Dopexamine hydrochloride in the human kidney: localization, receptor binding and effect on 3'-5'-cyclic adenosine monophosphate generation

Dopexamine hydrochloride is a synthetic dopamine analogue recently developed to improve myocardial and renal performance in patients suffering from low cardiac output states. The present study was designed to assess the pharmacological profile and the anatomical localization of [3H]-dopexamine binding sites within the human nephron. The effects of dopexamine on the 3'-5'-cyclic adenosine monophosphate (cAMP)-generating system in membrane particles of the human kidney were also investigated. It was found that [3H]-dopexamine was specifically bound by sections of the human kidney. The binding was partly inhibited by the DA-1 receptor antagonist SCH 23390, by the beta 2-adrenoceptor antagonist ICI 118,551 and by the DA-2 receptor antagonist domperidone. The 3 antagonists in combination reduced [3H]-dopexamine binding to nonspecific values. Light microscope autoradiography revealed the accumulation of silver grains, corresponding to [3H]-dopexamine binding sites, within the different portions of the human nephron. The incubation of sections of the human kidney with [3H]-dopexamine plus SCH 23390 caused a remarkable reduction in the density of silver grains within the proximal tubule and the macula densa and a moderate decrease in the density of silver grains within the ascending and descending limbs of the loop of Henle as well as within the distal tubule. The incubation of sections of human kidney with [3H]-dopexamine plus ICI 118,551 caused a pronounced reduction in the density of silver grains within the glomerulus, the limbs of the loop of Henle, the distal tubule and the medullary collecting tubules and a moderate decrease in the density of silver grains within the macula densa and the proximal collecting tubule.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopexamine hydrochloride in the human heart: receptor binding and effects on cAMP generation

Dopexamine hydrochloride is a synthetic catecholamine proposed for the short-term treatment of heart failure and postoperative low cardiac output. The pharmacological profile and anatomical localization of dopexamine binding were investigated in sections of right and left ventricle using [3H]-dopexamine and ligand techniques associated with light microscope autoradiography. Its effects on the 3-5-cyclic adenosine monophosphate (cAMP) generating system in membrane particles of the human right or left ventricle were also studied. [3H]-Dopexamine was specifically bound to sections of human right or left ventricle. The binding was time-, temperature- and concentration-dependent and was dissociable. The apparent equilibrium constant of dissociation was 3.5 nM. A decreased [3H]-dopexamine binding capacity from the base to the apex and ventricles was noticeable. The pharmacological profile of [3H]-dopexamine binding to sections of right or left ventricle was consistent with the labelling of both beta 2-adrenoceptors and dopamine DA-2 receptors. The most potent displacer of [3H]-dopexamine was the beta 2-adrenoceptor antagonist ICI 118,551 followed by dopamine, noradrenaline and domperidone. The beta 1-adrenoceptor antagonist metoprolol or the dopamine DA-1 receptor antagonist SCH 23390 were ineffective as displacers of [3H]-dopexamine binding. Light microscope autoradiography revealed the localization of [3H]-dopexamine binding sites within the wall of the human right and left ventricle. The density of silver grains was slightly higher in the right than in the left ventricle and showed a uniform transmural distribution across the ventricular wall.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological characterization and autoradiographic localization of dopamine receptors in human epicardial arteries

The pharmacological properties and the anatomical localization of dopamine (DA) D1 and D2 receptor sites were studied in normal samples of the human right coronary and anterior interventricular arteries by assessing the effect of DA on the cyclic AMP generating system and by using combined radioreceptor binding and autoradiographic techniques. DA caused a concentration-dependent accumulation of cyclic AMP in membranes of right and anterior interventricular coronary arteries. This effect was antagonized by the selective D1 receptor antagonist SCH 23390 and by other DA receptor antagonists. D2 receptor responses negatively coupled to cyclic AMP generation were obtained by incubating membranes of coronary arteries with DA together with SCH 23390 or with D2 receptor agonists. This D2 effect was abolished by the selective D2 receptor antagonist (-)-sulpiride. [3H]SCH 23390 was bound to sections of the coronary arteries in a manner consistent with the labeling of D1 sites. Light microscope autoradiography revealed the localization of D1 sites in the medial layer of the coronary arteries. [3H]Spiroperidol, in the presence of ketanserin, was bound to sections of the coronary arteries in a manner consistent with the labeling of D2 sites. D2 receptor sites were located within the adventitia and the adventitial-medial border of the two arteries, and are probably prejunctional in nature. These findings indicate the existence of both D1 and D2 receptor sites in human right and anterior interventricular arteries. Moreover, they suggest that coronary vasodilation induced by DA or DA receptor agonists may be the result of a direct coronary vasodilatory activity.

