[Genomic epidemiology of Vibrio parahaemolyticus from acute diarrheal patients in Shenzhen City from 2013 to 2021].

Objective: To characterize the prevalence and genomic epidemiology of Vibrio parahaemolyticus from acute diarrheal patients in Shenzhen City from 2013 to 2021. Methods: Based on the Shenzhen Infectious Diarrhea Surveillance System, acute diarrheal patients were actively monitored in sentinel hospitals from 2013 to 2021. Whole-genome sequencing (WGS) of Vibrio parahaemolyticus isolates was performed, and the genomic population structure, serotypes, virulence genes and multilocus sequence typing were analyzed. Outbreak clusters from 2019 to 2021 were explored based on single-nucleotide polymorphism analysis. Results: A total of 48 623 acute diarrhea cases were monitored in 15 sentinel hospitals from 2013 to 2021, and 1 135 Vibrio parahaemolyticus strains were isolated, with a positive isolation rate of 2.3%. Qualified whole-genome sequencing data of 852 isolates were obtained. Eighty-nine serotypes, 21 known ST types and 5 new ST types were identified by sequence analysis, and 93.2% of strains were detected with toxin profile of tdh+trh-. 8 clonal groups (CGs) were captured, with CG3 as the absolute predominance, followed by CG189. The CG3 group was dominated by O3:K6 serotype and ST3 sequence type, while CG189 group was mainly O4:KUT, O4:K8 serotypes and ST189a and ST189 type. A total of 13 clusters were identified, containing 154 cases. About 30 outbreak clusters with 29 outbreak clusters caused by CG3 strains from 2019 to 2021. Conclusion: Vibrio parahaemolyticus is a major pathogen of acute infectious diarrhea in Shenzhen City, with diverse population structures. CG3 and CG189 have been prevalent and predominant in Shenzhen City for a long time. Scattered outbreaks and persistent sources of contamination ignored by traditional methods could be captured by WGS analysis. Tracing the source of epidemic clone groups and taking precise prevention and control measures are expected to significantly reduce the burden of diarrhea diseases caused by Vibrio parahaemolyticus infection in Shenzhen City.

[Comparison of follow-up treatment regimens for colorectal cancer liver metastases without objective response to neoadjuvant chemotherapy: direct surgery or surgery after second-line chemotherapy].

