Blockade of in vivo binding of 125I-labeled 3-iodobenzamide (IBZM) to dopamine receptors by D2 antagonist and agonist

The in vivo binding of [125I]3-iodobenzamide (IBZM), a substituted benzamide, to DA receptor binding sites in the caudate nucleus, nucleus accumbens, and olfactory tubercle was investigated by using ex vivo autoradiography. The in vivo binding of IBZM seems to be selective to D2 dopamine receptors, since the binding was blocked by pretreatment of animals with D2 agonist LY-171555 or antagonist YM-09151-2. Furthermore, in vitro binding assays in striatal membranes confirmed that IBZM binding was highly selective to D2 sites. Thus, IBZM, when labeled with 123I (T1/2: 13h; 159 kev), could be a potential ligand for imaging D2 dopamine receptors by single photon emission computerized tomography procedures.

Neurotoxic damage to the nigrostriatal system in rats following intranigral administration of MPDP+ and MPP+

Unilateral intranigral administration of the oxidative metabolites of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 1-methyl-4-phenyl-dihydropyridine (MPDP+) or 1-methyl-4-phenylpyridine (MPP+) produced dose-dependently a depletion of dopamine in the ipsilateral striatum of rats two weeks following treatment. d-Amphetamine and apomorphine induced circling toward the lesioned side in these unilaterally treated animals. No contralateral circling behavior was observed after challenging with apomorphine. This dopamine lesioning effect of MPP+ was not blocked by pretreatment of animals with a dopamine uptake blocker, GBR 12909. Furthermore, MPP+ increased the 45Ca accumulation into cells at the site of injection and produced "nonspecific" cell membrane and/or cytotoxic damage seen by histological procedures. These results indicate that MPDP+ and MPP+ produced localized cytotoxic damage to nigrostriatal neurons, caused a decrease in striatal dopamine, and disrupted the nigrostriatal system's functioning following intranigral administration to rats. It is postulated that the cationic surfactant properties of MPDP+ and MPP+ might contribute to its neurotoxic effects.

Asymmetric distribution of catecholamine-containing neuronal perikarya in the upper cervical spinal cord of rat

Hitherto undescribed catecholamine-containing neuronal perikarya (CCNP) were demonstrated in the white and grey matter of the rat cervical spinal cord. In the white matter they were mainly located in the dorsal part of the lateral funiculus; the number of CCNP in the left lateral funiculus was significantly higher than that in the right and they also extended further caudally. After colchicine treatment, a greater number of CCNP were visible on both sides, the left side again containing more CCNP than the right. In addition, CCNP in colchicine-treated animals were observed further caudally than in untreated animals. In contrast, no lateralization was apparent in the grey matter CCNP.

Microspectrofluorometric characterization of the fluorescent derivatives of biogenic amines produced by aqueous aldehyde (Faglu) fixation

The fluorescent derivatives of the reaction between an aqueous aldehyde (Faglu) solution and the biogenic amines (5-hydroxytryptamine, dopamine and noradrenaline) have been examined in the order to determine the conditions required for maximal fluorescence yield. The fluorescence intensity and spectra of the final reaction products have been characterized and found to be highly dependent on the pH of the reaction mixture, Fluorophores derived from catecholamines have maximal yield and are most easily characterized when the reaction is performed at pH 7.3, whilst those derived from 5-hydroxytryptamine have maximal yield and are most readily characterized when the reaction is performed at pH 10.0. The addition of potassium ferricyanide to the Faglu further enhances the fluorescence yield of 5-hydroxytryptamine-containing models and tissues at both pH 10.0 and pH 7.3. Using the modified Faglu reaction mixture, it has been possible to demonstrate 5-hydroxytryptamine in the central nervous system without the need for pharmacological manipulation.