Direct demonstration of dopamine D1-like receptor sites in the ciliary body of the rabbit eye by light microscope autoradiography

The pharmacological characteristics and the anatomical localization of [3H]-SCH 23390 in sections of the ciliary body of the rabbit eye were analyzed using a radioreceptor assay and autoradiographic techniques. [3H]-SCH 23390 was bound to sections of rabbit ciliary body in a manner consistent with the labelling of D1-like receptor sites. The dissociation constant (Kd) was 0.62 nmol/l, while the maximum binding capacity (Bmax) was 117 +/- 9 fmol/mg tissue. Light microscope autoradiography revealed [3H]-SCH 23390 binding sites within the epithelium of the ciliary processes, which is the ocular structure involved in the secretion of aqueous humor. No specific accumulation of silver grains was noticeable within the iridocorneal angle, which is the structure involved in the outflow of aqueous humor. These findings suggest that the rise in intraocular pressure caused by D1 receptor agonists is probably mediated by an increase of aqueous humor formation rather than by an inhibition of the outflow of aqueous humor.

Oral choline alfoscerate counteracts age-dependent loss of mossy fibres in the rat hippocampus

Mossy fibres represent a major intrahippocampal associative pathway. They consist of axons of granule cells of the dentate gyrus and show an age-dependent loss as do the granule cells of the dentate gyrus. The present study was designed to assess whether long-term treatment of rats with choline alfoscerate in their drinking water would be effective in countering the loss of mossy fibres and of granule cells occurring with aging. Choline alfoscerate is a precursor in the biosynthesis of brain phospholipids and increases the bioavailability of choline in nervous tissue. Male Sprague-Dawley rats of 18 months of age were divided into two groups. One group received a daily dose of 100 mg/kg choline alfoscerate for 6 months; the other group was used as an untreated control. Twelve-month-old untreated animals were used as a reference group. The area occupied by mossy fibres, as well as their density, was significantly reduced in 24-month-old control rats in comparison with 12-month-old rats. The same is true for the density granule cells of the dentate gyrus which was decreased by about 20% in the oldest animals. In choline alfoscerate-treated rats both the area occupied by mossy fibres and their density were significantly higher than in age-matched controls. Moreover, the number of granule neurons of the hippocampus was higher by about 7% in choline alfoscerate-treated than in control 24-month-old rats. The above data suggest that choline alfoscerate treatment counteracts some anatomical changes of the rat hippocampus occurring in old age.

Age-related changes in sulfide-silver staining in the rat neostriatum: a quantitative histochemical study

The density and distribution of sulfide-silver staining in the neostriatum of 3-, 12-, and 24-month-old male Sprague-Dawley rats were analyzed using the neo-Timm sulfide-silver histochemical technique associated with microdensitometry. This technique stains zinc-containing terminals in the striatum and the density of neo-Timm staining is considered to be parallel to the density of synaptic boutons containing zinc. In the neostriatum sulfide-silver, staining was intense in the matrix, although the striosomes did not show appreciable reactivity. The density of sulfide-silver staining was significantly reduced (p less than 0.001) in the matrix of 12-month-old in comparison to 3-month-old rats. No further changes were noticeable between 24- and 12-month-old rats. In contrast, the area and the perimeter of neostriatum that were assessed by quantitative image analysis did not show age-related changes. The present results indicated that similar to the observations for a variety of neurochemical parameters of rat neostriatum such as local cerebral glucose utilization, cholinergic muscarinic receptors, and dopamine D-1 receptors, zinc-containing striatal terminal were primarily decreased between young and adult subjects but not between adult and aged animals.

