Journal of Neuroscience, Vol 9, 2151-2162, Copyright © 1989 by Society for Neuroscience
Synaptogenesis in the rat suprachiasmatic nucleus demonstrated by electron microscopy and synapsin I immunoreactivity
RY Moore and ME Bernstein
Department of Neurology, State University of New York, Stony Brook 11794.
Synaptogenesis was studied in the rat suprachiasmatic nucleus (SCN) using
quantitative ultrastructural analysis and synapsin I immunohistochemistry.
SCN neurons are formed between embryonic days 13 and 17 (E13-E17), and the
SCN is a distinct hypothalamic nucleus by E18. At E19 the nucleus is very
immature and there are few synapses. Synaptogenesis proceeds slowly until
P4 but increases rapidly between P4 and P10. At P10 the number of synapses
per unit area is the same as in the adult SCN and all synaptic types
present in the adult are evident. However, the SCN continues to increase in
volume to the adult with approximately 30% of total synaptic number added
between P10 and a young adult age. The appearance of synapsin I
immunoreactivity correlates very precisely with the development of synapses
in the SCN as shown by ultrastructural analysis between E19 and P6. The
pattern of appearance of synapsin I immunoreactivity demonstrates that
synaptogenesis in the SCN is significantly delayed in comparison to
adjacent hypothalamic nuclei. Synapsin I immunohistochemistry is a reliable
marker of synapse formation in the developing SCN. A correlation of these
anatomical data with prior functional studies suggests that SCN neurons are
born as individual circadian oscillators that undergo a rapid development
in the first 10 days after birth to form a functional neural network
subserving circadian rhythm generation and regulation.