Aa. Battaglia et al., A CONFOCAL APPROACH TO THE MORPHOFUNCTIONAL CHARACTERIZATION OF THE TRANSIENT TYROSINE-HYDROXYLASE SYSTEM IN THE RAT SUPRACHIASMATIC NUCLEUS, Brain research, 696(1-2), 1995, pp. 7-14
The suprachiasmatic nucleus (SCN) of the neonatal rat is transiently i
nnervated by tyrosine hydroxylase (TH) fibers of unknown origin and wh
ose catecholaminergic nature is rather doubtful. In order to character
ize this system morphofunctionally, immunocytochemical double labellin
g and confocal laser scanning microscopy analysis were employed on cry
ostat brain sections of 10-day-old rats. Simultaneous stainings for ne
uropeptide Y (NPY) and tyrosine hydroxylase (TH) immunoreactivity show
ed that they are not colocalized, neither in the SCN fibers nor in the
intergeniculate leaflet (IGL) neurons, site of origin of the NPY proj
ection to the SCN. Therefore, the possibility that SCN transient TH fi
ber system originates from the IGL could be excluded. Double labelling
for TH and aromatic L-aminoacid decarboxylase (AADC) demonstrated tha
t transient SCN TH immunoreactive (IR) fibers are AADC negative, thus
supporting the hypothesis of their non-catecholaminergic nature. Moreo
ver two new group of cells which are TH positive and AADC negative wer
e found: one in the SCN and the other in the periventricular hypothala
mic nucleus (PHN). The presence of somatostatin (SRIF) and TH in PHN n
eurons and SCN fibers suggested their possible colocalization, but dou
ble immunolabellings gave negative results. Simultaneous immunocytoche
mical staining for vasoactive intestinal polypeptide (VIP) and TH show
ed that TH fibers may interact with ventrolateral SCN VIP neurons. Thi
s result suggests a possible involvement of TH fibers in regulating VI
P cells activity in the entrainment of circadian rhythms.