Organization of spatiotemporal pattern of spontaneous activity and its role in coding temporal sequence were investigated in the hippocampal network model. Automatic alteration of synaptic conductances through STDP organized radially propagating burst activities (RPAs) that initiated at local regions and acted as pacemakers in the CA3 region. The frequency of the rhythmic activity converged into one specific frequency with time, indicating that spontaneous rhythmic activity was regulated by STDP. By applying theta burst stimulation that resembled the activity of place cells, RPAs were organized at the stimulus sites in CA3. The RPAs then modified Schaffer collateral synapses due to STDP, and finally organized neuronal assemblies that coded temporal sequences in CA1.

The effect of theta-burst stimulation on carbachol-induced oscillation was studied using 4-500 μm-thick rat hippocampal slices. With the application of 30 μM carbachol, the rhythmical activity whose frequency was 12-20 Hz were recorded from CA3 region of hippocampal slices. The frequencies were in beta range. The frequency was 17.29+- 0.37 (mean +-s.e.m.)Hz. When you added bicuculline, GABAa receptor antagonist, the frequency of the activity decreased and the amplitude decreased below 1 μM and above the concentration, it increased. With the application of 30μM carbachol and 5μM bicuculline, the frequency was 12.31 +- 0.36 Hz. Under this condition, the schaffer collaterals were stimulated with the theta-burst stimulation (TBS) by tungsten bipolar electrode. Then long-term potentiation (LTP) in CA3 was immediately induced just after TBS. The frequency of the carbachol-induced activity was not changed then, while twenty minutes after the stimulation, the period of the activity gradually decreased. When LTP was suppressed by AP5, the frequency did not change. These results suggest that the LTP induced by TBS decreases in the frequency of carbachol-induced beta activity.

A gene encoding a precursor polyprotein of diapause hormone (DH) and other four related peptides is expressed by three groups of neurosecretory cells in the suboesophageal ganglion of Bombyx mori. Chronic recordings were made from the axonal tract (NCC-3) of labial (posterior) cells and the common axonal tract (the maxillary nerve) of mandibular (anterior) and maxillary (medial) cells during the pupal period. Firing activity patterns of the labial cells differed significantly between diapause-egg (D) and non-diapause-egg (ND) producers: cells in the former were active throughout pupal period, whereas the same cells in the latter maintained an inactive state until the last quarter of pupal period. On the other hand, firing activity of mandibular and maxillary cells did not differ significantly between D and ND producers: the cells in both types of pupae were active throughout pupal period. The results suggest that pupal labial cells are responsible for the secretion of DH, while mandibular and maxillary cells are involved in the secretion of other neuropeptides. There may be different posttranslational processing of the precursor polyprotein in different neurosecretory cell groups.

The effects of orexin-A on the performance of Wistar rats during the Morris water maze test and the long-term potentiation in Schaffer collateral/commissural-CA1 synapses in hippocampal slices wre examined. The results of the Morris water maze test show that 1.0 and 10 nmol of orexin-A, when administered intracerebroventricularly, retarded both spatial learning and memory. A probe test also showed an impairment. The open-field test did not show any remarkable abnormality in either the motor activity and/or emotionality. The results of an electrophysiological study using hippocampal slices demonstrated that 1.0 to 30 nM of orexin-A applied to the perfusate produces a dose-dependent and time dependent suppression of the long-term potentiation that was not affected by 6-cyano-7-nitroquinoxaline-2,3-dione, CNQX, which is a non-NMDA receptor antagonist, thereby implicating NMDA receptors. These results show that orexin-A impairs spatial and these impairments can be attributed to a suppression of long-term potentiation in the Schaffer collateral-CA1 hippocampal synapses.

Purpose: We compared multifocal responses obtained to conventional Contrast Reversing (CR) and temporally sparse ternary stimuli. A Hierarchical Decomposition[1] (HD) allowed the responses to be decomposed into components in feed-forward and feed back relationships, permitting the HD components to be characterised as being more related to cortical inputs or to cortical processing. Methods: Stimuli containing 8 cortically scaled checkerboards/eye were presented dichoptically at 50.5 frames/eye/s. For CR stimuli each region had contrast -1 or 1 with probability 1/2. For the sparse stimuli the contrasts are {-1, 0, 1}, where 0 indicates a blank region at the mean luminance, and the transient stimuli were delivered to each region at 6 stimuli/eye/s. Data are presented for 92 eyes. The HD method computes Principal Components (PC) and then effects a linear transformation that satisfies an autoregressive (AR) model. The AR model indicates how much the HD components contribute to themselves, or other the components, at several temporal lags, thus characterising feed -forward and -back relationships. We also examined the effects of varying the temporal sparseness of the multifocal stimuli, and also of changing their contrast. Results: HD models were computed for each of the 16 stimulus regions, and using a 95% c.l., AR models having 2 lags (10 ms each) were routinely fitted. The proportion of variance accounted for was higher for sparse stimuli, reflecting the better SNRs obtained for sparse (5.32 ± 0.84) vs. CR (3.31 ± 0.53se) stimuli in the 46 subjects. HD analysis showed that the first component provided substantial hierarchical drive to the higher components but little feedback was apparent. A multiple regression model indicated that peak (N1) responses to the monocular Sparse16 stimulus were 4.47 times larger (13.0 dB ± 0.54 SE) than for the conventional CR stimulus. For dichoptic presentation Sparse16 responses were 6.23 times larger, binocular suppression being greatest for the Binary stimulus (-4.17 dB ± 0.54 SE). About half the responses to Sparse16 stimuli exceeded 6 SE. Consideration of the signal to noise ratios (SNRs) indicated that to achieve a given level of reliability CR monocular stimulation would require 1.37 times longer trials than Sparse16 stimuli. Recording time for dichoptically presented CR stimuli would be 3.49 times longer. The contrast dependence was summarised by simultaneously fitting a power law for each stimulus type, such that R =MCZ, binocular suprresion acted at higher contrasts. Conclusions: Transiently presented stimuli delivered at rate at or less than 6 Hz provide marked increases in response size and SNR, particularly for dichoptic presentation. In the dichoptic case the recording time improvement is between 2.4 and 3.5 times. The hierarchical relationships found indicated that the first component is most likely influenced by cortical input. The ratio of hierarchical / direct drives was greatest in nasal and inferior visual fields (p=0.05). Superior-peripheral regions had the weakest responses, however, and so were more difficult to characterise. From the perspective of multifocal VEPs as a tool for perimetry the better SNR indicates that sparse stimuli would require about 2.6 × less recording time to achieve the same level of accuracy. The mean recording time here of 3.97 min, was equal for both stimulus conditions.
[1]Repucci MA et al. (2001) Ann Biomed Eng 29:1135-1149.