serine/threonine kinases tested, calphostin C, a specific inhibitor of protein kinase C, inhibited cell spreading rather than cell adhesion, and it induced the decrease of intracellular FAK within 30 min. Inhibitors of tyrosine kinase, A kinase, G kinase, and myosin light chain kinase did not induce such a rapid and specific decrease of FAK. When calphostin C (20 microM) was added to sub-confluent monolayer cultures, serine-phosphorylation of FAK was inhibited by 67% within 2 h, and decrease in the amount of FAK and rounding up of the cells began after 4 h. Label-chase experiments indicated that about 60% of 35S-labeled FAK degraded within 1-2 h after addition of calphostin C to monolayer cultures. These results indicated that serine-phosphorylation of FAK induced by protein kinase C was important in the regulation of metabolic stability of FAK.

Ultrasonographic evaluation of the carpal tunnel syndrome in hemodialysis patients

The carpal tunnel syndrome (CTS) is the most frequent clinical symptom of dialysis-related amyloidosis. We examined CTS by ultrasound imaging and correlation between CTS and bone amyloidosis was sought. One hundred and forty-two wrists of 71 hemodialysis (HD) patients and 28 of 14 normal volunteers (group 1) were studied. Patients on HD were divided into 4 groups based on HD duration: Group 2, less than 5 years; group 3, 5-10 years; group 4, 10-15 years; and group 5, more than 15 years. The frequency of CTS increased gradually with HD duration: 0% in group 2, 35.3% in group 3, 36.4% in group 4 and 74.1% in group 5. The thickness of the palmar radiocarpal ligament (PRL), corresponding to the posterior wall of the carpal tunnel was significantly greater in groups 4 (p < 0.05), and 5 (p < 0.05) than in group 1 (2.25 +/- 1.30 and 3.11 +/- 1.02 in group 4 and 5 vs 1.15 +/- 0.34 mm in group 1); and the width of the carpal tunnel (CT) was significantly larger in group 5 than in group 1 (6.92 +/- 1.78 in group 5 vs 5.53 +/- 1.48 mm in group 1, p < 0.05). Wrists operated on for CTS had significantly increased PRL and CT compared to the control group and patients without CTS. Patients with CTS had wider PRL than the control and HD patients without CTS. Cystic radiolucent lesions (CRL) of carpal bones characteristic of bone amyloidosis were noted in 15 of 71 HD patients. The thickness of PRL and width of CT in HD patients with CRL exceeded those in patients without CRL. These data indicated that ultrasonographic findings of wrists were closely correlated with the degree of CTS and CRL. The usefulness of ultrasonographic evaluation of PRL thickness and CT width in the evaluation of dialysis-related amyloidosis should be evaluated.

[Cardiovascular alpha-, beta 1- and beta 2-adrenoceptor functions in neurogenic orthostatic hypotension]

It has been believed that patients with neurogenic orthostatic hypotension (NOH) usually develop denervation supersensitivity of cardiovascular alpha-, beta 1- and beta 2-adrenoceptors, because the majority studies have shown augmented cardiovascular responses to intravenously given noradrenaline (NA) or isoprenaline (IP) in these patients. This view, however, leaves room for discussion. First, drugs were administered by means of drip infusion method in most of the previous studies. Since this method necessarily provokes baroreflex, which is buffering fluctuations in blood pressure and heart rate, the results may reflect diminished baroreflex rather than denervation supersensitivity. Second, adrenoceptor functions are modulated by multiple factors, such as ageing, thyroid hormone and chronic inflammation. It is, thus, inappropriate to explain the whole picture of functional change in adrenoceptors by the denervation mechanism only. In order to look over the cardiovascular adrenoceptor functions in NOH, we performed bolus infusion tests of NA and IP on the patients. The subjects comprised 7 cases of NOH with pre-ganglionic sympathetic deficit (NOH-I), 6 cases with post-ganglionic deficit (NOH-II) and 15 healthy controls. NOH-I group included 6 patients with multiple system atrophy and one with Parkinson disease, while NOH-II group consisted of 3 patients with idiopathic orthostatic hypotension (pure autonomic failure) and 3 with diabetic autonomic neuropathy. Both NA and IP infusion tests were carried out under the continuous measurement of blood pressure and heart rate. In NA test, different bolus doses (0.01, 0.02, 0.05 and 0.1 microgram/kg) of NA were intravenously administered, and a degree of subsequent rise in mean blood pressure was used as an index for alpha-adrenoceptor function. IP test was performed in the same manner, and an increase in heart rate and a fall in mean blood pressure in response to the drug (0.001, 0.002 and 0.005 microgram/kg) were measured as indices for beta 1- and beta 2-functions, respectively. A rise in blood pressure following the administration of any dose of NA did not statistically differ among three groups. An increase in heart rate in IP test was generally lower in both NOH groups, and a significant difference was obtained between NOH-I and control when a given dose was 0.005 microgram/kg) (p < 0.02). A fall in blood pressure in IP test was significantly greater in NOH-I compared to control when doses were 0.002 and 0.005 microgram/kg (p < 0.02 and 0.01, respectively). It was also greater in NOH-II than in control when a dose was 0.002 microgram/kg (p < 0.01). In disagreement with most of the previous studies, the present results suggest that alpha-adrenoceptor function is hardly altered, beta 1-function is suppressed, and beta 2-function is augmented in NOH.

