Localization of connexins in neurons and glia cells of the Helix aspersa suboesophageal brain ganglia by immunocytochemistry.

The aim of the present study was to examine the distribution of cells expressing connexin 26 (Cx26) in the suboesophageal visceral, left and right parietal and left and right pleural ganglia of the snail Helix aspersa by immunocytochemistry. Altogether we have found approximately 452 immunoreactive neurons which represent the 4.7% of the total neurons counted. The stained large neurons (measured diameter 55-140 microm) occurred mostly on the peripheral surface of the ganglia while the small immunostained cells (5-25 microm diameter) were observed in groups near the neuropil. The number of large neurons giving positive Cx26-like immunostaining was small in comparison with that for medium (30-50 microm diameter) and small sized cells. The expression of Cx26 was also observed in the processes of glia cells localized among neurons somata and in the neuropil showing that the antiserum recognized epitopes in both protoplasmic and fibrous glia cells of Helix aspersa. The neuropils of all ganglia showed fibers densely immunostained. While we have observed a good specificity for Cx26-antiserum in neurons, a lack of reaction for Cx43 antiserum was observed in neurons and glia cells. The reaction for enolase antiserum in neurons was light and non-specific and a lack of reaction in glia cells and processes for GFAP antiserum was observed. Although the percentage of positive neurons for Cx26 antiserum was low is suggested that in normal physiological conditions or under stimulation the expression of connexin could be increased. The observed results can be considered of interest in the interpretation of Helix aspersa elemental two neuron networks synchronizing activity, observed under applied extremely low frequency magnetic fields.