Localization of 5-hydroxytryptamine-like immunoreactive cells and nerve fibers in the rat female reproductive system

The presence of 5-hydroxytryptamine (5-HT)-like immunoreactivity (IR) was studied in the rat female reproductive system using polyclonal antibodies directed against 5-HT. Moreover, 5-HT levels in the ovary, oviduct, uterus, and cervix were measured by high-pressure liquid chromatography with electrochemical detection. The highest 5-HT concentrations were found in the oviduct, followed in descending order by the cervix, the ovary, and the uterus. Most 5-HT-like IR was observed in the cytoplasm of mast cells. These cells were found in the connective tissue around the fimbria, in the oviduct, in the uterus, and in the ovary. Mast cells are clustered in the proximity of the parenchymal blood vessels. Moreover, a few 5-HT-like nerve fibers were found distributed mainly perivascularily in the uterine cervix and in the uterine horns as well as in the oviduct. IR nerve fibers were rarely seen within the ovary. The present data provide direct evidence that 5-HT in the female reproductive system not only is associated with mast cells but is located in nerve fibre-like structures as well. The functional significance of this probable 5-HT-ergic innervation of the female reproductive tract discovered in the present study should be clarified in future investigations.

Effect of nicardipine treatment upon cardiac hypertrophy in spontaneously hypertensive rats: a morphometric and ultrastructural study

OBJECTIVE

The present study was designed to investigate the effect of nicardipine administration upon systolic blood pressure (SBP) and cardiac hypertrophy in spontaneously hypertensive rats (SHR).

DESIGN

SBP, heart: and left ventricle: body weight ratios, the cross-sectional area of cardiocytes, and the ultrastructure of the left ventricle were evaluated.

METHODS

Ten-week old male SHR and age-matched normotensive Wistar-Kyoto rats were studied for 12 weeks. One group of SHR was treated for 12 weeks with a daily oral dose of 1 mg/kg nicardipine and another group with 1 mg/kg hydralazine; Wistar-Kyoto rats were used as a normotensive control group. Light and electron microscope techniques associated with image analysis and morphometry were used.

RESULTS

Nicardipine administration normalized SBP values and significantly reduced the heart: and left ventricle: body weight ratios. Moreover, administration reduced the cross-sectional area of cardiocytes by approximately 38% in subendocardium and by 24% in subepicardium. Hydralazine administration significantly reduced SBP values but had no effect upon heart: or left ventricle: body weight ratios or the cross-sectional area of cardiocytes. Electron microscopy showed that nicardipine treatment was able to reduce the hypertension-dependent changes in cardiac ultrastructure consisting of alternations to intercalated discs and line Z morphology as well as in the decrease of the mitochondria: myofibrils ratio.

CONCLUSIONS

The above data indicate that nicardipine administration is able to reduce SBP and to counter the development of structural and ultrastructural changes in cardiac morphology which represent a common complication of arterial hypertension.

Changes in glutathione content and localization in rat heart as a function of age

The influence of aging on glutathione levels and distribution in the heart was studied in male Sprague-Dawley rats of 3 (young), 12 (adult) and 24 (old) months of age using biochemical and histofluorescence techniques, respectively. Biochemical assays of reduced glutathione (GSH) in the right and left ventricles and in the septum showed a significant decrease in GSH levels in adult in comparison with young animals. No further changes were noticeable between adult and old rats. GSH histofluorescence revealed a rather homogeneous distribution of the product of histochemical reaction within both right and left atria in 3-month-old rats. In 12-month-old rats a reduction of GSH histofluorescence in comparison with younger animals was noticeable. The loss is more consistent in the epicardial portion of the right atrium and in the endocardial region of the left atrium. In the atria of 24-month-old rats GSH reactivity was homogeneously distributed throughout the atrial wall and was significantly lower than in young or adult rats. In 3-month-old rats GSH histofluorescence was slightly lower in the epicardial than in the endocardial portions of both ventricles. In adult rats a significant decrease of GSH histofluorescence was noticeable in comparison with 3-month-old rats. The loss is particularly pronounced within the endocardial region of the left ventricle. In 24-month-old rats GSH histofluorescence showed no significant differences between adult rats. However, GSH was more homogeneously distributed throughout the ventricular wall than in adult animals. The significance of these data is discussed in relation to the role that GSH plays in protecting the myocytes against free radical damage.

