Physiological characterization, localization and synaptic inputs of bursting and nonbursting neurons in the trigeminal principal sensory nucleus of the rat

• A population of neurons in the trigeminal principal sensory nucleus (NVsnpr) fire rhythmically during fictive mastication induced in the in vivo rabbit. To elucidate whether these neurons form part of the central pattern generator (CPG) for mastication, we performed intracellular recordings in brainstem slices taken from young rats. Two cell types were defined, nonbursting (63%) and bursting (37%). In response to membrane depolarization, bursting cells, which dominated in the dorsal part of the NVsnpr, fired an initial burst followed by single spikes or recurring bursts. Non-bursting neurons, scattered throughout the nucleus, fired single action potentials. Microstimulation applied to the trigeminal motor nucleus (NVmt), the reticular border zone surrounding the NVmt, the parvocellular reticular formation or the nucleus reticularis pontis caudalis (NPontc) elicited a postsynaptic potential in 81% of the neurons tested for synaptic inputs. Responses obtained were predominately excitatory and sensitive to glutamatergic antagonists DNQX and/or APV. Some inhibitory and biphasic responses were also evoked. Bicuculline methiodide or strychnine blocked the IPSPs indicating that they were mediated by GABA(A) or glycinergic receptors. About one-third of the stimulations activated both types of neurons antidromically, mostly from the masseteric motoneuron pool of NVmt and dorsal part of NPontc. In conclusion, our new findings show that some neurons in the dorsal NVsnpr display both firing properties and axonal connections which support the hypothesis that they may participate in masticatory pattern generation. Thus, the present data provide an extended basis for further studies on the organization of the masticatory CPG network.

Keyword

Action Potentials/drug effects/*physiology/radiation effects

Animals

Animals; Newborn

Biotin/analogs & derivatives/metabolism

Dose-Response Relationship; Radiation

Drug Interactions

Electric Stimulation/methods

Evoked Potentials/drug effects/physiology/radiation effects

Excitatory Amino Acid Antagonists/pharmacology

Glycine Agents/pharmacology

Neurons/*classification/drug effects/*physiology/radiation effects

Patch-Clamp Techniques/methods

Quinoxalines/pharmacology

Rats

Rats; Sprague-Dawley

Strychnine/pharmacology

Synaptic Transmission/drug effects/*physiology/radiation effects

Trigeminal Nuclei/*cytology

Publication and Content Type

ref (subject category)

art (subject category)