Erowid References Database
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MacDonald JF, Berry MS.
“Further Identification of Multiple Responses Mediated by Dopamine in the CNS of Planorbis corneas”.
Canad.J.Physiol.Pharmacol.. 1978;56(1):7-18.
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Abstract
Multiple responses mediated by dopamine (DA) in the CNS of Planorbis corneus were investigated. Method Isolated subesophageal ganglionic rings from the gastropod mollusc (Planorbis corneas), perfused with Planorbis saline, were fitted in the some of the DA ganglion (left pedal ganglion) and into the some of one of its followers (visceral or left parietal ganglion). DA was applied iontophoretically to the vicinity of follower neurones, the tip of the pipette being juxtaposed to the axon hillock, in order to evoke a response, The effects of various agonists and antagonists, which were added to the perfusing fluid, were studied, Results Follower neurones in the visceral ganglion responded charac teristically with inhibitory postsynaptic potentials (IPSPs) to intracellular stimulation of the DA neurons. Perfusion with apomorphine 10-100uM (Sandoz) did not influence dopaminergic IPSPs. When D-LSD 5M (Wellcome) was added to the perfusion fluid, it abolished IPSPs. This drug depolarized (at 5-10 mV) the follower neurones and decreased their input resistance, In the left parietal ganglion only follower neurones responded to iontophoretically applied DA, The majority responded with "slow" excitatory postsynaptic potentials (lDsPsPs; 900 msec) Most parietal follower neurones were not influenced by apomorphine (1-100 mcM). The dopaminergic responses of these neurones were rapidly reduced or abolished by 100 mcM tubocurarine (Wellcome). In certain visceral neurones when hyperpolarized to -100 mV, a small depolarization was observed. Similar 'fast' EfPSPs were seen in some parietal neurones without the presence of hyper polarization. Various combinations of synaptic potentials were recorded. Perfusion with haloperidol (Janssen), fluphenazine (Squibb) or metoclopramide at concentrations of 50-100 mcM reduced IPSPs and/or abolished EsPSPs. Perfusion with these drugs at 125-150 mcM was accompanied by membrane depolarization, an increase in the frequency of spontaneous action potentials and reduction in spike height. Responses to iontophoresized ACh and each neuroleptic were occasionally reduced. Conclusion Results support the hypothesis that DA is the transmitter mediating multiple synaptic responses in Planorbis.
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