Localization of dopamine receptor subtypes in systemic arteries

Dopamine D1-D5 receptor protein immunoreactivity was investigated in different sized pial, renal and mesenteric artery branches using immunohistochemical techniques and anti-dopamine D1-D5 receptor protein antibodies. Faint dopamine D1 receptor protein immunoreactivity was observed in smooth muscle of tunica media of pial, renal and mesenteric artery branches. Dopamine D2 receptor protein immunoreactivity was located in the adventitia and adventitia-media border of pial and renal artery branches and to a lesser extent of mesenteric artery branches. No dopamine D3 receptor protein immunoreactivity was observed in pial and mesenteric arteries. In renal arteries a moderate dopamine D3 receptor immunoreactivity was detectable in the adventitia and adventitia-media border. A strong dopamine D4 receptor protein immunoreactivity displaying the same localization of dopamine D2 receptor protein was observed in pial and mesenteric arteries, but not in renal artery branches. Moderate dopamine D5 receptor protein immunoreactivity was observed in smooth muscle of the tunica media of pial, renal and mesenteric artery branches. Bilateral removal of superior cervical ganglia, from which sympathetic supply to cerebral circulation originate abolished dopamine D2 and D4 receptor protein immunoreactivity in pial arteries but was without effect on dopamine D1 and D5 receptor protein immunoreactivity. These findings indicate that systemic arteries express dopamine D1-like (D1 and D5) and D2-like (D2, D3 and D4) receptor subtypes displaying respectively a muscular (postjunctional) and prejunctional localization. The specific distribution of dopamine D2-like receptor subtypes in systemic arteries suggests that they may have a different role in regulating blood flow through the vascular beds investigated.

Microanatomical localization of dopamine receptor protein immunoreactivity in the rat cerebellar cortex

Dopamine (DA) receptor subtype localization was investigated in rat cerebellar cortex using immunohistochemical techniques with antibodies raised against D1-D5 receptor protein. A faint D1 receptor protein immunoreactivity was developed in molecular and Purkinje neurons layers. D2 receptor protein immunoreactivity was found primarily in cerebellar white matter followed by molecular and granular layers and Purkinje neurons. Antibodies against D2S receptor protein were localized in molecular layer and to a lesser extent, in granular layer. A few Purkinje neurons displayed a faint D2S receptor protein immunoreactivity. D3 receptor protein immunoreactivity was observed primarily in molecular and in Purkinje neurons layers of lobules 9 and 10. A faint D3 receptor protein immunoreactivity was also localized in Purkinje neurons and to a lesser extent, in molecular and granular layers of cerebellar lobules 1-8. D4 receptor protein immunoreactivity was found in cerebellar white matter. A pale immunostaining was also visualized in molecular layer. D5 receptor protein immunoreactivity was localized primarily in molecular and Purkinje neurons layers and to a lesser extent, in granular layer and in white matter. The above results indicate that rat cerebellar cortex expresses the DA receptor subtypes so far identified. Purkinje neurons, which are the only efferent neurons of cerebellum, are richest in DA receptor protein immunoreactivity. This suggests that dopaminergic neurotransmission may modulate efferent inputs from cerebellum. The localization of the majority of D2 and D4 and of a faint D5 protein receptor immunoreactivity in cerebellar white matter suggests that these receptors may be presynaptic and transported axonally.

Age-related changes of glial fibrillary acidic protein immunoreactive astrocytes in the rat cerebellar cortex

