M. Memo

Aging process affects a single class of dopamine receptors

[3H]Spiroperidol and [3H](-)-sulpiride specific binding have been used to assay for D1 and D2 dopaminergic recognition sites in striatal membranes of aged rats. While [3H]spiroperidol binding shows a decreased number of binding sites, no changes have been detected in [3H](-)-sulpiride binding, which is a marker for D2 dopaminergic receptors. Data obtained with GTP and DA-dependent adenylyl cyclase activity confirm the hypothesis that aging selectively affects in rats those dopaminergic receptors coupled to the formation of cyclic AMP (D1).

Impairment of brain neurotransmitter receptors in aged rats.

Dopamine and gamma-aminobutyric acid (GABA) receptor functions have been measured in various brain areas of aged rats. [3H] Spiroperidol binding is decreased in various dopaminergic brain areas, particularly in striatum and tuberculum olfactorium. In striatum the number of binding sites for [3H] spiroperidol is similar in both groups of animals, while the affinity is reduced in senescent rats. Moreover, in the pituitary a 50% increase of [3H] spiroperidol binding was detected in the group of senescent animals. On the other hand, [3H] GABA binding is significantly decreased in substantia nigra and hypothalamus of aged rats, while it is unmodified in cerebral cortex, cerebellum, striatum and nucleus accumbens.

MGLUR5 METABOTROPIC GLUTAMATE RECEPTOR DISTRIBUTION IN RAT AND HUMAN SPINAL CORD : A DEVELOPMENTAL STUDY

By combining biochemical, molecular and immunohistochemical approaches, we have investigated the presence of metabotropic glutamate receptors (mGluRs) belonging to the subtype 5 in rat and human spinal cords and the developmental changes in their expression. A polyclonal antibody raised against the carboxy-terminal portion of mGluR5 was used to study the distribution of the receptor in rat foetal (Et15), neonatal (P8) and adult spinal cords and dorsal root ganglia (DRG). mGluR5 appeared to be predominantly expressed in regions containing the primary sensory afferents. Immunoblotting with anti-mGluR5 antibody revealed lower receptor protein levels in rat adult spinal cord when compared with P8 rat spinal cord. Reverse transcriptase-polymerase chain reaction showed both mGluR5a and mGluR5b mRNAs expression in rat spinal cord. The mGluR5a variant was found more abundant in young animals than in adults. The pattern of mGluR5 immunostaining was also studied in foetal (6-8, 10, 12 and 22 weeks of gestation) and adult human spinal cord. At all stages of human development, a strong mGluR5 immunoreactivity was observed in the dorsal roots and in the dorsal and dorsolateral funiculi with maximum levels of staining at week 12 of gestation. Foetal DRG neurons were heterogeneously labeled. mGluR5 was also diffusely detectable in the mantle layer. In adult human spinal cords, immunoreactivity was confined to laminae I and II of the dorsal horns. These results demonstrate for the first time the presence of mGluR5 in human spinal cord. The distribution of this receptor suggests a role in the development of somatosensory pathways and in the control of nociceptive neurotransmission.

Chronic lead treatment differentially affects dopamine synthesis in various rat brain areas

The effect of chronic dietary lead exposure on brain nigrostriatal, mesolimbic and mesocortial systems was studied. The results show no modification of the dopamine receptors measured either as dopamine sensitive adenylate cyclase or as [3H]spiroperidol binding. On the other hand, dopamine synthesis seems to be reduced in striatum, unaffected in substantia nigra and increased in nucleus accumbens and in the frontal cortex. The increase of DA synthesis observed in some brain areas might be involved in determining the hyperactive behaviour that follows lead intoxication.

Dopamine D2, D3, and D4 receptor mRNA levels in rat brain and pituitary during aging

Reverse Transcriptase-Polymerase Chain Reaction technique was used to determine the levels of the mRNAs encoding different receptors belonging to the D2 family in various brain areas of 6-, 12-, 18-, and 24-month-old rats. We found a progressive, age-dependent reduction in the mRNA levels of D2 short and D2 long receptors in corpus striatum, substantia nigra, and frontal cortex. D2 short and D2 long receptor mRNA levels were unchanged in hippocampus and olfactory tubercle, while they increased in pituitary. D3 receptor mRNA levels were reduced in olfactory tubercle and unchanged in striatum. D4 receptor mRNA levels were unmodified in pituitary gland. These data suggest that the molecular mechanisms responsible for regulating the pattern of expression of the various dopamine receptors are differentially regulated by aging.

Identification of beta-adrenergic receptor binding sites in rat brain microvessels, using [125I]iodohydroxybenzylpindolol.

