alpha-tectorin is an extracellular matrix molecule of the inner ear. Mice homozygous for a targeted deletion in a-tectorin have tectorial membranes that are detached from the cochlear epithelium and lack all noncollagenous matrix, but the architecture of the organ of Corti is otherwise normal. The basilar membranes of wild-type and alpha-tectorin mutant mice are tuned, but the alpha-tectorin mutants are 35 dB less sensitive. Basilar membrane responses of wild-type mice exhibit a second resonance, indicating that the tectorial membrane provides an inertial mass against which outer hair cells can exert forces. Cochlear microphonics recorded in alpha-tectorin mutants differ in both phase and symmetry relative to those of wild-type mice. Thus, the tectorial membrane ensures that outer hair cells can effectively respond to basilar membrane motion and that feedback is delivered with the appropriate gain and timing required for amplification.

The transient receptor potential vanilloid type 1 channel (TRPV1) (formerly called vanilloid receptor VR1) is known for its key role of functions in sensory nerves such as perception of inflammatory and thermal pain. Much less is known about the physiological significance of the TRPV1 expression in the brain. Here we demonstrate that TRPV1 knock-out mice (TRPV1-KO) show less anxiety-related behavior in the light-dark test and in the elevated plus maze than their wild-type littermates with no differences in locomotion. Furthermore, TRPV1-KO mice showed less freezing to a tone after auditory fear conditioning and stress sensitization. This reduction of conditioned and sensitized fear could not be explained by alterations in nociception. Also, tone perception per se was unaffected, as revealed by determination of auditory thresholds through auditory brainstem responses and distortion-product otoacoustic emissions. TRPV1-KO showed also less contextual fear if assessed 1 d or 1 month after strong conditioning protocols. These impairments in hippocampusdependent learning were mirrored by a decrease in long-term potentiation in the Schaffer collateral-commissural pathway to CA1 hippocampal neurons. Our data provide first evidence for fear-promoting effects of TRPV1 with respect to both innate and conditioned fear and for a decisive role of this receptor in synaptic plasticity.

Changes in the sensory environment are good indicators for behaviorally relevant events and strong triggers for the reallocation of attention. In the auditory domain, violations of a pattern of repetitive stimuli precipitate in the event-related potentials as mismatch negativity (MMN). Stimulus-specific adaptation (SSA) of single neurons in the auditory cortex has been proposed to be the cellular substrate of MMN (Nelken and Ulanovsky, 2007). However, until now, the existence of SSA in the awake auditory cortex has not been shown. In the present study, we recorded single and multiunits in parallel with evoked local field potentials (eLFPs) in the primary auditory cortex of the awake rat. Both neurons and eLFPs in the awake animal adapted in a stimulus-specific manner, and SSA was controlled by stimulus probability and frequency separation. SSA of isolated units was significant during the first stimulus-evoked "on" response but not in the following inhibition and rebound of activity. The eLFPs exhibited SSA in the first negative deflection and, to a lesser degree, in a slower positive deflection but no MMN. Spike adaptation correlated closely with adaptation of the fast negative deflection but not the positive deflection. Therefore, we conclude that single neurons in the auditory cortex of the awake rat adapt in a stimulus-specific manner and contribute to corresponding changes in eLFP but do not generate a late deviant response component directly equivalent to the human MMN. Nevertheless, the described effect may reflect a certain part of the process needed for sound discrimination.

Summary. The functional role of GABA and glycine in monaural and binaural signal analysis was studied in single unit recordings from the central nucleus of the inferior colliculus (IC) of horseshoe bats (Rhinolophus rouxi) employing microiontophoresis of the putative neurotransmitters and their antagonists bicuculline and strychnine.Most neurons were inhibited by GABA (98%; N= 107) and glycine (92%; N = 118). Both neurotransmitters appear involved in several functional contexts, but to different degrees.Bicuculline-induced increases of discharge activity (99% of cells; N= 191) were accompanied by changes of temporal response patterns in 35 % of neurons distributed throughout the IC. Strychnine enhanced activity in only 53% of neurons (N= 147); cells exhibiting response pattern changes were rare (9%) and confined to greater recording depths. In individual cells, the effects of both antagonists could markedly differ, suggesting a differential supply by GABAergic and glycinergic networks.Bicuculline changed the shape of the excitatory tuning curve by antagonizing lateral inhibition at neighboring frequencies and/or inhibition at high stimulation levels. Such effects were rarely observed with strychnine.Binaural response properties of single units were influenced either by antagonization of inhibition mediated by ipsilateral stimulation (bicuculline) or by changing the strength of the main excitatory input (bicuculline and strychnine).

Topographic cortical representation of echo delay, the cue for target range, is an organizational feature implemented in the auditory cortices of certain bats dedicated to catch flying insects. Such cortical echo-delay maps provide a calibrated neural representation of object spatial distance. To assess general requirements for echo-delay computations, cortical delay sensitivity was examined in the short-tailed fruit bat Carollia perspicillata that uses frequency-modulated (FM) echolocation signals. Delay-tuned neurons with temporal specificity comparable to those of insectivorous bats are located within the high-frequency (HF) field of the auditory cortex. All recorded neurons in the HF field respond well to single pure-tone and FM-FM stimulus pairs. The neurons respond to identical FM harmonic components in echolocation pulse and delayed echo (e.g., FM(2)-FM(2)). Their characteristic delays (CDs) for low echo amplitudes range between 1 and 24 ms, which is comparable to other bat species. Maps of the topography of FM-FM neurons show that they are distributed across the entire HF area and organized along a rostrocaudal echo-delay axis representing object distance. Rostrally located neurons tuned to delays of 2-8 ms are overrepresented (66% of CDs). Neurons with longer delays (>/=10 ms) are located throughout the caudal half of the HF field. The delay-sensitive chronotopic area covers approximately 3.3 mm in rostrocaudal and approximately 3.7 mm in dorsoventral direction, which is comparable or slightly larger than the size of cortical delay-tuned areas in insectivorous constant frequency bats, the only other bat species for which cortical chronotopy has been demonstrated. This indicates that chronotopic cortical organization is not only used exclusively for precise insect localization in constant frequency bats but could also be of advantage for general orientation tasks.