Biomedical subjects

M Kim

Publications and source records attributed to M Kim.

At least 325 records · Page 18Linked to original sources

PubMed1994

Efficacy of primary chemoprophylaxis against Pneumocystis carinii pneumonia during the first year of life in infants infected with human immunodeficiency virus type 1.

To evaluate the efficacy of primary chemoprophylaxis in preventing Pneumocystis carinii pneumonia (PCP) in infants with perinatal human immunodeficiency virus-1 infection during the first year of life, we conducted a retrospective chart review of infants with human immunodeficiency virus-1 infection born at New York University Medical Center-Bellevue Hospital Center, in New York. Between March 1989 and March 1993, 24 infants received primary chemoprophylaxis with trimethoprim-sulfamethoxazole in the first year of life and 24 infants did not receive primary prophylaxis. The CD4+ T-lymphocyte counts in the two groups did not differ during the first year of life. The median age at the time of initiation of prophylaxis was 3 months, and the average duration of prophylaxis was 5.5 months. Among the infants who had not received prophylaxis, five cases of PCP were diagnosed at a median age of 5 months; in contrast, no cases of PCP were observed in the infants receiving prophylaxis (log-rank test, p = 0.017). The probability of surviving after 1 year of age was 92% for the children who received prophylaxis and 74% for those who did not (log-rank test, p = 0.035). These data indicate that chemoprophylaxis is highly effective in preventing primary PCP and improving survival time in infants with human immunodeficiency virus-1 infection.

AIDS-Related Opportunistic Infections↗

PubMed1994

Increased urinary saturation and kidney calcium content in genetic hypercalciuric rats.

We have established a colony of genetic hypercalciuric (IH) rats as a model of idiopathic hypercalciuria in humans. To test the hypothesis that hypercalciuria can cause crystallization in kidneys through increased supersaturation, in the absence of confounding effects of diet and whatever complex inhibitor disorders underlay stone disease, we fed males and females of the 21st generation of IH rats 13 g per day of a low calcium (LCD, 0.02% Ca), followed by a normal calcium (NCD, 0.6% Ca) and then a high calcium (HCD, 1.2% Ca) diet, each for seven days. During the last 24 hours of each period complete urine collections were obtained and analyzed for all substances known to affect urinary calcium oxalate (CaOx) and brushite (CaHPO4) supersaturation. Relative supersaturation with respect to the solid phases of CaOx and CaHPO4 were then calculated. Compared to same gender controls (Ctl) urine calcium excretion was higher in the female IH rats on all diets and in the male IH rats on NCD and HCD. The female and male IH rats on NCD and HCD were supersaturated with respect to CaOx; however, the male and female Ctl were supersaturated with respect CaOx only on HCD. The female IH rats on NCD and HCD and the male IH rats on NCD were supersaturated with respect to CaHPO4; however, neither the male nor female Ctl rats were supersaturated with respect to CaHPO4 on any diet. On NCD and HCD urine supersaturation with respect to CaHPO4 by females exceeded that of males.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Streptococcus pneumoniae in human immunodeficiency virus type 1-infected children.

The purpose of this study was to characterize systemic Streptococcus pneumoniae disease in human immunodeficiency virus type 1 (HIV-1)-infected children. All cases of bacteremia and meningitis caused by S. pneumoniae among children less than 18 years old were collected by review of the Microbiology Laboratory records at the Bellevue Hospital Center during the period August 1, 1978, through July 31, 1993. There were 31 bouts of systemic S. pneumoniae disease in 19 of 235 HIV-1-infected children cared for by the Pediatric Infectious Disease staff and 116 bouts in 113 children not known to be HIV-1-infected. Four of the 19 HIV-1-infected children had multiple episodes of S. pneumoniae bacteremia as compared with 3 of 113 in the general population (P = 0.008). The frequency of serotypes and distribution of infections by season of the year did not differ between the 2 groups. The median ages at the time of the S. pneumoniae infection were 1.8 and 1.1 years for the HIV-1-infected children and the general population of children, respectively, when those children with multiple episodes were included for their initial episode only (P = 0.06). In the HIV-1-infected patients, 10 episodes were associated with pneumonia, 5 with pneumonia and otitis media, 5 with otitis media only, 1 with pneumonia and meningitis, 1 with meningitis only and 1 with periorbital cellulitis; 5 had no apparent focus of infection. One episode of pneumonia was complicated by lung abscess and there were 2 deaths. Most HIV-1-infected patients recovered without significant sequelae, and the clinical course of their systemic infections did not appear to be markedly different than that of healthy children.