Objective: To compare the effect of direct surgery or surgery after second-line chemotherapy for colorectal cancer patients with liver metastases who did not achieve objective remission after neoadjuvant chemotherapy. Methods: A retrospective case cohort study was used. The clinical and pathological data of 107 patients with colorectal cancer liver metastases who did not achieve objective response to neoadjuvant chemotherapy at Department of Hepatobiliary Surgery,Cancer Hospital,Chinese Academy of Medical Sciences from December 2008 to December 2016 were retrospectively collected. There were 71 males and 36 females, median age was 57 years (range: 28 to 79 years). According to the different treatment regimens after neoadjuvant chemotherapy,107 cases were divided into a direct surgery group (direct group,n=65) and an operation after receiving second-line chemotherapy group (second-line group,n=42). The propensity score matching(PSM) of the Logistic regression model was used to match the bilobar distribution of liver metastases and the number of first-line chemotherapy cycles in the two groups of patients. The caliper value was set to 0.10 and the matching ratio was 1∶2. T test, Mann-Whitney U test, χ2 test or Fisher's exat test was used to analyzed the data between the tuo groups, respectively. Survival analysis design was used to investigate the difference in prognosis between the two groups of patients. Results: The follow-up time(M(IQR)) was 56.3(34.3) months (range: 2.1 to 95.0 months),and all patients were followed up. After PSM,there were 28 cases in the direct group and 42 cases in the second-line group, there were no significant differences in whether R0 resection was feasible,blood loss,blood transfusion,postoperative complications and postoperative hospital stay between the two groups (all P>0.05). The 1,3,and 5-year progression-free survival(PFS) rates of the direct group were 40.0%,16.5%,and 11.0%,and the 1,3,and 5-year overall survival(OS) rates were 98.5%,61.2%,and 41.4%,respectively, the second-line group 1,3,5 years PFS rates were 35.7%,14.3%,14.3%,1,3,5-year OS rate were 95.2%,55.1%,44.4%,respectively. The median PFS time of the direct group and the second-line group was 8.5 months and 7.5 months,respectively,and the difference was not statistically significant (P=0.826). The median OS time of the direct group and the second-line group were 33.8 months and 46.9 months,respectively. The difference was not statistically significant(P=0.646).The median PFS time of the direct group and second-line chemotherapy complete remission and partial remission group(CR/PR group) was 10.2 months and 9.1 months,respectively,and the difference was not statistically significant(P=0.669). The median OS time of the direct group and the second-line CR/PR group was 51.0 months and 46.9 months,respectively,and the difference was not statistically significant(P=0.427). The results of survival analysis suggested that major liver resection was an independent prognosis factor for PFS (HR=1.809,95%CI: 1.067 to 3.067,P=0.028) and OS(HR=2.751,95%CI: 1.317 to 5.747,P=0.007). Second-line chemotherapy was not an independent prognostic factor for PFS (HR=0.945, 95%CI:0.570 to 1.567,P=0.828) and OS (HR=0.866,95%CI: 0.468 to 1.602,P=0.646). Conclusions: There is no significant difference in the short-term outcome and long-term prognosis between direct surgery patients and second-line chemotherapy followed by surgery. Second-line chemotherapy is not an independent prognostic factor for colorectal cancer liver metastases patients who fail to achieve objective response after neoadjuvant chemotherapy.

[Effects of intermittent hypoxia intestinal bacterial translocation on mesenteric lymph node injury].

Objective: To observe the effect of intermittent hypoxia on intestinal bacterial translocation and mesenteric lymph node (MLN) structure and explore its mechanism. Methods: Twenty-four adult male Wistar rats were randomly divided into an experimental group (HI group) and a control group (UC group), with 12 rats in each. During the experiment, both groups were fed under the same conditions, but the HI group received simulated sleep apnea with hypoxic treatment. On the last day of the 2nd and 4th week of the experiment, 20% urethane(0.7 ml/100g) was used for anesthesia, and MLNs and corresponding small intestinal tissues were aseptically collected.HE staining was used to observe the microscopic changes of the tissues. The lymph node tissue was sent for pathogenic culture. The levels of oxide dismutase (SOD), lipid peroxide (MDA) and reactive oxygen species (ROS) were measured for the extent of oxidative stress. Serum diamine oxidase (DAO) was measured to assess the extent of intestinal mucosal damage. Result: MLNs and their corresponding small intestines were damaged in the HI group as compared to the UC group. With the prolongation of intermittent hypoxic time, the number of germinal centers in MLNs was significantly reduced, with the volume reduced, cortical medullary fusion aggravated, and the area ratio increased. The intestinal tissue showed severe damage to the intestinal epithelium, increased permeability, mucosal edema, and changes of the crypts. At the 4th week, MLNs in the HI group grew Clostridium perfringens under anaerobic conditions, confirming intestinal bacterial translocation. The contents of ROS, SOD and MDA in MLNs of the HI group were significantly higher than those in the UC group (P<0.05). At the 2nd week and the 4th week, the contents of ROS, SOD and MDA were not significantly changed in the UC group(P>0.05). While the content of ROS and MDA in MLNs of the HI group at 4th week was significantly higher than that in the second week (P<0.05), but no change of SOD was observed (P>0.05). Serum DAO levels in the HI group were higher than those in the UC group at week 2 and week 4 (P<0.05), suggesting that the degree of intestinal mucosal injury in the HI group was more serious than that in the UC group. Conclusion: Hypoxic exposure aggravated the degree of oxidative stress in rats. With the prolongation of intermittent hypoxia, the intestinal mucosa of rats was seriously damaged. The intestinal flora shifted to damage the structure of mesenteric lymph nodes, and oxidative stress was further aggravated, which in turn affected the integrity of the intestinal autoimmune function.