Age-related changes of glial fibrillary acidic protein (GFAP) immunoreactivity were investigated in the cerebellar cortex of young (3 months), adult (12 months) and old (24 months) rats using immunohistochemical techniques associated with image analysis. In young rats, cell bodies of GFAP-immunoreactive astrocytes were found in the white matter and in the granular layer of cerebellar cortex. Radially-oriented branches of astrocytes which are sited in the granular layer were also observed in the molecular layer. The number of GFAP-immunoreactivity astrocytes of white matter was decreased in adult and old rats in comparison with young cohorts, whereas their size increased progressively from 3 to 24 months old. The number and the size of GFAP-immunoreactive astrocytes of the granular layer was similar in young and adult rats. An increased number and size of GFAP-immunoreactive astrocytes was noticeable in old rats in comparison with younger cohorts. The number of radially oriented branches of the molecular layer was the same in the three age groups investigated. The above results indicate that GFAP-immunoreactive astrocytes of rat cerebellar cortex undergo age-related changes. The not homogeneous sensitivity to aging of cerebellar astrocytes suggests that evaluation of changes of different cell populations of cerebellar cortex should represent an important step of research on aging cerebellum.

Dopamine D1-like receptor subtypes in the rat kidney: a microanatomical study

The microanatomical localization of dopamine D1A and D1B receptor subtypes was investigated in sections of rat kidney using immunohistochemicals techniques with antidopamine D1A and D1B receptor antibodies. Microanatomical analysis was limited to the various components of nephron. Dopamine D1A receptor immunoreactivity was found primarily in the epithelium of loop of nephron (loop of Henle) and of collecting tubules. A less intense immunoreactivity was observed within proximal and distal convoluted tubules as well as in juxtaglomerular complex. Dopamine D1B receptor immunoreactivity was found primarily in proximal and distal convoluted tubules and within the juxtaglomerular complex. A less intense immunoreactivity was observed in the epithelium of collecting tubules followed by the loop of nephron. The demonstration of the localization of dopamine D1A and D1B, receptor subtypes along the nephron may contribute to better define their significance in physiological and pathological conditions.

Sensitivity to ageing of the limbic dopaminergic system: a review

The limbic system includes the complex of brain centres, nuclei and connections that provide the anatomical substrate for emotions. Although the presence of small amounts of dopamine (DA) in several limbic structures has been recognized for a long time, for many years it was thought that limbic DA represented a precursor of noradrenaline in the biosynthetic pathway of catecholamines. More recent evidence has shown that limbic centres and nuclei are supplied with a dopaminergic innervation arising from the ventral tegmental area (field A10) and in smaller amounts from the mesencephalic A9 field. The dopaminergic limbic system is sensitive to ageing. Parameters of dopaminergic neurotransmission (DA levels, biosynthetic and catabolic markers and DA receptors) undergo age-related changes which depend on the structure and species investigated and are characterized mainly by a decline of different parameters examined. In this paper, the influence of ageing on DA biosynthesis, levels, metabolism and receptors are reviewed in laboratory rodents, monkeys and humans as well as in cases of Alzheimer's disease and Parkinson's disease. The possibility that changes of dopaminergic neurotransmission markers in the limbic system are associated with cognitive impairment and psychotic symptoms affecting the elderly is discussed. Better knowledge of dopaminergic neurotransmission mechanisms in the so-called physiological ageing and in senile dementia may provide new insights in the treatment of behavioural alterations frequently occurring in old age.

Influence of neonatal treatment with the pyrethroid insecticide cypermethrin on the development of dopamine receptors in the rat kidney

The influence of neonatal treatment with the pyrethroid insecticide cypermethrin ((R,S)alpha-cyano-3-phenoxybenzyl (1R,S)-cis-trans-3-(2,2-dichloro-vinyl)-2,2-dimethylcyclopropane carboxylate) on postnatal development of renal dopamine receptors was investigated by radioligand binding assay techniques. Treatment with cypermethrin was made on rats from the 10th to the 16th day after birth. Dopamine D1- and D2-like receptors were assayed in frozen sections of kidney of 21-, 30-, 60- and 90-day-old rats using as ligands of dopamine D1- and D2-like receptors [3H]([R](+)-(chloro-2,3,4,5,-tetrahydro-5-phenyl-1,4,-benzazepinal hemimaleate) (SCH 23390) and [3H]spiperone, respectively. Treatment with cypermethrin was without effect on the affinity (Kd value) or the density (Bmax value) of dopamine D1- and D2-like receptors of rats of 21 days of age. In older groups, treatment with the compound reduced the affinity and increased the density of dopamine D1-like receptors, whereas it was without effect on the affinity of dopamine D2-like receptors and decreased their density. These findings indicate that neonatal treatment with the pyrethroid insecticide cypermethrin induces long-lasting impairment of renal dopamine D1- and D2-like receptors and that kidney is a target of the toxic action of the compound. Renal dopamine receptor changes caused by cypermethrin are consistent with possible alterations of renal tubular function and of sympathetic neuroeffector modulation. The above data suggest also that, different from the adult, neonatal exposure to pyrethroid insecticides may induce toxic effects.