Endothelial dopamine DA-1 receptor sites in the rabbit pulmonary artery: autoradiographic demonstration

Combined in vivo radioreceptor binding and autoradiographic techniques were used to characterized the pharmacological profile and to study the anatomical localization of dopamine (DA) DA-1 receptor sites in sections of rabbit pulmonary artery. [3H]R-(+)-8-chloro-2,3,4,5-tetrahydro-5-phenyl-1H-3-benzazepin-7- alhemimaleate (SCH 23390), which was used as a ligand, was bound by sections of rabbit pulmonary artery in a manner consistent with the binding of DA DA-1 sites. The Kd value was 4.75 nM, whereas the Bmax value was 78.3 +/- 5.7 fmol/mg tissue. Light microscope autoradiography demonstrated specific [3H]SCH 23390 binding sites primarily in the endothelium of the rabbit pulmonary artery. Moreover, sparse receptor sites were visualized in the medial layer. Mechanical removal of endothelium caused the disappearance of [3H]SCH 23390 binding sites showing the endothelial localization, but was without effect on the receptor sites of the medial layer. The present findings suggest that differently from systemic arteries, where DA-1 receptor sites are localized in the medial layer, probably within smooth muscle, the majority of DA-1 sites in the rabbit pulmonary artery are endothelial. The possible significance of these sites visualized in the present study for the first time is discussed.

Age-related changes in sulfide-silver stainable fibres in the rat cerebral cortex

The present study was designed to assess the age-dependent changes in sulfide-silver stainable fibres in frontal, parietal and occipital cortex areas of the rat cerebral cortex. Male Sprague-Dawley rats of 2 months (young), 12 months (adult) and 24 months (aged) were used. Sulfide-silver stainable fibres, which represent predominantly zinc-containing associational fibres arising from local cortical interneurons, were visualized using the neo-Timm histochemical technique. The density of sulfide-silver stainable fibres within the neuropil of laminae I-III (upper zone) and of lamina V (lower zone) of the different cerebral cortex areas was assessed microdensitometrically. In the frontal and parietal cortices the density of sulfide-silver stainable fibres was higher in adult and in aged than in young rats both in the upper and in the lower zones. No significant differences were noticeable in the density of sulfide-silver stainable fibres between adult and old rats. In the occipital cortex the density of sulfide-silver stainable fibres was similar in young or adult rats. but was remarkably increased in old animals. The possibility that the increase in the density of sulfide-silver stainable fibres represents a compensatory mechanism in the cerebral cortex area showing the most consistent nerve cell loss is discussed.

Muscarinic cholinergic receptors in the human right coronary artery: a receptor binding and autoradiographic study

We used a combination of radioreceptor binding and autoradiographic techniques to study the pharmacological characteristics and anatomical localization of [3H]-quinuclidinyl benzilate (QNB) binding sites in the human right coronary artery. The ligand was bound to sections of the human right coronary artery in a manner consistent with the labelling of muscarinic receptors. The addition of pirenzepine or of carbachol to the incubation medium to generate displacement curves was indicative of the presence of M1 and M2 receptors in the right coronary artery. Autoradiography showed the localization of M1 sites primarily in the medial layer of the right coronary artery. M2 sites were located primarily in the adventitia. No [3H]-QNB binding sites were observed in the endothelium. A possible role of muscarinic receptors in the pathogenesis of coronary vasospasm is discussed.

Autoradiographic localization of the gamma-aminobutyric acid type A receptor agonist 3H-muscimol in the rat superior cervical ganglion

The anatomical localization of gamma-aminobutyric acid type A (GABA-A) receptor sites in the rat superior cervical ganglion was studied using combined radioreceptor binding and autoradiographic techniques. 3H-Muscimol was used as a ligand of GABA-A receptor sites. The binding was consistent with the labelling of GABA-A sites. The dissociation constant value was 6.4 nmol/l, and the maximum density of binding sites was 146 +/- 7.8 fmol/mg tissue. Light microscope autoradiography revealed the accumulation of 3H-muscimol mainly in superior portions of the ganglion. Binding sites are located primarily in the neuropil rather than within ganglionic neurons. It is probable that the sites revealed by autoradiography are involved in the inhibition of acetylcholine release from ganglionic neurons.

