Mj. Bourque et A. Kolta, Properties and interconnections of trigeminal interneurons of the lateral pontine reticular formation in the rat, J NEUROPHYS, 86(5), 2001, pp. 2583-2596
Numerous evidence suggests that interneurons located in the lateral tegment
um at the level of the trigeminal motor nucleus contribute importantly to t
he circuitry involved in mastication. However, the question of whether thes
e neurons participate actively to genesis of the rhythmic motor pattern or
simply relay it to trigeminal motoneurons remains open. To answer this ques
tion, intracellular recordings were performed in an in vitro slice preparat
ion comprising interneurons of the peritrigeminal area (PeriV) surrounding
the trigeminal motor nucleus (NVmt) and the parvocellular reticular formati
on ventral and caudal to it (PCRt). Intracellular and extracellular injecti
ons of anterograde tracers were also used to examine the local connections
established by these neurons. In 97% of recordings, electrical stimulation
of adjacent areas evoked a postsynaptic potential (PSP). These PSPs were pr
imarily excitatory, but inhibitory and biphasic responses were also induced
. Most occurred at latencies longer than those required for monosynaptic tr
ansmission and were considered to involve oligosynaptic pathways. Both the
anatomical and physiological findings show that all divisions of PeriV and
PCRt are extensively interconnected. Most responses followed high-frequency
stimulation (50 Hz) and showed little variability in latency indicating th
at the network reliably distributes inputs across all areas. In all neurons
but one, excitatory postsynaptic potentials (EPSPs) or inhibitory postsyna
ptic potentials (IPSPs) were also elicited by stimulation of NVmt, suggesti
ng the existence of excitatory and inhibitory interneurons within the motor
nucleus. In a number of cases, these PSPs were reproduced by local injecti
on of glutamate in lieu of the electrical stimulation. All EPSPs induced by
stimulation of PeriV, PCRt, or NVmt were sensitive to ionotropic glutamate
receptor antagonists 6-cyano-7-dinitroquinoxaline and D,L-2-amino-5-phosph
onovaleric acid, while IPSPs were blocked by bicuculline and strychnine, an
tagonists of GABAA and glycine receptors. Examination of PeriV and PCRt int
rinsic properties indicate that they form a fairly uniform network. Three t
ypes of neurons were identified on the basis of their firing adaptation pro
perties. These types were not associated with particular regions. Only 5% o
f all neurons showed bursting behavior. Our results do not support the hypo
thesis that neurons of PeriV and PCRt participate actively to rhythm genera
tion, but suggest instead that they are driven by rhythmical synaptic input
s. The organization of the network allows for rapid distribution of this rh
ythmic input across premotoneuron groups.