Effects of N‐(2‐chloroethyl)‐N‐ethyl‐2‐bromobenzylamine (DSP4) on α₂‐Adrenoceptors which Regulate the Synthesis and Release of Noradrenaline in the Rat Brain

Abstract

N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4) induces a degeneration of noradrenergic axons originating in the locus coeruleus. The sensitivity of a 2 -adrenoceptors which regulate the synthesis and release of noradrenaline was investigated in three brain regions which receive an unequal innervation from locus coeruleus, 21 days after DSP4 (50 mg/kg) administration. After giving treated rats a dopa decarboxylase inhibitor, the in vivo tyrosine hydroxylase activity and the tissue concentrations of noradrenaline were also evaluated. Relevant reductions of noradrenaline levels were found in hippocampus and parietal cortex (91% and 77.5%, respectively; PϽ0.001) together with a less pronounced reduction in hypothalamus (32%, PϽ0.01). The administration of the neurotoxin led to decreases of the basal tyrosine hydroxylase activity, determined as the accumulation of 3,4-dihydroxyphenylalanine, in hippocampus and parietal cortex (75% and 50.5%, respectively; PϽ0.001), but not in hypothalamus. The inhibitory effect of clonidine on tyrosine hydroxylase activity was markedly reduced in hippocampus of rats treated with DSP4 (10∫5% vs 57∫3% in the control group, PϽ0.001) but was not changed in parietal cortex and hypothalamus. Moreover, in hippocampus, a lack of functionality of the a 2 -adrenoceptors which regulate K π -evoked [ 3 H]noradrenaline release was determined. However, in cortical synaptosomes the concentration-effect curve for the oxymetazoline shifted to the right. The administration of the neurotoxin did not modify the inhibitory effects of the agonist in hypothalamus. These results support the previously described selectivity of DSP4 for noradrenergic terminals arising from locus coeruleus and suggest a more severe lesioning of the hippocampus than the parietal cortex.

Absence and Rescue of Morphine Withdrawal in GIRK/Kir3 Knock-out Mice

“…DSP4 binds to the adrenergic transporters located on adrenergic neuron terminals (Lee et al, 1982). DSP4 shows strong selectivity for adrenergic terminals arising from the LC, as evidenced by immunohistochemical analysis of dopamine ␤-hydroxylase (a marker of adrenergic terminals) (Fritschy and Grzanna, 1991) and biochemical measurements of NA that showed abolished levels only in regions targeted by the LC (Prieto and Giralt, 2001). It is important to note that the molecular basis for this selectivity remains elusive.…”

Desensitization of α₂-Adrenoceptors which Regulate Noradrenaline Synthesis and Release after Chronic Treatment with Clorgyline in the Rat Brain

“…In order to provide further evidence of the fact that the clorgyline-induced desensitization of · 2 -adrenoceptors depends on the endogenous noradrenaline content, we compared the sensitivity of the · 2 -adrenoceptors which regulate release in cortical synaptosomes obtained from rats treated with DSP4 and the MAO-A inhibitor with that observed in rats treated only with the neurotoxin. These experiments were performed in parietal cortex, as we had previously demonstrated the existence of remnant noradrenergic terminals endowed with functioning · 2 -adrenoceptors despite the severe reduction in noradrenaline content and the lesioning induced by DSP4 [28]. We did not assay the · 2 -adrenoceptor sensitivity in the hippocampus due to the fact that we had seen that in this brain region there was a lack of · 2 -adrenoceptor functionality in animals which had only been treated with the neurotoxin [28].…”

“…These experiments were performed in parietal cortex, as we had previously demonstrated the existence of remnant noradrenergic terminals endowed with functioning · 2 -adrenoceptors despite the severe reduction in noradrenaline content and the lesioning induced by DSP4 [28]. We did not assay the · 2 -adrenoceptor sensitivity in the hippocampus due to the fact that we had seen that in this brain region there was a lack of · 2 -adrenoceptor functionality in animals which had only been treated with the neurotoxin [28]. After chronic treatment with clorgyline in DSP4-treated rats, the sensitivity of · 2 -adrenoceptors which regulate noradrenaline release was similar to that found after the administration of only DSP4.…”

“…The homogenates were processed following the technique used by Pi and García-Sevilla [27]. Aliquots (50 Ìl) of the final eluates were analyzed by means of a high-performance liquid chromatograph (Waters, Milford, Mass., USA) with electrochemical detection (LC-4B; Bioanalytical Systems, Indianapolis, Ind., USA), as described in a previous study [28]. The concentrations of DOPA and noradrenaline were determined by comparing the peak heights of each sample with the corresponding standard peak heights.…”

Neonatal DSP-4 treatment modifies GABAergic neurotransmission in the prefrontal cortex of adult rats

“…In these cells DSP-4 produces morphological changes, inhibits norepinephrine (NE) reuptake, stimulates NE release, and increases turnover rate of NE (JaimEtcheverry, 1998;Prieto et al, 2001). DSP-4 interacts with the NE uptake system, accumulates intraneuronally, and produces nerve terminal degeneration via alkylation of diverse neuronal structures.…”