Neurotransmitters, neuroreceptors and aging

At first glance, it is satisfying to see the progress which has been made in the study of neurotransmitters. We have learned a great deal in the last number of years. First, we have been able to identify previously unknown compounds which affect the nervous system or associated peripheral organs. We now know a great deal about the metabolism of these molecules including their synthesis and catabolism. We have learned to identify and to classify their receptors. We have learned that alterations in the effects of neurotransmitters may be responsible for certain pathologies or may be a function of normal aging. Yet, we still have far to go in our research. There are neurotransmitters still to be discovered. We need to continue our efforts because there is still a large amount of confusion in the literature, for example, far too many contradictory reports concerning the effects of age confuse rather than clarify. Possibly order may return to the literature if investigators can agree on some basic tenets. For example, we need a basic definition of old. Some research groups consider 12-month-old rats as old while other groups consider them to be young individuals. We need to have standardization of methodology so that the conclusions can have validity. Once again certain investigators use whole brain homogenates while others use only discrete portions. We need to consider whether the effect we see in our experiment is primary or secondary to aging. We can be certain that due to the aging population, the importance of basic research of age-dependent changes in neurotransmitters and neuroreceptors will increase in the future.

Enzyme histochemistry of aging rat kidney

Aging-dependent changes of some enzymatic activities related to the glycolytic anaerobic pathway (lactate-dehydrogenase, LDH), to the Krebs's cycle (succinate dehydrogenase, SDH) and to the activity of the respiratory oxidative chain (NADH2 - tetrazolium reductase, NADH-D) were studied in the nephron of 4-(young) and 24- (aged) month-old female Wistar rats. In the renal glomeruli LDH and NADH-D activities were reduced with aging, while SDH did not undergo aging-dependent changes. In both the proximal and the distal convoluted tubules, LDH reactivity slightly increased while NADH-D remarkably decreased in old rats; SDH did not show aging-dependent changes. In the loop of Henle LDH was slightly increased, SDH was unchanged and NADH-D was decreased in aged in comparison to young rats. The three enzyme activities investigated were significantly reduced in the collecting tubules of aged animals. The above results are suggestive of the existence of aging changes in mechanisms related with energy transduction in the rat kidney, affecting at a different extent the cell populations of the nephron.

Age-related structural changes in the rat cerebellar cortex: effect of choline alfoscerate treatment

The influence of ageing and of 3 months choline alfoscerate treatment on age-related microstructural changes in cerebellar cortex was studied in 3-, 12- and 24-month-old male Sprague-Dawley rats. The number of Purkinje and granule neurons, the density of Nissl bodies in the cytoplasm of Purkinje and granule neurons and the density of silver-gold impregnated fibres within molecular and granule cells layers were assessed by neurohistological and neurohistochemical techniques associated with microdensitometry and quantitative image analysis. The number of Purkinje and granule neurons was approximately the same in rats of 3 and 12 months and significantly decreased in 24-month-old animals. The density of Nissl bodies and of fine processes of silver-gold impregnated fibres were greatest in the cerebellar cortex of rats of 12 months of age, followed in descending order by 3- and 24-month-old rats. Both the density of Nissl bodies and of silver-gold impregnated fibres were significantly lower in the cerebellar cortex of the oldest age group considered in comparison with the young and middle age groups. Treatment with choline alfoscerate, a precursor in the biosynthesis of brain phospholipids which increases bioavailability of choline in the nervous tissue, noticeably reduced the loss of Purkinje and granule neurons in rats of 24 months. Moreover, it restored the density of Nissl bodies in the cytoplasm of Purkinje and granule neurons as well as the density of silver-gold stained fibres in the molecular and in the granule cells layers to values not significantly different from those found in rats of 3 months. These findings suggest that choline alfoscerate treatment may be effective in counteracting the age-dependent disarrangement of rat cerebellar cortex. The possible mechanisms of action of the compound on the microstructural changes of cerebellar cortex occurring with age are discussed.

Anatomical distribution and function of dopamine receptors in the kidney

Dopamine receptors of DA-1 and DA-2 subtypes are localized in various regions within the kidney including the renal vasculature (DA-1) as well as sympathetic nerve terminals innervating the renal blood vessels (DA-2). More recent studies using receptor-ligand binding and receptor autoradiography have shown that DA-1 receptors are localized at both the luminal and basolateral membranes at the level of the proximal tubules. Activation of these DA-1 receptors by dopamine and by selective DA-1 receptor agonists results in natriuresis and diuresis. The cellular signaling mechanisms responsible for this response appear to be DA-1 receptor-induced activation of adenylate cyclase and phospholipase C, which via the generation of various intracellular messenger systems cause inhibition of Na(+)-H+ antiport (luminal) and Na+, K(+)-ATPase (basolateral), respectively. Both of these events consequently inhibit sodium reabsorption leading to natriuresis and diuresis. It is also known that dopamine can be synthesized within proximal tubular cells from L-dopa, which is taken up from the tubular lumen, and this locally produced dopamine plays an important role in the regulation of sodium excretion particularly during increases in sodium intake. Furthermore, a defect in the renal dopaminergic mechanism may be one of the pathogenic factors in certain forms of hypertension. Finally, whereas DA-1 receptor agonists are shown to be of therapeutic benefit in the treatment of hypertension, heart failure, and acute renal failure, some selective DA-2 receptor agonists are effective antihypertensive agents.

