Kubke Lab:Research/CND/Summary VII

Stage 24

Case nf002

(look at record for staging issues) (St 23-25)

Distal end of VII nerve with VIII removed. DiI crystal, unilateral.

MN labelled unilaterally. There is also a thin lateral fascicle of short afferent axons on the ipsilateral side. Stack does not cover full thickness of hindbrain - I am missing the bundle of axons that are going to the motoneurons in the caudal segment.

The caudal group of motoneurons seem to have extensions on or crossing the floor plate.

Rostral sensory fascicle seems separated into 2 discrete bundles. Caudally it seems to be the case too, but they appear to come back together at a more caudal level (not so for rostral bundles).

Stage 26

case nf005

(St 26) Distal VII, DiI crystal, bilateral. Colabelling with VIII.

Nerve entry well differentiated from VIII nerve, entering ventromedially to the entry of caudal VIII.

Both rostral and caudal afferent bundles seem to be loosely fasciculated, but do not appear to form separate discrete bundles. There are clear varicosities and "filopodia-like" structures along the axons, but don't see clear collaterals. The rostral bundle seems to be travelling in between the two rostral caudal VIII bundles, and some close apposition between the two types of axons can be seen.

Efferent neurons form a dispersed column. Their axons in r5 course laterally reaching or almost reaching the sensory bundle where they make a sharp turn towards the nerve exit point. Axons from efferents in r4 seem to have their axons coursing directly to the nerve exit point.

There are numerous processes crossing the floor plate.

case nf020

(St 26)

Some slight differences in the motoneuron pattern of labelling - it looks like caudal contributing more to motoneurons whereas rostral contributes more to afferents.

Posterior Facial Branch

• Afferents: Clearly projecting both caudally and rostrally. Rostral branch seems to be in a somewhat more lateral position, except for what appears to be a very thin bundle of a few axons on the lateral-most edge of the wholemount on the caudal side.
• Efferents: Caudal branch clearly labels more lateral column of mn on both r4 and r5, and also the more medial column on both r4 and r5 (although staining seems more intense in r4)

Anterior Facial Branch

• Afferents: Looks like the rostral afferents labelled from rostral facial form a rather defasciulated rostral branch that seems to stop short probably near the edge of r4/r3. The caudal branch clearly has 2 branches, with the lateral seeming more defasciculated, but neither of then forms a tight bundle.
• Efferents: The lateral motoneuron column seems to be more intensely labelled in r5, although there might be a bit of labelling in r4. The more medial group is labelled in both r4 and r5, but not as much as with DiI from the rostral branch

case nf021

(St 26, 26+)

(green)

• Afferents:The posterior branch does not appear to contribute much to the afferent bundles.

The afferent bundles from the anterior branch look a bit defasciculated and not very dense. The rostral bundle is quite short, probalby extending short of the entry of V, and not too fasciculated. There is a little branch going medially that might be the axons of motoneurons going in to meet the nerve entry. If this is the case, then those axons would seem to be coming from r3. The caudal branch is clearly more defasciculated and extends until the entry of IX - it is also in a more medial position that the rostral one.

• Efferents: The posterior branch labels both columns motoneurons. The anterior branch contributes nicely to both groups of motoneuron.

• there seems to be an interesting meshwork of axons crossing coming and going at the level of the entry of the nerve.

I also wonder if the same BMN are projecting through both branches - t

case nf011

(st. 26-26.5)

• Afferents: Caudal afferents (maybe mechano to trigeminal?) form a rather defasciculated bundle that reaches about halfway through the rootlets of the caudal nerve exit of IX/X. Rostral afferents stop short of the exit of V.

• Efferents: Two clear groups. A more lateral group that spans r4-5 and in r4 a clear group primarily in r4 (perhaps a little in r5, axons seem to be at different depth than the motoneuron cluster in r5, according to the depth coded image). Axons from r4 go straight to exit point whereas those in r5 go laterally and then 'ride on' the afferent bundle. There is a small bundle of motoneurons rostrally that also seems to go ride on the rostral afferent bundle. The cell bodies of the of MNs seem to form chains on top of mini-fascicules of axons going towards the exit nerve.

Case nf003

(St 26-27) Distal VII with VIII removed - DiI crystal, unilateral.

Series 020 (Red, Facial labelling) shows an interesting "loop" of the axons around the nerve entry stump. The caudal branch of the afferent is split in 2. It looks like the more medial of these two is where the axons of the MNs seem to be riding on.The more rostral afferent bundle also seems split in 2 with the more medial half seeming more defasciculated.

Motoneurons: MNs from r5 group seem to hit afferent bundle at more of a right angle and then ride on, rostrally, to get to the exit point, whereas the MNs from r4 segment seem to be going straight towards the brainstem exit point.