Functional roles of neurotrophic factors in the olfactory nervous system

We investigated survival of cholinergic neurons in the horizontal limb of the diagonal band of Broca(HLDB)following lesions of olfactory-related areas expressing neurotrophic factors in the rats.In order to label HLDB neurons projecting to the olfactory bulb，a retrograde fluorescent neuronal tracer(fast blue，FB)was injected into the bulb。After FB injections，we made lesions in the anterior olfactory nucleus(AON)，and combined lesions in the AON and the olfactory bulb(OB)。After4weeks‘survival，the rats were perfused with a fixative，and the brains were removed。Frozen brain sections were serially made，and FB-positive HLDB neurons were counted to know neuronal survival in the control and lesioned rats.The brain sections were，in part，processed for immunohistochemistry for choline acetyltransferase(ChAT)to know survival of cholinergic HLDB neurons.In the AON-lesioned rats，no neuronal cell death occurred in the HLDB.In the AON·OB-lesioned rats，neuronal cell death occurred in the HLDB with marked decrease of the number of FB-positive neurons(n=124)compared with that of FB-positive neurons of the control rats(n=547)。ChAT-positive HLDB neurons were also decreased in number in the AON·OB-lesioned rats.Thus these results show that cholinergic HLDB neurons are dependent，in their survival，on neurotrophic factors produced in the AON and OB。

We investigated survival of cholinergic neurons in the horizontal limb of the diagonal band of Broca (HLDB) following lesions of olfactory-related areas expressing neurotrophic factors in the rats. In order to label HLDB neurons projecting to the olfactory bulb, a retrograde fluorescent neuronal tracer (fast blue, FB) was injected into the bulb. After FB injections, we made lesions in the anterior olfactory nucleus (AON), and combined lesions in the AON and the olfactory bulb (OB). After 4 weeks'survival, the rats were perfused with a fixative, and the brains were removed. Frozen brain sections were serially made, and FB-positive HLDB neurons were counted to know neuronal survival in the control and lesioned rats. The brain sections were, in part, processed for immunohistochemistry for choline acetyltransferase (ChAT) to know survival of cholinergic HLDB neurons. In the AON-lesioned rats, no neuronal cell death occurred in the HLDB.In the AON・OB-lesioned rats, neuronal cell death occurred in the HLDB with marked decrease of the number of FB-positive neurons (n=124) compared with that of FB-positive neurons of the control rats (n=547). ChAT-positive HLDB neurons were also decreased in number in the AON・OB-lesioned rats. Thus these results show that cholinergic HLDB neurons are dependent, in their survival, on neurotrophic factors produced in the AON and OB.