Diminution of preprosomatostatin-mRNA in cerebral cortex of the aged rat

The aim of the present study was to examine the effect of normal aging on somatostatin neurotransmission. Somatostatin gene expression was analysed in several regions of the cerebral cortex and hippocampus in 3, 7 and 21 month-old Sprague-Dawley rats using quantitative in situ hybridization with a 48mer oligodeoxynucleotide antisense probe. Furthermore the distribution of ¹²⁵I-Tyr¹¹ somatostatin receptor binding sites was studied using quantitative receptor autoradiography. The results demonstrated a significant reduction of preprosomatostatin-mRNA in the frontal cortex of the aged (21 month) group compared with the young (3 month) and the middle-aged (7 month) groups. The receptor binding densities of the aged (21 month) group tended to be lower, compared to the other groups although no significant region-specific changes were evident. These results indicate neurochemical changes in somatostatin-containing neurons in the frontal cortex during aging.     

Muscarinic receptor plasticity in the brain of senescent rats: down-regulation after repeated administration of diisopropyl fluorophosphate

Potential age-related differences in the response of Fischer 344 rats to subchronic treatment with diisopropylfluorophosphate (DFP) were evaluated in terms of brain cholinesterase (ChE) inhibition and muscarinic receptor sites. Male 3- and 24-month old rats were sc injected with sublethal doses of DFP (first dose 1.6, subsequent doses 1.1 mg/kg on alternate days) for 2 weeks and killed 48 hrs after the last treatment. In the cerebral cortex, hippocampus and striatum of control rats a significant age-related reduction of ChE and of maximum number of 3H-QNB binding sites (Bmax) was observed. The administration of DFP to senescent rats resulted in more pronounced and longer lasting syndrome of cholinergic stimulation, with marked body weight loss and 60% mortality. The percentage inhibition of brain ChE induced by DFP (over 80% in all regions) did not differ between young and senescent rats. As expected, in young rats DFP caused a significant decrease of Bmax (without apparent changes in affinity), which in the cerebral cortex reached about 40%. In the surviving senescent rats, the percentage decrease of Bmax due to DFP with respect to age-matched controls was very similar to that of young animals, especially in the cerebral cortex. Thus, there is great variability in the response of aged rats to DFP treatment, from total failure of adaptive mechanisms resulting in death to considerable muscarinic receptor plasticity. The data support the view that the ability of central neurotransmitter systems to compensate for pathological or xenobiotic induced insult is an essential part of the aging process.     

Alpha 1 adrenergic receptor control of renal blood vessels during aging

Aging humans and rats have a reduced renal vascular constriction response to stress, change in posture, or exercise. In this study, renal interlobar arteries from 9- (intermediate age) to 15-month-old (aging) male Wistar rats constricted less to alpha-adrenergic agonists than those of 4-month-old (young adult) rats. The reduced contraction to A61603 (alpha 1 A agonist) was similar to that to norepinephrine and phenylephrine. Therefore, it appears that the reduction in constriction is primarily related to alpha 1 A receptor stimulation. GeneChip microarray hybridization analysis of the interlobar arteries with the RAE 230A GeneChip indicated that there were no significant differences in gene expression for alpha 1 A/C, 1B, or 1D receptors between 4-month-old (young adult) and 1-year-old (aging) male Wistar rats. Competitive binding experiments (prazosin) revealed that maximal binding (Bmax, fmol/mg protein) of the alpha 1 receptors of interlobar arteries was reduced 25% by 10 months of age and 50% by 18+ months of age. Alpha 1 receptor-induced arterial constriction and prazosin binding were both down-regulated. The loss of receptor-initiated constriction likely includes down-regulation of maximum agonist binding by alpha 1 adrenergic receptors.     

