Odor input generates similar to 1.5 Hz and similar to 3 Hz spectral peaks in the Helix pedal ganglion

In 1999 we reported that odorants evoke in the Helix pedal ganglion (PG) ac tivity patterns which are largely odorant-specific and related to the natur e of odor and its behavioral output. Notably, some activities (for example, similar to1.5 and similar to3 Hz), nonspecific to odorants, were consisten tly evoked in PG. The present contribution goes farther in a deeper survey of the intrinsic and odorant-evoked activities of PG with special weight on the nonspecific fluctuations. We address the following questions. (i) What are the features of the activities? (ii) Are they comparable to the activi ties found in the motor systems of the other invertebrates? (iii) To what f unctions can they be related? Three main frequency components represented b y power peaks at <1 Hz, 1-2 Hz and 2-8 Hz seem to feature the response acti vities of PG. (a) The aversive odorants induce odorant-specific patterns re presented by peak power frequencies at <1 Hz. (b) The oscillation at simila r to1 Hz, which exists intrinsically in the Helix PG, can be specifically e nhanced by appetitive odors. Activities induced in the procerebrum (PC), th e visceral ganglion (VG) and PG by appetitive odorants, such as ethanol and apple, peak at 1.3-2 Hz, whereas those induced by aversive ones, such as f ormic acid and onion at <1 Hz. (c) The 2-8 Hz components always accompany t he odorant-evoked activities of the PG either as the second or third strong est component, or in the form of conspicuous, long-lasting <similar to>3 Hz oscillations. (d) The nonspecific odor-evoked 1-2 Hz and similar to3 Hz ac tivities, and the intrinsic similar to1 Hz activity of the PG seem to be in terrelated by a degree of mutual exclusion. We may therefore consider these activities as elementary, slow components that are involved in the process ing of signals in this ganglion. It can be inferred from the findings in ot her invertebrates that the 1-3 Hz spontaneous discharge is strongly connect ed with motor activity that involves the feedback mechanism of the procereb ro-cerebro-buccal or -procerebro-cerebro-pedal circuit. Our approach differ s from most others reported so far in the following aspects: (i) use of gro ss steel electrodes for recording population activities; (ii) lengthy stimu lation (10 min); (iii) long observation during and after stimulation; (iv) power spectral presentation of temporal evolution of activity patterns; (v) estimation of peak power frequency by Frequency-Amplitude Plot (FAP) (obta ined from signals averaged in the frequency domain; a method based on syste ms theory). (C) 2000 Elsevier Science B.V. All rights reserved.