Dopamine D2-like receptors in the kidney of spontaneously hypertensive rats: a radioligand binding assay and light microscope autoradiography study

1. Dopamine D2-like receptors were investigated in sections of kidney from male spontaneously hypertensive rats (SHRs) at 6 and 14 weeks of age using radioligand binding assay and autoradiographic techniques with [3H]-spiperone as a ligand. 2. Systolic blood pressure values were slightly higher in 6-week-old SHRs in comparison with age-matched normotensive Wistar-Kyoto (WKY) rats and considerably higher in 14-week-old SHRs in comparison with the other groups investigated. Renal dopamine levels were higher in SHRs aged 6 and 14 weeks in comparison with age-matched WKY rats. Noradrenaline concentrations were similar in 6-week-old SHRs and normotensive WKY rats, and increased slightly in SHRs aged 14 weeks. 3. The density of [3H]-spiperone binding sites was similar in SHRs and WKY rats at 6 weeks of age, and decreased in SHRs at 14 weeks in comparison with age-matched normotensive animals. Light microscope autoradiography revealed the accumulation of silver grains in the tunica adventitia, in the adventitia-media border of intrarenal arteries and within cortical tubules. A few specific silver grains were also developed in the glomerular tuft. No changes in the density and pattern of silver grains were noticeable between SHRs and WKY rats at 6 weeks of age, whereas a reduction in silver grains largely affecting vascular binding sites was observed at 14 weeks of age. 4. Renal denervation considerably decreased the density of [3H]-spiperone binding sites in sections of rat kidney, with an almost complete loss of vascular binding sites. 5. The above findings indicate the occurrence of a decrease of dopamine D2-like receptors in the kidney of SHRs with the progress of hypertension. Dopamine D2-like receptors which are mainly prejunctional are involved in the modulation of sympathetic neurotransmission in the kidney. The loss of these receptors in SHRs may contribute to the pathophysiology of hypertension.

Age-related changes of sulphide-silver staining in the rat hippocampus

The influence of ageing on sulphide-silver positive zinc stores was assessed in the stratum radiatum of the CA1-CA3 sub fields of the rat hippocampus and in the molecular layer of the dentate gyrus using a silver amplification histochemical technique associated with microdensitometry. The volume of areas examined for microdensitometry was evaluated as well by quantitative image analysis. Male Sprague-Dawley rats aged 3 months (considered to be young), 12 months (considered to be adult) and 24 months (considered to be old) were used. Microdensitometric analysis of values of sulphide-silver staining corrected for the volume of hippocampal areas investigated revealed no age-dependent changes of staining in the CA1 sub field of the hippocampus. In the CA2 sub field a decrease of sulphide-silver staining was noticeable in aged rats in comparison with younger cohorts. A progressive reduction in the intensity of sulphide-silver staining was observed in the CA3 sub field of the hippocampus. In the molecular layer of the dentate gyrus, the intensity of staining was decreased in adult and old rats in comparison with young animals. These findings indicate a different sensitivity to ageing of histochemically detectable zinc stores of rat hippocampus. The possibility of a specific sensitivity to senescence of different zinc-containing pathways of the hippocampus is discussed.

