Inferior Olivary nucleus
Immediately dorsal to the pyramidal tract, the olivary nucleus was located on the ventral surface on each half of the coronal sections of the medulla oblongata in the three groups. However, this nucleus was not visible throughout the rostrocaudal extent of the medulla oblongata in the three groups.
In neonates, the inferior olivary nucleus was well represented at 7.5 mm rostral to the obex. The extracellular matrix of this nucleus had distinct radial glial fibre shaft making the neurons appear within a sheet (Fig. 1, depicted by yellow arrows). Within these shafts separating each neuron were located migrating/immature neurons (Fig. 1, depicted by red arrows). The neurons of this nucleus were a mixture of elongated and pyramidal neurons whose nuclei were either eccentric or indistinguishable from the nucleolus (Fig. 1, depicted by black arrows).
The inferior olive principal nucleus was located between the inferior olive dorsal nucleus dorsally, the inferior olive medial nucleus caudally and the inferior olive Beta subnucleus medially (Fig. 3: i, labeled as b). It was presented in two concentric layers resembling a long constricted letter-V when viewed dorsocaudally, with the dorsal and ventral limbs continued after a bridge by the inferior olive dorsal nucleus and inferior olive ventrolateral protrusion respectively (Fig. 3: i, labeled as b1 and b2, respectively). It was the second longest of all the nuclei. The neuron of this nucleus was small and roughly oval, some large conical or pyramidal or spindle in shape. Oligodendrocytes were also well distributed (Fig. 3: iii, labeled as b and, depicted by black, yellow and red arrows, respectively).
The inferior olive ventrolateral protrusion was lateral to the pyramidal tract and was oval in shape (Fig. 3: i, labeled as c). Its neurons were very few, both small and large conical shaped just as in the inferior olive principal nucleus (Fig. 3: iii, labeled as c and depicted by black and yellow arrows, respectively). It was the smallest of the entire nuclei observed. Oligodendrocytes were also observed (Fig. 3: iii, labeled as c and depicted by arrow head).
The inferior olive Beta nucleus was located more medial to the pyramidal tract and it was triangular in shape (Fig. 3: i, labeled as d). Its neurons were large and oval in shape (Fig. 3: iv, labeled as d and depicted by black arrow). Oligodendrocytes were observed (Fig. 3: iv, labeled as d and depicted by arrow head). The inferior olive medial nucleus was located caudal to the inferior olive principal nucleus, just on top of the pyramid and was separated from the inferior olive Beta subnucleus medially by a bridge containing blood vessel. It was the third biggest of the nuclei observed. It was oval in shape (Fig. 3: i, labeled as e). Its neurons were a mixture of few large round and oval with small conical cells (Fig. 3: iv, labeled as e, depicted by black arrow). Oligodendrocytes were observed (Fig. 3: iv, labeled as e and depicted by arrow head).
Dorsal nucleus of corpus trapezoideum
This nucleus was located on the dorsal surface of the closed medulla oblongata in the adult, juvenile and neonate AGR. The spinal nucleus of trigeminal nerve was lateral to this nucleus; the motor nucleus of vagus nerve dorsomedial to it while the solitary tract nucleus was dorsolateral to it.
In neonates, this nucleus was well represented caudal to the obex. The neurons were a mixture of giant, medium and elongated cells with thick axons (Fig. 4, depicted by black, red and green arrows, respectively). The nucleus could not be differentiated from the nucleolus and few oligodendrocytes and blood vessels were observed (Fig. 4, depicted by arrow heads and white arrow, respectively). The nucleus was eccentric and dense-stained.
Lateral nucleus of reticular formation
The nucleus of the lateral reticular formation was located on the ventrolateral surface of the closed medulla oblongata. The nucleus ambiguous lied dorsal, the spinal trigeminal nucleus ventromedial and the olivary nucleus lateral to it. This nucleus was made up of dorsal and ventral subnuclei except in juveniles. The reticular formation arrangement in the medulla oblongata was characterized by the reticular alba which was entirely axon-ladened and the reticular grisea which was delineated by the lateral nucleus of reticular formation. The reticular alba was very prominent on either side of the midline of the adult, juvenile and neonate AGR.
In neonates, the lateral nucleus of reticular formation was well represented in the microscopic sections of 7.5 mm caudal to the closed medulla oblongata. The dorsal and ventral subnuclei were well differentiated and highly distinctive just as in adults. The neurons were large and arranged in oval manner, had different shapes of oval or conical and unipolar pyramidal cells (Fig. 7, depicted by red and black arrows, respectively). The nucleus of each neuron was centric with clear nucleolus. Immature migrating neurons within the radial glial fibre shaft of the intracellular matrix were distributed in the nucleus (Fig. 7, depicted by yellow arrows). Very peculiar in this nucleus was the numerous blood vessels surrounding the nucleus (Fig. 7, depicted by white arrows).
Medial nucleus of corpus trapezoideum
This nucleus was located immediately lateral to the pyramidal tracts and caudomedial to the superior olivary nucleus of the neonate, juvenile and adult AGR in both sides of the medulla oblongata.
In neonates, the medial nucleus of corpus trapezoideum was well represented at 5.5 mm microscopic section of the medulla oblongata rostral to the obex. The neurons were basically a mixture of two cell types viz medium-sized bipolar pyramidal and medium-sized elongated cells (Fig. 10, depicted by black and red arrows, respectively). The nucleus of each of the neurons was small, conical and centrally located with very clear nucleolus. The neurons were eccentric with well-established nucleoplasm and delineable axons (Fig. 10, depicted by yellow arrow).