Brain
cholecystokinin (CCK)- and noradrenergic activities are two neurochemical systems implicated in anxiety and deficits in novelty-related behaviour. In order to clarify a possible interaction between CCK- and noradrenergic neurotransmission in the brain,
DSP-4 [N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine], a
neurotoxin that selectively destroys
noradrenaline-containing nerve terminals originating from the locus coeruleus, was administered to rats IP (10 and 50 mg/kg) seven days before
decapitation.
Noradrenaline uptake was very markedly reduced in the frontal cortex and hippocampus of the
DSP-4 treated animals, whereas the decrease in the hypothalamus was smaller but still statistically significant.
Dopamine uptake in the corpus striatum, as well as
serotonin uptake in the frontal cortex, hippocampus and hypothalamus, were not influenced by
DSP-4 treatment. Concomitantly,
CCK receptor binding in certain brain regions was markedly affected. Thus,
CCK receptor density was significantly higher in the frontal cortex and hippocampus of DSP-4-treated rats. If
desipramine (25 mg/kg) was administered before
DSP-4 treatment, the DSP-4-induced changes both in
noradrenaline uptake and
CCK receptor binding were not present, suggesting that both effects were exerted after uptake of the
neurotoxin by the nerve terminals. The time-course of the development of changes in
CCK-8 binding paralleled with some lag the development of changes in
noradrenaline uptake. These findings demonstrate the
denervation of noradrenergic input from the locus coeruleus induces certain alterations in the CCKergic neurotransmission. These alterations are similar to those seen in rats with deficits in response to novel stimuli, and may therefore mediate the neophobic responses observed in animals after lesions of noradrenergic innervation of the forebrain.