Effect of angiotensin II on striatal dopamine release in the spontaneous hypertensive rat

Losartan enhances cognitive and structural neuroplasticity impairments in spontaneously hypertensive rats

Hypertension is a risk factor for vascular dementia, which is the second most prevalent type of dementia, just behind Alzheimer's disease. This highlights the brain vulnerability due to hypertension, which may increase with aging. Thus, studying how hypertension affects neural cells and behavior, as well as the effects of antihypertensives on these alterations, it's important to understand the hypertension consequences in the brain. The spontaneously hypertensive rat (SHR) has been useful for the study of hypertension alterations in diverse organs, including the brain. Thus, we studied the losartan effects on cognitive and structural neuroplasticity impairments in SHR of 10 months of age. In the first instance, we evaluated the losartan effects on exploratory behavior and novel object recognition test (NORT) in the SHR. Then, we assessed the density and morphology of dendritic spines of pyramidal neurons from the prefrontal cortex (PFC) layers 3 and 5, and CA1 of the dorsal Hp (dHp). Our results indicate that in SHR, losartan treatment (2 months, 15 mg/Kg/day) reduces high blood pressure to age-matched vehicle-treated Wistar-Kyoto (WKY) rat levels. Moreover, losartan improved long-term memory in SHR compared with age-matched vehicle-treated WKY rats, without affecting the locomotor and anxiety behaviors. The behavioral improvement of the SHR can be associated with the increase in the number of dendritic spines and the mushroom spine population in the PFC and the dHp. In conclusion, losartan enhances cognitive impairments by controlling the high blood pressure and improving neuroplasticity in animals with chronic hypertension.

The Renin-Angiotensin System in Huntington's Disease: Villain or Hero?

Huntington’s Disease (HD) is an autosomal dominant, progressive neurodegenerative disorder characterized by severe symptoms, including motor impairment, cognitive decline, and psychiatric alterations. Several systems, molecules, and mediators have been associated with the pathophysiology of HD. Among these, there is the Renin-Angiotensin System (RAS), a peptide hormone system that has been associated with the pathology of neuropsychiatric and neurodegenerative disorders. Important alterations in this system have been demonstrated in HD. However, the role of RAS components in HD is still unclear and needs further investigation. Nonetheless, modulation of the RAS components may represent a potential therapeutic strategy for the treatment of HD.

Brain Angiotensin II AT1 receptors are involved in the acute and long-term amphetamine-induced neurocognitive alterations

RATIONALE

Angiotensin II, by activation of its brain AT1-receptors, plays an active role as neuromodulator in dopaminergic transmission. These receptors participate in the development of amphetamine-induced behavioral and dopamine release sensitization. Dopamine is involved in cognitive processes and provides connectivity between brain areas related to these processes. Amphetamine by its mimetic activity over dopamine neurotransmission elicits differential responses after acute administration or after re-exposure following long-term withdrawal periods in different cognitive processes.

OBJECTIVE

The purpose of this study is to evaluate the AT1-receptor involvement in the acute and long-term amphetamine-induced alterations in long-term memory and in cellular-related events.

METHODS

Male Wistar rats (250-300 g) were used in this study. Acute effects: Amphetamine (0.5/2.5 mg/kg i.p.) was administered after post-training in the inhibitory avoidance (IA) response. The AT1-receptor blocker Losartan was administered i.c.v. before a single dose of amphetamine (0.5 mg/kg i.p.). Long-term effects: The AT1-receptors blocker Candesartan (3 mg/kg p.o.) was administered for 5 days followed by 5 consecutive days of amphetamine (2.5 mg/kg/day, i.p.). The neuroadaptive changes were evidenced after 1 week of withdrawal by an amphetamine challenge (0.5 mg/kg i.p.). The IA response, the neuronal activation pattern, and the hippocampal synaptic transmission were evaluated.

