Multiple tooth-losses during development suppress age-dependent emergence of oscillatory neural activities in the oral somatosensory cortex.

Tooth and tooth-related organs play important roles in not only mastication, but also sensory perception in the oral region. In general, sensory neural inputs during the developmental period are required for the maturation of functions in the sensory cortex. However, whether maturations of oral somatosensory cortex (OSC) require certain levels of sensory input from oral regions has been unclear.

Component-dependent urine responses in the rat accessory olfactory bulb.

To investigate how pheromonal information is processed in the rat accessory olfactory bulb, we optically imaged intrinsic signals to obtain high-resolution maps of activation induced by urinary stimulation. Application of volatile components in male urine mainly induced activation in the anterior accessory olfactory bulb, irrespective of the sex, whereas volatile female urine elicited activation not only in the anterior but also to some extent in the caudal part of the posterior accessory olfactory bulb of male, but not female, rats. Nonvolatile components of both male and female urine induced activation mainly in the rostral part of the posterior and to a lesser extent in the anterior accessory olfactory bulb, irrespective of the sex.

Cyclic AMP-dependent attenuation of oscillatory-activity-induced intercortical strengthening of horizontal pathways between insular and parietal cortices.

Cyclic AMP (cAMP) is a key intracellular second messenger, and the intracellular cAMP signaling pathway acts to modulate various brain functions. We have previously reported that low-frequency insular cortex stimulation in rat brain slices switches on a voltage oscillator in the parietal cortex that delivers signals horizontally back and forth under caffeine application. The oscillatory activities are N-methyl-D-aspartate (NMDA) receptor-dependent, and the role of oscillation is to strengthen functional intercortical connections.

NMDA receptor-dependent oscillatory signal outputs from the retrosplenial cortex triggered by a non-NMDA receptor-dependent signal input from the visual cortex.

The retrosplenial cortex is located at a critical juncture between the visual cortex and hippocampal formation. Functions of the retrosplenial cortex at the local circuit level, however, remain unclear. Herein, we show how signals traveling from the visual cortex behave in local circuits of the retrosplenial cortex, using optical recording methods and application of caffeine to rat brain slices.

Strengthening of non-NMDA receptor-dependent horizontal pathways between primary and lateral secondary visual cortices after NMDA receptor-dependent oscillatory neural activities.

Emergence of oscillatory signal flows between the primary visual cortex (Oc1) and medial secondary visual cortex (Oc2M) was previously dynamically demonstrated in rat brain slices by us. Applying caffeine, a neural modulator, to the slices and using optical recording methods revealed this facilitation along horizontal intrinsic pathways in which initial forward propagation from Oc1 to Oc2M was dependent on both N-methyl-D-aspartate receptors (NMDARs) and non-NMDARs. Conversely, oscillatory backward propagation from Oc2M to Oc1 was entirely dependent on NMDARs.

To-and-fro optical voltage signal propagation between the insular gustatory and parietal oral somatosensory areas in rat cortex slices.

Taste perception depends not only on special taste information processed in the insular cortex, but also on oral somesthetic processing in the parietal cortex. Many insular cortex neurons show multimodal responsiveness. Such multimodality may be enabled by signal exchange between these two cortices.

Cortical spatial aspects of optical intrinsic signals in response to sucrose and NaCl stimuli.

To examine whether cortical taste neurons use spatial codes for discriminating taste information, we investigated the spatial aspects of optical intrinsic signal (OIS) responses in the gustatory insular cortex (GC) elicited by the administration of two essential tastants, sucrose and NaCl, on the tongue. OIS responses to sucrose appeared in the rostral part of the GC, whereas those to NaCl appeared in the central part of the GC. Local anesthetization of the tongue abolished OIS responses, and the administration of distilled water elicited no OIS response.

Age-dependent emergence of a parieto-insular corticocortical signal flow in developing rats.

By using the procedure that we developed for inducing population oscillation, it was previously demonstrated that insular cortex stimulation can evoke insulo-parietal field potential propagation and synchronized population oscillation in the parietal cortex in slices obtained from mature rats (27-35 days old). By using the same procedure, we have now studied the reciprocal parieto-insular projection. Parietal cortex stimulation elicited synchronized population oscillation in the parietal--but not insular--cortex in mature tissues.

Postsynaptic metabotropic glutamate receptor mGluR1 mediates the late component of signal propagation in the guinea pig piriform cortex: optical imaging study.

Metabotropic glutamate receptors (mGluRs) were previously shown to mediate a postsynaptic late propagation component elicited by layer Ib stimulation in guinea pig piriform cortex slices. In the present study, the effects of some group specific or subtype specific mGluR antagonists on the late propagation component were investigated using an optical imaging method, in order to identify mGluR subtypes mediating it. A selective mGluR1 antagonist (RS)-1-aminoindan-1,5-dicarboxylic acid most effectively suppressed the late component whereas a selective mGluR5 antagonist, selective group II or group III antagonists showed little or no suppressive effect.

Age-dependent emergence of oscillatory signal flow between the primary and secondary visual cortices in rat brain slices.

Developmental changes in dynamics of signal propagation between the primary (Oc1) and secondary visual cortex (Oc2) were investigated by using optical recording methods with voltage-sensitive dyes. Propagating oscillatory optical responses were evoked by our previously reported procedure, and were recorded on stimulation to white matter of Oc1 in rat visual cortex slices. In immature slices, evoked signals spread out from the stimulation site by way of deep layers, but were restricted largely to Oc1.

Age-dependent appearance of an insulo-parietal cortical signal propagation that elicits a synchronized population oscillation in the parietal cortex in rats.

We investigated postnatal development of a functional connectivity from the gustatory insular cortex to the parietal cortex, which is known to contain many more neurons responding to oral somesthetic stimulation than the insular cortex, in slices obtained from 9-35-day-old rats. Field potentials were evoked by stimulation to the insular cortex. In the mature cortex, insular stimulation elicited a solitary field potential in both the insular and parietal cortices and, as the simulation continued, the initial solitary potential came to be followed by a population oscillation of field potential in the parietal cortex, but not in the insular cortex.

Postsynaptic activity of metabotropic glutamate receptors in the piriform cortex.

Effects of some glutamate receptor antagonists on signal propagation elicited by stimulation of association fibers in guinea pig piriform cortex slices were investigated using optical imaging. During simultaneous application of both NMDA and non-NMDA receptor antagonists (D-2-amino-5-phosphonopentanoic acid and 6-cyano-7-nitroquinoxaline-2,3-dione, respectively) the postsynaptic activity was largely suppressed, and a weak although distinct late propagation component was found to survive. This latter component was reversibly suppressed by application of low Ca(2+) solution or a group I/II specific metabotropic glutamate receptor (mGluR) antagonist (+)-alpha-methyl-4-carboxyphenylglycine.

Age-dependent occurrence of synchronized population oscillation suggestive of a developing functional coupling between NMDA and ryanodine receptors in the neocortex.

Synchronized population oscillation of delta to alpha range frequencies was synaptically induced in rat visual cortex neurons, depending on (1) the extent of N-methyl-D-aspartate (NMDA) receptor activation, (2) occurrence of calcium-induced calcium release (CICR), and (3) the age of animals. In adult slices bathed with 0.1 mM Mg(2+), as white matter stimulation continued, solitary synaptic potentials gradually became enlarged and overridden by small wavelets oscillating at alpha range frequencies.