H. Elbizri et al., INTRANEURONAL ACCUMULATION AND PERSISTENCE OF RADIOLABEL IN RAT-BRAINFOLLOWING IN-VIVO ADMINISTRATION OF [H-3] CHLORISONDAMINE, British Journal of Pharmacology, 116(5), 1995, pp. 2503-2509
1 Chlorisondamine (CHL), a bisquaternary amine, produces a remarkably
long-lasting blockade of central responses to nicotine. The mechanism
underlying this blockade is not known. The main aim of this study was
to test for possible accumulation of [H-3]-CHL in rat brain during the
period of chronic blockade. 2 Rats received CHL, either systemically
(10 mg kg(-1)) or centrally (10 mu g i.c.v.). Seven days later, striat
al synaptosomes prepared from these animals were tested for nicotine-i
nduced [H-3]-dopamine release. This experiment showed that i.c.v. admi
nistration of CHL was as effective as systemic administration in produ
cing ex vivo blockade of central nicotinic receptors. 3 Rats received
bilateral i.c.v. infusions of [H-3]-CHL (10 pg) and radioactivity was
subsequently quantified in dissected cerebral cortex, striatum, hippoc
ampus, midbrain and cerebellum. Radiolabel was detected at all three s
urvival times (1, 7, and 21 days). Regional heterogeneity was apparent
at 7 and 21 days survival. Radiolabel was almost exclusively confined
to the insoluble subcellular fraction in all areas sampled. 4 The ana
tomical distribution of radiolabel was also visualized in brain sectio
ns. Rats received bilateral i.c.v. infusions of [H-3]-CHL (10 mu g) an
d were killed at 1, 7, 21 or 84 days. Immediately before they were kil
led, all rats were tested behaviourally, and central nicotinic blockad
e was demonstrated at 1, 7 and 21 days; partial recovery was observed
at 84 days. Particularly at longer survival times, tritium was found t
o be heavily concentrated in the substantia nigra pars compacta, ventr
al tegmental area, dorsal raphe nucleus, and the granular layer of the
cerebellum. 5 The possibility of retrograde axonal transport of radio
label was then examined. Rats received a unilateral intrastriatal infu
sion of [H-3]-CHL (0.34 or 0.034 mu g) one week before they were kille
d. Autoradiographic labelling was largely confined to the site of infu
sion and to the ipsilateral substantia nigra pars compacta and dorsal
raphe nucleus. 6 Thus, after i.c.v. administration, CHL (and/or centra
lly-formed derivatives) is initially widely distributed within the bra
in and is then selectively retained within a few brain areas. A persis
tent accumulation occurs within putative dopaminergic and 5-hydroxytry
ptaminergic neurones, at least partly through uptake by terminals and/
or axons followed by retrograde transport. This persistent and anatomi
cally-selective intraneuronal accumulation possibly underlies the long
-term central nicotinic blockade associated with chlorisondamine.