Manno-oligosaccharide preparation by the hydrolysis of konjac flour with a thermostable endo-mannanase from Talaromyces cellulolyticus.

AIMS: A thermostable endo-mannanase from the fungus Talaromyces cellulolyticus was identified to facilitate manno-oligosaccharide preparation from Konjac (Amorphophallus konjac) flour. METHODS AND RESULTS: A putative endo-1,4-ß-mannanase from the T. cellulolyticus was obtained and efficiently expressed by improving its gene dosage in the genome of the host. After cultivation in a bench-top bioreactor for about 120 h, the protein content and enzyme activity of mannanase increased to 3·4 g l-1 and 17 500 U ml-1 respectively. Enzymatic characterization showed that this enzyme has an optimal temperature of 80°C, optimal pH of 5·0. Under the optimized hydrolysis conditions of pH 5·0, 70°C, and an enzyme concentration of 200 U l-1 solution, this enzyme could efficiently hydrolyse 0·5% konjac flour into manno-oligosaccharides (MOSs) with the degree of polymerization range from 3 to 7. The possible mechanism by which the enzyme produced MOSs was also discussed. CONCLUSION: Talaromyces cellulolyticus endo-mannanase is thermostable and has a broad pH range adaptability. Method of improving the dosage of mannanase gene in the genome could realized its high-level impression. This enzyme could efficiently hydrolyse konjac flour into manno-oligosaccharide products. SIGNIFICANCE AND IMPACT OF THE STUDY: This study has enriched endo-mannanase resources, facilitated its bulk production and provided a strong reference for its application in manno-oligosaccharide preparation from the natural glucomannan of konjac flour.

[Progress in studies on obstructive sleep apnea and intestinal microecological balance].

SummaryObstructive sleep apnea （OSA） is closely related to the development of various diseases. Hypoxic perfusion caused by OSA can mediate the occurrence of inflammatory reactions or aggravate metabolic disorders to affect intestinal microecological balance. Intestinal bacteria can participate in the development of inflammatory reaction or metabolic disorder by itself or its components, and the oxidative stress reaction of the body develops in a vicious circle. The mechanism has not yet been fully elucidated, so we reviewed the research progress on OSA and intestinal microecological balance.

[Diagnostic efficiency of NO/ET-1 and HCY level in severe OSAHS patients with cognitive impairment].

Objective:To investigate the diagnostic efficiency of HCY and NO/ET-1 to cognitive dysfunction in patients with severe obstructive sleep apnea hypopnea syndrome, and to interfere with the cognitive function of severe OSAHS patients. Method: Eighty-six patients with OSAHS were divided into mild group (22 cases), moderate group (23 cases), severe group (41 cases) and healthy physical examination group (50 cases). The levels of serum HCY and NO/ET-1 were compared between the four groups. The Montreal cognitive assessment scale was used to evaluate the incidence of mild cognitive impairment in severe OSAHS group, and the correlation between the level of serum HCY, NO/ET-1 and cognitive function in severe OSAHS group was analyzed. Result:The level of serum HCY in patients with severe OSAHS with cognitive impairment was(32.28±3.92)µmol/L, higher than that of the cognitive moderate group(26.34±4.05)µmol/L, and mild group (18.62±3.29)µmol/L. The level of serum NO/ET-1 in patients with severe OSAHS with cognitive impairment was (0.69±0.19), higher than that of the cognitive moderate group(2.76±0.28), and mild group (3.98±0.37), the difference was statistically significant (P<0.05). In severe group, there was a negative correlation between the level of serum HCY and the score of MoCA and its subscores (P<0.05), and there was a positive correlation between the total scores of NO/ET-1 and MoCA and their subscores (P<0.05), and negative correlation between HCY and NO/ET-1 (P<0.05). The area under the ROC curve of predicting serum HCY and NO/ET-1 levels in severe OSAHS patients with cognitive impairment were 0.788(95%CI0.654-0.921) and 0.770 (95%CI0.642-0.899). Conclusion:Serum HCY and NO/ET-1 were the factors influencing the formation of cognitive impairment in severe OSAHS patients. The level of HCY was negatively correlated with the degree of cognitive impairment, and NO/ET-1 was positively correlated with the degree of cognitive impairment.

