Blagburn J M, Beadle D J, Sattelle D B
J Embryol Exp Morphol. 1985 Apr;86:227-46.
The cercal afferent, giant interneurone pathway in Periplaneta americana was used as a model for synapse formation. The morphology of the two identified filiform hair sensory neurones (FHSNs) and of two giant interneurones (GI2 and GI3) was followed throughout embryogenesis by cobalt injection. The FHSN axons enter the CNS at the 45% stage of embryogenesis, branch at 50% and form complete arborizations by 70%. The giant interneurones send out a primary dendrite at 45%. Secondary branches form between 50% and 60% and elaboration of the branching pattern takes place until 80% embryogenesis. At early stages the FHSN axons are within filopodial range of GI dendrites which may use these sensory processes as guidance cues. Synapse formation between the main FHSN axon shafts and GI dendrites was investigated by injection of the latter with HRP. From 55% to 65% the process is initiated by desmosome-like filopodial contacts, with subsequent vesicle clustering and formation of a small synaptic density. Numbers of contacts did not significantly increase after about 70%, but the number of synapses doubled between 65% and 75%, with each GI process becoming postsynaptic to two FHSN synapses and the presynaptic densities lengthening to become bars. From 75% embryogenesis to hatching there is a further small increase in synaptic bar length. In the first instar GI3 is postsynaptic to both FHSN axons, whereas GI2 forms very few synapses with the axon of the lateral FHSN (LFHSN). This imbalance of contacts is present throughout synaptogenesis, apart from some early filopodial contacts. GI3 forms synapses with the lateral side of the LFHSN axon from 60% embryogenesis but these are totally absent at hatching. The growth of glia along this side of the axon during the last 30% of development appears to be associated with degeneration of synapses in this region. Thus, as the dendrites of the GIs grow to form a miniature version of the adult without loss of branches, there is little evidence of an initial overproduction of FHSN-GI synapses. Similarly there is no evidence that GI2 forms 'incorrect' synapses with the axon of LFHSN. However, GI3 contacts are removed from an inappropriate region of a correct synaptic partner, LFHSN.
美洲大蠊的尾须传入、巨中间神经元通路被用作突触形成的模型。通过注射钴，在整个胚胎发育过程中追踪了两种已鉴定的丝状毛感觉神经元（FHSN）和两种巨中间神经元（GI2和GI3）的形态。FHSN轴突在胚胎发育的45%阶段进入中枢神经系统，在50%阶段分支，并在70%阶段形成完整的分支。巨中间神经元在45%阶段发出初级树突。二级分支在50%至60%阶段形成，分支模式的细化一直持续到胚胎发育的80%。在早期阶段，FHSN轴突处于GI树突的丝状伪足范围内，GI树突可能将这些感觉过程用作引导线索。通过向GI树突注射辣根过氧化物酶（HRP），研究了主要FHSN轴突主干与GI树突之间的突触形成。从55%到65%，这个过程由类似桥粒的丝状伪足接触启动，随后是囊泡聚集和小突触密度的形成。大约70%之后，接触数量没有显著增加，但在65%到75%之间，突触数量翻倍，每个GI过程成为两个FHSN突触的突触后成分，突触前密度延长形成条带。从胚胎发育的75%到孵化，突触条带长度进一步略有增加。在第一龄期，GI3是两个FHSN轴突的突触后成分，而GI2与外侧FHSN（LFHSN）的轴突形成的突触很少。除了一些早期的丝状伪足接触外，这种接触的不平衡在整个突触形成过程中都存在。GI3从胚胎发育的60%开始与LFHSN轴突的外侧形成突触，但在孵化时这些突触完全消失。在发育的最后30%期间，轴突这一侧的神经胶质细胞生长似乎与该区域突触的退化有关。因此，随着GI树突生长形成成年期的微型版本且分支不减少，几乎没有证据表明FHSN - GI突触最初过度产生。同样，也没有证据表明GI2与LFHSN的轴突形成“错误”的突触。然而，GI3的接触从正确的突触伙伴LFHSN的不适当区域被移除。
