| Recent work has suggested that particular functions can be ascribed to specific neurons in distributed networks. To investigate this issue, we carried out hyperpolarization “removal” studies of the Lateral Pyloric (LP) and Ventricular Dilator (VD) neurons in the lobster (Panulirus interruptus) pyloric network. We found that these neurons regulate network cycle period; the LP neuron slows the network when present and the VD neuron speeds it. When sufficient current is injected into the pacemaker Anterior Burster (AB) neuron to force the network to cycle outside of its physiological range, the LP neuron disrupts normal patterning when the network is driven too slow, and the VD neuron disrupts when the network is driven too fast.; If larger AB current depolarizations are employed, the VD neuron role switches from network disruption to network pacemaker and entrains the other network neurons to follow its slow cycling. Hyperpolarization studies have shown that the other network neurons can cycle faster in the absence of the VD neuron and that the AB neuron is entrained to the slow VD neuron rhythm through the LP neuron's synapse. Thus, this anomalously slowed rhythm is VD neuron driven and mediated onto the network pacemaker by the LP neuron.; Finally, hyperpolarization studies of the LP or VD neuron have shown significant differences in pyloric neuron spiking and phasing activity compared with that of the intact network. However, there are confounding changes in network cycle period in the absence of either neuron which must be accounted for to assess the direct effects of each neuron removal. When this compensation is applied, consistent effects of removal are not observed.; In the unmodulated “ground” state, these neurons seem to play little role in network activity. However, these neurons do play a significant role in pyloric network cycle period regulation. That is, the LP neuron slows the network when present and the VD neuron speeds the network when present. Additionally, the VD neuron can serve as network pacemaker and the LP neuron mediates this pacemaker effect onto the AB neuron. Thus, we have suggested two roles for these neurons in the absence of modulation. |
