A dopamine- and octopamine-sensitive adenylate cyclase in the nervous system of Octopus vulgaris

Serotonin is a facilitatory neuromodulator of synaptic transmission and "reinforces" long-term potentiation induction in the vertical lobe of Octopus vulgaris

The modern cephalopod mollusks (coleoids) are considered the most behaviorally advanced invertebrate, yet little is known about the neurophysiological basis of their behaviors. Previous work suggested that the vertical lobe (VL) of cephalopods is a crucial site for the learning and memory components of these behaviors. We are therefore studying the neurophysiology of the VL in Octopus vulgaris and have discovered a robust activity-dependent long-term potentiation (LTP) of the synaptic input to the VL. Moreover, we have shown that the VL and its LTP are involved in behavioral long-term memory acquisition. To advance our understanding of the VL as a learning neural network we explore the possible involvement of neuromodulation in VL function. Here we examine whether the well studied serotonergic modulation in simple models of learning in gastropods mollusks is conserved in the octopus VL. We demonstrate histochemically that the VL is innervated by afferent terminals containing 5-HT immunoreactivity (5-HT-IR). Physiologically, 5-HT has a robust facilitatory effect on synaptic transmission and activity-dependent LTP induction. These results suggest that serotonergic neuromodulation is a part of a reinforcing/reward signaling system conserved in both simple and complex learning systems of mollusks. However, there are notable functional differences. First, the effective concentration of 5-HT in the VL is rather high (100 microM); secondly, only neuropilar regions but not cell bodies in the VL are innervated by terminals containing 5-HT-IR. Thirdly, repetitive or long exposures to 5-HT do not lead to a clear long-term facilitation. We propose that in the octopus VL, while the basic facilitatory properties of molluscan 5-HT system are conserved, the system has adapted to convey signals from other brain areas to reinforce the activity-dependent associations at specific sites in the large connections matrix in the VL.

Evidence for multiple signaling pathways in single squid olfactory receptor neurons

At least two different G-protein-mediated transduction cascades, the adenylate cyclase and phospholipase C (PLC) pathway, process chemosensory stimuli for various species. In squid olfactory receptor neurons (ORNs), physiological studies indicate that both pathways may be present; however, confirmation of the transduction molecules at the protein level is absent. Here we provide evidence that the G-proteins involved in both adenylate cyclase and PLC pathways are present in squid ORNs (Lolliguncula brevis). We used immunoblotting to show that Galpha(olf), Galpha(q), and a downstream effector, enzyme PLC140, are present in the squid olfactory epithelium (OE). To localize these proteins to one or more of the five morphological cell types described for squid OE, paraformaldehyde-fixed olfactory organs were cryosectioned (10 microm), double-labeled for Galpha(olf), Galpha(q), or PLC140, and imaged. Analysis of serial sections from entire olfactory organs for epithelial area and patterns of immunofluorescence revealed a region of highest immunoreactivity at the anterior half of the organ. At the cellular level, type 1 cells could not be distinguished morphologically and were not included in the analysis. The three labeling patterns observed in type 2 cells were Galpha(q) alone, PLC140 alone, and colocalization of Galpha(q) and PLC140. Subsets of cell types 3, 4, and 5 showed colocalization of Galpha(olf) with Galpha(q) but not with PLC140. These data suggest that the PLC pathway predominates in type 2 cells; however, coexpression of Galpha(olf) with Galpha(q) in cell types 3, 4, and 5 suggests that both pathways may participate in olfactory transduction in non-type 2 squid ORNs.