The locus coeruleus of cat

Summary The locus coeruleus of cat is populated by two types of neurons: medium sized ones, with plump cell bodies and relatively short dendrites; and small ones, with triangular bodies and relatively long dendrites. The former type is regarded here as typical of the centre, whereas the second type could simply represent displaced neurons from the adjacent griseum centrale. Electron microscopy failed to reveal any outstanding richness in pigment granules in kittens up to five weeks old. Very characteristic somatic appendages were found, mostly in the medium sized neurons. These somatic spines communicate with the perikaryon by means of a narrow neck region. A complex, multilayered, glial sheath surrounds the cells. This glial sheath is pierced by the somatic appendages, which are not surrounded by glia and make contact with axonal knobs. Typical dendritic spines appear to be absent. Axodendritic synapses are made on medium sized dendritic trunks. By and large, most of the synaptic vesicles present in the centre are of the small, clear-centered type. However, dense core vesicles extremely variegated in size and appearance were found, both in presynaptic and postsynaptic profiles. The possibility that dense core vesicles should be regarded as atypical lysosomes rich in by-products of the metabolism of catecholamines (melanine) has been considered.Supported by grant MA 4183 from the Medical Research Council of Canada.     

Developmental Expression of Go in Neuronal Cultures from Rat Mesencephalon and Hypothalamus

The developmental expression of the alpha-subunit of Go was examined in neuronal cultures derived from rat mesencephalon (MES) and hypothalamus (HYP). These cultures were essentially free of contaminating glia and were maintained as a stable population for periods up to 3 weeks. Immunoblotting utilizing specific antisera against Go indicated that in neurons from both brain regions, membrane concentrations of Go increased dramatically during the first 2 weeks in vitro. Thereafter, increases in the amount of Go per neuron kept pace with increasing process (axons and dendrites) formation. Multiple forms of immunoreactive Go were detected in MES and HYP neurons, and the proportions of these forms changed between 4 and 14 days in culture. Finally, increasing neuron density significantly increased membrane levels of Go in MES but not HYP cultures.     

Glutamate Stimulation of [3H]Dopamine Release from Dissociated Cell Cultures of Rat Ventral Mesencephalon

In dissociated cell cultures of fetal rat ventral mesencephalon preloaded with [3H]dopamine, glutamate (10(-5)-10(-3) M) stimulated the release of [3H]dopamine. Glutamate stimulation of [3H]dopamine release was Ca2+ dependent and was blocked by the glutamate antagonist, cis-2,3-piperidine dicarboxylic acid. Glutamate stimulation of [3H]dopamine release was not due to glutamate neurotoxicity because (1) glutamate did not cause release of a cytosolic marker, lactate dehydrogenase, and (2) preincubation of cultures with glutamate did not impair subsequent ability of the cells to take up or release [3H]dopamine. Thus, these dissociated cell cultures appear to provide a good model system to characterize glutamate stimulation of dopamine release. Release of [3H]dopamine from these cultures was stimulated by veratridine, an activator of voltage-sensitive Na+ channels, and this stimulation was blocked by tetrodotoxin. However, glutamate-stimulated [3H]dopamine release was not blocked by tetrodotoxin or Zn2+. Substitution of NaCl in the extracellular medium by sucrose, LiCl, or Na2SO4 had no effect on glutamate stimulation of [3H]dopamine release; however, release was inhibited when NaCl was replaced by choline chloride or N-methyl-D-glucamine HCl. Glutamate-stimulated [3H]-dopamine release was well maintained (60-82% of control) in the presence of Co2+, which blocks Ca2+ action potentials, and was unaffected by the local anesthetic, lidocaine. These results are discussed in terms of the receptor and ionic mechanisms involved in the stimulation of dopamine release by excitatory amino acids.     