Integrative microRNA-mRNA and protein-protein interaction analysis in pancreatic neuroendocrine tumors.

OBJECTIVE: Pancreatic neuroendocrine tumors are relatively rare pancreatic neoplasms over the world. Investigations of the molecular biology of PNETs are insufficient for nowadays. We aimed to explore the expression of microRNA and messenger RNA and regulatory processes underlying pancreatic neuroendocrine tumors. MATERIALS AND METHODS: The messenger RNA and microRNA expression profile of GSE43796 were downloaded, including 6 samples with pancreatic neuroendocrine tumors and 5 healthy samples. First, the Limma package was utilized to distinguish the differentially expressed messenger RNA and microRNA separately. Then we used microRNA Walk databases to predict the target genes of the differentially expressed microRNAs (DE-microRNAs), and selected differentially expressed target genes whose expression was reversely correlated with microRNAs. Gene Ontology classification and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis were performed to explore the functions and pathways of target genes. In addition, we constructed a regulatory miRNAs-target genes network and a protein-protein interaction network. RESULTS: There were 28 differentially expressed microRNAs and 859 differentially expressed messenger RNAs, including 253 potential target genes. These target genes mainly enriched in ABC transporters pathway. In this network, hsa-miR-7-2-3p demonstrated the highest connectivities whereas KLF12 was the mRNAs with the highest connectivities. CXCL12 was identified as the hub of the protein-protein interaction sub-network. CONCLUSIONS: The genes involved in ABC transporters and Type II diabetes mellitus pathway, KLF12 and CXCL12 may play an important role in the progression of pancreatic neuroendocrine tumors. However, more experimental studies are required.

Hepatitis C virus upregulates B-cell receptor signaling: a novel mechanism for HCV-associated B-cell lymphoproliferative disorders.

B-cell receptor (BCR) signaling is essential for the development of B cells and has a critical role in B-cell neoplasia. Increasing evidence indicates an association between chronic hepatitis C virus (HCV) infection and B-cell lymphoma, however, the mechanisms by which HCV causes B-cell lymphoproliferative disorder are still unclear. Herein, we demonstrate the expression of HCV viral proteins in B cells of HCV-infected patients and show that HCV upregulates BCR signaling in human primary B cells. HCV nonstructural protein NS3/4A interacts with CHK2 and downregulates its activity, modulating HuR posttranscriptional regulation of a network of target mRNAs associated with B-cell lymphoproliferative disorders. Interestingly, the BCR signaling pathway was found to have the largest number of transcripts with increased association with HuR and was upregulated by NS3/4A. Our study reveals a previously unidentified role of NS3/4A in regulation of host BCR signaling during HCV infection, contributing to a better understanding of the molecular mechanisms underlying HCV-associated B-cell lymphoproliferative disorders.

Post-spike hyperpolarization participates in the formation of auditory behavior-related response patterns of inferior collicular neurons in Hipposideros pratti.

To probe the mechanism underlying the auditory behavior-related response patterns of inferior collicular neurons to constant frequency-frequency modulation (CF-FM) stimulus in Hipposideros pratti, we studied the role of post-spike hyperpolarization (PSH) in the formation of response patterns. Neurons obtained by in vivo extracellular (N=145) and intracellular (N=171) recordings could be consistently classified into single-on (SO) and double-on (DO) neurons. Using intracellular recording, we found that both SO and DO neurons have a PSH with different durations. Statistical analysis showed that most SO neurons had a longer PSH duration than DO neurons (p<0.01). These data suggested that the PSH directly participated in the formation of SO and DO neurons, and the PSH elicited by the CF component was the main synaptic mechanism underlying the SO and DO response patterns. The possible biological significance of these findings relevant to bat echolocation is discussed.