Decreased density of beta-adrenergic and muscarinic cholinergic receptor sites in the vasa nervorum of aged rats

The pharmacological profile and the anatomical localization of beta-adrenergic and muscarinic cholinergic receptors of the vasa nervorum were studied in sections of sciatic nerve using radioreceptor binding and light microscope autoradiography techniques. Sprague-Dawley rats of 4 and 24 months of age were used. [3H]Dihydroalprenolol (DHA) and [3H]quinuclidinyl benzilate (QNB) were used to label beta-adrenergic and muscarinic cholinergic receptors, respectively. The ligands were bound to sections of rat sciatic nerve in a manner consistent with the labelling of beta-adrenergic or muscarinic cholinergic receptors in the 2 age groups investigated. The dissociation constant (Kd) values (about 1.37 nM for [3H]DHA and 0.75 nM for [3H]QNB) did not significantly change between 4- and 24-month-old rats. The maximum concentration of binding sites (Bmax) for [3H]DHA was decreased by about 35% in 24 in comparison with 4-month-old rats. The Bmax value for [3H]QNB was reduced by about 50% in the aged rats. Light microscope autoradiography revealed the development of specific silver grains in the medial layer of epineurial and perineurial arteries in sections of sciatic nerve exposed either to [3H]DHA or [3H]QNB. The number of silver grains developed in epineurial and perineurial arteries of rats of 24 months is significantly lower than in animals of 4 months. The above results suggest the occurrence of an age-dependent loss in the density of beta-adrenergic and muscarinic cholinergic receptors of vasa nervorum. Vasa nervorum are the blood vessels which supply peripheral nerve trunks. They are constituted by outer (epineurial) and inner (perineurial) arteries and veins as well as by a capillary (endoneurial) plexus. Vasa nervorum are innervated by both sympathetic and non-sympathetic nerves which probably play a role in the pathogenesis of some neuropathies. Several different neurotransmitter containing nerve fibres have been identified in the vasa nervorum perivascular plexuses. However, no information is so far available concerning the neurotransmitter receptors of vasa nervorum. Moreover, although the occurrence of age-dependent changes in peripheral nerve morphology and function is well documented, very few reports were centered on the age-dependent changes of the vasa nervorum. The aims of the present study were to characterize pharmacologically and to localize anatomically the beta-adrenergic and muscarinic cholinergic receptors in the rat vasa nervorum. Moreover, the effect of ageing on the density and pattern of these receptors was investigated.

Vasoactive intestinal polypeptide receptors in rat cerebral vessels: an autoradiographic study

1. Localization and pharmacological properties of the vasoactive intestinal polypeptide (VIP) receptors in rat circle of Willis arteries and in the arteries of pial-arachnoid membrane were studied using light microscope autoradiography combined with radioreceptor binding techniques. 2. [125I]-VIP was specifically bound to sections of rat cerebral arteries with a dissociation constant value of 0.5 nM and a binding site density of 80 fmol mg protein-1. Radioreceptor binding experiments revealed that the binding characteristics of [125I]-VIP were consistent with the labelling of specific VIP receptors. The rank order of potency of various substances tested to inhibit [125I]-VIP binding was the following: VIP greater than peptide histidine methionine greater than secretin greater than glucagon. 3. Light microscope autoradiography revealed the localization of [125I]-VIP binding sites in the medial layer of circle of Willis and pial arteries. Quantitative determination of [125I]-VIP binding site density in the different circle of Willis arteries demonstrated a higher accumulation of silver grains in the anterior than in the posterior cerebral arteries. Pial arteries are richer in VIP receptor sites than circle of Willis arteries. 4. These results suggest that the physiological neurogenic vasodilation elicited by VIP on cerebral arteries is mediated by the interaction with specific receptor sites located primarily within cerebral vessels structures involved in the control of cerebrovascular resistances.