Involvement of Nerve Growth Factor and Its Receptor in the Regulation of the Cholinergic Function in Aged Rats

The role of nerve growth factor (NGF) and its receptor (NGFR) in the regulation of cholinergic activity has been studied during the aging process. NGFRs were quantified in cortical membranes using a radioactive binding assay. NGF levels and choline acetyltransferase (ChAT) activity were determined in cortex, hippocampus, neostriatum, and septum. These assays were performed in both adult (6-month-old) and aged (36-month-old) rats. High- and low-affinity 125I-NGF binding sites were present in cortex of adult and aged rats. Furthermore, we observed a decrease in number and affinity of both NGFRs in aged rats. ChAT activity in these rats was lower (approximately 30%) than in adult rats in all the brain regions examined. NGF levels were not modified in cortex and hippocampus and were decreased in neostriatum (55%) and septum (35%). In conclusion, our results suggest that, during the aging process, the cholinergic impairment is related to a decrease in NGF levels in neostriatum but not in cortex and hippocampus. The reduction in level of NGF protein in septum could be due to a decrease in number of high-affinity 125I-NGF binding sites.     

Effect of Monocular Deprivation on Uptake and Binding of [3H]Glutamate in the Visual System of Rat Brain

Abstract: [³H]Glutamate uptake and binding studies were performed in the visual cortices, lateral geniculate nuclei (LGN), and superior colliculi of 3-month-old rats with one eyelid surgically closed from postnatal day 10 (monocular deprivation). Uptake and binding were highest in the lateral geniculate nucleus followed by the visual cortex (69% and 15%, respectively compared to LGN values) and the superior colliculus (32% and 59% of LGN values). Monocular deprivation did not affect [³H]glutamate uptake in any of the visual regions examined. However, a 46% decrease in [³H]glutamate binding in the lateral geniculate nucleus ipsilateral to the sutured eye was detected. Binding levels in other regions were not affected.     

Changes in Cholinergic but Not in GABAergic Markers in Amygdala, Piriform Cortex, and Nucleus Basalis of the Rat Brain Following Systemic Administration of Kainic Acid

Three days after systemic administration of kainic acid (15 mg/kg, s.c.), selected cholinergic markers (choline acetyltransferase, acetylcholinesterase, muscarinic acetylcholine receptor, and high-affinity choline uptake) and GABAergic parameters [benzodiazepine and gamma-aminobutyric acid (GABA) receptors] were studied in the frontal and piriform cortex, dorsal hippocampus, amygdaloid complex, and nucleus basalis. Kainic acid treatment resulted in a significant reduction of choline acetyltransferase activity in the piriform cortex (by 20%), amygdala (by 19%), and nucleus basalis (by 31%) in comparison with vehicle-injected control rats. A lower activity of acetylcholinesterase was also determined in the piriform cortex following parenteral kainic acid administration. [3H]Quinuclidinyl benzilate binding to muscarinic acetylcholine receptors was significantly decreased in the piriform cortex (by 33%), amygdala (by 39%), and nucleus basalis (by 33%) in the group treated with kainic acid, whereas such binding in the hippocampus and frontal cortex was not affected by kainic acid. Sodium-dependent high-affinity choline uptake into cholinergic nerve terminals was decreased in the piriform cortex (by 25%) and amygdala (by 24%) after kainic acid treatment. In contrast, [3H]flunitrazepam binding to benzodiazepine receptors and [3H]muscimol binding to GABA receptors were not affected 3 days after parenteral kainic acid application in any of the brain regions studied. The data indicate that kainic acid-induced limbic seizures result in a loss of cholinergic cells in the nucleus basalis that is paralleled by degeneration of cholinergic fibers and cholinoceptive structures in the piriform cortex and amygdala, a finding emphasizing the important role of cholinergic mechanisms in generating and/or maintaining seizure activity.     