Symptomatic response to imatinib mesylate in cutaneous mastocytosis associated with chronic myelomonocytic leukemia.

Mastocytosis is an uncommon disorder defined by increased and abnormal mast cells in one or more tissues. Cutaneous mastocytosis (cm) is limited to the skin, with varying degrees of rash, pruritus, and disfigurement. Systemic mastocytosis (sm) typically involves the bone marrow, sometimes in association with other bone marrow disorders, including chronic myelomonocytic leukemia (cmml). Mastocytosis has been associated with somatic mutations in the gene encoding the tyrosine kinase Kit, leading to identification of Kit as a therapeutic target. The Kit inhibitor imatinib mesylate is approved for aggressive sm. We present an unusual patient with disabling pruritus from telangiectasia macularis eruptiva perstans, a subtype of cm, and cmml, but with no evidence of systemic mast cell disease. She was treated with imatinib and experienced marked improvement in her pruritus. Concomitant cm and cmml have not previously been reported, and the present report is the first of successful imatinib therapy in an adult patient with cm.

Bilateral collicular interaction: modulation of auditory signal processing in frequency domain.

In the ascending auditory pathway, the inferior colliculus (IC) receives and integrates excitatory and inhibitory inputs from a variety of lower auditory nuclei, intrinsic projections within the IC, contralateral IC through the commissure of the IC and the auditory cortex. All these connections make the IC a major center for subcortical temporal and spectral integration of auditory information. In this study, we examine bilateral collicular interaction in the modulation of frequency-domain signal processing of mice using electrophysiological recording and focal electrical stimulation. Focal electrical stimulation of neurons in one IC produces widespread inhibition and focused facilitation of responses of neurons in the other IC. This bilateral collicular interaction decreases the response magnitude and lengthens the response latency of inhibited IC neurons but produces an opposite effect on the response of facilitated IC neurons. In the frequency domain, the focal electrical stimulation of one IC sharpens or expands the frequency tuning curves (FTCs) of neurons in the other IC to improve frequency sensitivity and the frequency response range. The focal electrical stimulation also produces a shift in the best frequency (BF) of modulated IC (ICMdu) neurons toward that of electrically stimulated IC (ICES) neurons. The degree of bilateral collicular interaction is dependent upon the difference in the BF between the ICES neurons and ICMdu neurons. These data suggest that bilateral collicular interaction is a part of dynamic acoustic signal processing that adjusts and improves signal processing as well as reorganizes collicular representation of signal parameters according to the acoustic experience.

Responses of inferior colliculus neurons to sounds presented at different rates in anesthetized albino mouse.

We recorded extracellular activity from 402 single units located in the inferior colliculus (IC) of barbiturate-anesthetized albino mice. The stimuli were pure tones at characteristic frequency (CF) with durations of 10, 40 and 100 ms and intensities ranged from 5 to 25 dB above unit's minimum threshold (MT). The tones were presented with different repetition rates (RRs) ranging from 0.2 to 20.0 Hz. At low intensities (5 dB above MT, determined at RR of 0.5 Hz) the great majority of units exhibited a strong decline of their responses when the stimulus RR was increased. About one-half of the units did not respond to 40 ms tones when they were stimulated with the RR of 3.0 Hz. This effect was even more pronounced for 100 ms tones. Generally, the increase in stimulus intensity led to an increase in the high-frequency border of RR. Nevertheless, even at intensities of 20-30 dB above MT, some units showed no response when the RR exceeded 5.0 Hz. In many cases the band-pass or high-pass duration tuning of the single unit was transformed to low-pass or all-pass when the rate was low enough to guarantee the independence of successive presentations of the stimuli. Responses of a very small group of IC units, however, were enhanced when the RR was increased. Our data have shown that the changes in the RR radically modify many features of the neural response (number of spikes, latency, discharge pattern, duration selectivity). We suggest that long-lasting inhibitory processes may be induced by low intensity stimuli in many units of the IC.

