P. van Dijk

Functional imaging of unilateral tinnitus using fMRI

Conclusions. This article shows that the inferior colliculus plays a key role in unilateral subjective tinnitus. Objectives. The major aim of this study was to determine tinnitus-related neural activity in the central auditory system of unilateral tinnitus subjects and compare this to control subjects without tinnitus. Subjects and methods. Functional MRI (fMRI) was performed in 10 patients (5 males) with unilateral tinnitus (5 left-sided, 5 right-sided) and 12 healthy subjects (6 males); both groups had normal hearing or mild hearing loss. fMRI experiments were performed using a 3T Philips Intera Scanner. Auditory stimuli were presented left or right and consisted of dynamically rippled broadband noise with a sound pressure level of 40 or 70 dB SPL. The responses of the inferior colliculus and the auditory cortex to the stimuli were measured. Results. The response to sound in the inferior colliculus was elevated in tinnitus patients compared with controls without tinnitus.

Simulations of flowering time displacement between two cytotypes that form inviable hybrids

The evolution of reproductive isolation by flowering time displacement between two cytotypes that produce inviable hybrids was studied by computer simulations in an isolation-by-distance model. Flowering time distribution was stabilized by mass-action, both by the mating procedure and by pollen-limited seed-production in early or late flowering plants. Coexistence had to last long enough for flowering time divergence to evolve. This could only be achieved in a mosaic of local patches or parapatry. The model showed that flowering time displacement occurred despite the stabilizing effect of mass-action and the restricted width of the interaction zone. Initially an inverse cline for flowering time was formed but after 200 generations this cline had become monotonic. In contrast to the possible swamping effect by gene flow from outside the zone, there was a spread of genes into the allopatric ranges.

The role of tetraploids in the sexual-asexual cycle in dandelions (Taraxacum).

Apomictic plants often produce pollen that can function in crosses with related sexuals. Moreover, facultative apomicts can produce some sexual offspring. In dandelions, Taraxacum, a sexual–asexual cycle between diploid sexuals and triploid apomicts, has been described, based on experimental crosses and population genetic studies. Little is known about the actual hybridization processes in nature. We therefore studied the sexual–asexual cycle in a mixed dandelion population in the Netherlands. In this population, the frequencies of sexual diploids and triploids were 0.31 and 0.68, respectively. In addition, less than 1% tetraploids were detected. Diploids were strict sexuals, triploids were obligate apomicts, but tetraploids were most often only partly apomictic, lacking certain elements of apomixis. Tetraploid seed fertility in the field was significantly lower than that of apomictic triploids. Field-pollinated sexual diploids produced on average less than 2% polyploid offspring, implying that the effect of hybridization in the 2x–3x cycle in Taraxacum will be low. Until now, 2x–3x crosses were assumed to be the main pathway of new formation of triploid apomicts in the sexual–asexual cycle in Taraxacum. However, tetraploid pollen donors produced 28 times more triploid offspring in experimental crosses with diploid sexuals than triploid pollen donors. Rare tetraploids may therefore act as an important bridge in the formation of new triploid apomicts.

Neural correlates of human somatosensory integration in tinnitus

Possible neural correlates of somatosensory modulation of tinnitus were assessed. Functional magnetic resonance imaging (fMRI) was used to investigate differences in neural activity between subjects that can modulate their tinnitus by jaw protrusion and normal hearing controls. We measured responses to bilateral sound and responses to jaw protrusion. Additionally we studied multimodal integration of somatosensory jaw protrusion and sound. The auditory system responded to both sound and jaw protrusion. Jaw responses were enhanced in the cochlear nucleus (CN) and the inferior colliculus (IC) in tinnitus patients. The responses of the auditory brain areas to jaw protrusion presumable account for the modulation of tinnitus as described by the patients. The somatosensory system responded to jaw protrusion and not to sound. These responses occurred both in subjects with tinnitus and controls. Unexpectedly, the cerebellum responded to sound in normal hearing subjects, but not in tinnitus patients. Together, these results provide a neurophysiological basis for the effect of jaw protrusion on tinnitus.

Evidence for autotetraploidy in Plantago media and comparisons between natural and artificial cytotypes concerning cell size and fertility

The hypothesis of autotetraploidy in Plantago media (2n = 12 and 2n = 24) was tested. The two cytotypes are morphologically very similar. Rare 4X and 3X hybrids were obtained in inter-ploidy crosses. The reproductive isolation between 2X and 4X is post-zygotic and can be broken down and introduced by colchicine treatment. The studied diploid and tetraploid populations shared the same alleles for nine allozyme loci. Together this provides strong evidence for autotetraploid origin of tetraploid P. media. Fertility of colchicine tetraploids was comparable to natural tetraploids and slightly lower than natural diploids. In contrast to colchicine tetraploids, natural tetraploids did not show gigas-characteristics. Tetraploid hybrids between diploids and natural tetraploids showed partial gigas-characteristics. The possible reasons for the differences in cell size between cytotypes are discussed. Differentiating characters between the natural cytotypes were not affected by colchicine treatment and are therefore not a direct consequence of polyploidization.The hypothesis of autotetraploidy in Plantago media (2n = 12 and 2n = 24) was tested. The two cytotypes are morphologically very similar. Rare 4X and 3X hybrids were obtained in inter-ploidy crosses. The reproductive isolation between 2X and 4X is post-zygotic and can be broken down and introduced by colchicine treatment. The studied diploid and tetraploid populations shared the same alleles for nine allozyme loci. Together this provides strong evidence for autotetraploid origin of tetraploid P. media. Fertility of colchicine tetraploids was comparable to natural tetraploids and slightly lower than natural diploids. In contrast to colchicine tetraploids, natural tetraploids did not show gigas-characteristics. Tetraploid hybrids between diploids and natural tetraploids showed partial gigas-characteristics. The possible reasons for the differences in cell size between cytotypes are discussed. Differentiating characters between the natural cytotypes were not affected by colchicine treatment and are therefore not a direct consequence of polyploidization.

