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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 106 (1995), S. 391-402 
    ISSN: 1432-1106
    Keywords: Taste ; Insular cortex ; Excitatory amino acid receptor ; Iontophoresis ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Two main subclasses of ionotropic receptors for excitatory amino acids (EAAs), N-methyl-d-aspartate (NMDA) receptors and non-NMDA receptors, are involved in neurotransmission in the cortex of mammals. To examine whether EAAs are transmitters at the cortical taste area (CTA) in rats and to elucidate which types of the two ionotropic receptors operate at these synapses, we studied the effects of microiontophoretic administration of EAA antagonists on the responses of 64 taste cortical neurons to four basic taste stimuli in urethane-anesthetized rats. Both d-2-amino-5-phosphonovalerate (APV), a selective antagonist for NMDA receptors, and 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX), a selective antagonist for non-NMDA receptors, suppressed most of the taste responses. The percentage of neurons suppressed by APV (70.3%) was almost the same as that suppressed by CNQX (64.1%). These suppressive effects were independent of the effects of background discharges during the prestimulus, water-rinsing period. The percentage of neurons suppressed by the antagonists did not differ between any pairs of taste stimuli. The number of neurons possessing both receptors was larger in the granular insular area (area GI), one of the two CTAs, than in the dysgranular insular area (area DI). In addition, taste responses were suppressed by CNQX or by both APV and CNQX in area GI in a significantly larger number of layer V neurons than in area DI. The present results indicate that normal excitatory transmission of taste afferents in the CTA in rats was mediated by both NMDA and non-NMDA receptors. The finding that a large fraction of neurons in the CTA in rats mediated taste information through NMDA receptors in normal transmission might be related to the higher potency of the plasticity observed in the CTA.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 68 (1987), S. 458-465 
    ISSN: 1432-1106
    Keywords: Parabrachio-thalamic relay neurons ; Parabrachial nucleus ; Taste ; Mechanoreception ; Receptive field ; Oral cavity ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Receptive fields (RFs) of 36 taste (the 22 parabrachio-thalamic relay (P-T) and 14 non-P-T) and 23 mechanoreceptive neurons (7 P-T and 16 non P-T) were located in the oral cavity of rats. All of the taste and most of the mechanoreceptive units examined had an RF on the ipsilateral side of the tongue or palate, but some mechanoreceptive P-T and non-P-T units had RFs bilaterally. When the RFs of taste neurons were examined with the most effective of the four basic taste (the best stimulus) and non-best stimuli, no difference was noticed in the location of RFs between the P-T and non-P-T neurons. Though most of the P-T neurons (7/11) and all of the non-P-T neurons (6/6) had an RF for non-best stimuli at a region similar to that for the best stimulus, some P-T neurons (4/11) had an RFs for non-best stimulus outside the RF for the best stimulus and/or on the region separate from the RF for the best stimulus. The P-T neurons, responding vigorously to non-optimal stimuli as well as to the best stimulus, had an RF outside the RF for the best stimulus. RFs for mechanical stimulation were also examined in some taste and mechanoreceptive neurons. The mechanoreceptive P-T units rarely had an RF exclusively on the palate. Some mechanoreceptive units had an RF on the region where no taste RF has been found, e.g. the intermolar eminence and the folium of the hard palate.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 91 (1992), S. 408-414 
    ISSN: 1432-1106
    Keywords: Taste ; Cortex ; Receptive fields ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Receptive fields (RFs) of 59 cortical taste neurons (35 in the granular insular area, area GI, 21 in the dysgranular insular area, area DI, and 3 in the agranular insular area, area AI) were identified in the oral cavity of the rat. The fraction of the neurons with RFs in the anterior oral cavity only was significantly larger in area GI (74.3%) than in area DI (42.9%). On the other hand, the fraction of neurons with RFs in both the anterior and posterior oral cavity was larger in area DI (42.9%) than in area GI (11.4%). On the whole, it is suggested that area GI is involved in discrimination of several taste stimuli in the oral cavity, whereas in area DI taste information originating from various regions of the oral cavity is integrated. When neurons were classified according to the best stimulus which most excited the neuron among the four basic tastes, different categories of taste neurons had RFs in different parts of the oral cavity. It is suggested that, in either taste area, different categories of taste neurons are involved in different sorts of taste coding. The majority of neurons in both areas had bilateral RFs. In area GI, neurons with RFs on single subpopulations of taste buds were significantly more numerous at the rostral region of the cortex than at the caudal region. There was no such relation between RF types and cortical localization in area DI. Otherwise, topographic representation of the oral cavity by taste neurons on the cortical surface was not obvious. RF features of taste neurons did not differ across layers in either cortical area.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 91 (1992), S. 415-424 
    ISSN: 1432-1106
    Keywords: Taste ; Insular cortex ; Response profile ; Inhibitory response ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The responses of 84 taste neurons to stimulation of the oral cavity in rats were examined; most taste neurons were found in either a granular insular area (area GI; n = 55) or dysgranular insular area (DI; n = 25), and the others (n = 4) were in an agranular insular area (area AI). The fraction of neurons responding to only one of the four basic stimuli was significantly larger in area GI than in area DI. When neurons were classified by the stimulus which most excited the neuron among the four basic stimuli, every “best-stimulus category” of neurons was found in both GI and DI areas. Quinine-best and “multistimulus-type” neurons, whose responses to some non-best stimulus exceeded 90% of the maximum, were more numerous in the cortex than in the thalamocortical relay neurons. When responses were plotted against taste stimuli arranged in the order of sucrose, NaCl, HCl, and quinine along the abscissa (taste coordinate), response profiles of taste neurons often showed two peaks. The double-peaked type of response profiles were found in every best-stimulus category of neurons in both areas; though, a significantly large fraction of quinine-best neurons in area GI were of the double-peaked type. Some taste neurons in area GI (n = 21) and in area DI (n = 7) were inhibited by one to two taste stimuli, particularly by the stimuli present next to the best one along the taste coordinate. In correlation profiles — correlation coefficients between sucrose and NaCl and between HCl and quinine — pairs of stimuli which were located next to each other on the taste coordinate were significantly smaller in area GI than in area DI. It is thus highly probable that area GI plays an important role in fine taste discrimination and area DI in integration of taste information.
    Type of Medium: Electronic Resource
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