An electrophysiological study of neural pathways for corticofugally inhibited neurons in the central nucleus of the inferior colliculus of the big brown bat, Eptesicus fuscus.

This electrophysiological study tests the hypothesis that one possible neural pathway for corticofugally inhibited neurons in the central nucleus of the inferior colliculus (ICc) of the big brown bat, Eptesicus fuscus, is mediated through excitatory projections from the auditory cortex (AC) to the external nucleus of the IC (ICx), which then sends inhibitory inputs to the ICc. This study shows that all neurons in the ICx are broadly tuned to stimulus frequency. Electrical stimulation in the AC typically increases the number of impulses, expands the auditory spatial response areas, and broadens the frequency tuning curves (FTCs) of neurons in the ICx. This corticofugal facilitation is mediated at least in part through NMDA receptors, since application of DL-2-amino-5-phosphonovaleric acid (APV), an antagonist for NMDA, decreases these response properties of neurons in the ICx. Electrical stimulation in the ICx typically decreases the number of impulses, reduces the auditory spatial response areas, and narrows the FTCs of neurons in the ICc. This inhibition is mediated at least in part through GABAA receptors, since application of bicuculline, an antagonist for GABA, increases these response properties of neurons in the ICc. These data suggest that corticofugal facilitation of the ICx and the inhibition of the ICx to the ICc may be one of the polysynaptic pathways for corticofugal inhibition of neurons in the ICc. Possible functions of this polysynaptic pathway in acoustic orientation and signal processing are discussed.

[Simultaneous determination of various food additives by high performance liquid chromatography].

A novel method is proposed for the simultaneous separation and determination of eight food additives, acesulfame potassium (AK), aspartame (ASP), benzoic acid (BA), caffeine (CA), saccharin sodium (SA), sorbic acid (SOR), theobromine (TB) and theophylline (TP) by reversed-phase high performance liquid chromatography. The separation was achieved within 23 min by using an Alltech Econosphere C18 column with 10 mmol/L NaH2PO4(pH 4.00)-acetonitrile (90:10, V/V) as mobile phase. The qualification and quantitation were accomplished by using a photodiode array detector. The detection limits (S/N = 3) for all analytes were below mg/L level. Under the experimental conditions, other common food additives and organic acids such as cyclamate, citric acid, malic acid, tartaric acid and ascorbic acid, did not interfere with the determination. The method has been successfully applied to the analysis of various foods as well as pharmaceutical preparation, and the average recoveries for real samples ranged from 78.5% to 107.2%.

Simultaneous determination of artificial sweeteners, preservatives, caffeine, theobromine and theophylline in food and pharmaceutical preparations by ion chromatography.

A novel ion chromatographic method was proposed for the simultaneous determination of artificial sweeteners (sodium saccharin, aspartame, acesulfame-K), preservatives (benzoic acid, sorbic acid), caffeine, theobromine and theophylline. The separation was performed on an anion-exchange analytical column operated at 40 degrees C within 45 min by an isocratic elution with 5 mM aqueous NaH2PO4 (pH 8.20) solution containing 4% (v/v) acetonitrile as eluent, and the determination by wavelength-switching ultraviolet absorbance detection. The detection limits (signal-to-noise ratio 3:1) for all analytes were below the sub-microg/ml level. Under the experimental conditions, several organic acids, including citric acid, malic acid, tartaric acid and ascorbic acid, did not interfere with the determination. The method has been successfully applied to the analysis of various food and pharmaceutical preparations, and the average recoveries for real samples ranged from 85 to 104%. The levels of all analytes determined by this method were in good agreement with those obtained by the high-performance liquid chromatographic procedure. The results also indicated that ion chromatography would be possibly a beneficial alternative to conventional high-performance liquid chromatography for the separation and determination of these compounds.

