Inhibition of the Aplysia sensory neuron calcium current with dopamine and serotonin

Abstract

Dunn TW, Sossin WS. Inhibition of the Aplysia sensory neuron calcium current with dopamine and serotonin. J Neurophysiol 110: 2071-2081, 2013. First published August 7, 2013 doi:10.1152/jn.00217.2013.-The inhibition of Aplysia pleural mechanosensory neuron synapses by dopamine and serotonin through activation of endogenous dopaminergic and expressed 5-HT 1Apl(a)/b receptors, respectively, involves a reduction in action potential-associated calcium influx. We show that the inhibition of synaptic efficacy is downstream of the readily releasable pool, suggesting that inhibition is at the level of calcium secretion coupling, likely a result of the changes in the calcium current. Indeed, the inhibitory responses directly reduce a Ca V 2-like calcium current in isolated sensory neurons. The inhibition of the calcium current is voltage independent as it is not affected by a strong depolarizing prepulse, consistent with other invertebrate Ca V 2 calcium currents. Similar to voltage-independent inhibition of vertebrate nociceptors, inhibition was blocked with Src tyrosine kinase inhibitors. The data suggest a conserved mechanism by which G protein-coupled receptor activation can inhibit the Ca V 2 calcium current in nociceptive neurons.Aplysia; calcium current; dopamine; nocioceptor; voltage-dependent inhibition THE PLEURAL SENSORY NEURONS of the marine mollusk Aplysia californica function as body wall mechanosensory neurons with a nociceptive role (Walters et al. 1983a(Walters et al. ,b, 2004. Stimulation of the pleural sensory neurons excite defensive withdrawal motorneurons resulting in defensive behaviors (Walters et al. 1983a). Modulatory substances such as FMRFamide and dopamine reduce pleural sensory neuron excitability and synaptic efficacy to withdrawal motorneurons (Dunn et al. 2012;Edmonds et al. 1990;Guan et al. 2003). Such inhibition of pleural sensory neuron activity would serve an analgesic or hypoalgesic role, reducing the sensation of stimuli to the body wall and foot of the animal.Previously we reported that dopamine had a strong inhibitory effect on synaptic efficacy at synapses between Aplysia pleural mechanosensory neurons and defensive withdrawal motor neurons in culture (Dunn et al. 2012). The inhibitory response also included a large reduction in the presynaptic calcium flux. However, it was not determined whether the reduction in the action potential-associated calcium transient was through direct inhibition of the Ca V 2-like calcium current, the current responsible for triggering transmitter release, as was suggested previously for FMRFamide (Edmonds et al. 1990). Alternatively, the reduction in the calcium transient may be indirect, through changes in potassium currents that affect action potential duration, or from failure of the action potential to propagate to and depolarize all the presynaptic terminals.Here we further examine the mechanisms of dopaminergic inhibition of synaptic efficacy at Aplysia sensory to motor neuron pairs in culture. We show that the action potential does conduct ...

Isoform specificity of PKMs during long-term facilitation in Aplysia is mediated through stabilization by KIBRA

“…Cultures were left at 19ºC for 2 hours, at which time the second recording was performed. Initial PSP rise-rate was measured as previously described (Dunn and Sossin, 2013). For PKM overexpression experiments ( Figure 1), EPSP amplitudes were measured prior to microinjection (day 0 = 96 h after cell plating to insure stable synapses), and again on days 1, 3, and 5 as described (Bougie et al, 2012;Hu et al, 2017a).…”

Investigating the Potential Signaling Pathways That Regulate Activation of the Novel PKC Downstream of Serotonin in Aplysia

“…We first tried PP1 and PP2, both inhibitors of the non-receptor tyrosine kinase Src family [30]. PP2 had previously been effectively used by our lab to block a likely tyrosine kinase phosphorylation-mediated inhibition of calcium currents in Aplysia [31]. As shown in Fig 4, neither PP1 nor PP2 inhibited membrane enrichment of PKC Apl II.…”

Repetition priming-induced changes in sensorimotor transmission

“…B21 was impaled with electrodes filled with 3 M CsCl with resistances of ϳ2 M⍀. Ca 2ϩ currents were isolated by bath applying a Na ϩ -free solution, and using Ba 2ϩ as the charge carrier, which increases the amplitude of the evoked current, and avoids Ca 2ϩ -dependent inhibition of Ca 2ϩ channels (e.g., Dunn and Sossin 2013;Yue et al 1990). The seawater used in these experiments also included drugs to block other currents induced by depolarization.…”