Comparison of severe hypercholesterolemia patients with and without pathogenic variants

Introduction

A pathogenic variant causally related to familial hypercholesterolemia (FH) is found in less than half of adults with severe hypercholesterolemia. The characteristics of adults with severe hypercholesterolemia without pathogenic variant have been poorly described, and it remains unclear whether intensive preventive strategies should be recommended. In this study we compared the characteristics of adults with severe hypercholesterolemia with and without pathogenic variant for FH.

Methods

Between November 2020 and February 2022, we recruited individuals older than 16 years with a Dutch Lipid Clinic Network (DLCN) score ≥6 and genotyped LDLR, APOB and PCSK9. Participants were part of the multicenter CATCH study, testing the implementation of genetic cascade screening for FH in Switzerland. All genetic analyses were performed in a single central laboratory. Variants classified as likely pathogenic or pathogenic were interpreted as FH-causing. We also assessed socio-economic status, cardiovascular risk factors, lifestyle behavior, and use of lipid-lowering drugs.

Results

In total, 150 non-related adults with a DLCN score of ≥6 were included, out of whom 62 (41.3%) had genetically confirmed FH. Most variants were found in the LDLR gene (77%). Overall, 70% were using a lipid-lowering drug and 20% were current smokers. Compared to adults with genetically confirmed FH, those without pathogenic variants were older (57.6 vs 50.4 years old), had lower untreated LDL-cholesterol levels (p<0.001), higher triglyceride levels (p=0.032), higher BMI (p=0.014), and had more frequently hypertension (62.5% vs 36.1%). No socio-economic differences were observed. Although adherence to Mediterranean diet was higher among adults without pathogenic variant, they reached less frequently the recommended level of physical activity than adults with genetically confirmed FH (66.2% vs 82.1%). Xanthomas or xanthelasmas, but not corneal arcus, were more frequent among genetically confirmed FH (5.7% vs 20.3%).

Conclusions

Adults with severe hypercholesterolemia and without a pathogenic FH variant had less optimal control of cardiovascular risk factors than genetically confirmed FH. One fifth were smokers and one third of all patients included in this study were not taking any lipid-lowering drugs, regardless of the presence of a pathogenic variant.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): Swiss Heart Foundation

Lipoprotein(a) levels are not independently associated with endogenous steroid hormone levels, in contrast to other non-genetic and genetic factors: the population-based SKIPOGH study

Introduction

Lipoprotein(a) [Lp(a)] is an LDL-like molecule that is likely causally related to cardiovascular events. Lp(a) levels are highly variable, by more two orders of magnitude, and most of this variability appears to be of genetic origin. Exogenous hormones (hormone replacement therapy) seem to influence Lp(a) levels, but the impact of the variation of endogenous hormone levels on Lp(a) is unknown.

Purpose

To investigate the association between Lp(a) levels and non-genetic factors, as endogenous steroid hormone levels, in contrast to genetic factors.

Methods

We investigated the association of 28 endogenous steroids with Lp(a) levels and compared the association to other non-genetic and genetic variables in a prospective, population-based sample (N=1,021).

Results

The average age of the participants was 51 years and 53% were female. Median Lp(a) levels were 62 (±204) mg/l and the 90th and 99th percentile of Lp(a) was 616mg/l and 1035 mg/l respectively. The prevalence of a Lp(a) elevation ≥700mg/l was 3.2% and Lp(a) varied greatly from undetectable to 1,690mg/l. Age explained 2.0% of Lp(a) variability (p<0.001), 1% was explained by LDL levels (p=0.001), and 40% by two single nucleotide polymorphisms near the Lp(a) gene that have been previously described. Lp(a) levels were on average almost two times more elevated in secondary prevention and in individuals with very elevated LDL levels (≥4.9 mmol/l). Of the 28 endogenous steroid hormones assessed, 5-androstene-3b,16α,17β-triol, androsterone, 16α-hydroxy DHEA, and estriol were nominatively associated with serum Lp(a) levels and explained 0.4–1% of Lp(a) variability in univariate analyses, but they did not reach significance in multi-variate models.

Conclusion

Our results confirm previous findings demonstrating that the majority of the Lp(a) variation in the general population is of genetic origin. Age and LDL-levels explain a further small part of Lp(a) variability. Endogenous hormone levels do not contribute significantly to the wide range of variability.

Funding Acknowledgement

Type of funding sources: None. Coefficient plot Lp(a) and variables

Genomic analyses of all known putative familial hypercholesterolemia mutations showcase the value and limitations of public familial hypercholesterolemia mutation databases

Background/Introduction

Familial hypercholesterolemia (FH) is genetically very heterogeneous and genomic and locus-specific public databases describing putative FH mutations are assumed to be of limited clinical utility because of classification errors.

Purpose

A description of all currently known publicly available putative FH mutations in order to determine the reliability of the classification of FH mutations described.