Age-related anatomical changes in the rat hippocampus: retardation by choline alfoscerate treatment

The age-related anatomical changes in the rat hippocampus were evaluated in male Sprague-Dawley rats of 3 (young), 12 (mature) and 24 (aged) months by counting the number of nerve cells in the CA1 and CA3 fields and in the dentate gyrus and by measuring the density of Nissl bodies in the cytoplasm of the pyramidal and granule neurons of the above areas. Moreover, the effect of 3 months choline alfoscerate treatment on the anatomical parameters examined was evaluated. The number of pyramidal neurons of the CA1 field and of granule neurons of the dentate gyrus was not significantly changed between young and mature animals, but it was decreased in aged rats. The number of pyramidal neurons of the CA3 field showed a progressive age-dependent reduction. The density of Nissl bodies was the highest in the cytoplasm of pyramidal or granule neurons in mature rats followed in descending order by young and aged animals. Choline alfoscerate treatment counteracted the age-related loss of nerve cells in the 3 hippocampal portions examined and slow-drown the decrease of Nissl bodies in the cytoplasm of pyramidal or of granule neurons in the hippocampus. The significance of changes induced by choline alfoscerate in the hippocampus of aged rats and the possible mechanism of action of the compound are discussed.

Changes in the intensity of sulfide staining in fronto-parietal cortex of the rat following nucleus basalis magnocellularis lesions: possible relevance to Alzheimer's disease

The sulfide staining technique, known also as neo-Timm staining, predominantly stains associational fibres arising from cortical interneurons located primarily in the neuropil of layers I-III of the rat cerebral cortex. The density of these fibres, considered to have a possible role in cognitive and mnemonic processes, has been demonstrated to be related to the density of zinc-containing presynaptic buttons in the cerebral cortex. The unilateral injection of ibotenic acid into the nucleus basalis magnocellularis (NBM) resulted in no changes in the density of sulfide staining in the first 3 weeks after neurotoxin injection and in a significant loss of sulfide staining in the neuropil of cortical layers I-III 4 weeks after NBM lesion in the fronto-parietal cortex ipsilaterally to the lesion. These data suggest that unilateral lesioning of the NMB may cause changes of chemo-specific zinc-containing intracortical pathways. Moreover, they indicate that, in a manner similar to that described in the brain of Alzheimer's disease patients, NBM-lesioned rats show a decrease of zinc tissue stores in the fronto-parietal cortex.

Dopamine DA-2 receptor sites in the rat renal cortex: a light microscope autoradiographic study

The binding of the DA-2 receptor antagonist [3H]-spiroperidol, in the presence of appropriate concentrations of ketanserin to avoid the possible labelling of 5-HT-2 sites, was studied in sections of rat kidney using combined radioreceptor assay and light microscope autoradiography. [3H]-Spiroperidol was bound by sections of rat kidney in a manner consistent with the labelling of a single class of high affinity of DA-2 sites. Scatchard analysis of the binding isotherms showed a Kd value of 2.5 +/- 0.2 nmol/l and a Bmax value of 129.5 +/- 6.8 fmol/mg protein. Light microscope autoradiography, centered on the renal cortex, revealed the development of silver grains within cortical convoluted tubules. Silver grains were rather homogeneously distributed to both proximal and distal convoluted tubules, with no specific glomerular localization. These findings do not support the assumption of the existence of glomerular DA-2 receptors in the rat kidney.

Similarity of age-dependent changes in renal and striatal dopamine receptors

A comparative analysis of the age-dependent changes in renal DA-1 and striatal D-1 dopamine receptors was performed in 3-(young), 12-(adult) and 27-(aged) month-old male Wistar rats by means of combined radioreceptor binding and autoradiographic techniques. 3H-SCH 23390 was used as a ligand of DA-1 or D-1 receptors. Experiments were performed on frozen sections of the kidney and of the striatum. The affinity of the ligand for both renal or striatal receptors did not show age-dependent changes. A significant loss in the density of DA-1 and D-1 sites was observed in the adult in comparison with young rats. A further decrease in the density of these sites was noticeable between adult and aged animals. These results suggest that renal DA-1 and striatal D-1 receptors are sensitive to aging to the same extent.