Abstract: Brain microvessels were prepared from rat cerebral cortex. The purity was confirmed by phase‐contrast microscopy and by the measurement of an enzymatic marker, γ‐glutamyltranspeptidase. The microvessel preparation was subjected to radioreceptor assay using a 125I‐labelled β‐adrenergic antagonist, hydroxybenzylpindolol (IHYP). The binding was linear with protein concentration up to at least 80 μg per tube. It was saturated at 200 PM IHYP concentration. The KD, value calculated by Scatchard analysis was 69.4 ± 9.9 PM. The maximum binding (Bmax) was 107 ± 4 fmol/mg protein. The binding reached equilibrium within 30 min and was dissociated by addition of (−)‐propranolol. The inhibitory effects of isomers of propranolol and iso‐proterenol on this binding showed that (−)‐isomers were two orders of magnitude more potent than the (+)‐isomers. Other neurotransmitters did not affect IHYP binding. The characteristics of the binding, saturability, high affinity, reversibility and stereospecificity, suggest that IHYP is bound to β‐adrenergic receptor sites located on brain microvessels.

Brain neurotransmitter systems and chronic lead intoxication

Summary The neurotoxic effect of lead has been studied measuring the function of different neurotransmitters in various rat brain areas. Dopaminergic and GABAergic systems are modified at various steps: both at presynaptic and postsvnaptic (receptors) levels. The changes observed, together with those related with other brain neurotransmitters, suggest the hypothesis that the behavioural and clinical changes observed in humans exposed to lead may be explained on the bases of selective actions of lead on neurotransmitters in discrete brain areas.

Brain benzodiazepine receptor changes during ageing

The medical and social relevance of the side effects induced in the elderly by benzodiazepines imposes various pharmacological problems. In particular it has been hypothesized that they are related with the possible pharmacokinetic and pharmacodynamic changes which, in the aged people, produce unwanted reactions such as drowsiness and unsteadiness of gait (Saltzman et al 1975). We report that beside the possible pharmacokinetic differences which characterize the ageing process, some changes may be detected also at the level of specific brain receptors with which benzodiazepines interact. The presence of specific benzodiazepine receptors in various human and animal brain areas is now well established (Braestrup & Squires 1977; Braestrup et al 1977). However, various neurotransmitter receptors are significantly affected by ageing. Greenberg & Weiss (1979) reported the reduced capacity of central 8adrenoceptors to develop supersensitivity after decreased neuronal input, while Govoni et al (1980) found a diminished number of dopamine receptors in aged rats. Mature (3-4 months) and aged (24-28 months) male Sprague-Dawley rats were housed at constant temperature and humidity with free access to food and water. [aH]Diazepam specific binding was measured according

Chronic lead treatment induces in rat a specific and differential effect on dopamine receptors in different brain areas

There is now evidence that two classes of dopaminergic receptors are present in CNS of the rat: D1, associated, and D2, not associated with adenylate cyclase activity. Drugs which interact specifically with D2 receptor are more capable of antagonizing the hyperkinetic behavior induced by lead exposure in rat. They also have a beneficial effect in children with hyperkinetic disorders. We found that the dose (-)sulpiride which causes sedation is lower in lead intoxicated animals than in controls. On the contrary, haloperidol produces sedation with the same potency in lead-treated and in control rats. The reported behavioral effects were found to be correlated with biochemical changes. In fact, in lead exposed rats D2 receptors, measured by (-)-[3H]sulpiride stereospecific binding, are altered, while D1 receptors seem not to be affected. The alterations are different according to the area examined: D2 receptor function is increased in the striatum and decreased in the nucleus accumbens. The impairment of D2 receptor might explain the better capacity of substituted benzamides to improve the hyperkinetic behavior observed in lead exposed rats.

Characterization of tau proteins in human neuroblastoma SH-SY5Y cell line.

Here we report three experimental paradigms in which tau proteins are differentially localized and expressed in human neuroblastoma cells SH-SY5Y. We found that in undifferentiated cells, tau proteins were predominantly localized in the nucleus. Western blot analysis of nuclear extracts revealed, among the others, a high molecular weight tau isoform and evaluation of tau mRNA levels showed a single tau isoform. After differentiation, tau immunoreactivity was detected only in cytosol and along neuritic processes. The high molecular weight tau isoform disappeared and an additional tau mRNA species was detected. Treatment of differentiated cells with doxorubicin or okadaic acid resulted in an increase of tau immunoreactivity and in a subsequent cell loss. Our results indicate that both subcellular localization and pattern of expression of tau proteins vary depending on the developmental and functional state of the cells, thus suggesting different roles in cell function.