Methods

The LOVD and ClinVar databases were interrogated for the phenotype and genes of interest. Additional information on each variant was obtained using the Bioconductor toolset, gnomAD, and GETex.

Results

Currently know putative FH variants included 4,529 variants (97.2%) in the classical FH-genes LDLR (61%), PCSK9 (10%), and APOB (29%). Single nucleotide variants constituted 83% and 17% were copy number variants. Exonic variants contributed 78%, 14% of the variants were intronic, 7% large CNV, and 1% in upstream or downstream regions. Of the 4,529 variants, 45% were classified as pathogenic or likely-pathogenic (Fig. 1a).

The ratio of exonic/intronic variants was 10.1 for pathogenic variants, 6.9 for likely pathogenic variants, 2.8 for likely benign and 1.4 for benign variants (p-value for class difference <2x10–6).

For 502 frameshift mutations in exons that are particularly damaging, only 93.2% were classified as pathogenic or likely-pathogenic and 1.7% as benign or likely benign (Fig. 1b). Across 222 exon-covering deletions of >100 nucleotides, also particularly damaging, only 90.5% were classified as pathogenic or likely-pathogenic.

Of the 4,529 variants, 1,561 (34.5%) were polymorphic in gnomAD. For these variants, the gnomAD sample size was on average 227420 (26102–282902). Of all 1,561 polymorphic variants in gnomAD 182 (11.6%) were classified as pathogenic or likely-pathogenic (Fig. 1c) and the variant frequency ranged from 10–4 to 10–6 (average 1.8x10–5), 43 with a frequency >1.8x10–5. Among variants found in gnomAD and classified as non-pathogenic, we observed ∼2000x higher frequencies (average 0.04).

Of the 4,529 variants, 100 matched eQTLs or sQTLs in GTEx, none was annotated as pathogenic (Fig. 1d).

Conclusion

We review all currently known putative FH mutations with pathogenic or likely-pathogenic variants being mostly exonic. Highly damaging mutations are largely classified as pathogenic or likely-pathogenic, but up to 9% are not classified as pathogenic in the two public FH mutation databases.

Assuming an FH population prevalence of 1/250 and 2000 pathogenic variants with the most frequent variant 10x more frequent than the average, we expect most pathogenic FH mutations at frequencies <2x10–5. We found 46 pathogenic or likely pathogenic variants to have a frequencies of >2x10–5 in the general population, evidence for misclassification.

No pathogenic FH variant was found among GETEx eQTLs or sQTLs.

Our data showcase the utility and weaknesses of the current public FH mutation databases.

FH variants overview

Funding Acknowledgement

Type of funding source: Public hospital(s). Main funding source(s): Hôpitaux Universitaire de Genève - Fonds privés

Exploring the relation between methylxanthines and plasma lipids in two population-based studies

Background

Chronic intake of caffeinated beverages might be associated with plasma lipids via disturbed lipid metabolism. Previous investigations have been limited by the use of self-reported caffeine intake instead of measured caffeine, whereas the associations between plasma lipids and other methylxanthines (paraxanthine, theobromine, theophylline) are unknown. Here, we investigated the associations of plasma lipids with caffeine and its metabolites in plasma and urine in two European populations.

Methods

Individuals were selected from the general population of North Belgium (FLEMENGHO) and Switzerland (SKIPOGH). Total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides were measured in plasma using standard enzymatic methods. Plasma and 24h urinary caffeine, paraxanthine, theophylline, and theobromine excretions were measured using ultra-high performance liquid chromatography tandem mass spectrometry. We used mixed models to explore the associations of methylxanthines with plasma lipids while adjusting for major confounders.

Results

Overall, 1946 FLEMENGHO participants (911 men, age 45.9±15.2 years) and 990 SKIPOGH participants (467 men, age 47.1±17.3 years) were included. Mean plasma total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides in FLEMENGHO/SKIPOGH were 5.37/5.06, 3.12/3.12, 1.43/1.50, and 2.4/1.02 mmol/L. In both cohorts, adjusted mean total cholesterol, LDL cholesterol, and HDL cholesterol, increased with quartile of plasma caffeine, with stronger associations in men. Similar positive associations were observed for paraxanthine and theophylline. Similar associations were observed using 24h urine excretions in SKIPOGH.

Conclusions

Plasma and urinary caffeine, paraxanthine, and theophylline were positively associated with plasma lipids in men, whereas there were fewer meaningful associations in women. The increase in plasma lipids might mitigate the overall beneficial impact of caffeinated beverages on health.

Key messages

Caffeine constitutes one of the most widely consumed biological active substances. Plasma concentration and urinary excretion of caffeine and its derived metabolites is positively associated with plasma lipids.