Dietary lithium during development: Changes in amino acid levels,ionic content,and [3H]spiperone binding in the brain of rats

We found that chronic lithium diet affects the sensitivity of neuroleptic receptors and the content of amino acids in the brain, and that the changes in adult animals differ from those in young rats. Pregnant rats were kept on lithium diet (pellets with 0.21% Li2CO3 and 0.21% NaCl) during the gestation period and the offspring were kept on lithium for six weeks after delivery. Control rats were kept on normal diet under identical conditions. In corpus striatum and cerebral cortex of lithium-treated young rats a reduction in apparent dissociation constant and no change in (3H)spiperone total binding sites were found, suggesting a sensitization of the neuroleptic receptor; this result was unlike that obtained with adult lithium-treated rats, where the total number of binding sites was decreased. The lithium content of brain was very high (2.32 meq/kg of wet weight), whereas in the serum only 0.75 meq/l was recorded. K+ and Na+ levels increased by 20% and 9% respectively in the brain and remained at normal levels in the serum. Analysis of free amino acids in the cerebral cortex, midbrain, and cerebellum showed increases in GABA and glycine levels in all three regions, a significant increase in taurine in midbrain, and an increase in lysine in cerebral cortex and cerebellum. The results indicate that the effect of chronic dietary lithium given during pregnancy on the neuroleptic receptor in young rats is different from that in adult animals. It produces an increase in the number of the neuroleptic receptor sites instead of the decline in the number of binding sites found in adult rats. It remains to be established whether this effect is related more to the age of the animal tested or to the stage of development of the CNS at which the lithium was administered.     

Anatomically distinct activation of endothelin-3 and the L-arginine/nitric oxide pathway in the kidney with advanced aging

Aging is associated with spontaneous degenerative changes of renal function and structure. The aim of this study was to determine changes of the endothelin (ET) system and NO tissue bioactivity during the physiological aging process. Renal protein expression of ET-1 and ET-3, ETA, and ETB receptor mRNA expression, ET receptor binding and distribution, and tissue NO metabolite content were determined in adult, middle-aged, and senescent normotensive female Wistar rats. In senescent animals, medullary ET-3 content increased 3.4-fold (p<0.05 vs. adult), whereas aging did not affect ET-3 levels in the cortex. Local NO bioavailability, determined by NO metabolite tissue measurements, decreased in the cortex only. ET receptor binding capacity--predominantly due to ETB receptor binding--was lower in medulla than in cortex. Aging had no effect on ET-1 binding capacity or ET receptor distribution, whereas with advanced age gene expression of both receptors decreased. In conclusion, aging causes distinctive expressional changes of the renal endothelin system in otherwise healthy rats. The pronounced increase of endothelin-3 in the renal medulla is associated with preservation of local NO metabolite levels, changes not observed in the cortex. These findings could be important for pathologies and possibly therapy associated with renal aging.     

