A study of neuromodulation using the isolated locust (Schistocerca gregaria) first basalar motoneurone as an 'in vitro' model

Abstract

1. A technique has been developed to isolate the first basalar (BA1) motoneurone of the locust (Schistocerca gregaria) from its ganglionic environment. The isolated neurone soma remained viable (often for up to 9hrs), enabling its electrophysiological and pharmacological properties to be investigated. The findings of these studies were comparable with those from the BA1 motoneurone in situ, and with other insect neurones whether studied in vitro or in situ. 2. The application of selected agonists to the isolated BA1 motoneurone soma demonstrated the presence of nicotinic and muscarinic acetylcholine receptors, GABA receptors and dopamine (DA) receptors. The membrane depolarization evoked by nicotine was blocked by BTX, while the GABA- induced membrane hyperpolarization response was sensitive to picrotoxin. Muscarinic receptor and DA receptor activation both induced membrane depolarization which was evoked without a detectable change in membrane conductance. The ionic dependency of these agonist-induced responses is discussed. 3. When applied between pressure applications of GABA, DA could induce either membrane depolarization or hyperpolarization, both of which were associated with an increase in membrane conductance. Furthermore, the amplitude and/or duration of the GABA response was potentiated by DA. Possible mechanisms underlying these observations are proposed. 4. Using the Ca2+-sensitive fluorescence probe, fluo-3, and confocal laser scarming microscopy, the effects of the muscarinic agonist, McN A-343, and DA on [Ca2+]i in the isolated BA1 motoneurone were examined. McN evoked an increase in [Ca2+]i, whilst DA evoked a decrease in [Ca2+]i. Similar observations were made from isolated cockroach fast coxal depressor (Df) motoneurones. The cellular events underlying these observations are discussed. 5. A technique was established to maintain dissociated unidentified adult locust neurones in culture for up to two weeks; a similar protocol was used to maintain isolated BA1 motoneurones in culture. Electrophysiological recording techniques demonstrated that the neurones remained viable in culture.