Exploring the relation between socioeconomic position and DNA methylation in a European population

Background

Previous investigations have reported that adverse socioeconomic circumstances across the life-course lead to the alteration of major biological processes, eventually resulting in a higher disease risk and premature death. In particular, a low life-course socioeconomic position (SEP) has been associated with a modified epigenetic signature of loci involved in inflammation, the physiological response to stress, and other regulatory processes.

Methods

In this study, we investigated the association between nine indicators of SEP across the life-course and the differential methylation of 451'000 genome-wide CpG markers, using data from 690 adults included in a Swiss population-based study. We further examined the interrelations between the SEP-related CpGs, and the biological pathways in which the identified markers are involved.

Results

Three SEP indicators in adulthood were associated the differential methylation of 161 genome-wide CpG markers, whereby 156 CpGs were less methylated in people with low versus high SEP. Among the identified CpGs, a substantial proportion of markers were no longer associated with SEP upon accounting for health behaviors and cardiometabolic disorders. In addition, the identified CpGs were found to be involved in immune, inflammatory, and cancer-related processes.

Conclusions

Our results support the hypothesis that adverse socioeconomic circumstances may lead to the dysregulation of inflammatory processes, eventually resulting in the occurrence of serious chronic conditions such as atherosclerosis, diabetes, or cancer.

Key messages

Socioeconomic position is a major determinant of health-related outcomes. Epigenetic modifications may constitute a biological mechanism through which socioeconomic circumstances affect health.

P1894Serum light-chain neurofilament is associated with brain atrophy in patients with atrial fibrillation

Background and aims

There is emerging evidence that atrial fibrillation (AF) is associated with cognitive dysfunction, increased risk for dementia and reduced brain volume independent of stroke, but the underlying mechanisms of these associations remain unclear. Here, we investigated the association of serum light-chain neurofilament (sNfL), a neuroaxonal injury biomarker, with brain atrophy in AF patients.

Methods

Explorative analysis from the Swiss-AF cohort study, a multicenter prospective observationalstudy which recruited patients aged ≥45 years with documented AF (NCT02105844). In baseline blood samples, sNfL concentrations were measured in duplicates using a single-molecule array assay. Brain MRI was obtained at baseline and at two years using a standardized protocol including a 3D T1-weighted MPRAGE sequence, on which Structural Image Evaluation using Normalization of Atrophy (SIENA) with optimized parameters for brain extraction was applied to calculate the two-year percentage whole brain volume change (PBVC).

Results

We included 245 Swiss-AF patients (median age 73, 73% male). Two-year PBVC was significantly associated with baseline sNfL in linear regression, with a 0.09% whole brain volume decrease per 10 pg/ml sNfL increase (95% CI [0.05–0.13], p<0.001). This association remained significant after adjustment for age, history of stroke and other vascular risk factors.

Neurofilament and brain atrophy

Conclusion

Increasing baseline sNfL was predictive of higher two-year brain atrophy rates independent of stroke history in AF patients. This association might reflect a chronic neurodegenerative process in AF.

Acknowledgement/Funding

Swiss National Science Foundation

Copeptin and insulin resistance: effect modification by age and 11 β-HSD2 activity in a population-based study

PURPOSE

Arginine vasopressin (AVP) may be involved in metabolic syndrome (MetS) by altering liver glycogenolysis, insulin and glucagon secretion, and pituitary ACTH release. Moreover, AVP stimulates the expression of 11β-hydroxysteroid-dehydrogenase-type 2 (11β-HSD2) in mineralocorticosteroid cells. We explored whether apparent 11β-HSD2 activity, estimated using urinary cortisol-to-cortisone ratio, modulates the association between plasma copeptin, as AVP surrogate, and insulin resistance/MetS in the general adult population.

METHODS

This was a multicentric, family-based, cross-sectional sample of 1089 subjects, aged 18-90 years, 47% men, 13.4% MetS, in Switzerland. Mixed multivariable linear and logistic regression models were built to investigate the association of insulin resistance (HOMA-IR)/fasting glucose and MetS/Type 2 Diabetes with copeptin, while considering potential confounders or effect modifiers into account. Stratified results by age and 11β-HSD2 activity were presented as appropriate.

RESULTS

Plasma copeptin was higher in men [median 5.2, IQR (3.7-7.8) pmol/L] than in women [median 3.0, IQR (2.2-4.3) pmol/L], P < 0.0001. HOMA-IR was positively associated with copeptin after full adjustment if 11β-HSD2 activity was high [β (95% CI) = 0.32 (0.17-0.46), P < 0.001] or if age was high [β (95% CI) = 0.34 (0.20-0.48), P < 0.001], but not if either 11β-HSD2 activity or age was low. There was a positive association of type 2 diabetes with copeptin [OR (95% CI) = 2.07 (1.10-3.89), P = 0.024), but not for MetS (OR (95% CI) = 1.12 (0.74-1.69), P = 0.605), after full adjustment.

