Dopaminergic innervation of the parahippocampal and hippocampal regions in the rat

In spite of extensive investigations of the rat's meso-cortico-limbic system, the dopaminergic (DA) innervation of the hippocampal formation (HF) has not heretofore been visualized by histochemical techniques. However pharmacological and biochemical studies strongly suggested its existence. We used tyrosine-hydroxylase (TH) as an immunocytochemical marker of DA neurons in rats in which the noradrenaline cortical innervation was previously destroyed by neurotoxins. The absence of noradrenergic axons was routinely controlled with dopamine-beta-hydroxylase immunocytochemistry. TH-positive axons, thus DA axons, reach the HF primarily through the fimbria in which they occupy a specific lateral sector. They innervate the ventral and caudal parts of the HF, the subiculum and the adjacent CA1 hippocampal field being the main targets. This DA terminal field in the HF, matches with the area projecting toward the nucleus accumbens. Thus the hippocampo-striatal projections which represent a link of functional importance between the limbic and central motor systems might be modulated by the dopaminergic meso-cortico-limbic pathway. The present immunocytochemical study confirms the very dense innervation of the entorhinal cortex (EC): DA axons are organized in dense fiber islands and occupy primarily the superficial layers (I-II-III). Da innervation predominates in the lateral part of EC, which is the site of multimodal cortical afferences and therefore relays information between the whole neocortex and the hippocampus. Thus the DA system could play an important role of modulation on hippocampal and parahippocampal functions.     

Effect of tryptophan on hepatic polyribosomal disaggregation due to hypertonic sodium chloride.

The effect of tryptophan on the disaggregation of hepatic polyribosomes and on the inhibition of hepatic protein synthesis in rats due to the administration of hypertonic NaCl solutions was studied. Overnight-fasted rats were given by stomach tube or intraperitoneally hypertonic (6.2 to 10.7 per cent) NaCl alone or with 30 mg. of L-tryptophan and were killed 30 minutes later. The hypertonic NaCl treated rats revealed marked hepatic polyribosomal disaggregation and inhibition of hepatic protein synthesis (in vitro incorporation of 14C-leucine into proteins). Rats that received tryptophan alone or in a complete amino acid mixture in addition to hypertonic NaCl revealed a marked improvement in the patterns of hepatic polyribosomes and an increase in in vitro hepatic protein synthesis over that in hypertonic NaCl treated rats. The incorporation of 14C-orotate in hepatic messenger RNA (peak appearing between the 4 S and 18 S RNA fractions) associated with hepatic polyribosomes was studied. Administration of hypertonic NaCl alone caused a decrease in incorporation into hepatic messenger RNA whereas administration of hypertonic NaCl plus tryptophan caused an increase in incorporation into hepatic messenger RNA. Thus, tryptophan appears to cause an increase in hepatic messenger RNA as well as to prevent to a great extent the hepatic polyribosomal disaggregation and the inhibition of hepatic protein synthesis due to hypertonic NaCl.     

Effect of tryptophan on hepatoma and host liver of rats: Influence after treatment with hypertonic sodium chloride and carbon tetrachloride

Female inbred Buffalo rats bearing intrahepatically transplanted hepatoma 5123 were subjected intraperitoneally to the acute administration of hypertonic NaCl or CCl₄ followed by a tube-feeding of l-tryptophan. The responses in terms of changes in polyribosomal aggregation and protein synthesis (in vitro) of host liver and hepatoma were evaluated. While treatment with hypertonic NaCl or CCl₄ caused disaggregation of polyribosomes and inhibition of protein synthesis in both host liver and hepatoma, the subsequent administration of tryptophan caused some improvement in both parameters in host liver but not in hepatoma. Administration of hypertonic NaCl alone caused a decrease in [¹⁴C]orotate incorporation into poly(A)-mRNA of host liver and hepatoma, whereas administration of tryptophan after hypertonic NaCl caused a significant improvement in host liver alone. Following the tryptophan administration, the activities of nuclear DNA-dependent RNA polymerases I and II, and of nuclear-envelope nucleoside triphosphatase, as well as labeled nuclear RNA release in vitro were slightly elevated in host liver but not in hepatoma. Tryptophan-related compounds, 5-hydroxy-dl-tryptophan, 5-fluorotryptophan, indole, and 3-hydroxyanthranilic acid, when administered in place of l-tryptophan, did not appreciably affect polyribosomal aggregation or protein synthesis in vitro in host liver or hepatoma.     

