| Prenatal cocaine exposure induces alterations in attentional function that presumably involve locus coeruleus (LC) noradrenergic neurons and their projections. Previous reports indicate that embryonic rat LC neurons exposed to cocaine, both in vitro and in vivo, showed decreased cell survival and inhibition of neurite outgrowth. The present study performed in vitro addressed the specificity of the inhibitory effects of cocaine by comparing embryonic day 14 LC neurite formation and extension to that of dopaminergic substantia nigra (SN) neurons following exposure to a pharmacologically-active dose of cocaine (500 ng/ml) during peak neuritogenesis. Results. Cocaine treatment decreased neurite initiation, elongation, and branching of LC neurons, compared to SN neurons. Cocaine exposure resulted in decreased LC neuron survival, which correlated with activation of apoptosis. Apoptotic cell signaling events were determined at 30 min, 1 h, 4 h and 24 h, post cocaine treatment. Cocaine exposure significantly increased caspase-9 and caspase-3 activities at all time points, with no changes in capase-8 activity, followed by cleavage of caspase-3 target proteins, alpha-fodrin and poly(ADP-ribose) polymerase (PARP) in LC neurons, compared to controls and SN neurons. Further, cocaine triggered tumor necrosis factor-alpha (TNF-alpha) expression at 30 min (ELISA). To investigate the role of TNF-alpha in cocaine induced apoptosis, cells were exposed to recombinant (r)TNF-alpha (10 ng/ml) and neutralizing (n)TNF-alpha (1 mug/ml) and correlated with cocaine induced apoptotic signaling. Exogenous rTNF-alpha decreased LC neuron survival, which correlated with increased apoptosis. Caspase-3 was not activated by rTNF-alpha alone, but nTNF-alpha attenuated cocaine- and rTNF-alpha-induced caspase-3 activity."{09}"In LC neurons, cocaine alone and recombinant TNF-alpha alone induced phosphorylated c-Jun NH2-terminal kinase (PJNK) and altered the Bax/Bcl-2 ratio by increasing Bax protein levels at 30 min and 1 h, with no changes in Bcl-2. PJNK and Bax expressions were attenuated by nTNF-alpha. Cocaine, but not rTNF-alpha, induced phospho p38-MAPK showing no changes in combination with nTNF-alpha. Conclusions. Selective targeting of LC neuron outgrowth and survival by cocaine may occur through TNF-alpha mediated induction of PJNK and Bax leading to caspase-3 signaling, to initiate programmed cell death. |
