The nervus terminalis (cranial nerve zero) was investigated in
22 routine microslide series of different bat genera, mainly Myotis
myotis, from 14 mm crown-rump length (CRL) up to adulthood,
including cell measurements. Additionally, sections of other juvenile
and adult bats treated immunocytochemically for LHRH were used.
The total number of terminalis cells within the cranial vault
was counted using conventional cytological criteria.
At 14 mm CRL, Myotis embryos already show a relatively
large number of cells (about 700 cells on each side). In
slightly larger specimens, the terminalis cell number first increases
but then decreases markedly. It reaches its peak in late fetal
stages and eventually is reduced to a minimum after birth. Interestingly,
the number of meningeal terminalis cells is not correlated with
body size. In this respect, Myotis holds an intermediate
level while cetaceans show the absolute maximum in terminalis
cell number within mammals.
The nervus terminalis, which includes at least two or more neurone
populations, may play a different role both in successive ontogenetic
periods and in the adult stages of various mammalian groups. The
potential functional implications of the terminalis system in
ontogeny and physiology are discussed.