Transient hepatic fibrin-ring granulomas in a patient with acute hepatitis A

A case of acute hepatitis A associated with fibrin-ring granulomas in the liver is presented. Because a relationship between acute hepatitis A infection and granuloma formation had not previously been established, liver specimens were examined from both the hepatitic and recovery phases. Numerous fibrin-ring granulomas were observed in the parenchyma during the hepatitic phase. The cellular components of the granulomas were largely macrophages and CD4-positive T-cells. Granulomas had disappeared completely by the recovery phase. These results suggest that fibrin-ring granulomas were caused by hepatitis A virus infection. This virus may activate macrophages and CD4-positive T-cells through an as-yet undetermined mechanism.

[Study on sepsis in the elderly at Nagoyashi-Koseiin Geriatric Hospital]

A study based on clinical analysis was conducted regarding the 125 episodes in the elderly 112 patients of sepsis who were 70 (average 83.8 +/- 7.5) years old at Nagoyashi-Koseiin Geriatric Hospital from 1985 through 1994. 1) The backgrounds of the elderly patients with sepsis were as follows: bedridden (72.8%), urinary catheter in place (61.2%), central venous catheter in place (48.8%), and prior antibiotic use (40.8%). All patients had an underlying disease. 2) Organisms isolated were Escherichia coli (21.2%), Staphylococcus aureus (18.4%); Coagulase-negative staphylococci (CNS) (17.4%) and Candida albicans (6.1%). Chronologically, the quantity of gram-positive cocci increased while that of gram-negative bacilli decreased. As the age of the patients increased, the frequency of infections by Methicillin-resistant Staphylococcus aureus (MRSA), E. coli, and/or multiple bacteria increased, while that of infections by CNS and gram-negative bacilli excluding E. coli decreased. 3) The primary infected sites were the urinary tract system (24.8%), central venous catheter (21.6%) and unknown (31.2%). 4) The primary clinical observations were fever exceeding 38.0 degrees C (88.0%), tachycardia (60.8%), shivering (44.0%) and cyanosis (32.8%). 5) Complications were multiple organ failure (33.6%), septic shock (26.4%) and disseminated intravascular coagulation (22.4%). 6) The prognosis indicated that 65.6% were survivors, and 34.4% were nonsurvivors. At the onset of sepsis, weight, blood pressure, serum albumin, and total cholesterol in the nonsurvivors were significantly lower than those in the survivors, whereas heart rate, GOT, LDH, and BUN in the nonsurvivors were significantly higher than those in the survivors.

Epidural hematoma associated with cephalohematoma in a neonate--case report

A female neonate presented with cephalohematoma over the temporoparietal region on the right side. Computed tomography (CT) revealed the presence of an underlying epidural hematoma (EDH) and associated skull fracture with communication between the hematomas. Aspiration of the cephalohematoma was followed by reduction in the size of the EDH. CT revealed cure without the need for an operative procedure. Aspiration is indicated for neonatal EDH with mild symptoms and liquefied cephalohematoma.