AIDS-Related Opportunistic Infections↗

PubMed1994

Isolation of Helicobacter strains from wild bird and swine feces.

We report the first isolations of Helicobacter strains from wild birds and swine. Genus-specific oligonucleotide probes identified nine Cape Cod isolates from gull, tern, house sparrow, and pig feces as Helicobacter spp. and not Campylobacter spp. Antibiotic sensitivity and urease tests distinguished three phenotypes. Strains examined rapidly lost culturability under simulated natural conditions.

Animals↗

PubMed1994

Age-related changes in the pyridinoline content of guinea pigs cartilage and Achilles tendon collagen.

Age-related changes of pyridinoline, a mature cross-link of collagen fibers, in tissues of guinea pigs which cannot synthesize L-ascorbic acid (AsA) were investigated. Male guinea pigs, 2 weeks old, were fed a commercial diet until they were 40 weeks old. Based on the data of body weight gain, it is assumed that guinea pigs require 10 weeks to reach maturity. The content of AsA in serum, adrenals, and liver of the animals increased with growth, then decreased after 8-10 weeks. The pyridinoline content in cartilage and tendon collagen was very low in 2-week-old animals, whereas it increased markedly with growth. After 10 weeks, the pyridinoline tended to decrease in cartilage collagen; however, it was not changed in tendon collagen. The age-related changes of pyridinoline content in guinea pigs cartilage were similar to those of humans--increasing with growth and decreasing after adolescence.

Achilles Tendon↗

PubMed1994

Optimization of methods to achieve mRNA-mediated transfection of tumor cells in vitro and in vivo employing cationic liposome vectors.

Direct in vivo transfection of tumor nodules in situ via liposome-DNA complexes has been employed as a strategy to accomplish antitumor immunization. To circumvent the potential safety hazards associated with systemic localization of delivered DNA, the utility of mRNA transcript-mediated gene delivery was explored. Capped, polyadenylated mRNA transcripts encoding the firefly luciferase and Escherichia coli lacZ reporter genes were derived by in vitro transcription. Transfection of the human breast cancer cell line MDA-MB-435 in vitro was accomplished employing cationic liposome-mRNA complexes. Evaluation of a panel of cationic liposome preparations demonstrated significant differences in the capacity of the various preparations to accomplish mRNA-mediated transfection. Quantitative evaluation of in vitro transfection demonstrated that target cells could be transfected at a high level of efficiency. The mRNA liposome-complexes were evaluated for in vivo transfection of tumor nodules in human xenografts in athymic nude mice. It could be demonstrated the liposome-mRNA complexes were comparable in efficacy to liposome-DNA complexes in accomplishing in situ tumor transfection. Thus, mRNA may be considered as an alternative to plasmid DNA as a gene transfer vector for genetic immunopotentiation applications.

Breast Neoplasms↗

PubMed1994

Soluble urokinase receptor from fibrosarcoma HT-1080 cells.

A soluble form of urokinase-binding protein has been isolated from the human fibrosarcoma cell line HT-1080 and cell lines derived from it. Conditioned media of these cells were collected after overnight incubation under serum-free conditions, and were concentrated and passed through a column of Sepharose 4B to which high-molecular-weight urokinase had been attached. After thorough washing, a polypeptide could be eluted from the column with 1 M acetic acid. This material appeared to be a single band of approximately 60 kDa on SDS polyacrylamide gel. It cross-reacted with commercial antibodies made against urokinase receptor, and could be chemically cross-linked to the amino terminal fragment of urokinase. This material was similar to the urokinase receptor that was cleaved from HT-1080 cells by means of phosphatidylinositol-specific phospholipase C.

Chromatography, Affinity↗

PubMed1994

Alteration in the proportion of CD4 T lymphocytes in a subgroup of human immunodeficiency virus-exposed-uninfected children.