Asymmetry in primary auditory cortex activity in tinnitus patients and controls

Tinnitus is a bothersome phantom sound percept and its neural correlates are not yet disentangled. Previously published papers, using [(18)F]-fluoro-deoxyglucose positron emission tomography (FDG-PET), have suggested an increased metabolism in the left primary auditory cortex in tinnitus patients. This unilateral hyperactivity has been used as a target in localized treatments such as transcranial magnetic stimulation. The purpose of the current study was to test whether left-sided hyperactivity in the auditory cortex is specific to tinnitus or is a general characteristic of the auditory system unrelated to tinnitus. Therefore, FDG-PET was used to measure brain metabolism in 20 tinnitus patients and to compare their results to those in 19 control subjects without tinnitus. In contrast to our expectation, there was no hyperactivity associated with tinnitus. Nevertheless, the activity in the left primary auditory cortex was higher than in the right primary auditory cortex, but this asymmetry was present in both tinnitus patients and control subjects. In contrast, the lateralization in secondary auditory cortex was opposite, with higher activation in the right hemisphere. These data show that hemisphere asymmetries in the metabolic resting activity of the auditory cortex are present, but these are not associated with tinnitus and are a normal characteristic of the normal brain.

The effect of sulfide in the ambient air on amino acid metabolism of spinach leaves

Exposure of spinach plants to 250 ppb H2S for two days resulted in a 70% decrease of the serine concentration of the leaves. The concentration of most amino acids increased on average by 100%, cyst(e)ine at least by 1400%. Also the ammonia concentration increased upon H2S exposure. The concentrations of glutamate, glutamine and aspartate were unaltered by exposure. The relation between glutathione and cyst(e)ine accumulation and changes in amino acid metabolism upon H2S exposure is discussed. The kinetics of glutamine synthetase and glutamate dehydrogenase of spinach leaves were not affected by short-term H2S exposure.

Association Between Subjective Tinnitus and Cervical Spine or Temporomandibular Disorders: A Systematic Review

Movements of the neck and jaw may modulate the loudness and pitch of tinnitus. The aim of the present study was to systematically analyze the strength of associations between subjective tinnitus, cervical spine disorders (CSD), and temporomandibular disorders (TMD). A systematic literature search of the Medline, Embase, and Pedro databases was carried out on articles published up to September 2017. This covered studies in which tinnitus and CSD or TMD were studied as a primary or a secondary outcome and in which outcomes were compared with a control group. Included articles were evaluated on nine methodological quality criteria. Associations between tinnitus and CSD or TMD were expressed as odds ratios. In total, 2,139 articles were identified, of which 24 studies met the inclusion criteria. Twice, two studies were based on the same data set; consequently, 22 studies were included in the meta-analysis. Methodological quality was generally limited by a lack of blinding, comparability of groups, and nonvalidated instruments for assessing CSD. Results indicated that patients with tinnitus more frequently reported CSD than subjects without tinnitus. The odds ratio was 2.6 (95% CI [1.1, 6.4]). For TMD, a bidirectional association with tinnitus was found; odds ratios ranged from 2.3 (95%CI [1.5, 3.6]) for arthrogenous TMD to 6.7 (95%CI [2.4, 18.8]) for unspecified TMD. Funnel plots suggested a publication bias. After adjusting for this, the odds ratios decreased, but associations persisted. There is weak evidence for an association between subjective tinnitus and CSD and a bidirectional association between tinnitus and TMD.

The mechanical response of the tectorial membrane in the frog inner ear

The basilar papilla is the high-frequency auditory papilla in the frog inner ear. We show that the tectorial membrane in the basilar papilla has a frequency selective responds that corresponds to that of auditory neurons. These results show that frequency selectivity in the papilla is based on the mechanical tuning of the tectorial membrane.

Genetic Variation Within Plantago Populations

Genetic variation is one of the means which enable a species to occupy an extensive geographic distribution and to occur in large numbers in heterogeneous environments. Genetic differentiation within a species can be manifested on different levels. Geographic races may occur in geographically different parts of the species range. In that case only a limited exchange of genes between remote parts of the distribution will occur. Genetic differences between populations can be brought about by chance processes, by selection and by a combination of both. If selection is the main cause for differentiation both geographical distance and genetic isolation will be relatively less important factors in structuring the genetic variation. In that case different specific genotypes (ecotypes) each adapted to specific environmental conditions, will occur. In many cases populations will consist of a single, particular, ecotype though also several ecotypes within a population may occur, depending on the level of hybridization and the habitat heterogeneity