Michio Sugitani

Properties of cells responding to visual stimuli in the rat ventral lateral geniculate nucleus

Abstract Single-unit recordings were made of the ventral lateral geniculate nucleus (LGv) in the albino rat anesthetized with urethane. Visual receptive field properties as well as the characteristics of responses elicited by electrical stimuli to the optic tract and to the visual cortex were examined. Compared with the relay cells of the dorsal lateral geniculate nucleus (LGd), LGv cells were characterized by the following properties. (i) They responded to visual cortex stimuli orthodromically as well as to optic tract shocks. (ii) The postexcitatory inhibition they showed after single optic tract or visual cortex stimuli was only short-lasting, at most 100 ms. (iii) Conduction velocities of the optic nerve afferent fibers were mostly in the range of slow fibers, 2 to 10 m/s. (iv) The receptive fields were essentially homogeneous in type; about 90% of the sample of 53 cells were On-tonic. (v) Receptive field sizes were substantially large, from 6.3 to 45.6° (mean, 22.3°). (vi) On-tonic cells revealed a regular maintained discharge whose level changed monotonically as a function of the luminous intensity of the stimulating light. The functional implications of these findings were compared with those of the relay cells in the LGd.

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 Ca2+ solution or a group I/II specific metabotropic glutamate receptor (mGluR) antagonist (+)-&agr;-methyl-4-carboxyphenylglycine. These results suggest that mGluRs mediate postsynaptic excitation, which would play a crucial role in activating the reverberating positive feedback circuit effectively.

Retinal inputs to the geniculate relay cells in the eastern chipmunk (Tamias sibiricus asiaticus): a comparison between color and non-color sensitive cells

Single unit recordings were made from the relay cells of the lateral geniculate nucleus in the eastern chipmunk. Of 362 relay cells, 47 cells (13%) were classified as color sensitive and the rest as non-color sensitive cells. Non-color sensitive cells were further classified into 5 subclasses: off-phasic, on-phasic, on-off-phasic, on-tonic and uncommon types. Within the color sensitive cells there were 3 subclasses; blue excited and green inhibited (+B-G), blue inhibited and green excited (-B+G), and blue excited (+B) cells. Retinal afferents to color sensitive relay cells had the following characteristics: ganglion cells of their origin were distributed in the central high density areas of the retina and axonal conduction velocities were in the intermediate range, though they were somewhat slow in +B cells.

Effects of double pulse stimulation on signal propagation in guinea pig piriform cortex slices with a cut in layer Ia or Ib revealed by optical imaging

We previously showed that signal propagation in the piriform cortex (PC) elicited by stimulation of layer In was severely damaged when either layer Ia or Ib was cut. In the present study, double pulse stimulation was applied to layer Ia of slices where either layer Ia or Ib 0.4-0.7 mm caudal to the site of stimulation was cut, to investigate if temporal summation of excitation from the remaining fiber system to pyramidal cells could recover the damaged signal propagation. In 74% of samples with layer Ia cut and in 68% of those with layer Ib cut, double pulse stimulation, as compared with single pulse, obviously increased the excitability in the region caudal to the cut. The excitability induced by double pulse, however, reached to at most 50% of that in the same region induced by single pulse before the cut was made. Thus, it is suggested that convergence of inputs from afferent and association fibers onto pyramidal cells is indispensable for generating strong signal propagation in PC.

1907 Effects of a cut in layer Ib on signal propagation in guinea pig piriform cortex—Optical imaging study

YOICHI OGAWA Single unit activities from the olfactory bulb were recorded during the period that the rat was sniffing. Spectral analysis by Walsh transform was applied to the spike train of unit. In addition, the inter spike intervals were measured to estimate post-spike excitability and serial correlations. The modulation of firing due to respiration cycles was observed in only 4 units (10%). Thirty-three units (82.5%) displayed low-frequency fluctuation in the spectrum of spike train. These units also showed recurrent facilitation in post spike excitability. Furthermore, the serial correlation of the first order was significantly positive in 36 units (90%). The degree of fluctuation was significantly correlated with the amplitude of recurrent facilitation and with the serial correlation. These results suggest that recurrent facilitation cause fluctuation in firing.

Symposium 7. Molecular biological approach to behavioral neuroscience20. Chemical senses, olfaction and taste2008 Effects of a cut in layer ia on signal propagation in guinea pig piriform cortex — optical imaging study

We have elucidated some patterns of signal propagation in slices of guinea pig pirifotm cortex (PC) stained with a voltage-sensitive dye (RH482) using optical imaging. In sagittal slices, neural activity evoked by elect&al stimulation of layer Ia propagates mainly to the caudal direction along layer II/IlI. This propagation is considered to be mediated by afferent fibers in layer Ia and association fibers in layer Ib. To estimate degrees of participation of these two groups of fibers in signal propagation, layer Ia 0.4-0.7 mm caudal to the site of stimulation was cut vertical@ to the cortical stir&e and patterns of propagation to Ia stimulation before and after the cut were compared. In about 60% of 59 samples, although layer lb was left. intact, excitability in the region caudal to the cut was reduced to less than 5% of that before the cut, which means that, in these samples, propagation to the region caudal to the cut suffered a severe damage or completely disappeared. In 29% of the samples, excitability was reduced to 5-25%. In only 7% of the samples, excitability of more than 50% of the control was maintained in the region caudal to the cut Thus, so tar, it is likely that the participation of afferent fibers to signal propagation in PC is much greater than that of association fibers. When layer lb was stimulated in intact slices, however, fairly strong propagation akmg layer II/Ill coukl be elicited. It would therefore be necessary to investigate effects of layer Ib cut on propagation evoked by stimulation of layer Ia and Ib, to evaluate properly the role of association fibers in signal propagation.