OBJECTIVE: The age-related changes in the proportion of CD4 and CD8 lymphocytes in human immunodeficiency virus (HIV)-seronegative children born to HIV-infected mothers (seroreverters) were compared with the changes in these lymphocyte subsets in children born to seronegative women to assess a possible effect of exposure to HIV without infection. DESIGN: There were 146 seroreverter and 72 seronegative children. The median CD4 and CD8 percentages for each of these two groups of children were compared retrospectively at 3-month intervals from birth through 27 months and at a tenth interval for the time beyond 27 months. The weighted average of the within-subject rate of change of CD4 and CD8 percentages were also compared between the two groups. Finally, for each subject, the proportion of the subject's CD4 percentage assays which were <10th percentile of the entire study population (30%) was calculated, and the distributions of the subject-specific proportions were then compared between the seronegative and seroreverter groups using the Wilcoxon rank sum test. The proportion of CD8 assays <10th percentile (12%) or > 90th percentile (26%) were also computed for each subject, and the distributions of the proportions were compared similarly. . RESULTS: The median CD4 percentage of seroreverter children was lower than that for the seronegative children at every interval from birth through 27 months and for the last interval for values obtained at greater than 27 months, although the comparison was statistically significant only at the 4- to 6-month period. The weighted average of the within-subject rate of change of CD4 percentage was -0.09 and -3.0 per year (P = .04), and of CD8 percentage was 1.3 and 1.0 (P = .67), for the seroreverter and seronegative children, respectively. There were significantly more children in the seroreverter group than in the seronegative group who had repeated assays in which the CD4 percentage was < 10th percentile for age (P < .00005). In addition, there was a subset of 10 seroreverter children (6.8%) who had CD4 percentages < 30% on > 50% of their assays, as compared with only one (1.4%) seronegative child. The proportion of CD8 assays < 10th percentile or > 90th percentile were not significantly different between the two groups of children. CONCLUSIONS: The CD4 proportions were persistently lower in the seroreverter than in the seronegative population, although only reaching statistical significance in 1 of 10 3-month intervals. This finding may be due to a subgroup of seroreverter children who have persistently low CD4 lymphocyte percentages.

CD4-CD8 Ratio↗

PubMed1994

The distribution of ascorbic acid and dehydroascorbic acid during tissue regeneration in wounded dorsal skin of guinea pigs.

The distribution of L-ascorbic acid AA and dehydroascorbic acid DHA in wounded and intact skin of guinea pig was investigated to elucidate the utilization of AA during tissue regeneration. Male guinea pigs fed an AA-free diet for 14 days were surgically injured on the dorsal skin, followed by intraperitoneal supplementation of AA (0.5, 5 and 50 mg/day/animal) for 4 days. The wounded skin, its surroundings and intact skin in each animal were removed for the determination of AA, DHA and collagen. The collagen content in wounded and intact skin increased in dose-dependent manner up to 5 mg AA/day, although neither the wounded nor the intact skin of the group supplemented with 50 mg AA had a higher content of collagen than those supplemented with 5 mg. In each group, the wounded skin had only about half the collagen of intact skin. AA content in the wounded skin of the groups supplemented with 5 and 50 mg AA were significantly lower than that in the other parts of their skin, whereas DHA content in wounded skin increased markedly. These results indicate that other factors besides collagen synthesis may enhance the oxidation of AA in the early stage of tissue regeneration.

Animals↗

PubMed1994

Bleach use and HIV seroconversion among New York City injection drug users.

We employed a nested case-control study design to evaluate the efficacy of bleach-cleaning of needles and syringes among injecting drug users (IDUs) as a means of preventing human immunodeficiency virus (HIV) infection. Sixteen HIV-seroconverters who responded to bleach use questions and who reported injecting with shared or used equipment in the 6 months prior to their first positive visit were compared with 89 controls. Controls had remained HIV-seronegative at two or more visits, reported injecting with shared or used equipment, responded to bleach-cleaning questions, and were seen at recall visits +/- 6 months from the date of seroconversion of the index case. Risk factors associated with HIV seroconversion in univariate analyses were a history of sexual intercourse with an HIV-infected partner and the frequency of speedball (mixed heroin and cocaine) injections. After adjusting for confounders, we found no evidence that bleach use protected against HIV infection.

Adult↗

PubMed1993

Fear-potentiated startle: a neural and pharmacological analysis.