CONCLUSIONS

Our data suggest that age and apparent 11β-HSD2 activity modulate the association of copeptin with insulin resistance at the population level but not MeTS or diabetes. Further research is needed to corroborate these results and to understand the mechanisms underlying these findings.

Analysis of a random modulation single photon counting differential absorption lidar system for space-borne atmospheric CO2 sensing

The ability to observe the Earth's carbon cycles from space provides scientists an important tool to analyze climate change. Current proposed systems are mainly based on pulsed integrated path differential absorption lidar, in which two high energy pulses at different wavelengths interrogate the atmosphere sequentially for its transmission properties and are back-scattered by the ground. In this work an alternative approach based on random modulation single photon counting is proposed and analyzed; this system can take advantage of a less power demanding semiconductor laser in intensity modulated continuous wave operation, benefiting from a better efficiency, reliability and radiation hardness. Our approach is validated via numerical simulations considering current technological readiness, demonstrating its potential to obtain a 1.5 ppm retrieval precision for 50 km averaging with 2.5 W average power in a space-borne scenario. A major limiting factor is the ambient shot noise, if ultra-narrow band filtering technology could be applied, 0.5 ppm retrieval precision would be attainable.

Ultrasonic vocalizations of adult male Foxp2-mutant mice: behavioral contexts of arousal and emotion

Adult mouse ultrasonic vocalizations (USVs) occur in multiple behavioral and stimulus contexts associated with various levels of arousal, emotion and social interaction. Here, in three experiments of increasing stimulus intensity (water; female urine; male interacting with adult female), we tested the hypothesis that USVs of adult males express the strength of arousal and emotion via different USV parameters (18 parameters analyzed). Furthermore, we analyzed two mouse lines with heterozygous Foxp2 mutations (R552H missense, S321X nonsense), known to produce severe speech and language disorders in humans. These experiments allowed us to test whether intact Foxp2 function is necessary for developing full adult USV repertoires, and whether mutations of this gene influence instinctive vocal expressions based on arousal and emotion. The results suggest that USV calling rate characterizes the arousal level, while sound pressure and spectrotemporal call complexity (overtones/harmonics, type of frequency jumps) may provide indices of levels of positive emotion. The presence of Foxp2 mutations did not qualitatively affect the USVs; all USV types that were found in wild-type animals also occurred in heterozygous mutants. However, mice with Foxp2 mutations displayed quantitative differences in USVs as compared to wild-types, and these changes were context dependent. Compared to wild-type animals, heterozygous mutants emitted mainly longer and louder USVs at higher minimum frequencies with a higher occurrence rate of overtones/harmonics and complex frequency jump types. We discuss possible hypotheses about Foxp2 influence on emotional vocal expressions, which can be investigated in future experiments using selective knockdown of Foxp2 in specific brain circuits.

[My patient is too old for a lipid-lowering therapy: myths and reality]

Lipid-lowering treatment in the elderly patient is conditioned by a high incidence and prevalence of cardiovascular disease in the setting of a limited remaining life span. The clinical benefit of statin therapy can be seen after a few months, thus supporting use in secondary prevention even when the lifespan is restricted to a few years. Recent guidelines propose the use of moderate doses in the elderly > 75 years. The evidence for treatment in primary prevention is weaker and the evaluation of the total cardiovascular risk is complicated by the high baseline risk of many elderly. Rational treatment decisions should be based on biologic rather than chronologic age. Statins are generally well tolerated in the elderly, requiring clinical monitoring only, with particular attention to pharmacokinetic interactions and renal failure.

[Screening and management of hypertension in elderly]

The prevalence of hypertension in elderly is extremely high. Because of the burden of ageing of population, this condition considered as the most important risk factor for mortality is supposed to increase. There are some specific pitfalls in the diagnosis and management of hypertension in elderly. The definition of hypertension is the same in all age groups, however the phenotype is different in the elderly: white coat effect, non-dipping pattern, orthostatic hypotension, dysautonomia and pseudohypertension. The hallmark of hypertension in the elderly is pure systolic hypertension and an increased variability of blood pressure. The diagnosis is often difficult to establish. The elderly can be overtreated with undesirable effects of falls or hypoperfusion, particularly when there is frailty, or polymedication.

Hydrolysis of R7T7 Nuclear Waste Glass in Dilute Media: Mechanisms and Rate as a function of Ph

R7T7 nuclear waste glass dissolution in highly dilute aqueous media under static conditions at 90°C occurs according to two different mechanisms depending on the solution acidity. In acid media (pH 4.8 and 5.5), preferential extraction of glass network modifiers results in the formation of an alkali metal-depleted surface region on which amorphous and crystallized (phosphate) compounds rich in transition elements precipitate. Steady-state dissolution conditions are not reached, as attested by variable normalized SI, B and Na mass losses. Glass dissolution is stoichiometric in basic media (pH 7 to 10): the strong bonds of the silicated network are broken at a rate that increases with the pH: the glass dissolution rate increases by a factor of 15 between pH 7 and 10. Under these conditions, alteration products at the glass/solution interface do not constitute a short-term kinetic barrier against the release of the major glass components.