Pharmacological characterisation and autoradiographic localisation of a putative dopamine D3 receptor in the rat kidney

The pharmacological profile and the microanatomical localisation of a putative dopamine D3 receptor in the rat renal cortex were investigated using radioligand binding assay and light microscope autoradiography techniques. [3H]7-hydroxy-N,N-di-n-propyl-2-aminotetraline ([3H]7-OH-DPAT) was used as a ligand. [3H]7-OH-DPAT was bound specifically to sections of renal cortex. The binding was time-, temperature- and concentration-dependent, of high affinity and guanine nucleotide-insensitive. The dissociation constant (Kd) value was 0.57 +/- 0.02 nM and the maximum density of binding sites (Bmax) was 62.4 +/- 3.5 fmol/mg tissue. The pharmacological profile of [3H]7-OH-DPAT binding to sections of rat renal cortex suggests the labelling of a dopamine D3 receptor. Light microscope autoradiography revealed the accumulation of the radioligand primarily within cortical tubules and to a lesser extent in the glomerular tuft. In glomeruli, binding sites were found mainly in mesangium and mesangial cells. The demonstration of a putative dopamine D3 receptor in slide-mounted sections of rat renal cortex suggests that appropriate radioligand binding assay techniques combined with autoradiography, may contribute to characterise peripheral dopamine receptor subtypes.

Dopamine D2-like receptors in the rat kidney: effect of denervation

The effects of monolateral denervation induced by renal artery occlusion on dopamine D2-like receptors were assessed in rat kidney using radioligand binding assay and autoradiographic techniques. [3H]spiperone was used as a ligand. [3H]spiperone was bound specifically to sections of control innervated kidneys with a dissociation constant (Kd) value of 0.07 +/- 0.003 nM and a maximum density of binding sites (Bmax) value of 35.4 +/- 0.16 fmol/mg tissue. Light microscope autoradiography showed the accumulation of silver grains both in the arterial tree and in cortical tubules. At the vascular level, [3H]spiperone binding sites were accumulated primarily in the adventitia and in adventitia-media transitional zone. In cortical tubules, the higher density of [3H]spiperone binding sites was noticeable in proximal convoluted tubules. A few binding sites were also found in the glomerular tuft. In denervated kidneys, noradrenaline and dopamine levels were reduced by about 90% and 60% respectively in comparison with control innervated kidneys. Denervation reduced the density of [3H]spiperone binding sites by more than 85%. In denervated kidneys, light microscope autoradiography showed the disappearance of specific vascular binding sites and a remarkable reduction of tubular [3H]spiperone binding sites. The above results indicate that the largest majority of renal dopamine D2-like receptors labelled by [3H]spiperone is prejunctional in location.

Postnatal development of dopamine D1-like and D2-like receptors in the rat kidney: a radioligand binding study

Dopamine exerts important natriuretic and renal haemodynamic changes mediated through the interaction with dopamine D1-like and D2-like receptors. Dopamine-mediated natriuresis and renal vascular effects are less in younger than in older animals. The pharmacological profile and the density of dopamine D1-like and D2-like receptors were assessed in the kidney of rats ranging from 2 to 90 days of age by using radioligand binding assay techniques. [3H]SCH 23390 was used as ligand of dopamine D1-like receptors. [3H]Spiperone was used as a ligand of dopamine D2-like receptors. The dissociation constant (Kd) value of [3H]SCH 23390 binding was slightly decreased from the 21st day of age in comparison with animals of 2 and 7 days of age. The maximum density (Bmax) of [3H]SCH 23390 binding sites increased progressively until the 21st day of age and then plateauned. A similar trend was found for [3H]Spiperone binding sites. In [3H]Spiperone binding experiments, the Kd value was remarkably decreased from the 21st to the 90th day of life. Bmax value of [3H]Spiperone binding sites were similar in rats of 2 and 7 days of age and subsequently increased to values similar to those found in adult rats from the 21st day of life. The pharmacological profile of [3H]SCH 23390 and [3H]Spiperone was similar in rats of the different ages investigated. These findings suggest that renal dopamine D1-like and D2-like receptors undergo maturational changes in the first 3 weeks after birth and then are stabilized at the adult levels. The possibility that the increased expression of renal dopamine receptors postnatally may be linked with the gradual appearance of dopamine-mediated renal responses after birth is discussed.