The fear-potentiated startle paradigm has proven to be a useful system with which to analyze neural systems involved in fear and anxiety. This test measures conditioned fear by an increase in the amplitude of a simple reflex (the acoustic startle reflex) in the presence of a cue previously paired with a shock. Fear-potentiated startle is sensitive to a variety of drugs such as diazepam, morphine, and buspirone that reduce anxiety in people and can be measured reliably in humans when the eyeblink component of startle is elicited at a time when they are anticipating a shock. Electrical stimulation techniques suggest that a visual conditioned stimulus ultimately alters acoustic startle at a specific point along the acoustic startle pathway. The lateral, basolateral and central amygdaloid nuclei and the caudal branch of the ventral amygdalofugal pathway projecting to the brainstem are necessary for potentiated startle to occur. The central nucleus of the amygdala projects directly to one of the brainstem nuclei critical for startle and electrical stimulation of this nucleus increases startle amplitude. Chemical or electrolytic lesions of either the central nucleus or the lateral and basolateral nuclei of the amygdala block the expression of fear-potentiated startle. The perirhinal cortex, which projects directly to the lateral and basolateral amygdaloid nuclei, plays a critical role in the expression of fear-potentiated startle using either visual or auditory conditioned stimuli. These latter amygdaloid nuclei may actually be the site of plasticity for fear conditioning, because local infusion of the NMDA antagonist AP5 into these nuclei blocks the acquisition of fear-potentiated startle. On the other hand, the expression of fear-potentiated startle is blocked by local infusion of the non-NMDA ionotropic antagonist CNQX or the G-protein inactivating toxin, pertussis toxin, but not by AP5. Finally, we have begun to investigate brain systems that might be involved in the inhibition of fear. Local infusion of AP5 into the amygdala was found to block the acquisition of experimental extinction, a prototypical method for reducing fear. We have also established a reliable procedure for producing both external and conditioned inhibition of fear-potentiated startle and hope to eventually understand the neural systems involved in these phenomena.

Animals↗

PubMed1993

Increased sensitivity to TNF-mediated cytotoxicity of BL6 melanoma cells after H-2Kb gene transfection.

Transfection of the H-2Kb and neor genes into BL6-8 (H-2Kb-, H-2Db+) melanoma clone resulted in various phenotypic changes with appearance of soybean agglutinin (SBA) and Grifonia Simplicifolia 1-B4 (GS1B4) lectin binding carbohydrates and loss of melanoma-associated antigen (MAA). In parallel H-2Kb gene-transfected melanoma cells showed increased sensitivity to TNF lysis. To further delineate the ability of H-2Kb gene to induce the phenotypic changes and TNF sensitivity, BL6-8 melanoma clone was transfected with the H-2Kb gene alone without cotransfection with neor gene and transfected cells were selected for adherence to SBA lectin-conjugated agarose beads. Analysis of isolated clones revealed that 38 of 47 tested clones have been found to be expressing the H-2Kb Ag, SBA, and GS1B4 lectin binding carbohydrates but lost MAA, e.g., H-2Kb+, lectin+, MAA-, and in parallel these cells became sensitive to TNF lysis. Although all clones with high expression of H-2Kb Ag were sensitive to TNF lysis, it seems unlikely that H-2K molecules are directly required for or involved in TNF-induced melanoma cell lysis. This conclusion is based on findings that four H-2Kb-transfected clones selected on SBA-agarose beads did not expressed H-2Kb Ag but manifested increase in SBA and GS1B4 lectin binding and loss of MAA and also became sensitive to TNF lysis. It seems that increase in TNF sensitivity is a part of the broad phenotypic changes induced by the H-2K gene that remained stable even in the clones in which the transfected H-2Kb gene was lost or down-regulated. We believe that the effects of the H-2Kb gene on melanoma cell phenotype and TNF sensitivity are indirect and are probably mediated via its inhibition of the melanoma-associated ecotropic retrovirus production and activation of some repressed cellular genes. Study of the mechanisms responsible for TNF sensitivity of BL6 melanoma cells revealed that the H-2Kb gene transfection resulted in an increase in p55 TNF receptor expression. TNF-induced activation of phospholipase A2 and release of arachidonic acid metabolites was observed only in the H-2Kb transfected, but not in BL6-8 melanoma cells transfected with neor or class II H-21Ak genes. TNF resistance of BL6 melanoma cells appeared to be due to a block in transduction of the lytic signal that was reversed after transfection with H-2Kb gene.

Animals↗

PubMed1993

4-Aminopyridine reduces chorda tympani nerve taste responses to potassium and alkali salts in rat.