Genetic association of the very low density lipoprotein (VLDL) receptor gene with sporadic Alzheimer's disease

A specific isoform of apolipoprotein E has been associated with the accelerated rate of disease expression of sporadic Alzheimer's disease (AD) and late-onset familial AD (FAD). An earlier age at onset has also been demonstrated in familial AD patients with mutations in the amyloid precursor protein (APP) gene (APP717 and APP670/671)13 carrying the APOE epsilon-4 allele compared to those who do not, but not in familial AD patients with APP692 or 693 mutations, or in chromosome 14-linked familial AD patients. Hypothesizing that receptors for apoE-containing lipoproteins act as a potential risk factor for AD, we performed an association study using a polymorphic triplet (CGG) repeat in the gene for the VLDL receptor (VLDL-R), a receptor for apoE-containing lipoproteins. The frequency of the 5-repeat allele was significantly higher in all of the Japanese sporadic AD patients (P < 0.02) than in the Japanese controls. Moreover, the odds ratio was significantly increased in the AD patients homozygous for the 5-repeat allele (OR = 2.1, 95% CI = [1.1-4.2]). Multiple logistic regression analysis reveals that the relative risk conferred by the presence of two copies of the 5-repeat allele and at least one copy of the APOE epsilon-4 allele is 8.7 (95% CI = [2.9-25.8]). Our results suggest that the VLDL-R gene is a susceptibility gene for AD.

Thalamo-olivary degeneration in a patient with laryngopharyngeal dystonia

A 67 year old woman with a two year history of laryngopharyngeal dystonia, spasmodic dysphonia, and parkinsonism succumbed to Wernicke's encephalopathy and died six months later. Necropsy showed, besides Wernicke's encephalopathy, degenerative changes in selected thalamic nuclei (dorsomedial, pulvinar, and the medial geniculate bodies) and the inferior olives and numerous cerebellar torpedoes. The substantia nigra and basal ganglia were spared. Immunostaining for prion protein was negative. This patient indicated a new type of presentation of so-called pure thalamic degeneration, or more precisely thalamo-olivary degeneration.

Functional mapping of the sensorimotor cortex: combined use of magnetoencephalography, functional MRI, and motor evoked potentials

Combined use of magnetoencephalography (MEG), functional magnetic resonance imaging (f-MRI), and motor evoked potentials (MEPs) was carried out on one patient in an attempt to localise precisely a structural lesion to the central sulcus. A small cyst in the right frontoparietal region was thought to be the cause of generalised seizures in an otherwise asymptomatic woman. First the primary sensory cortex was identified with magnetic source imaging (MSI) of somatosensory evoked magnetic fields using MEG and MRI. Second, the motor area of the hand was identified using f-MRI during hand-squeezing. Then transcranial magnetic stimulation localised the hand motor area on the scalp, which was mapped onto the MRI. There was a good agreement between MSI, f-MRI and MEP as to the location of the sensorimotor cortex and its relationship to the lesion. Multimodality mapping techniques may thus prove useful in the precise localisation of cortical lesions, and in the preoperative determination of the best treatment for peri-rolandic lesions.

Dermatofibroma with myxoid changes in a patient with psoriasis

A 38-year-old female with psoriatic arthritis developed a dermatofibroma (DF) on her upper arm. Its position was not exactly on a psoriatic plaque; however, psoriatic lesions were present diffusely around the DF lesion. Histological examination revealed the typical features of DF with myxoid changes in the portion between the tumor nest and the overlying epidermis. The mast cell number was significantly increased over that of solitary DFs without myxomatous lesions. It was suggested that mast cells may play a role in induction of the myxoid changes in the DF lesion in this case.

Expression and localization of inducible nitric oxide synthase in anti-Thy-1 glomerulonephritis

