FINE-STRUCTURE OF THE AFFERENT SYNAPSES IN THE PARATYMPANIC ORGAN OF THE CHICKEN, WITH SPECIAL REFERENCE TO THE SYNAPTIC BODIES

The afferent synapses of the paratympanic organ in the chicken were st udied by TEM. These synapses were formed by non-myelinated fibres whic h reached the basal part of the hair cells. The fibres contained a num ber of irregular mitochondria and a few pale vesicles. In the hair cel ls, near the presynaptic membrane, typical synaptic bodies formed by a n electron-dense core surrounded by several small pale vesicles were p resent. The core was connected with the vesicles by numerous thin fila ments, and at same time with the presynaptic membrane by some dense pr ojections. Moreover, we have observed that the connections between the core and the adjacent vesicles also consisted of similar structures t o the dense projections. We suggest that this device is involved in th e movement of the vesicles towards the presynaptic membrane. Our hypot hesis is in agreement with that formulated by some authors who believe that the electron-dense core of the synaptic bodies is able to channe l the vesicles to the presynaptic membrane (conveyor-belt hypothesis). Moreover, our work showed that the synaptic bodies of the paratympani c organ in the chicken are variable in density and in shape. These mor phological aspects might be linked to regression-reconstitution cycles of the SBs and to the functional level of the afferent synapses.