To study the potential role of potassium channels in the taste response to potassium salts, we applied 4-aminopyridine (4-AP) to the anterior rat tongue and recorded chorda tympani nerve taste responses to chemical stimuli. 4-aminopyridine is a pharmacological blocker that reduces potassium conductance through potassium channels in nerve and muscle. Summated neural responses to stimuli dissolved in water and in 4-AP were compared. Chemical stimuli included concentration ranges of KCl, KBr, KH2PO4, CsCl, RbCl, NH4Cl, NaCl and sucrose. The blocker reduced chorda tympani responses to KCl and other potassium salts, from 0.025 to 0.25 M. Responses to ammonium, rubidium and cesium salts also were reduced, in order of effectiveness that would be predicted from known ion selectivity properties of potassium channels. Responses to NaCl and sucrose were not reduced. Other channel blockers, including tetraethylammonium chloride (TEA), BaCl2 and quinidine, did not reduce the response to KCl. These are the first detailed reports of effects of potassium channel blockers on the peripheral, neural taste response. The results are consistent with a role for potassium channels in apical taste bud cell membranes in transduction for potassium salts.

4-Aminopyridine↗

PubMed1993

Cirrhosis of undefined pathogenesis: absence of evidence for unknown viruses or autoimmune processes.

To examine whether unknown viruses or autoimmune processes contribute to the development of cryptogenic liver disease, we studied 48 patients undergoing liver transplantation who had non-A, non-B cirrhosis; non-blood-borne cirrhosis of unknown etiology; or autoimmune cirrhosis. After the diagnosis of hepatitis C virus infection was established by the presence of viral antibodies or viral RNA, patients were reclassified into three groups: hepatitis C virus infection, autoimmune cirrhosis and cryptogenic cirrhosis. Explant histological appearance, incidence of posttransplant hepatitis and immunological features were compared in the three groups. Thirty-one percent of patients had neither hepatitis C virus infection nor classical autoimmune cirrhosis and were classified as having cryptogenic cirrhosis. Unlike histological appearance in hepatitis C virus infection but similar to that in autoimmune cirrhosis, explant histological appearance of cryptogenic cirrhosis showed inactive cirrhosis with little inflammation. After transplantation, histological hepatitis of the allograft was demonstrated in 44% of patients with hepatitis C infection but in no patient with autoimmune or cryptogenic cirrhosis. The autoimmune score, developed from clinical criteria associated with autoimmune liver disease, was significantly lower in cryptogenic cirrhosis and hepatitis C virus infection than in autoimmune cirrhosis. Autoantibodies--including antinuclear antibodies, smooth muscle antibodies and liver-kidney microsomal antibodies--were not commonly present in serum of patients with cryptogenic cirrhosis, whereas antibodies to soluble liver antigens were found with increased frequency in this entity. We conclude that in many patients with liver disease, no pathogenesis can be identified.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoimmune Diseases↗

PubMed1993

Direct evidence for selective modulation of psbA, rpoA, rbcL and 16S RNA stability during barley chloroplast development.

The turnover of RNAs encoded by seven different barley chloroplast genes was analyzed after treatment of barley shoots with tagetitoxin, a selective inhibitor of chloroplast transcription. Changes in RNA stability were examined during chloroplast development using basal and apical leaf sections of 4.5-day-old dark-grown seedlings and apical leaf sections of 4.0-day-old dark-grown seedlings which had been illuminated for 12 h. Of the RNAs examined, a 2.6 kb unspliced precursor of tRNA(lys) exhibited the shortest half-life, which was estimated to be 3 h. The 16S rRNA and psbA mRNA had the longest estimated half-lives, which were greater than 40 h. Among mRNAs, half-lives were estimated to range from 6 h for psaA mRNA, to over 40 h for psbA mRNA. Therefore, barley chloroplast mRNAs have long half-lives relative to bacterial mRNAs. The stability of atpB mRNA and the unspliced precursor of tRNA-lys was not altered during chloroplast development, while the stability of psaA mRNA decreased 2-fold. In contrast, the stability of the 16S rRNA and mRNAs for rpoA, psbA and rbcL increased during chloroplast development. The stability of 16S rRNA increased markedly during chloroplast development in the dark and this increase was maintained in illuminated seedlings. The stability of rbcL mRNA increased 2.5-fold during chloroplast development in the dark, and then decreased 2-fold in chloroplasts of light-grown plants. The initial increase in rpoA and psbA mRNA stability was also light-independent, with total increases in stability of at least 5-fold. In the case of rpoA, the stability of 2 of the 13 polycistronic rpoA transcripts that were detected in dark-grown plants was selectively increased during chloroplast development. In conclusion, the stability of some transcripts is selectively increased and further modulated during chloroplast development in barley. We propose that the selective stabilization of chloroplast mRNA, which occurred independent of light, is an indication that non-light regulated developmental signals are involved in barley chloroplast mRNA stability.

