Nicotinic alteration of functional thalamocortical topography

Propagating wave activity in a tangential cortical slice

Propagating neural waves in the cerebral cortex influence the integration of incoming sensory information with ongoing cortical activity. However, the neural circuit elements that support these cortical waves remain to be fully defined. Here, a novel tangential slice preparation was developed that exhibited propagating wave activity across the dorsal cortical sheet, as assessed using autofluorescence imaging following focal electrical stimulation. Analysis of functional connectivity in the slice preparation with laser-scanning photostimulation via glutamate uncaging revealed a lack of short-latency, presumed monosynaptic, long-range connections (>300 μm) in the slice preparation. These results establish a novel slice preparation for assessing cortical dynamics and support the proposition that interactions among local cortical elements are sufficient to enable widespread propagating wave activity.

Functional Topography and Development of Inhibitory Reticulothalamic Barreloid Projections

The thalamic reticular nucleus (TRN) is the main source of inhibition to the somatosensory thalamus (ventrobasal nucleus, VB) in mice. However, the functional topography and development of these projections with respect to the VB barreloids has been largely unexplored. In this respect, to assist in the study of these projections, we have utilized a vesicular gamma-aminobutryic acid (GABA) transporter (VGAT)-Venus transgenic mouse line to develop a brain slice preparation that enables the rapid identification of inhibitory neurons and projections. We demonstrate the utility of our in vitro brain slice preparation for physiologically mapping inhibitory reticulothalamic (RT) topography, using laser-scanning photostimulation via glutamate uncaging. Furthermore, we utilized this slice preparation to compare the development of excitatory and inhibitory projections to VB. We found that excitatory projections to the barreloids, created by ascending projections from the brain stem, develop by postnatal day 2-3 (P2-P3). By contrast, inhibitory projections to the barreloids lag ~5 days behind excitatory projections to the barreloids, developing by P7-P8. We probed this lag in inhibitory projection development through early postnatal whisker lesions. We found that in whisker-lesioned animals, the development of inhibitory projections to the barreloids closed by P4, in register with that of the excitatory projections to the barreloids. Our findings demonstrate both developmental and topographic organizational features of the RT projection to the VB barreloids, whose mechanisms can now be further examined utilizing the VGAT-Venus mouse slice preparation that we have characterized.

Wisteria Floribunda Agglutinin-Labeled Perineuronal Nets in the Mouse Inferior Colliculus, Thalamic Reticular Nucleus and Auditory Cortex

Perineuronal nets (PNNs) are specialized extracellular matrix molecules that are associated with the closing of the critical period, among other functions. In the adult brain, PNNs surround specific types of neurons, however the expression of PNNs in the auditory system of the mouse, particularly at the level of the midbrain and forebrain, has not been fully described. In addition, the association of PNNs with excitatory and inhibitory cell types in these structures remains unknown. Therefore, we sought to investigate the expression of PNNs in the inferior colliculus (IC), thalamic reticular nucleus (TRN) and primary auditory cortex (A1) of the mouse brain by labeling with wisteria floribunda agglutinin (WFA). To aid in the identification of inhibitory neurons in these structures, we employed the vesicular GABA transporter (VGAT)-Venus transgenic mouse strain, which robustly expresses an enhanced yellow-fluorescent protein (Venus) natively in nearly all gamma-amino butyric acid (GABA)-ergic inhibitory neurons, thus enabling a rapid and unambiguous assessment of inhibitory neurons throughout the nervous system. Our results demonstrate that PNNs are expressed throughout the auditory midbrain and forebrain, but vary in their local distribution. PNNs are most dense in the TRN and least dense in A1. Furthermore, PNNs are preferentially associated with inhibitory neurons in A1 and the TRN, but not in the IC of the mouse. These data suggest regionally specific roles for PNNs in auditory information processing.