Mice homozygous for the barrelless (brl) mutation, mapped here to chromosome 11, lack barrel-shaped arrays of cell clusters termed "barrels" in the primary somatosensory cortex. Deoxyglucose uptake demonstrated that the topology of the cortical whisker representation is nevertheless preserved. Anterograde tracers revealed a lack of spatial segregation of thalamic afferents into individual barrel territories, and single-cell recordings demonstrated a lack of temporal discrimination of center from surround information. Thus, structural segregation of thalamic inputs is not essential to generate topological order in the somatosensory cortex, but it is required for discrete spatiotemporal relay of sensory information to the cortex.

Barrelless mice (BRL) homozygous for the BRL mutation that disrupts the gene coding for adenylyl cyclase type I on chromosome 11 lack spatial segregation of layer IV cortical cells and of the thalamocortical axons (TCAs) into barrel domains. Despite these morphological perturbations, a functional topographic map has been demonstrated. We reconstructed individual biocytin-injected TCAs from thalamus to barrel cortex in NOR (normal) and BRL mice to analyze to what extent the TCA arborization pattern and bouton distribution could explain the topographic representation of the whisker follicles. In BRL, the geometry of TCA is modified within layer IV as well as in infragranular layers. However, in both strains, the spatial distribution of TCA in layer IV reflects the spatial relationship of their cell bodies in the ventrobasal nucleus of the thalamus. The morphometric analysis revealed that TCAs of both strains have the same length, branch number, and number of axonal boutons in layer IV. However, in barrelless, the boutons are distributed within a larger tangential extent. Analysis of the distribution of boutons from neighboring thalamic neurons demonstrated the existence in layer IV of domains of high bouton density that in both strains equal the size and shape of individual barrels. We propose that the domains of high bouton density are at the basis of the whisker map in barrelless mice.

No abstract

No abstract

Wide-field direction-selective neurones from the optic lobes of the butterfly Papilio aegeus show some properties similar to those displayed by the large neurones of the fly lobula plate. Temporal and spatial frequency threshold tuning curves show that butterfly optic lobe neurones sensitive to different directions of image motion are fed by presynaptic subunits similar to those of the fly. However, unlike fly lobula plate neurones, the butterfly optic lobe neurones show a steep low-spatial-frequency roll-off which persists even at high temporal frequencies. Also exceptional is the temporal resolution of rapid changes in image speed by the butterfly neurones. When the cells are adapted to continuous motion their responses indicate a further increase in temporal resolution. Evidence is provided that in any one state of adaptation the neurones may be thought of as piece-wise linear and, thus, their responses can be predicted by convolution with a velocity kernel measured for that adaptation state. Adaptation to continuous motion results in the cells responding to motion in proportion to the mean motion signal. Motion in the non-preferred direction also appears to adapt the cells. Velocity impulse responses of both butterfly and blowfly neurones were determined with one-dimensional gratings and two-dimensional textured patterns and the results for the two stimuli are shown to be very similar.