EFFECTS OF INTRANIGRAL INJECTIONS OF COLCHICINE ON THE EXPRESSION OF SOME NEUROPEPTIDES IN THE RAT FOREBRAIN - AN IMMUNOHISTOCHEMICAL AND IN-SITU HYBRIDIZATION STUDY
Pa. Boyer et al., EFFECTS OF INTRANIGRAL INJECTIONS OF COLCHICINE ON THE EXPRESSION OF SOME NEUROPEPTIDES IN THE RAT FOREBRAIN - AN IMMUNOHISTOCHEMICAL AND IN-SITU HYBRIDIZATION STUDY, Brain research bulletin, 33(5), 1994, pp. 541-560
In the present study, we describe the neurochemical effects of intrani
gral injections of colchicine in the rat forebrain using immunohistoch
emistry and in situ hybridization. The observations on the injected si
de are compared to the contralateral one and to the sham-operated rats
. We demonstrate that such injections are able to strongly enhance the
immunoreactivity for Met-enkephalin (ME), substance P (SP) and neurop
eptide Y (NPY) in numerous nerve cell bodies of the limbic system (inj
ected side), whereas the levels of the corresponding mRNAs are differe
ntly modified according to the region examined. A clear correlation be
tween the enhancement of the immunostaining for ME and SP and that of
the preproenkephalin (PPA) and preprotachychinin gene transcripts was
observed in neuronal perikarya of the medial amygdaloid nucleus (SP),
of the dorsolateral hypothalamus (ME) and of the ventromedial hypothal
amic nucleus (SP). These observations are interpreted as an induction-
or increased expression-of neuropeptide genes in neuronal perikarya po
stsynaptic to nerve fibers originating in the midbrain and brain stem.
In this case, colchicine is thought to block the electrophysiological
activity of ascending nerve fibers (anterograde and postsynaptic effe
ct). In the case where the enhancement of the immunoreactivity for the
studied neuropeptides was associated with no change or a decreased ex
pression of the corresponding genes in the same brain areas, colchicin
e may have blocked the axoplasmic transport of peptides in nerve fiber
s projecting to the midbrain and/or brain stem (6). This may result in
a retrograde accumulation of peptides in the nerve cell bodies of ori
gin and, eventually, in a negative feedback regulation of the correspo
nding encoding genes in these perikarya (retrograde and presynaptic ef
fect of colchicine). The drastic behavioral effects of bilateral intra
nigral injections of colchicine, on ingestive behavior in particular,
have been studied in a following paper.