Protein Kinase FA/Glycogen Synthase Kinase-3α After Heparin Potentiation Phosphorylates τ on Sites Abnormally Phosphorylated in Alzheimer''s Disease Brain

In this work, we tested the effect of ion channel blockers and of phorbol ester treatments on [³H]dopamine ([³H]DA) release and neurotensin (NT)-induced facilitation of [³H]DA release from cultures of rat fetal mesencephalic cells. The potassium channel blockers tetraethylammonium and 4-aminopyridine increased basal [³H]DA release and decreased K⁺-evoked [³H]DA release, whereas apamin was without effect. K⁺-evoked [³H]DA release was decreased by ω-conotoxin and nifedipine, totally suppressed by cadmium, and unaffected by amiloride. These results show the differential sensitivity of [³H]DA release to blockade of various ion channels and suggest the involvement of N-type, L-type, and non-L-non-N-type, but not T-type, voltage-sensitive calcium channels in K⁺-evoked release. Phorbol 12-myristate 13-acetate increased both spontaneous and K⁺-evoked [³H]DA release, suggesting a modulatory action of protein kinase C on DA release in this system. Unexpectedly, however, the effects of the phorbol ester were not counteracted by the protein kinase C inhibitors H7, staurosporine, or polymyxin B. NT-induced facilitation of K⁺-evoked [³H]DA release was insensitive to most of the ion channel blockers, except cadmium (64% decrease in NT effect), suggesting that the corresponding potassium' and calcium channels were not involved in the effect of NT on [³H]DA release in this system. The NT effect was totally suppressed by phorbol ester treatments, indicating a possible desensitization of the corresponding transduction mechanisms after protein kinase C activation.     

Immunocytochemical Quantification of Tyrosine Hydroxylase at a Cellular Level in the Mesencephalon of Control Subjects and Patients with Parkinson's and Alzheimer's Disease

Abstract: Parkinson's disease is characterized by massive degeneration of the melanized dopaminergic neurons in the substantia nigra. The functional capacity of the surviving nigral neurons is affected, as indicated by the subnormal levels of tyrosine hydroxylase (TH) mRNA in these neurons and the presence in the parkinsonian mesencephalon of melanized neurons lacking TH immunoreactivity. This is apparently in contradiction with the known overactivity of dopamine synthesis and release that occurs in the remaining dopaminergic terminals. To test the ability of the surviving neurons to express TH protein, a semiquantitative immunocytochemical method was developed. The relative amounts of TH were estimated with a computer-assisted image analysis system in the dopaminergic neurons of representative mesencephalic sections of control and parkinsonian brains and for comparison in brains from patients with Alzheimer's disease. In control brains, the mean TH content per neuron differed from one subject to another and between the different dopaminergic cell groups of the mesencephalon in the same subject. Within a given dopaminergic region, the level of TH was variable among neurons. In patients with Parkinson's disease, the ratio of TH protein content per neuron in the substantia nigra by reference to that of the central gray substance was reduced. In patients with Alzheimer's disease, the amount of TH was selectively reduced in the remaining dopaminergic neurons of the ventral tegmental area, a region characterized by a loss in dopaminergic neurons. The decrease in cellular TH content might therefore be related to the presence of the neurodegenerative process in the area considered. In patients with Parkinson's disease, the incapacity of the surviving neurons to express normal TH levels may reduce the efficiency of the hyperactivity mechanisms that develop in the remaining striatal dopaminergic terminals.     

中脑星形胶质细胞表达生长抑素mRNA的离体研究

利用细胞培养技术,取胎龄１８天Ｗｉｓｔａｒ大鼠中脑腹侧组织,纯化培养星形胶质细胞,以原位杂交组织化学法检测了体外培养的不同时间的生长抑素（Ｓｏｍａｔｏｓｔａｔｉｎ,ＳＳ）ｍＲＮＡ表达,结果表明中脑星形胶质细胞能合成生长抑素,并且其相对含量随培养时间的延长而逐渐下降。本文并对星形胶质细胞合成神经肽ＳＳ的功能意义进行了初步探讨