To elucidate a possible involvement of nitric oxide in the development of a mesangial proliferative glomerulonephritis induced by anti-Thy-1 antibody administration, glomerular expression of three isoforms of NO synthase (NOS), inducible NOS (iNOS), brain NOS, and endothelial NOS, was examined at both mRNA and protein levels by ribonuclease protection assay and immunofluorescence microscopy. Light microscopy showed an accumulation of polymorphonuclear leukocytes at 1 hour, lysis of mesangial cells at 1 day, a mesangial proliferative lesion at 4 to 10 days, and minimal residual glomerular lesions by 28 days. Ribonuclease protection assay showed that the glomerular expression of iNOS mRNA peaked at 1 hour and decreased thereafter. No substantial expression of iNOS mRNA was observed in normal glomeruli or in the nephritic glomeruli obtained at different time points (1, 4, 10, or 28 days). By immunofluorescence microscopy with a specific monoclonal antibody, an intense reaction for iNOS was demonstrated in a few cells in the glomeruli at 1 hour. Most of the iNOS-positive cells were identified as polymorphonuclear leukocytes. iNOS-positive cells were found less frequently in the glomeruli on days 1 and 4. Endothelial NOS mRNA was constitutively expressed in normal glomeruli and increased biphasically with two peaks at 1 hour and at 4 days or later; however, the peak expression was much less than that of iNOS mRNA at 1 hour. Expression of brain NOS mRNA was not detectable in either normal or nephritic glomeruli. These results show that iNOS is predominantly expressed in polymorphonuclear leukocytes accumulating at 1 hour in the glomeruli of anti-Thy-1 glomerulonephritis and suggest an involvement of NO in the initiation of the disease.

An unclassified cerebral small cell tumor in a patient with human T-cell lymphotropic virus type 1-induced primary extranodal lymphoma

We describe an autopsy case of a thalamic tumor in a patient with human T-cell lymphotropic virus type 1 (HTLV-1)-induced extranodal lymphoma of the skull. Neither brain tumors associated with adult T-cell leukemia nor HTLV-1-induced extranodal lymphoma of bone have previously been reported. The tumor, which resembled an oligodendroglioma or dysembryoplastic neuroepithelial tumor, was composed of medium-sized cells with dark, round-to-polygonal nuclei and a mucinous matrix that formed pericellular lakes. Tumor cells were immunoreactive with S-100 protein and neuron-specific enolase but not with glial fibrillary acid protein, synaptophysin, or vimentin. Tumor cells had prominent rough endoplasmic reticulum and free ribosomes with short processes, compatible with an oligodendroglial or small neuronal nature. Many atypical lymphocytes had infiltrated the leptomeningeal space, subependymal zone along the ventricular walls, fornices, corpus callosum, and right frontal lobe. Multinucleated or bizarre astrocytes and macrophages were found exclusively in the right frontal white matter. The coexistence of this unclassified peculiar brain tumor with bizarre astrocytosis suggests a cytopathic effect of HTLV-1 on human glioneuronal cells.

Endothelin 1 stimulates Na+,K(+)-ATPase and Na(+)-K(+)-Cl- cotransport through ETA receptors and protein kinase C-dependent pathway in cerebral capillary endothelium

The effect of endothelins (ET-1 and ET-3) on 86Rb+ uptake as a measure of K+ uptake was investigated in cultured rat brain capillary endothelium. ET-1 or ET-3 dose-dependently enhanced K+ uptake (EC50 = 0.60 +/- 0.15 and 21.5 +/- 4.1 nM, respectively), which was inhibited by the selective ETA receptor antagonist BQ 123 (cyclo-D-Trp-D-Asp-Pro-D-Val-Leu). Neither the selective ETB agonists IRL 1620 [N-succinyl-(Glu9,-Ala11,15)-ET-1] and sarafotoxin S6c, nor the ETB receptor antagonist IRL 1038 [(Cys11,Cys15)-ET-1] had any effect on K+ uptake. Ouabain (inhibitor of Na+,K(+)-ATPase) and bumetanide (inhibitor of Na(+)-K(+)-Cl- cotransport) reduced (up to 40% and up to 70%, respectively) the ET-1-stimulated K+ uptake. Complete inhibition was seen with both agents. Phorbol 12-myristate 13-acetate (PMA), activator of protein kinase C (PKC), stimulated Na+,K(+)-ATPase and Na(+)-K(+)-Cl- cotransport. ET-1- but not PMA-stimulated K+ uptake was inhibited by 5-(N-ethyl-N-isopropyl)amiloride (inhibitor of Na+/H+ exchange system), suggesting a linkage of Na+/H+ exchange with ET-1-stimulated Na+,K(+)-ATPase and Na(+)-K(+)-Cl- cotransport activity that is not mediated by PKC.