耐力运动对增龄大鼠脑皮层突触可塑性的影响及相关调控机制*

目的:探讨规律性耐力运动对脑皮层增龄性老化适应性的作用与机制。方法:将三个不同年龄段的健康SPF级雄性Sprague-Dawley大鼠分为3月龄 (青年,n=20)、13月龄 (中年,n=24)和23月龄 (老年,n=24)组,每组又随机分为静息组和运动组;静息组三组静息,运动组三组实施10周递增负荷规律的中等强度耐力运动:运动方式为跑台运动(坡度0),运动强度从最大摄氧量(V·O2max) 60%～65%逐渐递增到70%～75%,运动时间为10周;取大鼠脑皮层,HE染色测试大鼠脑皮层增龄性形态学变化,检测BDNF和SOD的蛋白表达及突触素-1(SYN1)和CaMK IIα/AMPKα1/ mTOR通路等相关基因。结果:静息各组大鼠的脑皮层结构呈现年龄增龄性衰老变化,脑皮层SOD表达呈增龄性下降趋势,BDNF表达变化呈增龄性上升趋势,SYN1和CaMK IIα表达水平随增龄性趋势变化不大,AMPKα1和SirT2以及 IP3R、AKT1、mTOR mRNA表达水平随年龄变化呈现中年略上升而老年下降趋势;与静息各组大鼠相比,运动各组大鼠脑皮层神经细胞核排列紧密有序,显微镜下观察细胞核的数量明显增加,运动促进大鼠脑皮层SOD、BDNF和突触素SYN1表达水平增加,其中老年大鼠SOD、BDNF表达水平显著上调(P＜0.01),青年和老年大鼠SYN1表达水平显著上调(P＜0.05),运动上调中年和老年大鼠脑皮层CaMK IIα表达水平上调(P＜0.01),而对青年大鼠CaMK IIα表达水平却是下调(P＜0.01),运动可上调青年大鼠脑皮层的AMPKα1表达水平(P＜0.05),而对中年和老年大鼠AMPKα1的影响不显著,运动均可上调各年龄大鼠脑皮层的SirT2表达水平(P＜0.05),运动上调各年龄大鼠脑皮层的IP3R/AKT1/ mTOR表达水平,其中青年IP3R显著上调(P＜0.01),青年和中年mTOR显著上调(P＜0.01),老年mTOR也显著上调(P＜0.05)。结论:耐力运动通过上调BDNF的表达水平,调控CaMK IIα信号、激活AMPK信号通路和IP3R/AKT1/mTOR信号通路,改善脑皮层的突触可塑性。     

ABRA在正常成年大鼠大脑皮质和海马区的表达

目的观察ABRA(Actin binding Rho activator)在成年大鼠大脑皮质和海马中的表达。方法制备成年大鼠脑的冰冻切片,采用共聚焦免疫荧光技术和免疫荧光强度测量检测ABRA在大鼠大脑皮质和海马区的表达。结果 ABRA在神经元的胞核、胞浆、突起内可见,其中胞核着色最强。在大脑皮质,ABRA阳性的神经元胞体和突起广泛分布于皮质的分子层、外颗粒层、外锥体细胞层、内颗粒层、内锥体细胞层、多形细胞层,其免疫荧光强度分别为129.22±16.94、125.39±29.83、117.67±22.50、105.85±17.65、103.90±18.00、100.23±20.38,ABRA阳性细胞率分别为0.51±0.01、0.69±0.02、0.64±0.03、0.58±0.05、0.65±0.09、0.63±0.01。在海马,ABRA均匀分布于海马各部,阳性神经元集中于锥体细胞层,而其阳性突起弥散分布于海马分子层和多形层。海马锥体细胞层、分子层、多形层免疫荧光强度分别为141.19±35.48、53.19±10.38、43.32±9.59,ABRA阳性细胞率分别为0.62±0.04、0.27±0.07、0.25±0.03。结论 ABRA广泛表达于大鼠大脑皮质和海马各层,提示ABRA可能在大鼠这些部位的神经细胞功能活动方面起重要作用。     

Reduced muscarinic receptor plasticity in frontal cortex of aged rats after chronic administration of cholinergic drugs

Age-related differences in muscarinic receptor plasticity were observed in young, adult and senescent Fischer 344 rats (3, 9 and 27 months old, respectively) following the chronic, intracerebroventricular (ivt) administration of a cholinergic agonist, oxotremorine, or antagonist, methylatropine. After three weeks treatment of young rats with ivt oxotremorine, the maximum number (Bmax) of 3H-QNB binding sites in frontal cortex, determined by saturation experiments, was reduced by 27%, with no apparent change in the affinity (Kd) of 3H-QNB for the muscarinic receptor. Conversely, chronic ivt methylatropine administered to 3 month old animals caused a 29% increase in Bmax with no significant change in Kd. Adult animals showed a somewhat lesser degree of muscarinic receptor plasticity (16% down-regulation after oxotremorine, 22% up-regulation after methylatropine). However, 3H-QNB binding parameters in frontal cortex from senescent rats were not significantly altered following identical treatments with oxotremorine or methylatropine. Thus, muscarinic receptor adaptation to chronic, cholinergic drug administration was impaired in aged animals. This reduced receptor plasticity with aging could have important implications for the long-term drug treatment of elderly patients and for the therapeutic efficacy of cholinergic drugs in age-related neurological disorders, such as Alzheimer's disease.     