The structure of innate vocalizations in Foxp2-deficient mouse pups

Heterozygous mutations of the human FOXP2 gene are implicated in a severe speech and language disorder. Aetiological mutations of murine Foxp2 yield abnormal synaptic plasticity and impaired motor-skill learning in mutant mice, while knockdown of the avian orthologue in songbirds interferes with auditory-guided vocal learning. Here, we investigate influences of two distinct Foxp2 point mutations on vocalizations of 4-day-old mouse pups (Mus musculus). The R552H missense mutation is identical to that causing speech and language deficits in a large well-studied human family, while the S321X nonsense mutation represents a null allele that does not produce Foxp2 protein. We ask whether vocalizations, based solely on innate mechanisms of production, are affected by these alternative Foxp2 mutations. Sound recordings were taken in two different situations: isolation and distress, eliciting a range of call types, including broadband vocalizations of varying noise content, ultrasonic whistles and clicks. Sound production rates and several acoustic parameters showed that, despite absence of functional Foxp2, homozygous mutants could vocalize all types of sounds in a normal temporal pattern, but only at comparably low intensities. We suggest that altered vocal output of these homozygotes may be secondary to developmental delays and somatic weakness. Heterozygous mutants did not differ from wild-types in any of the measures that we studied (R552H ) or in only a few (S321X ), which were in the range of differences routinely observed for different mouse strains. Thus, Foxp2 is not essential for the innate production of emotional vocalizations with largely normal acoustic properties by mouse pups.

Messungen zum Lärmschutz bei der funktionellen MR-Tomographie

BACKGROUND

Functional magnetic resonance imaging (fMRI) can detect changes in oxygen saturation of the brain. Fast changing high gradient fields are necessary which produce high levels of noise. In studies of the auditory cortex, auditory stimuli have to be perceived and discriminated against the noise level of the activated tomograph.

MATERIAL AND METHODS

The generated frequency bands and their intensities during fMRI with a Siemens Magnetom Vision, 1.5 T, EPI sequence were measured in the outer ear canal of a dummy head. Noise attenuation was evaluated with four different noise muffs (simple/inexpensive products, quality product, specialized fMRI muffs).

RESULTS

Without protection, peak noise levels reached up to 111 dB(A) near 1000 Hz in the dummy ear canal. Major noise attenuation was only found at higher frequencies (4000 Hz by about 25 dB; 8000 Hz by about 35 dB) with the quality product and the specialized fMRI muffs.

CONCLUSION

Only quality noise products can sufficiently protect patients from high sound pressure levels of tomograph noise. If in the future higher gradient fields are applied at faster slew rates, acoustic stimuli can safely be applied only in combination with increased hearing protection systems in order to minimize the risk of noise trauma.

Local lattice distortions in spherical carbon nanoparticles as studied by HRTEM image analysis

The study of lattice distortions in structures with spherical or cylindrical geometry is of growing interest in the field of carbon nanoparticles (onions, nanotubes, etc.). We report an image analysis procedure entirely performed in reciprocal space which provides a global map of the inter-shell distances in carbon nanoparticles. This procedure is applied to carbon nanoparticles with a size of 100 nm that are generated under CVD conditions and exhibit positive as well as negative curvature of the basal lattice planes. These nanoparticles are subjected to intense electron irradiation under the beam of a high-voltage electron microscope with an acceleration voltage of 1.25 MeV. We observe a compression in their centre and a dilation of the outer shells. The reciprocal-space analysis of the high-resolution electron microscopy images opens the way to investigate the stability and equilibrium structure of carbon nanoparticles and to conclude on the formation mechanism.

Synthesis of CoFe2O4nanowire in carbon nanotubes. A new use of the confinement effect

Cobalt ferrite nanowires with an average diameter of 50 nm and lengths up to several micrometers were synthesized inside carbon nanotubes under mild reaction conditions using the confinement effect provided by the carbon tubular template.

Corticofugal reorganization of the midbrain tonotopic map in mice

Previous studies have indicated that frequency maps (tonotopies) in mammalian auditory brain centers are plastic. Here, we examined this plasticity in the mouse auditory midbrain through focal stimulation of the primary auditory cortex. Cortical activation shifted midbrain frequency tunings toward the best frequencies of the stimulated cortical neurons if these were either higher or lower than the cortical ones. Such corticofugal adjustments appear to minimize the difference between cortical and collicular frequency tuning within the critical bandwidths of the auditory system. Consequently, the neural representation is enhanced for the frequencies to which the cortical neurons were tuned. Our data suggest that the auditory cortex reorganizes midbrain tonotopy on the basis of which cortical frequencies are stimulated, mostly probably through corticofugal projections.