Age-dependent changes in the expression of dopamine receptor subtypes in human peripheral blood lymphocytes

The pharmacological profile and the density of dopamine D3 and D5 receptor subtypes expressed by human peripheral blood lymphocytes of subjects of different ages (ranging from 20 to 75 years) were assessed using radioligand binding techniques. Dopamine D3 receptor was assayed with [3H]7-hydroxy-N,N-di-n-propyl-2-aminotetraline ([3H]7-OH-DPAT) as a ligand. Dopamine D5 receptor was assayed using [3HIR]-(+)-(-chloro-2,3,4,5, tetrahydro-5-phenyl-1H-3-benzazepin-al-hemimaleate) ([3H]SCH 23390) as a ligand. The affinity and the pharmacological profile of [3H]7-OH-DPAT and [3H]SCH 23390 at dopamine D3 and D5 receptor, respectively, were similar in subjects of different ages. The density of dopamine D3 receptor binding sites was slightly decreased in subjects of 30-39 years in comparison with younger individuals. A remarkable loss of dopamine D3 receptor was then found between 40 and 49 years of age in comparison with younger subjects. A further slight decrease was noticeable between 50 and 59 years of age. The number of [3H]7-OH-DPAT binding sites was then stabilized after 60 years of age. The density of dopamine D5 receptor binding sites did not show age-dependent changes. The above findings indicate the occurrence of a decline in the density of lymphocyte dopamine D3 but not D5 receptor between adult and mature subjects. The possibility that dopamine D3 receptor assay in peripheral blood lymphocytes may represent a tool for investigating dopamine receptor function in aging and age-related neurological disorders is discussed.

Synthesis, resolution, and preliminary evaluation of trans-2-amino-6(5)-hydroxy-1-phenyl-2,3-dihydro-1H-indenes and related derivatives as dopamine receptors ligands

The present work reports the synthesis of enantiomeric pairs of the trans-2-amino-6-hydroxy-1-phenyl-2,3-dihydro-1H-indene [(+)-14a, (-)-14a] and trans-2-amino-5-hydroxy-1-phenyl-2,3-dihydro-1 H-indene [(+)-14b, (-)-14b] and their N,N-di-n-propyl [(+)-and (-)-15a,b], N-methyl-N-allyl [(+)-and (-)-16a,b], and N-methyl-N-n-propyl [(+) and (-)-17a,b] derivatives obtained by a combination of stereospecific reactions and optical resolution. The new compounds were evaluated for their affinity at the dopamine D1 and D2 receptors. The amines (+)- and (-)-14a, incorporating the D1 pharmacophore 2-phenyl-2-(3-hydroxyphenyl)ethylamine in a trans extended conformation, and their derivatives displayed D1 and D2 affinity in the nanomolar range. On the other hand, the enantiomers (+)- and (-)-14b, (+)- and (-)-15b displayed high affinity and selectivity for the D1 receptor. In a preliminary behavioral study on rats (+)-14b, and to a greater extent (+)-15b, promoted episodes of intense grooming, thus indicating that they act as central D1 agonists. The trans-2-amino-5-hydroxy-1-phenyl-2,3-dihydro-1H-indenes (+)-14b and (+)-15b represent selective D1 agonists lacking a catechol group, which should meet the prerequisites for a central nervous system penetration.