Increased dithiothreitol-insensitive,type 2 angiotensin II receptors in selected brain areas of young rats

1. Angiotensin II receptors have been studied by quantitative autoradiography in selected brain areas of young (2-week-old) and adult (8-week-old) rats. 2. In young rats, angiotensin II receptors were present in brain areas which did not express receptors in the adult brain, such as thalamic nuclei, cortical areas, and the cerebellum. 3. Young rats had more angiotensin II receptors in the subfornical organ than adult rats. In the inferior olive, the number of angiotensin receptors in young animals was 10 times higher than that in adult rats. Angiotensin II binding in the inferior olive was insensitive to incubation in the presence of dithiothreitol. 4. Conversely, the number of angiotensin II receptors in the nucleus of the solitary tract was lower in young rats compared to adults. Incubation in the presence of dithiothreitol resulted in a more than 90% inhibition of angiotensin II binding in the nucleus of the solitary tract. 5. Our results indicate the presence of two types of angiotensin II receptor in brain, one sensitive (type 1) and one insensitive (type 2) to the reducing agent dithiothreitol. 6. The expression of type 2 angiotensin II receptors, insensitive to dithiothreitol, is more marked in young rats, indicating a role for this type of angiotensin receptors in brain development.     

Metabonomic alterations in hippocampus, temporal and prefrontal cortex with age in rats

The metabolic changes in hippocampus, temporal cortex and prefrontal cortex in SD rats along with aging were explored using a metabonomic approach, which based on high resolution “magic angle spinning” ¹H NMR spectroscopy. The metabolite profiles were analyzed by partial least squares-discriminant analysis, and the results showed that the metabolites of the above three brain regions in old rats were dramatically different from that in the adult and young rats. The old rats showed increased myo-inositol and lactate in all of the three brain regions, and decreased N-acetylaspartate in temporal and frontal cortex, Glutamate–GABA level became imbalance in temporal cortex of old rats. In addition, compared with the adult female rats, male rats had higher levels of N-acetylaspartate, taurine, and creatine in temporal or frontal cortex. The age-related metabolic changes may indicate the early functional alterations of neural cells in these brain regions, especially the temporal cortex. The gender-related metabolic changes suggest the significance of the hormonal regulation in brain metabolism. Our work highlights the potential of metabolic profiling to enhance our understanding of biological mechanisms of brain aging.     

Asialoorosomucoid hepatobiliary transport is unaltered by the loss of liver asialoglycoprotein receptors in aged rats

The hepatobiliary transport of asialoorosomucoid (ASOR) was examined in aging male Fischer 344 rats. The time course of transport of 125I-ASOR from blood to bile was identical in both senescent and young adult rats. Peak secretion occurred at approximately 35 minutes after injection via the femoral vein. Total secretion of radiolabeled ASOR (3.6% of injected dose), bile secretion and rate of secretion of radiolabeled ligand (approximately 2% of administered dose/hr/gm bile/liver) were not significantly different for the two age groups. Determination of the binding capacity for 125I-ASOR with liver plasma membrane-enriched preparations showed the membranes from old animals capable of binding approximately 50% less radiolabeled ligand as the young adult animals. Analysis of the distribution of 125I-ASOR autoradiographic grains along the liver lobule indicated extensive uptake of ligand in Zone 2 and 3 cells in senescent animals, whereas uptake in young rats was essentially limited to Zone 1 parenchymal cells. These results indicate that, contrary to the age-related loss of hepatic receptors for dimeric IgA and the concomitant reduction in hepatobiliary secretion of IgA, loss of ASOR binding capacity on liver plasma membranes from old animals is not reflected in diminished hepatobiliary secretion of ASOR. The loss of ASOR binding capacity is offset by the recruitment of Zone 2 and 3 hepatocytes along the liver lobule. This result suggests that hepatic metabolism and hepatobiliary secretion of macromolecules which exhibit a lobular gradient of uptake (e.g. ASOR) will be relatively less affected by loss of receptors compared to ligands which do not display such a gradient (e.g. IgA).     