Frequency response areas of neurons in the mouse inferior colliculus. I. Threshold and tuning characteristics

Excitatory and inhibitory frequency response areas of 130 neurons of the central nucleus of the mouse inferior colliculus (ICC) were mapped by extracellular single-unit recordings and quantitatively evaluated with regard to thresholds, steepness of slopes of excitatory tuning, characteristic frequencies of excitation (CF(E)), inhibition (CFI), and bandwidths of response areas (sharpness of tuning). Two-tone stimuli were used to determine the shapes of inhibitory response areas. Class I neurons (n=54) had asymmetrical (with regard to the CF(E)) excitatory and inhibitory response areas, with inhibition above CF(E) having lower thresholds and covering larger areas than inhibition below CF(E). Quantitative relationships between CF(E) and CF(I) thresholds, and sharpness of tuning showed that the receptive fields of about two-thirds of these neurons had properties similar to auditory nerve fibers. Class II neurons (n=36) had small symmetrical or tilted excitatory areas of rather constant bandwidths and broad inhibitory areas reaching far into and often through the excitatory area, leading to closed excitatory areas in ten neurons. Class III neurons (n=32) had higher excitatory thresholds and the highest proportions of unilateral inhibitory areas compared with neurons of the other classes. Their excitatory area often widened symmetrically with increasing sound level. Their inhibitory areas did not overlap with the excitatory area. Class IV neurons (n=8) had two branches of excitatory areas (two-CFs(E)) and six of the neurons had a central inhibitory area in addition to the low- and high-frequency inhibitory areas. In most neurons, the shapes of excitatory response areas predicted the shapes of inhibitory areas. Altogether, 15 neurons from all 4 classes had areas of facilitation in addition to inhibitory areas. Facilitation in six class IV neurons occurred between the two branches of the excitatory area. All 130 neurons had large inhibitory areas, 106 of them on both sides of the excitatory area. That is, sound processing in the ICC shows strong inhibitory components. The close relationships between excitatory and inhibitory CFs found here indicate that inhibitory projections to and interactions within the ICC are tonotopically organized comparable to the excitatory ones.

Regional variations of noise-induced changes in operating range in cat AI

Regional differences in spectral integration of neurons in cat primary auditory cortex (AI) suggest that regions differ in effects of background noise on operating characteristics of neurons. Therefore, tone-response threshold, best level (peak-rate intensity), dynamic range, and sharpness of tuning in quiet and in continuous broadband noise were mapped for single neurons along the isofrequency domain of AI. Neurons did not show an excitatory response to the noise. Noise invariably increased the tone-response threshold and best levels. Consequently, the dynamic ranges and receptive fields shifted to higher intensity levels without changes of average sharpness of tuning. These shifts were linearly related to noise level and showed little inter-neuronal variability for neurons in the central, mostly sharply tuned part of AI. In more dorsal and ventral parts of AI, neurons were more variable in tone-response threshold, dynamic range and best level, and no systematic relationship between increase in noise level, threshold increase and best-level increase was observed. We conclude that linear shifts in the operating range of neurons in central AI in the presence of continuous noise backgrounds do not affect other response properties and may relate to the unaltered analysis and representation of spectral components of sounds. In contrast, neurons in dorsal and ventral AI change response properties in a non-predictable way in the presence of noise in accordance with the more complex receptive field properties in those areas.

Perception and recognition discriminated in the mouse auditory cortex by c-Fos labeling

The functions of the fields of the mammalian auditory cortex in sound perception and recognition are unknown. We used Fos (a protein of the inducible immediate-early gene c-fos) as a cellular marker of activated brain areas to show in the mouse (Mus domesticus) that sound is processed differentially in auditory cortical fields according to its actual significance in a behavioral context. Recognition, compared with perception of exactly the same sound, produced significantly less but well focused Fos-positive cells in a primary auditory cortical field and significantly more labeling in higher auditory and association fields. Thus, recognition means a state of distinctive spatial distribution of activity in auditory cortical fields with a predominance of activation in higher-order fields.

Inputs from three brainstem sources to identified neurons of the mouse inferior colliculus slice

