Pyloric Dilator Neurons Research Articles

Pharmacological dissection of pyloric network of the lobster stomatogastric ganglion using picrotoxin.

1. Picrotoxin (PTX) (10(-7)-10(-6) M) completely blocked most inhibitory synapses in the pyloric pattern generator of the lobster (Panulirus interruptus) stomatogastric ganglion. The sensitivity of synapses from most classes of identified neurons was examined. Blockade was at least partly reversible with prolonged washing. 2. The synapses from pyloric dilator (PD) neurons were the only inhibitory synapses that picrotoxin failed to block completely. 3. A correlation is derived that brief, fast-rise inhibitory postsynaptic potentials (IPSPs) are picrotoxin sensitive, whereas a slow rounded component of IPSPs from PD neurons is not picrotoxin sensitive. 4. Picrotoxin caused specific changes in the pattern of the motor rhythm produced by the 16-cell pyloric network. This sheds some light on the functional role of particular synapses in the pyloric generator. 5. The endogenously bursting neurons (PD and anterior burster (AB)), which drive the pyloric rhythm, kept a similar burst rate. 6. Under picrotoxin, the pyloric "follower" neurons all moved to later phase relative to the "driver" group. Some normally antagonistic cells, related by reciprocal inhibitor connections, became in-phase. These and other pattern changes could be related to blockade of particular synapses. 7. The pyloric rhythm was still quite recognizable under picrotoxin despite the drastically altered circuitry of the synaptic network. This supports the idea that periodic inhibition from the PD driver neurons plays a primary role in creating the pyloric pattern.

Generation of a fixed motor pattern

1. Electrical properties of neurons involved in the production of the pyloric output pattern of the stomatogastric ganglion of the crab,Cancer pagurus, as well as characteristics of synaptic connections of these neurons were investigated. 2. The bursting discharge activity of the medium sized pyloric dilator neurons (m-PD) is found to be of endogenous origin. The ionic mechanism of the bursting activity is suggested to consist of a coactivated sodium-calcium inward current opposed by a calcium dependent potassium outward current. The small-sized pyloric dilators (s-PD), lateral pyloric (LP) and pyloric neurons (PY) also have the capability to discharge spontaneously. 3. Low-pass properties of the neurite segment connecting the spike trigger zone to the soma is indicated. This seems to account for the small amplitudes of action potentials recorded usually at the soma. 4. The values of different electronic length parameters suggest differences in the collateral properties. The effect of passive collateral properties on synaptic parameters is discussed. 5. The pyloric neurons can be driven by excitatory synaptic (EPSP) input. With increased stimulus strength additional input fibres are recruited. Increasing the stimulus frequency augments the burst-frequency and spike-frequency per burst, however, the number of spikes per burst stays relatively constant. 6. The time-course and amplitude of EPSPs recorded from pacemaker neurons are reduced shortly after the burst. EPSP's late in the interburst phase however were prolonged. Active membrane processes underlying the pacemaker activity appear to be responsible for these modifications of synaptic parameters. 7. Hyperpolarizing current injection reduces EPSP-amplitude and shortens the time-course of EPSPs. Since no anomalous conductance changes of the soma membrane were found, it is presumed that the anomalous conductance changes occur at the collateral membrane. 8. Intraganglionic chemical synaptic interaction of the pyloric neurons is exclusively inhibitory. The IPSPs for the various neurons show characteristic differences in delay, amplitude and time-course. This may contribute to the sequencing of the LP-PY discharge in the pyloric pattern. The ionic mechanism of the postsynaptic inhibition of pyloric neurons is found to be chlorid-dependent. 9. It is concluded that the endogenous discharge properties of the pyloric neurons produces a basic level of activity and that the differences in passive and active membrane properties and their effect on synaptic parameters contributes to the generation of the pyloric output pattern.