Base Sequence↗

PubMed1993

Control of metastatic properties of BL6 melanoma cells by H-2Kb gene: immunological and nonimmunological mechanisms.

The effect of class I H-2 antigen expression on the metastatic properties of BL6 melanoma cells was investigated. The BL6-8 clone isolated from the highly metastatic BL6 melanoma did not express H-2Kb gene. Following transfection with the H-2Kb gene, BL6-8 cells displayed a low metastatic potential in the immunocompetent as well as immunosuppressed (X-irradiated) or triple-immunodeficient mice with impaired T, B and natural killer (NK) cells function. The expression of H-2Kb gene and the low metastatic ability of transfected BL6 melanoma cells were associated with appearance of cell membrane soybean agglutinin (SBA) and Griffonia simplicifolia 1B4 (GS1B4) lectin-binding carbohydrates. These alterations in cell surface carbohydrates were found to be a result of reduction in sialylation of SBA binding sites and upregulation of the alpha 1.3 galactosyltransferase (alpha 1.3GT) gene. To assess the importance of H-2Kb-induced alterations in cell surface carbohydrates for metastasis formation, BL6-8 melanoma cells were transfected with H-2Kb gene without neor gene cotransfection and selected for adherence to SBA-lectin-conjugated agarose beads. The transfected clones that expressed SBA and GS1B4 lectin-binding carbohydrates were low metastatic. Further analysis of these clones showed that presence of SBA and GS1B4 lectin-binding carbohydrates rather than expression of H-2Kb molecules per se might be responsible for low metastatic potentials of H-2Kb-transfected cells in the immunocompromised mice. Studies of the possible mechanisms responsible for low metastatic ability of H-2Kb-transfected melanoma cells revealed that these cells displayed a reduced ability to adhere to murine pulmonary endothelial cells as well as to laminin and collagen IV. We hypothesized that the observed nonimmunological effects of H-2Kb gene in BL6 melanoma cells is a result of an interaction between the H-2Kb gene and B16 melanoma-specific ecotropic retrovirus. It results in inhibition of this retrovirus production with consecutive alteration in the expression of cellular genes controlling cell surface glycosylation and adhesion properties essential for the metastatic phenotype of BL6 melanoma.

Animals↗

PubMed1993

Infusion of the non-NMDA receptor antagonist CNQX into the amygdala blocks the expression of fear-potentiated startle.

The involvement of non-N-methyl-D-aspartate receptors in the amygdala in the expression of conditioned fear was examined using the fear-potentiated startle paradigm. Rats implanted with bilateral cannulae in the basolateral amygdaloid nuclei received 10 pairings of either a visual or auditory conditioned stimulus with footshock on each of 2 days. The next day, they were tested by eliciting the acoustic startle reflex in the presence or absence of the conditioned stimulus and divided into groups with equivalent levels of potentiation. One or two days later, rats were tested again following intra-amygdala infusion of vehicle or 0.025, 0.25, or 2.5 micrograms of 6-cyano-7-nitroquinoxaline-2,3-dione. The drug dose-dependently blocked the expression of potentiated startle in both sensory modalities, indicating that activation of non-NMDA receptors in the amygdala is necessary for the expression of conditioned fear.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1993

Electrolytic lesions of the amygdala block acquisition and expression of fear-potentiated startle even with extensive training but do not prevent reacquisition.

Lesions of the amygdala have been shown to block the expression of fear-potentiated startle (increased acoustic startle in the presence of a cue previously paired with shock). In the present study, bilateral lesions of the central nucleus of the amygdala given after extensive training totally blocked the expression of fear-potentiated startle but did not prevent reacquisition. In contrast, when the lesions were made before any training, the lesioned rats did not show potentiated startle even with extensive training. Thus, the central nucleus of the amygdala normally seems to be required for the initial acquisition and expression of potentiated startle regardless of the degree of learning. However, reacquisition of potentiated startle can occur without the central nucleus, which implies the presence of a secondary brain system that can compensate for the loss of the central nucleus of the amygdala under some circumstances.

Amygdala↗