Kubke Lab:Research/CND/Summary VIII

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stage 25

case nf010

(St 25.5) DiO/DiI peanut oil tip of cochlea

  • Afferents: I see a single bundle of axons which run quite along the length of the hindbrain - but cant find well defined branches. Rostrally, the afferent bundle seems to project rotral to the level of the trigeminal nerve root, and caaudally all the way caudal as well. At the level of r3, there are some side branches coming out of the nerve, but cant see very many. The few I see seem to be coming out rostral to the VIIIn root. Quite a lot of lateral branching on the caudal afferent bundle.
  • Efferents: Not too dense, a lot of varicosities. Clearly on r4 and r5.
  • Other: Dont see any fibres crossing the midline.

stage 26

case nf005

(St 26) Caudal cochleovestibular ganglion, DiO crystal, bilateral. Collabelling with VII.

Nerve entry well differentiated from VII nerve, entering in a more dorsolateral position with respect to VII.

Both rostral and caudal sensory bundles seem to be split. The rostral bundle seems to be split into a longer thinner dorsolateral bundle and a seemingly less fasciculated medial bundle. The caudal bundle seems to be split into two and perhaps 3 bundles. Both bundles rostral and caudal show perpendicular projections of axons coursing towards the midline.

Efferent neurons are found in both r4-r5 and appear to occupy a more ventral position than the VII efferents. Labelling appears to be more intense in r4, where there seem to be two groups - a more dorsal one in a more lateral position and a more ventral one with cells all the way to the floor plate.

High magnification of the floor plate also shows extensions crossing the floor plate, as well as some fibres that seem to be coursing rostrocaudally at the edge of the floor plate.

There are also clearly labelled cell bodies in the dorsolateral edge of the wholemount, most likely in the alar plate. These lateral cell bodies can be found in r4 and r5 but they also seem to be present in r3.

case nf006

(St 26) Caudal afferent branch seems like a large unfasciculated bundle. Cannot see a separation into discrete components. The rostral branch seems to have 2 discrete bundles separated by what seems to be a black hole of where other input/output fibres might be going through. There is a medial bundle that seems to be associated with the turning axons of the more rostral motor axons, and a more lateral bundle that is not. Both bundles project to approximately the same extent rostrally, crossing R3 at least and probably beyond that. The rostral end of this injection seems to stop a lot shorter than in case nf007.

case nf007

(St 26)

cochlear/lagenar branch of caudal cochleovestibular The nerve makes a well defined loop coming into the brainstem.

  • Afferents: Seem to form a single well defined bundle, one running caudal and one rostral. They obviously extend beyond the segments where the efferents are found.
  • Efferents: Very few labelled despite strong labelling at the nerve entry. There is clear label on efferents, especially in r4, although some r5 can be seem too, but there seem to be less of those.

case nf009

(St 26) Cochleovestibular -

  • Afferents Have two very distinct and separate afferent bundles. Caudal afferents seem to have a clear separation into 2 bundles, but this is less clear in the rostral branch. It seems that there are lots of side branches coming out of the afferent bundles. There also seems to be, at the depth where the efferent axons seem to meet the afferent bundles a more medial, shorter and more defasciculated bundle - but only see this on the caudal side.
  • Efferents: cell bodies seem to be crossing floor plate. There seem to be 2 groups both of which span r4/r5. A column which is more lateral with well compacted cell bodies, and a column closer to the floor plate.
  • Other: looks like neurites crossing the floorplate and also what appears as cell bodies going into it too. in Series 028 it appears that there are a few neurites crossing the floor plate, probalb only on r5. Image nf009-Series040-z025 shows a neuroblast in really close apposition with a nearby "fibre" There seem to be not just neurites but also cell bodies on the floor plate. I also notice some labelled fibres that are travelling on what seems to be the border between the floor plate and the basal plate. It is also quite clear that many of these processes are crossing all the way to the contralateral side

case mf023

(St 26) Otic vesicle injected with DiI in MetOH

  • Afferents: The caudal bundle appears to run in a bit of a medial position with respect to the rostral one. The rostral bundle is clearly separated into a longer more lateral one and a shorter more medial one at low magnification. When a slice stack is taken in a narrower part of VIII there are 2 clearly distinct groups of afferents - forming two bundles that run parallel and next to each other. I can see this clearly on the right side but not so much on the left side
  • Efferents: Not a huge number compared to facial, but a singificant amount of labeling. All in the superficial group no deep column. Processes also cross the floor plate.
  • 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+) VIII - posterior vestibular (green)

  • Afferents: Nicely labelled - caudal fascicle appears a bit more medially positioned than rostral fascile. Be careful, there might have been some spill into VIII ganglion
  • Efferents: No labelled efferents

VIII posterior cochlear (red) (see notes - contamination with IX)

  • Afferents: Two clear bundles, with caudal fascicle in a more medial position
  • Efferents: Can defnitely see efferents, but few and far between - seem to be on both r4 and r5, although probably more in r5. Not that many of them!

Other:

There doesn't seem to be segregation in the afferent path of the 2 branches, although would need to look at this more carefully in the stacks.

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