Comparison of magnetoencephalography, functional MRI, and motor evoked potentials in the localization of the sensory-motor cortex

To clarify the topographical relationship between peri-Rolandic lesions and the central sulcus, we carried out presurgical functional mapping by using magnetoencephalography (MEG), functional magnetic resonance imaging (f-MRI), and motor evoked potentials (MEPs) on 5 patients. The sensory cortex was identified by somatosensory evoked magnetic fields using MEG (magnetic source imaging (MSI)). The motor area of the hand region was identified using f-MRI, during a hand squeezing task. In addition, transcranial magnetic stimulation localized the hand motor area on the scalp, which was mapped onto the MRI. In all cases, the sensory cortex was easily identified by MSI and the results of MSI correlated well with the findings obtained by the intraoperative recording of somatosensory evoked potentials. In contrast, the motor cortex could not be localized by f-MRI due to either the activated signal of the large cortical vein or the lack of any functional activation in the area of peri-lesional edema. MEPs were also unable to localize the entire motor strip. Therefore, at present, MSI is considered to be the most reliable method to localize peri-Rolandic lesions [corrected].

Analysis of cytochrome P-450 side-chain cleavage gene promoter activation during trophoblast cell differentiation

Trophoblast giant cell differentiation is accompanied by transcriptional activation of the cytochrome P-450 side-chain cleavage (P450scc) gene. The Rcho-1 trophoblast cell line has the capacity to differentiate along the trophoblast giant cell lineage and has been used to study trophoblast-specific P450scc gene expression. In this report, P450scc gene promoter activities in trophoblast-specific P450scc gene expression. In this report, P450scc gene promoter activities in trophoblast cells have been mapped and the involvement of known modulators of steroid hydroxylase gene expression, the cyclic AMP/protein kinase A pathway and steroidogenic factor-1 (SF-1), evaluated. Comparisons were made with Y-1 adrenal and R2C Leydig cells. The cumulative results from transient and stable transfection experiments implicate the region between -428 and -511 bp of 5'-flanking DNA in the developmental activation of the P450scc promoter during trophoblast giant cell differentiation. Differences in basal activities of the P450scc promoter constructs were also observed in Y-1 adrenal and R2C Leydig cells; however, the magnitude of the differences was modest. Activators of the protein kinase A pathway stimulated P450scc promoter activity in Y-1 cells, whereas similar treatment of Rcho-1 trophoblast cells did not stimulate but actually inhibited P450scc promoter activity. The inhibitory activity was localized between -639 and -894 bp of the P450scc promoter. SF-1 mRNA and protein were detected in adrenal and gonadal cells but not in rat placenta or Rcho-1 trophoblast cells by Northern and Western blotting, respectively. Thus, P450scc gene activation during trophoblast cell differentiation involves an 83-bp region of its 5'-flanking DNA between -428 and -511 but does not appear to involve cyclic AMP-activated pathways or SF-1. In conclusion, the mechanism of P450scc gene activation during trophoblast cell differentiation appears different from the regulation of P450scc gene activation in other steroidogenic tissues.

Enkephalin-immunoreactive fastigial neurons in the rat cerebellum project to upper cervical cord segments

By using enkephalin immunohistochemistry combined with retrograde fluorescent labelling, a great majority of neurons in the rat cerebellum sending their axons to the spinal cord were shown to contain enkephalin immunoreactivity. These neurons were numerous and clustered in the fastigial nucleus but far less abundant in other cerebellar nuclei. Enkephalin-immunoreactive fibers present in the ventral horn and the central cervical nucleus of upper cervical cord segments almost completely disappeared contralaterally following kainic acid-induced cell loss in the fastigial nucleus. The results indicate that fastigial and some other cerebellar nucleus neurons provide enkephalin-containing projections toward these spinal sites.

Immunohistochemical evidence for enkephalin and neuropeptide Y in rat inferior colliculus neurons that provide ascending or commissural fibers

Enkephalin- and neuropeptide Y-expressing neurons which offer commissural axons or axons toward auditory thalamus were identified in the rat inferior colliculus. These neurons exhibited a differential distribution pattern. The results provide evidence for regional specificity and chemical heterogeneity of neurons in the auditory midbrain.

