Recording from two neurons: second-order stimulus reconstruction from spike trains and population coding.

We study the reconstruction of visual stimuli from spike trains, representing the reconstructed stimulus by a Volterra series up to second order. We illustrate this procedure in a prominent example of spiking neurons, recording simultaneously from the two H1 neurons located in the lobula plate of the fly Chrysomya megacephala. The fly views two types of stimuli, corresponding to rotational and translational displacements. Second-order reconstructions require the manipulation of potentially very large matrices, which obstructs the use of this approach when there are many neurons. We avoid the computation and inversion of these matrices using a convenient set of basis functions to expand our variables in. This requires approximating the spike train four-point functions by combinations of two-point functions similar to relations, which would be true for gaussian stochastic processes. In our test case, this approximation does not reduce the quality of the reconstruction. The overall contribution to stimulus reconstruction of the second-order kernels, measured by the mean squared error, is only about 5% of the first-order contribution. Yet at specific stimulus-dependent instants, the addition of second-order kernels represents up to 100% improvement, but only for rotational stimuli. We present a perturbative scheme to facilitate the application of our method to weakly correlated neurons.

Post-epidemic serological survey for JE virus antibodies in south Arcot district (Tamil Nadu).

Following an extensive epidemic of Japanese encephalitis (JE) in 1981, a serological survey was carried out in the South Arcot district of Tamil Nadu in April 1982. Serum specimens were obtained from 10 villages with serologically proven infections and 6 villages with no reported case of encephalitis during the 1981 epidemic. The serum specimens tested for haemagglutination inhibition, complement fixing and neutralizing antibodies, showed a high prevalence of JE (49.17%), West Nile (40.78%) and dengue (18.14%) viruses with predominance of JE. The prevalence did not differ between the villages with or without Japanese encephalities. There was also no difference between the family members and neighbours.

Neutralizing antibody response to Japanese encephalitis inactivated mouse brain vaccine among laboratory personnel.

Among vaccinees given two doses of JE Nakayama strain liquid vaccine, 41.8% had significant neutralizing (N) antibody response to the P20778 strain and 48.6% to the Japanese Nakayama strain. Among vaccinees who received three doses of the freeze-dried vaccine, the proportion of positive reactors was 53.8% when the sera were tested with the P20778 strain and 47.4% with the Nakayama strain. A fairly large proportion of those vaccinees who had responded positively to the latter vaccine were found to have lost detectable N antibodies to the P20778 strain and a smaller proportion to the Nakayama strain 13 to 17 months after the third dose of vaccine. Following the administration of a booster dose of the vaccine after this time interval, 65.2% and 56.5% of vaccinees responded positively to the P20778 strain and the Nakayama strain, respectively. The differences between the proportion of positive reactors to the two strains were not significant either for the liquid vaccine or the freeze-dried vaccine. An important finding was the priming effect of infection with West Nile (WN) virus before vaccination. Those vaccinees who had N antibody to WN virus before vaccination had a significantly higher N antibody response to the P20778 strain of JE virus than those who had no detectable antibody to WN virus. These findings indicate that the JE Nakayama strain vaccine would be efficacious in India, particularly in view of the widespread prevalence of WN virus infection.

Prevalence of antibodies to Japanese encephalitis and West Nile viruses among wild birds in the Krishna-Godavari Delta, Andhra Pradesh, India.

In the Krishna-Godavari Delta region of the State of Andhra Pradesh, India, 866 sera obtained from trapped birds of 13 species were tested for neutralizing antibody to Japanese encephalitis (JE) virus; two species of birds belonging to the family Ardeidae, Ardeola grayii (pond heron) and Bubulcus ibis (cattle egret), contributed 514 of these sera. Neutralizing antibody to JE virus--i.e. sera giving positive reactions--was detected in 179 sera (34.8%) from these two species; in addition, two sera (0.4%) gave equivocal reactions, presumably indicating partial protection. There were only nine positive reactors (2.6%) among the remaining 352 sera from all other bird species. Of the 181 sera from ardeid birds in which neutralizing activity was detected, 174 were tested for neutralizing antibody to West Nile (WN) virus. The results indicated that 35.6% of these 179 sera had antibody specific to JE virus only and 63.8% possessed neutralizing antibodies to JE virus or to WN virus or to both; these figures represent 12.5% and 22.5% , respectively, of the total of 514 birds of these two species which were tested for neutralizing antibody to JE virus. The findings suggest that ardeid birds may be involved in the natural cycle of JE virus and, possibly, also of WN virus in India.