Immunocytochemical analysis of the development of chemically defined neurons in the olfactory bulb

在大鼠嗅球中，肾小球层（GL）和外丛状层（EPL）的大部分中间神经元应该是在出生后第一周产生的。在本研究中，我们研究了1)多巴胺能神经元和2)含有钙结合蛋白小白蛋白（PV）的神经元的发育。1)多巴胺能神经元的发育可塑性。用体视学和免疫细胞化学方法研究了新生儿x射线照射对成年动物嗅球神经元，特别是多巴胺能神经元（TH阳性神经元）的影响。在照射后的嗅球中，GABA(-)TH（+）细胞占TH（+）细胞的比例增加到对照组的2倍左右，估计照射后大鼠GABA(-)TH（+）细胞总数为对照组的95%（800rad）和40% （1200rad）。这些观察结果表明，大多数GABA(-)TH（+）神经元在出生后第一周受到x射线照射的影响较小，因此它们可能在产前产生。由于在出生后的前2周，在GL中未见GABA(-)TH（+）神经元（Kosaka et al.1987a），因此假设成人嗅球中的大多数GABA(-)TH（+）神经元在出生后的某个发育时期改变了其表型。2) PV神经元的发育首先研究了成年大鼠嗅球中PV神经元的层状分布和形态特征，然后研究了其出生后的发育变化。EPL的PV（+）神经元具有明显的异质性，似乎可分为几组。PV（+）神经元最早出现在P10，主要分布在EPL内缘，在P14 ~ P21期间PV（+）神经元数量显著增加。本研究进一步揭示了EPL内亚层与外亚层在出生后发育中的差异。

In the rat olfactory bulb, the majority of interneurons in the glomerular layr (GL) and external plexiform layr (EPL) are supposed to be generated during first postnatal week. In the present study we investigated developments of 1)dopaminergic neurons and 2)neurons containing a calcium-binding protein parvalbumin (PV).1)Developmental plasticity of dopaminergic neurons. The effects of neonatal X-rayirradiation , which were used to impair the development of interneurons, on olfactory bulb neurons, especially dopaminergic neurons (TH positive neurons) were examined stereologically and immunocytochemically in adult animals, In irradiated bulbs the proportion of GABA(-)TH(+) cells in TH(+) cells increased to about twice of control, and the estimated total numbers of GABA(-)TH(+) cells in irradiated rats were 95%(800rad) and 40% (1200rad) of control. These observations suggest that the majority of GABA(-)TH(+) neurons were less affected by X-ray irradiation during the first postnatal week and thus that they might be generated in the prenatal period. Since during the first 2 postnatal weeks, neurons showing GABA(-)TH(+) were not seen in GL (Kosaka et al.1987a), the majority of GABA(-)TH(+) neurons in adult olfactory bulb were assumed to change their phenotype at some postnatal developmental period.2)Development of PV neurons The laminar distribution and morphological features of PV neurons were firstly studied in the adult rat olfactory bulb and then their developmental changes were studies postnatally. PV(+) neurons in the EPL were apparently heterogeneous and appeared to be classifiable into several groups. PV(+) neurons first appeared at P10 mainly in the inner border of EPL and they were increased remarkably in number during P14 to P21. The present study further showed the difference between inner sublayr and outer sublayr of the EPL in the postnatal development.