A total of 40 neurons from of the central nucleus of the mouse inferior colliculus (IC) were recorded intracellularly from brain slices to determine input properties by electrical stimulation of the ipsilateral lateral lemniscus (LL), commissure of Probst (CP), and commissure of the IC (CoIC) together with cellular morphology (in 25 neurons) by biocytin injection and staining. Nine neurons had oriented (bipolar), 16 neurons non-oriented (multipolar) dendritic trees of various sizes. Axon collaterals of a given neuron often ran in several directions to provide multiple input to adjacent isofrequency laminae, the lateral nucleus of the IC, the brachium of the IC, the LL, the CP, and the IC commissure. Neurons were classified by spike response patterns to depolarizing current injection into onset- and sustained-spiking cells. The former had significantly shorter membrane-time constants, significantly less frequently and smaller hyperpolarizations after spike occurrence, and more Ca2+-humps. These properties and their preferred position in the dorsolateral ICC suggest a participation in binaural temporal processing. Almost all oriented cells showed only excitatory post-synaptic potentials (EPSPs) after LL stimulation, while in non-oriented cells inhibitory post-synaptic potentials (IPSPs) after the EPSPs were significantly more frequent. Neurons with largest dendritic trees and many dorsalward projecting axon collaterals were found in the ventral IC. There, neurons had average 4 ms (two synapses) shorter response latencies to LL stimulation than dorsally located neurons. Thus, neurons in the central and dorsal IC may receive mono- and disynaptic input from ventrally located neurons.

Frequency resolution and spectral integration (critical band analysis) in single units of the cat primary auditory cortex

Frequency resolution and spectral filtering in the cat primary auditory cortex (AI) were mapped by extracellular recordings of tone responses in white noise of various bandwidths. Single-tone excitatory tuning curves, critical bandwidths, and critical ratios were determined as a function of neuronal characteristic frequency and tone level. Single-tone excitatory tuning curves are inadequate measures of frequency resolution and spectral filtering in the AI, because their shapes (in most neurons) deviated substantially from the shapes of "tuning curves for complex sound analysis", the curves determined by the band limits of the critical bandwidths. Perceptual characteristics of spectral filtering (intensity independence and frequency dependence) were found in average critical bandwidths of neurons from the central and ventral AI. The highest frequency resolution (smallest critical bandwidths) reached by neurons in the central and ventral AI equaled the psychophysical frequency resolution. The dorsal AI is special, since most neurons there had response properties incompatible with psychophysical features of frequency resolution. Perceptual characteristics of critical ratios were not found in the average neuronal responses in any area of the AI. It seems that spectral integration in the way proposed to be the basis for the perception of tones in noise is not present at the level of the AI.

The auditory cortex of the house mouse: left-right differences, tonotopic organization and quantitative analysis of frequency representation

Multi-unit electrophysiological mapping was used to establish the area of the left- and right-hemisphere auditory cortex (AC) of the mouse and to characterize various fields within the AC. The AC of the left hemisphere covered a significantly larger (factor of 1.30) area compared to that of the right side. Based on best-frequency (BF) maps and other neuronal response characteristics to tone and noise bursts, five fields (primary auditory field, anterior auditory field, second auditory field, ultrasonic field, dorsoposterior field) and two small non-specified areas could be delimited on both hemispheres. The relative sizes of these fields and areas were similar on both sides. The primary and anterior auditory fields were tonotopically organized with counter running frequency gradients merging in the center of the AC. These fields covered BF ranges up to about 45 kHz. Higher BFs up to about 70 kHz were represented non-tonotopically in the separate ultrasonic field, part of which may be considered as belonging to the primary field. The dorsoposterior and second auditory fields were non-tonotopically organized and neurons had special response properties. These characteristics of the mouse AC were compared with auditory cortical maps of other mammals.

The auditory cortex

The division of the auditory cortex into various fields, functional aspects of these fields, and neuronal coding in the primary auditory cortical field (AI) are reviewed with stress on features that may be common to mammals. On the basis of 14 topographies and clustered distributions of neuronal response characteristics in the primary auditory cortical field, a hypothesis is developed of how a certain complex acoustic pattern may be encoded in an equivalent spatial activity pattern in AI, generated by time-coordinated firing of groups of neurons. The auditory cortex, demonstrated specifically for AI, appears to perform sound analysis by synthesis, i.e. by combining spatially distributed coincident or time-coordinated neuronal responses. The dynamics of sounds and the plasticity of cortical responses are considered as a topic for research.

Normal brainstem auditory evoked potentials in Pax5-deficient mice despite morphologic alterations in the auditory midbrain region

The inferior colliculus in the auditory midbrain region is underdeveloped near the midline in mice lacking the transcription factor Pax5. We have now tested whether hearing deficiencies occur in these mice by measuring auditory evoked brainstem responses. However, the responses and audiograms obtained in homozygous Pax5 mutants did not differ from those of control mice, suggesting that the observed morphologic alterations of the inferior colliculus do not affect hearing, as judged by auditory evoked potential recordings. The only detectable effect of the Pax5 mutation was a delay in the development of the auditory sensitivity and response latency that correlates with the general growth retardation observed in these mice.