Identification of cold-shock protein RBM3 as a possible regulator of skeletal muscle size through expression profiling

Changes in gene expression associated with skeletal muscle atrophy due to aging are distinct from those due to disuse, suggesting that the response of old muscle to inactivity may be altered. The goal of this study was to identify changes in muscle gene expression that may contribute to loss of adaptability of old muscle. Muscle atrophy was induced in young adult (6-mo) and old (32-mo) male Brown Norway/F344 rats by 2 wk of hindlimb suspension (HS), and soleus muscles were analyzed by cDNA microarrays. Overall, similar changes in gene expression with HS were observed in young and old muscles for genes encoding proteins involved in protein folding (heat shock proteins), muscle structure, and contraction, extracellular matrix, and nucleic acid binding. More genes encoding transport and receptor proteins were differentially expressed in the soleus muscle from young rats, while in soleus muscle from old rats more genes that encoded ribosomal proteins were upregulated. The gene encoding the cold-shock protein RNA-binding motif protein-3 (RBM3) was induced most highly with HS in muscle from old rats, verified by real-time RT-PCR, while no difference with age was observed. The cold-inducible RNA-binding protein (Cirp) gene was also overexpressed with HS, whereas cold-shock protein Y-box-binding protein-1 was not. A time course analysis of RBM3 mRNA abundance during HS showed that upregulation occurred after apoptotic nuclei and markers of protein degradation increased. We conclude that a cold-shock response may be part of a compensatory mechanism in muscles undergoing atrophy to preserve remaining muscle mass and that RBM3 may be a therapeutic target to prevent muscle loss.     

Increased susceptibility to intermittent hypoxia in aging rats: changes in proteasomal activity,neuronal apoptosis and spatial function

Obstructive sleep apnea (OSA) is a frequent medical condition characterized by intermittent hypoxia (IH) during sleep, and is associated with neurodegenerative changes in several brain regions along with learning deficits. We hypothesized that aging rats exposed to IH during sleep would be particularly susceptible. Young (3-4 months) and aging (20-22 months) Sprague-Dawley rats were therefore exposed to either room air or IH for 14 days. Learning and memory was assessed with a standard place-training version of the Morris water maze. Aging rats exposed to room air (RA) or IH displayed significant spatial learning impairments compared with similarly exposed young rats; furthermore, the decrements in performance between RA and IH were markedly greater in aging compared with young rats (p < 0.01), and coincided with the magnitude of IH-induced decreases in cyclic AMP response element binding (CREB) phosphorylation. Furthermore, decreases in proteasomal activity occurred in both young and aging rats exposed to IH, but were substantially greater in the latter (p < 0.001). Neuronal apoptosis, as shown by cleaved caspase 3 expression, was particularly increased in aging rats exposed to IH (p < 0.01 versus young rats exposed to IH). Collectively, these findings indicate unique vulnerability of the aging rodent brain to IH, which is reflected at least in part, by the more prominent decreases in CREB phosphorylation and a marked inability of the ubiquitin-proteasomal pathway to adequately clear degraded proteins.     

