The use of neurotoxins to characterize the rates and subcellular distributions of axonally transported dopamine-beta-hydroxylase, tyrosine hydroxylase and norepinephrine in the rat brain

The effect of 6-hydroxydopamine (6-OHDA), colchicine and cytochalasin B on the transport and subcellular distribution of proteins, tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH) and norepinephrine (NE) were studied in the noradrenergic neurons of the rat locus coeruleus (LC). Four waves of transported 3H-labeled proteins and glycoproteins, defined by previous studies, as well as hypothalamic levels of TH, DBH and NE, were examined after injection of each neurotoxin into the ascending dorsal noradrenergic bundle. Blockade of subcellular components of TH, DBH and NE was compared to their endogenous hypothalamic distributions. 6-Hydroxydopamine variably blocked transport of all 4 waves of 3H protein and bilateral injections decreased hypothalamic levels of TH, DBH and NE by 58.2, 56.9 and 52.2% of controls, respectively. Cytochalasin B blocked transport of protein waves I (72--192 mn/day) and III (13--20 mm/day) and decreased hypothalamic levels of TH to 60.1% of control after bilateral injections. Colchicine blocked transport of waves I, II (24--48 mm/day) and V (1.4--2.9 mm/day) and blocked [3H]NE transport, while decreasing hypothalamic levels of DBH and NE to 56.6 and 69.3% of control after bilateral injections. Colchicine and 6-OHDA, but not cytochalasin B, caused a backup of DBH immunofluorescence proximal to the injection site. DBH and NE appeared to be transported primarily in particulate form, while TH transport was predominantly soluble in distribution. None of the toxins differentially affected the transport of one particular subcellular component of TH, DBH or NE. Based on the differential blocking effects of these toxins, DBH and NE appeared to be associated with wave II, and TH with wave III, travelling at 24--48 mm/day and 13--20 mm/day respectively.