ULTRASTRUCTURAL ORGANIZATION OF THE NORADRENERGIC INNERVATION OF THE SUPERFICIAL GRAY LAYER OF THE HAMSTERS SUPERIOR COLLICULUS

Immunocytochemistry with an antibody-directed tyrosine hydroxylase (TH ) was combined with electron microscopy and serial-section analysis to examine the synaptic organization of the catecholaminergic projection to the stratum griseum superficiale (SGS) of the hamster's superior c olliculus (SC). A total of 250 TH-immunoreactive profiles within SGS w ere examined. Of these, 114 (45.6%) made synaptic contacts; 81 (71.1%) were axodendritic, and the remainder (33, 28.9%) were axo-axonic. Ser ial-section analysis was employed to evaluate the presence or absence of synaptic contacts for 26 profiles. Overall, 19 (73.1%) of the profi les followed through serial sections exhibited synaptic contacts. Doub le staining of single sections with antibodies directed against TH and dopamine-beta-hydroxylase (D beta H) and examination in the light mic roscope indicated that virtually all TH-positive fibers also contained D beta H. This indicated that the fibers examined at the electron mic roscopic level were noradrenergic rather than dopaminergic. These resu lts suggest that norepinephrine may have both pre- and postsynaptic ac tions in the hamster's SC and that at least some of these effects are mediated by conventional synapses. (C) 1994 Wiley-Liss, Inc.