Differential effect of fasting on IGF-BPs in serum of young and adult rats and its implication to impaired skin GAG content

During fasting or aging of animals there is a decreased content of skin glycosaminoglycans (GAGs). It has been found that the skin of adult rats contains about 60% of GAGs found in the skin of young animals. Fasting of both groups of animals (young and adult) resulted in decrease of GAG content. However, GAG content in the skin of fasted young rats decreased by 30% and in fasted adult rats by 15% only, compared to fed animals, respectively. The mechanism for the phenomena is not known. We considered insulin-like growth factor-I (IGF-I) as a potential candidate involved in regulation of GAG biosynthesis in both experimental models of animals. Adult rat sera were found to contain about 75% of IGF-I recovered from young rat sera. Fasting of both groups of animals resulted in dramatic decrease in serum IGF-I levels to about 50% of initial values. Since IGF-I activity and IGF-I serum half-life depends on the level of specific IGF-binding proteins (IGFBPs) we determined (i) relationship between main groups of IGFBPs, namely high molecular weight binding proteins (HMWBPs) and low molecular weight binding proteins (LMWBPs) and (ii) the amounts of IGF-I bound to respective proteins in the sera of all experimental animals. Control young rat serum was found to contain about 90% of HMWBPs and about 10% of LMWBPs as determined by ligand binding assay. In contrast, control adult rat serum contained about 60% of HMWBPs and about 40% of LMWBPs. Fasting of both groups of animals resulted in significant increase in serum levels of LMWBPs. Control young rat serum was found to contain about 8% IGF-I bound to LMWBPs while serum of control adult rats contained 18% IGF-I bound to these proteins. In sera of fasted young animals however, about 75% of the bound IGF-I was recovered from LMWBPs (about 60% of total serum IGF-I) while in sera of fasted adult animals only about 56% of the bound IGF-I was recovered from LMWBPs (about 50% of total serum IGF-I). Evidence was provided that during fasting of both groups of animals there is a significant decrease in serum BP-3 and dramatic increase in serum BP-1 concentrations, compared to respective controls. However, the concentration of BP-1 in serum of fasted young rats was increased by about 60 fold while in serum of fasted adult rats only by about 10 fold, compared to respective control animals. Negative correlation between skin GAG content and LMWBPs derived IGF-I during fasting of young (r = - 0.943, p < 0.001) and adult ( r = - 0.571, p < 0.01) rats was found.The data presented suggest that the effects of aging and fasting on decreased skin GAG content may be due to induction of LMWBPs that are known to (i) inhibit IGF-I dependent function and (ii) increase clearance of IGF-I from circulation. However, the effects of fasting are distinct in respect to young and adult rats suggesting that mechanisms involved in regulation of IGF-I bioactivity during aging are more complex that during fasting.     

Effect of kainic acid administration to prepubescent rats on cholinergic markers in selected brain regions of adult rats.

Systemic kainic acid administration to prepubescent rats, in a convulsant dose, results in permanent changes in behaviour, learning and memory in adulthood (Holmes et al., 1988, Epilepsia 29, 721-730). With regard to the hypothesis that cholinergic mechanisms play a crucial role in cognitive processes, M1- and M2-muscarinic acetylcholine receptors, choline acetyltransferase, and high-affinity choline uptake as well as benzodiazepine receptors were studied in selected cortical regions (frontal, temporal, somatosensory, visual, piriform cortex), in amygdala, hippocampus, and in the nucleus basalis of Meynert from adult rats, which received at the age of 25 days a single dosage of 11 mg/kg, s.c. kainic acid. Kainic acid treatment of prepubescent rats resulted in the adult brain in decreased numbers of the total population of muscarinic acetylcholine receptors in frontal (by 27%, P < 0.05, two-tailed Student's t-test), temporal (22%, P < 0.05), and piriform cortex (31%, P < 0.05), in amygdala (24%, P < 0.05), and nucleus basalis of Meynert (39%, P < 0.02). The binding affinity was unchanged in these regions. However, in the hippocampus, the dissociation constant was significantly increased following kainic acid treatment, while the receptor numbers remained unchanged. Analysis of competition experiments with the muscarinic antagonist pirenzepine revealed that the reductions of muscarinic acetylcholine receptors in the cortical regions after kainic acid treatment are mainly due to decreases in the number of the muscarinic M1-receptor subtype. In the amygdala, the numbers of both M1- and M2-receptor subtypes are reduced.(ABSTRACT TRUNCATED AT 250 WORDS)     