Experimental tracheal replacement using the esophagus and an expandable metallic stent

An experimental study was conducted to investigate whether a segment of autogenous esophagus with its lumen supported by an expandable metallic stent (EMS) could be successfully used as a tracheal substitute. Seven rings of the cervical trachea were circumferentially removed and reconstructed by interposing a pedicled segment of the esophagus with an EMS in six mongrel dogs. The interposed esophagus was observed endoscopically at various stages after the operation. By 1 month, the EMS was found to be buried under the esophageal mucosa, and the lumen was patent. The dogs died 5, 17, 61, 92, 210, and 478 days after the operation, but the cause of death could not be determined by postmortem examination and no respiratory tract complications were detected. The results of this study indicated that a segment of the esophagus with its lumen supported by an EMS could work as a reliable tracheal substitute, though its practical use is not clinically feasible. Nevertheless, we conclude that some autogenous material other than the esophagus with its lumen supported by an EMS could provide a feasible method for tracheal replacement.

Limitations of podocyte adaptation for glomerular injury in puromycin aminonucleoside nephrosis

Glomerular synechiae that occurred in nephrotic rats with a single intraperitoneal injection of puromycin aminonucleoside were analyzed by immunohistochemistry, radiolabeled thymidine ([3H]-thymidine) autoradiography, as well as light, electron and immunoelectron microscopy. To discriminate podocytes from parietal epithelial cells (PEC) and monocytes, monoclonal antibodies (mAb) against podocalyxin and ED1 were used. The cell kinetics of glomerular epithelial cells were autoradiographically assessed with isotope labeling procedures before and during nephrosis (co-labeled), and a mAb against proliferating cell nuclear antigen (PCNA). All the cell types except the podocyte of normal kidneys were labelled with [3H]-thymidine at different rates. Detachment of degenerated podocytes from the outside of the glomerular basement membrane (GBM) is the first step of synechia, and detached sites are confronted by PEC that were hypertrophied and frequently radiolabeled. Evidence that podocytes in glomeruli of nephrotic rats can proliferate was shown by the presence of mitoses, [3H]-thymidine uptake in the co-labeled experiment, and by PCNA staining, but re-epithelialization over bare segments of the GBM with proliferated podocytes is doubtful. It was concluded that glomerular synechia resulted from the limits of podocyte adaptation to glomerular injuries.

Cytokine profile of tumor cells in mycosis fungoides: successful treatment with intra-lesional interferon-gamma combined with chemotherapy

Two cases of mycosis fungoides (MF) in the tumor stage were treated with intra-lesional interferon-gamma (IFN-gamma) therapy. After systemic chemotherapy, intra-lesional recombinant interferon-gamma was applied to the residual tumors. Intra-lesional IFN-gamma was sufficiently effective in the treatment of MF tumors, especially small-sized ones. Reverse transcriptase polymerase chain reaction (RT-PCR) analysis of messenger RNA expression of cytokines commonly detected interleukin-6 (IL-6) and IFN-gamma in the tumor cells before intra-lesional IFN-gamma. However, in our study, tumor cells in these cases did not exhibit the definitive cytokine patterns of Th1 or Th2.

Pruning of rat cortical taste neurons by an artificial neural network model

1. Taste qualities are believed to be coded in the activity of ensembles of taste neurons. However, it is not clear whether all neurons are equally responsible for coding. To clarify the point, the relative contribution of each taste neuron to coding needs to be assessed. 2. We constructed simple three-layer neural networks with input units representing cortical taste neurons of the rat. The networks were trained by the back-propagation learning algorithm to classify the neural response patterns to the basic taste stimuli (sucrose, HCl, quinine hydrochloride, and NaCl). The networks had four output units representing the basic taste qualities, the values of which provide a measure for similarity of test stimuli (salts, tartaric acid, and umami substances) to the basic taste stimuli. 3. Trained networks discriminated the response patterns to the test stimuli in a plausible manner in light of previous physiological and psychological experiments. Profiles of output values of the networks paralleled those of across-neuron correlations with respect to the highest or second-highest values in the profiles. 4. We evaluated relative contributions of input units to the taste discrimination of the network by examining their significance Sj, which is defined as the sum of the absolute values of the connection weights from the jth input unit to the hidden layer. When the input units with weaker connection weights (e.g., 15 of 39 input units) were "pruned" from the trained network, the ability of the network to discriminate the basic taste qualities as well as other test stimuli was not greatly affected. On the other hand, the taste discrimination of the network progressively deteriorated much more rapidly with pruning of input units with stronger connection weights. 5. These results suggest that cortical taste neurons differentially contribute to the coding of taste qualities. The pruning technique may enable the evaluation of a given taste neuron in terms of its relative contribution to the coding, with Sj providing a quantitative measure for such evaluation.