Sucking rhythm is produced by the interneurons located in the medial pontobulbar reticular formation although the motor output of the sucking-like activity is recorded in the trigeminal motor nucleus (Mot V) in the newborn rat brainstem. In this study the author focused on the electrophysiological properties and morphological features of the neurons in the nucleus reticularis pontis caudalis (PnC)in rats in the sucking stage.
The study consisted of a series of the following four experiments: (1)evaluation of the growth and behavioral development of rats in the sucking stage, (2)observation of the cytoarchitectonical features of the neurons retrogradely labeled with DiI in both the trigeminal mesencephalic nucleus (Mes V)and Mot V for localizing PnC, (3)evaluation of the electrophysiological properties of the neurons in PnC with the whole cell patch clamp recording in the brain slice preparation and (4)observation of the morphological features of the neurons in PnC with the Klüver-Barrera stain.
I identified the eruption of the mandibular incisors at 9 days, maxillary incisors at 11 days and both maxillary and mandibular molars at 19 days. Beginning of solid food feeding was identified at 18days.
Neurons labeled with DiI were located in both the Mes V and Mot V. In the transverse brainstem slices Mes V was visualized as a non-fixed form region, which consisted of simple small size neurons, while Mot V was visualized as an oval region, which consisted of multipolar medium size neurons. The electrophysiological properties of the PnC neurons changed with aging. In the PnC neuron current-voltage relationship with NMDA bath application was divided into two groups, the positive current response group and the negative current response group.
Synaptic responses in the PnC neurons elicited by stimulation of Mes V, Mot V or peritrigeminal area (Peri V) were obtained in 17 cases at both monosynaptic and polysynaptic latency. Morphological features of neurons in the PnC developed with aging as follows: growth of dendrite and myelin sheath, as well as increase in the number of gliacyte and pyramidal cells.
These data indicate that the physiological and morphological properties of PnC neurons in the rat brainstem through development change through out the sucking stage.