Thymic nurse cells: entry of exogenous horseradish peroxidase via a transcytotic route

In order to address the question whether thymocytes inside thymic nurse cells (TNCs) are secluded against exogenous proteins, TNCs were isolated and kept in the presence of horseradish peroxidase. The distribution of horseradish peroxidase reaction product (HRP) within the TNCs was studied by light (LM) and electron microscopy (EM). Stained and unstained TNCs could be distinguished by LM. At the EM level, stained TNCs had a widened lumen and HRP lined the luminal surfaces. In unstained TNCs the lumen appeared normal and contained almost no HRP. In both types of TNCs the epithelial cell contained HRP in endosomes and, together with cellular debris, in larger vacuoles. Exocytosis of the latter was observed. Conglomerates of HRP were found inside the lumen and also within thymocytes. Data suggested that TNCs can shield secluded thymocytes against exogenous proteins except those which are provided by a transcytotic pathway. Such a pathway has not been demonstrated before in TNCs.

Discrimination training in a GO/NOGO-procedure alters the 2-deoxyglucose pattern in the Starling's forebrain

European starling's (Sturnus vulgaris L.) were used to measure differences in the glucose metabolism in the auditory forebrain between birds performing an auditory discrimination task and birds habituated to the same acoustic stimuli. One group (n = 5) of individuals was trained in an operant GO/NOGO-procedure to report 1-kHz tone signals in a background of 4-kHz stimuli. The other group (n = 5) was habituated to the experimental set-up and to the same sequence of tones presented to the trained birds. [14C]2-deoxyglucose (2DG) uptake was determined in the caudal auditory telencephalon and the nucleus ovoidalis of well trained and habituated birds by autoradiography of brain sections. The tissue areas having grey values above predefined threshold values of labelling were determined in every brain section of each bird and then combined to volumes of labelled tissue. No significant differences of the 2DG uptake in the nucleus ovoidalis were found between the two experimental groups. In the caudal auditory telencephalon, however, significant differences in 2DG-labelling were found. In the trained birds, the labelling in the caudal auditory telencephalon was confined to smaller brain regions than in the habituated birds. These results suggest a differential processing of sounds in the trained and habituated birds which is discussed in the context of sharpening of the frequency representation by GABAergic inhibition and processes of attention.

Development of tonotopy in the inferior colliculus II: 2-DG measurements in the kitten

The development of size and tonotopy in the inferior colliculus of the kitten was studied using the [14C]2-deoxyglucose technique and tone stimulation with 2 and 15 kHz at a maximum 110 dB sound pressure level. At 2 days of age, frequency-specific labelling cannot be detected. Two kilohertz labelling is distinctly visible in the rostral and central inferior colliculus at day 6; 15 kHz labelling occurs first at day 11. In the rostral and central inferior colliculus, 2 kHz labelling starts at a ventral and central position and shifts dorsalwards and to a more lateral location between postnatal days 6 and 21. Such a shift is not seen in the caudal inferior colliculus. There, the focus of 2 kHz labelling remains rather constant; only the extension of the labelling increases in the older animals. In all parts of the inferior colliculus, 15 kHz labelling starts at a ventromedial position and shifts to a more lateral location while extending also more dorsalwards as the age increases. These changes in 15 kHz labelling continue up to 3 months. In addition to the ventromedial-to-dorsolateral shift and expansion of labelling, there is also a rostral-to-caudal gradient of maturation, in that in older animals frequency-specific labelling reaches farther caudalwards. The reported changes in frequency representation in the inferior colliculus can be explained on the basis of a shift in frequency input and input sensitivity to the laminae of the inferior colliculus, mainly due to maturational changes within the cochlea and/or as a consequence of the increasing size of the inferior colliculus.

The lung-eardrum pathway in three treefrog and four dendrobatid frog species: some properties of sound transmission

Frequency-response curves of the tympanum and lateral body wall (lung area) were measured by laser Doppler vibrometry in three treefrog (Smilisca baudini, Hyla cinerea, Osteopilus septentrionalis) and four dendrobatid frog (Dendrobates tinctorius, D. histrionicus, Epipedobates tricolor, E. azureiventris) species. The high-frequency cut-off of the body wall response was always lower than that of the tympanum. The best response frequencies of the lateral body wall were lower than those of the tympanum in some species (S. baudini, O. septentrionalis, D. tinctorius), while in the others they were rather similar. Best tympanic frequencies and best body wall response frequencies tended to differ more with increasing body size. Stimulation of the tympanum by sound transfer through 3.14 mm2 areas of the lateral body wall showed that the lung-eardrum pathway can be in two states, depending on breathing activity within the lungs: 44% (in Smilisca), 39% (in Hyla) and 31% (in Osteopilus) of the eardrum vibrations were 2.5-8 times (8-18 dB) larger when the frogs were breathing with the lungs compared with non-breathing conditions. The vibration amplitudes of the tympanum and lateral body wall of the treefrogs followed the same dependence on sound intensity, only absolute amplitudes differed between species. Our results suggest that the lung-eardrum pathway attenuates high-frequency components of species-specific calls and enhances low-frequency components. In addition, an amplitude modulation is imposed on the low frequencies during the rhythm of breathing.