Abstract
In the widely divergent species, GABA neurons make widespread connections within neuronal networks and thus are capable of controlling network oscillations and their patterns. In the terrestrial mollusk Limax valentianus, oscillatory activity of the procerebrum (PC) neurons is considered to encode the odor information. Previous studies of immunohistochemistry and electrophysiology showed that GABA is present in the CNS and may be involved in the odor information processing of Limax. In the present study, we have applied immunohistochemical methods to the sectioned preparations of Limax CNS to identify GABA-like immunoreactive neurons and to assess the spatial patterns of innervations by these cells in the CNS. The neuronal cell bodies and fibers showing GABA-like immunoreactivity were distributed widely throughout the CNS, and they were also extensively observed near the PC lobes. Then, we examined the GABAergic effects on the generation of local field potential (LFP) in the PC lobes and the GABAergic effects on the neuronal activity in the PC neurons. Application of GABA-receptor antagonists to the whole CNS decreased the frequency of the oscillatory neural activity as a periodic LFP. On the other hand, application of GABA-receptor agonists increased or decreased the LFP frequency. These results suggested that the GABAergic synaptic transmission is involved in the oscillatory neural network of the PC in Limax and may play excitatory roles in the LFP generation. [J Physiol Sci. 2007;57 Suppl:S110]
