The behavioural actions of newly hatching chickens (Gallus domesticus) require an early but considerable development of CNS areas, responsible for basic motor actions, sensory functions and homeostasis. Thus are they able to walk, see, chirp or feed themselves, like all precocial avians. Previous studies revealed, that the macromolecules of the extracellular matrix (ECM) around neurons highly correspond to their activity, and vice-versa.

We intended the to study the expression of hyaluronan (HA) in the ECM assembly around neurons, during embryonic development, in the vestibular nuclei of chicken embryos. We gained embryos by aborting incubation at 9 different developmental stages. After paraffin embedding and sectioning histochemistry was performed to visualize the HA. Parallel with this the mRNA of hyaluronan synthases (HAS2 & HAS3) were detected with RT-PCR, in all stages. HA was present in all vestibular nuclei from the earliest stages of development. In the lateral vestibular nucleus its amount increased from 11 days (E11), but the perineuronal net (PNN), a condensation of the ECM around neurons, first formed moderately at E13, then its intensity gradually elevated, in the neuropil the staining intensity rose till E13. In the medial vestibular nucleus neuropil labelling enforced till E15, and moderate PNN was identifiable at hatching stage. In the superior vestibular nucleus HA presence grew in the neuropil till E15 stage, and moderate PNN was found in E20. In the descending vestibular nucleus it accelerated early, till E11, and PNN was visible from E15 on, coating not all neurons. Slight elevation of the mRNA expression of HAS2 and HAS3 was seen with RT-PCR analysis on E7 of chick development.

These results may suggest the HA's importance in neuronal circuit establishment, as well the strong ECM at vestibular areas may prove the early development of those, responsible for posture and gaze, motor and sensory modulation.

Supported by MTA TKI 242, and OTKA K67641.