Bicuculline application affects discharge patterns, rate-intensity functions, and frequency tuning characteristics of bat auditory cortical neurons.

This study examined the effect of bicuculline application on the auditory response properties in the auditory cortex of the big brown bat, Eptesicus fuscus. All auditory cortical neurons studied discharged either 1-2 or 3-7 impulses to 4 ms sound stimuli. Cortical neurons with high best frequencies tended to have high minimum thresholds. Bicuculline application increased the number of impulses and shortened the response latencies of all cortical neurons as well as changing the discharge patterns of half of the cortical neurons studied. Bicuculline application raised the rate-intensity functions but lowered the latency-intensity functions to varying degrees. Threshold-frequency tuning curves (FTCs) were either V-shaped, upper threshold or double-peaked. Threshold-FTCs and impulse-FTCs were mirror-images of each other. Bicuculline application expanded and raised the impulse-FTCs but lowered the threshold-FTCs, resulting in significantly decreased Q(n) values. Threshold-FTCs of cortical neurons determined within an orthogonally inserted electrode were very similar and expanded FTCs during bicuculline application were also very similar. Possible mechanisms for the contribution of GABAergic inhibition to shaping these response properties of cortical neurons are discussed.

[The latest applications of ion chromatography in food analysis].

The latest applications of ion chromatography in food analysis is reviewed with 60 references, and the development trend in this aspect is also discussed.

Corticofugal regulation of auditory sensitivity in the bat inferior colliculus.

Under free-field stimulation conditions, corticofugal regulation of auditory sensitivity of neurons in the central nucleus of the inferior colliculus of the big brown bat, Eptesicus fuscus, was studied by blocking activities of auditory cortical neurons with Lidocaine or by electrical stimulation in auditory cortical neuron recording sites. The corticocollicular pathway regulated the number of impulses, the auditory spatial response areas and the frequency-tuning curves of inferior colliculus neurons through facilitation or inhibition. Corticofugal regulation was most effective at low sound intensity and was dependent upon the time interval between acoustic and electrical stimuli. At optimal inter-stimulus intervals, inferior colliculus neurons had the smallest number of impulses and the longest response latency during corticofugal inhibition. The opposite effects were observed during corticofugal facilitation. Corticofugal inhibitory latency was longer than corticofugal facilitatory latency. Iontophoretic application of gamma-aminobutyric acid and bicuculline to inferior colliculus recording sites produced effects similar to what were observed during corticofugal inhibition and facilitation. We suggest that corticofugal regulation of central auditory sensitivity can provide an animal with a mechanism to regulate acoustic signal processing in the ascending auditory pathway.

The effect of pulse repetition rate, pulse intensity, and bicuculline on the minimum threshold and latency of bat inferior collicular neurons.

This study examines the effect of pulse repetition rate (PRR), pulse intensity, and bicuculline on the minimum threshold (MT) and latency of inferior collicular neurons of the big brown bat, Eptesicus fuscus, under free-field stimulation conditions. It tests the hypothesis that changes in MT and latency of collicular neurons are co-dependent on PRR. The number of impulses in inferior collicular neurons (n = 245) increased either monotonically (25%) or non-monotonically (75%) with pulse intensity. Latencies either decreased to a plateau (72%), fluctuated unpredictably within 3 ms (21%) or changed very little (7%) with increasing pulse intensity. Latencies and MTs of most collicular neurons increased by 1.5-24 ms (mean +/- SD = 4.8 +/- 3.3 ms) and 4-75 dB (mean +/- SD = 22.1 +/- 16.2 dB) with increasing PRR. In most neurons (94%), the latency increase was completely (42%) or partially (52%) eliminated when pulse intensity was compensated for the MT increase with PRR. Complete elimination of latency was achieved by bicuculline application. In a few neurons (6%), the latency increase with PRR was not affected by compensated pulse intensity or bicuculline application.