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) (see notes on spill on one side)

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. Caudal bundle appears in a more medial position, except for a few thin and tightly packed axons on the more lateral side. Only got afferents on injections on one of the sides

• Efferents: Caudal branch clearly labels more superficial/ medial column of mn on both r4 and r5, but primarily on R4. The more lateral deep colum is also well labelled.

• Other: Seem to see profiles on the floor plate

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 deep/lateral motoneuron column seems to be more intensely labelled in r5, although there might be a bit of labelling in r4. The more superficial/medial group is labelled in both r4 and r5, but not as much as with DiI from the rostral branch. There is in fact very little labelling.

case nf022

(St 26)

Facial Ganglion LEFT (red)

• Afferents: Both rostral and caudal bundles are labelled, with caudal bundle in a more medial position. Caudal bundle seems to show a bit of a separation with a more lateral group of axons and a more medial group which is larger. In the caudal bundle, I can see the main bundle, but there are clearly axons straying towards the mdiline. the staining is also quite granular and it may be just filling pattern or the presence of growth cones or varicosities from where side branches may eventually emerge. The rostral bundle seems thinner, more fasciculated into more than one fascile and some stray axon(s) that seem to be more medial having lost their way.
• Efferents: Both motoneuron groups are labelled quite well.

Facial Ganglion RIGHT (green)

• Afferents: Caudal afferents more labelled, though still some labelling on rostral afferents. Rostral afferents appear to project at least to the entry of V. Caudal axons seem to stop at the entry of IX, although some few solitary axons are seen beyond that point. Caudal afferent bundle seems to be positioned more medially, and axons show a good degree of fasciculation. There is some indication that this medial bundle might be subdivided into a larger more medial portion and a thinner more lateral portion. The lateral portion is more labelled with DiO than with DiI - and this could be a loading issue or simply a different topography. the two bundles of the caudal bundle seem to come together to criss-cross each other at the level of about r7. It reminds me of the embryonic lumbar plexus.
• Efferents: Both motoneuron groups are labelled quite well.

Posterior facial branch (RIGHT)(red)

• Afferents: Don't seem to have much afferent label, there might be some, but nothing compared to when the ganglion is labelled. The caudal bundle axons are very varicose.
• Efferents: Both groups of motoneurons seem to be labelled. There seems to be some sort of disorganisation of the efferent axons towards the border of r5/r6 (see nf022_FreeProjMax_05_ch00.tif. There is something definitely going on at that border, but cannot make out what that is.

Other

In the merged image of ganglion and posterior branch, ti seems that there is a good deal of overalp between green and red in the medial side of the caudal afferent bundle, whereas more laterally it looks like there is more segregation between read and green. They seem less segregated in the rostral afferent bundle.

Case nf023

(Stage 26)

• Afferents: Caudal bundle running in a more medial position than rostral bundle. Didnt get much labelling of rostral bundle on the right side (where the dye placement was localised more to the anterior branch. On both sides the caudal branch is somewhat desfasciulated with a larger with more tightly placked axons on a medial position and a few defasciculated ones more laterally. On the right side I see what appears to be some ectopic afferents, running along the area where the motoneuron= axons make their rostral turn. Axons do not seem to extend beyond the level of entry of IX
• Efferents: Both groups of motoneurons are labelled.

• Other: Low magnification of red/green shows that there is a clear separation of the auditory and facial afferent bundles, with the facial afferents running more medially than the auditory ones. In contrast, axons of motoneurons seem to be running in close contact to each other, and at least at this stage, they do not appear to be segregated in the hindbrain. Facial BMN do not seem to cross the midline, but it appears that chochlear do (series 050 and free proj max 09) . The red axons also seem to be quite mixed in the more rostral set of MNs of VII and not in the deep group.

case nf021

(St 26, 26+)

Anterior Facial branch

• Afferents: More clearly labelled - a few fibres, somewhat defasciculated. The rostral bundle is quite short, probably extending to the r3/r2 border, 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 are coming from r3. If they are afferents, they are going a funny route. 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: Beautiful labelling throughout the 2 motoneuron columns on both rhombomeres

Posterior Facial branch

• Afferents:No label on the afferent bundles.

• Efferents: The posterior branch labels both columns motoneurons.

Other:

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.