Pharmacological characterization and autoradiographic localization of dopamine receptors in the rat adrenal medulla

The pharmacological profile and the anatomical localization of dopamine D1-like and D2-like receptors were studied in sections of rat adrenal medulla, with radioligand binding and autoradiographic techniques, respectively. [3H]([R]-(+)-chloro-2,3,4,5-tetrahydro-5-phenyl-1 H-3benzazepin-al hemimaleate) (SCH 23390) was used as a ligand for dopamine D1-like receptors and [3H]spiperone was used as a ligand for dopamine D2-like receptors. Radioligand binding and light microscope autoradiography did not show specific [3H]SCH 23390 binding in sections of rat adrenal medulla. This suggests that rat adrenal medulla does not express dopamine D1-like receptors. [3H]Spiperone was specifically bound to sections of rat adrenal medulla. The binding was time-, temperature- and concentration-dependent, with a dissociation constant (Kd) of 1.05 nM and a maximum density of binding sites (Bmax) of 100.2 +/- 3.8 fmol/mg tissue. The pharmacological profile of [3H]spiperone binding to rat adrenal medulla was similar to that displayed by neostriatum, which is known to express dopamine D2 receptors. Light microscope autoradiography showed the accumulation of specifically bound [3H]spiperone as silver grains within sections of adrenal medulla. Silver grains were found primarily over the cellular membrane of chromaffin cells. The above data indicate that chromaffin cells of the rat adrenal medulla express dopamine receptors belonging to the dopamine D2 receptor subtype. These receptors are probably involved in the modulation of catecholamine release from chromaffin cells, as documented by functional studies.

Effect of treatment with L-deprenyl on age-dependent microanatomical changes in the rat kidney

The influence of aging and of treatment with L-deprenyl on the structure of the kidney was investigated in 24-month-cld male Sprague Dawley rats by microanatomical techniques associated with image analysis. L-Deprenyl was administrated orally for 5 months at a dose not inhibiting monoamine oxidase (MAO) B activity (1.25/mg/kg/day) and at a dose inhibiting MAO B activity (5 mg/kg/day). In 24 month-old-rats the number and the volume of glomeruli was reduced in comparison with 12-month-old rats used as reference adult animals. Vascular changes characterised by increased thickness of the tunica media, decreased size of arterial lumen and increased wall-to-lumen ratio were also noticeable in 24-month-old rats. Moreover, an increased MAO B reactivity was noticeable within glomerular tufts and renal tubules. Treatment with the low dose of L deprenyl did not cause changes in MAO B reactivity, or in the number of glomeruli, but increased glomerular volume and reduced the wall-to-lumen ratio in medium-sized renal artery branches. The dose of 5 mg/kg/day of L-deprenyl significantly decreased MAO B reactivity within both glomerular tufts and tubules, increased the number and the volume of glomeruli and countered-age-related vascular changes. The above results suggest that treatment with L-deprenyl counters to some extent microanatomical changes occurring in the kidney of aged rats. The observation that the dose of the compound inactive on MAO B activity reduces in part age dependent renal microanatomical changes, indicates that the renal protective effect of L-deprenyl is only in part related to MAO B inhibition.

Changes in the number of primary sensory neurons in normal and vitamin-E-deficient rats during aging

In the dorsal root ganglia (DRGs) of vitamin-E-deficient rats, we previously found an increase in the number of neurons during the first 5 months of life (Cecchini et al., 1993, 1994). This neurogenetic event seems to bring forward in time the increase in the number of primary sensory neurons that Devor et al. (1985) found in normal rats aged more than 1 year, but that other authors have not confirmed. The present study had two aims: first, to verify whether neurogenesis spontaneously occurs in DRGs of 14-month-old Sprague-Dawley rats; and, second, to determine whether the neurogenesis enhanced by vitamin E deficiency continues further in the long run, or whether it stops or reverses into neuron loss. A quantitative and morphometric analysis was performed on neurons of L3-L6 DRGs in 14-month-old normal and vitamin-E-deficient rats: the results obtained were compared to those previously obtained in 1-month-old and 5-month-old animals of both dietetic treatment groups, in order to observe the effects of aging on these neuronal populations. The total number of DRG neurons in the control group was higher in older than in younger animals, whereas the value in the vitamin-E-deficient group was lower in older than in younger animals. The present data confirm that neurogenesis occurs in DRGs of normal rats during adult life. Moreover, they show that once the premature neurogenesis in the deficient rats is completed, no further increase in the number of neurons takes place.