Age-related difference in cardiac adaptation to chronic hypertension in rats,with and without nifedipine treatement

Three myosin isozymes, V1 ( MHC = Myosin Heavy Chain gene), V2 ( MHC) and V3 ( MHC) that are identified in the cardiac ventricles of most mammals have been shown to shift to a V3 predominance pattern during cardiac growth and in response to left ventricular pressure overload, and to V1 predominance following anti hypertensive treatment. This study examined whether long-term hypertension impairs the ability of the adult heart to restructure myosin isozyme proportions. Using pyrophosphate gel electrophoresis, we studied proportions of cardiac myosin isozymes (V1 and V3) in young (16 weeks) and adult (36 weeks) spontaneously hypertensive rats (SHR), and following 12 weeks of nifedipine (N) treatment in age-matched SHR rats (SHR-N). The values of V1 and V3 myosin isozymes were derived by adding half of the value of V2 to each isozyme proportion. The V3 proportion in the young SHR control (SHR-C) group (49%) was 34% higher (p < 0.05) than in the young Wistar Kyoto control (WKY-C) group (37%). However, the proportion was similarly high, though not statistically significant, in both the adult SHRC (73%) and WKY-C (71%) groups. The proportion in the young SHR-N group (29%) was 41% lower (p < 0.05) than in the young SHR-C group (49%), and the proportion in the adult SHR-N group (47%) was 34% lower (p < 0.05) than in the adult SHR-C group (73%). The ratio of left ventricular weight to body weight (LVW/BW), which determines left ventricular hypertrophy (LVH), was higher in both young and adult SHR-C (26%, p < 0.05, and 42%, p < 0.05, respectively) than in WKY-C groups. The mean LVW/BW was 27% (p lt; 0.05) greater in adult than in young SHR-C rats. The LVW/BW in both age groups of treated SHR-N was similar to that in age matched WKY-C rats. Conclusion: Our study showed that a rise in the V3 level occurs in young hypertensive rats, but no rise occurs in the V3 level in adult hypertensive rats. High blood pressure seems to contribute to the high V3 level in young hypertensive rats, but in adult hypertensive rats, high blood pressure does not accentuate the V3 rise already acquired due to the aging process. Nifedipine treatment in both young and adult hypertensive rats prevented the V3 rise due to hypertension and to the aging process. This effect of nifedipine seems to be through its antihypertensive action.     

Intracardiac expression of neutral endopeptidase

Neutral endopeptidase (NEP), a proteolytic enzyme, is known to degrade several peptides which control cardiovascular homeostasis. This is a preliminary study of the pattern of the intracardiac regional expression of the NEP gene in the normal heart, and the age-related changes in this expression in the cardiac regions. The relative abundance of NEP mRNA was determined by RT-PCR in the right atrium (RA), right ventricle (RV), left atrium (LA), left ventricle (LV) and interventricular septum (IVS) in 2-month-old (young) and 12-month-old (advanced-age adult) Wistar Kyoto (WKY) rats. The NEP gene was expressed in all 5 cardiac regions in both age groups. In young rats, the NEP expression level was lowest in the RA; this level was significantly lower than in the septum (p > 0.05). In the advanced-age adult rats, the level was lowest in the LA; this level also was significantly lower than in the septum (p > 0.05). The level in the RA in advanced-age rats was higher than that in the young rats (p < 0.01), but the levels in other regions were not significantly different between the young rats and advanced-age adult rats. Our study showed that the NEP gene was expressed in all cardiac regions of both young rats and advanced-age adult rats. However, the regional distribution of the gene was different in each age group. The region-specific expression of the NEP gene and the age-related regional changes in the expression may be due to the structural and functional characteristics of the various regions.