Ethanol-Induced Stimulation of Hepatic Ornithine Decarboxylase Activity in the Rat

The effect of a single feeding of ethanol on hepatic ornithine decarboxylase (ODC) activity in rats was investigated. Ethanol (7.5 g/kg body weight) was tube-fed to overnight-fasted rats as a 50% (v/v) solution in water 1, 2, 3, 4, 8, 12, or 24 hr before sacrifice. The levels of ODC activity in the livers were assayed in vitro by measuring the release of ¹⁴C0₂ from 0L-1-¹⁴C-ornithine. Hepatic ODC activities were significantly stimulated by ethanol (7.5 g/kg body weight) beginning at 1 hr and reaching a peak at 4 hr (more than a 16-fold increase over zero time controls). Single feedings of varying doses of ethanol (2.5, 5.0, or 7.5 g/kg body weight) to overnight-fasted rats 3 hr before sacrifice also exhibited significant increases (3 to 13-fold) in the hepatic ODC activities. In vitro ¹⁴C-leucir>e incorporation into protein using hepatic microsomes of ethanol-treated rats was decreased in comparison with that of controls. The ethanoMnduced stimulation of hepatic ODC activity was not abolished by pretreatment with pyrazoie, an inhibitor of ethanol metabolism. However, the stimulation of hepatic ODC activity by ethanol was suppressed by actinomycin D or cycloheximide, indicating that the enhancement is attributable to the synthesis of new enzyme protein. Furthermore, abolition of the stimulation of hepatic ODC activity due to ethanol by prior adrenalectomy suggests that the induced increase is probably mediated through stimulation of adrenal hormones. These studies demonstrate that a single dose of ethanol per os can significantly enhance in the rat the activity of hepatic ODC, a key enzyyme in the biosynthesis of polyamines, and that the effect is indirect, via adrenal hormones.     

The importance of controls in immunohistochemistry: how to validate an antibody, from research to diagnosis

The specificity of an immunohistochemical reaction is guaranteed by two sets of controls. Positive controls verify the specificity of the primary antibody and demonstrate that it binds only to the protein which was used as an immunogen. Negative controls ensure that the labelling technique is specific and that the primary antibody is responsible for generation of the immunostaining. In fact, the production of a labelling may also be related to cross reactivity or to non-specific physical or chemical interactions. This paper reviews the characteristics of various epitopes and antibodies, describes different strategies which prove the specificity of the immunohistochemical reaction in research or diagnostic pathology and point towards the essential information which should be reported in a paper.     

Expression of calbindin D28K in the dopaminergic mesotelencephalic system in embryonic and fetal human brain

A subset of tyrosine-hydroxylase (TH) neurons of the substantia nigra (A9) containing calbindin D28K (CaBP) appeared to be less vulnerable to cell death induced by Parkinson's disease than the subset containing dopamine (DA) alone. Because grafting procedures of fetal human neurons are increasingly used in the therapy of Parkinson's disease, it is important to study the development of DA neurons coexpressing CaBP. In humans, the genesis of TH immunoreactivity of A9, of the ventral tegmental area (A10), and of the retrorubral area (A8) occurred during a 2-week period from the 4. 5th gestational week (g.w.) in the ventricular zone of the floor plate and the contiguous basal plate of the mesencephalon and diencephalon, i.e., the prosomeres p1-p3. Double-immunolabeled TH-CaBP neurons were detected from 5.5 g.w. on, in the first wave of DA neuron's migration, and were observed in their final residence in the dorsal A9 by 10.5 g.w. Calretinin immunoreactivity was expressed in TH-immunoreactive (IR) neurons from 10.5 g.w. on. Ascending TH-CaBP-IR axons were observed toward the telencephalon from 6-7 g.w. , reaching the anlage of the nucleus accumbens and amygdaloid complex at 10.5 g.w., but were not detected in the ganglionic eminence at this latter stage. Dopaminergic patches were detected at 13 g.w. in the anlage of the putamen, but no TH-CaBP-IR fibers were observed in the matrix at this stage. In conclusion, even if CaBP immunoreactivity was detected in TH-IR cell bodies during the embryonic period, the TH-CaBP-IR axonal terminal was observed earlier in some limbic-related areas than in the matrix compartment of the basal ganglia in humans.