RESULTS

The impairing effect in the IA response of post-training acute amphetamine was partially prevented by Losartan. The long-term changes induced by repeated amphetamine (resistance to acute amphetamine interference in the IA response, neurochemical altered response, and increased hippocampal synaptic transmission) were prevented by AT1-receptors blockade.

CONCLUSIONS

AT1-receptors are involved in the acute alterations and in the neuroadaptations induced by repeated amphetamine associated with neurocognitive processes.

Effects of AT1 receptor antagonism on kainate-induced seizures and concomitant changes in hippocampal extracellular noradrenaline, serotonin, and dopamine levels in Wistar-Kyoto and spontaneously hypertensive rats

In the management of epilepsy, AT1 receptor antagonists have been suggested as an additional treatment strategy. A hyperactive brain angiotensin (Ang) II system and upregulated AT1 receptors are implicated in the cerebrovascular alterations in a genetic form of hypertension. Uncontrolled hypertension could also, in turn, be a risk factor for a seizure threshold decrease and development of epileptogenesis. The present study aimed to assess the effects of the selective AT1 receptor antagonist ZD7155 on kainic acid (KA)-induced status epilepticus (SE) development and accompanying changes in the hippocampal extracellular (EC) neurotransmitter levels of noradrenaline (NAD), serotonin (5-HT), and dopamine (DA) in spontaneously hypertensive rats (SHRs) and their parent strain Wistar-Kyoto (WKY) rats, since monoamines are well-known neurotransmitters involved in mechanisms of both epilepsy and hypertension. Status epilepticus was evoked in freely moving rats by a repetitive intraperitoneal (i.p.) administration of KA in subconvulsant doses. In the treatment group, ZD7155 (5mg/kg i.p.) was coadministered with the first KA injection. Spontaneously hypertensive rats exhibited higher susceptibility to SE than WKY rats, but the AT1 receptor antagonist did not alter the development of SE in SHRs or in WKY rats. In vivo microdialysis demonstrated significant KA-induced increases of the hippocampal NAD and DA levels in SHRs and of NAD, 5-HT, and DA in WKY rats. Although SHRs developed more severe seizures while receiving a lower dose of KA compared to WKY rats, AT1 receptor antagonism completely prevented all KA-induced increases of hippocampal monoamine levels in both rat strains without affecting seizure development per se. These results suggest a lack of direct relationship between KA-induced seizure susceptibility and adaptive changes of hippocampal NAD, 5-HT, and DA levels in the effects of ZD7155 in WKY rats and SHRs.

Renin-Angiotensin system and sympathetic neurotransmitter release in the central nervous system of hypertension

Many Studies suggest that changes in sympathetic nerve activity in the central nervous system might have a crucial role in blood pressure control. The present paper discusses evidence in support of the concept that the brain renin-angiotensin system (RAS) might be linked to sympathetic nerve activity in hypertension. The amount of neurotransmitter release from sympathetic nerve endings can be regulated by presynaptic receptors located on nerve terminals. It has been proposed that alterations in sympathetic nervous activity in the central nervous system of hypertension might be partially due to abnormalities in presynaptic modulation of neurotransmitter release. Recent evidence indicates that all components of the RAS have been identified in the brain. It has been proposed that the brain RAS may actively participate in the modulation of neurotransmitter release and influence the central sympathetic outflow to the periphery. This paper summarizes the results of studies to evaluate the possible relationship between the brain RAS and sympathetic neurotransmitter release in the central nervous system of hypertension.

Genetic polymorphism of angiotensin I-converting enzyme (ACE), but not angiotensin II type I receptor (ATr1), has a gender-specific role in panic disorder

AIMS

Angiotensins were shown to have some role in the development of panic disorder (PD). In this study, we aimed to determine the frequency of polymorphisms in two angiotensin-related genes, angiotensin I-converting enzyme (ACE) and angiotensin II type I receptor (ATr1), in a sample of Turkish patients with PD and to evaluate their association with PD development.

METHODS

Polymerase chain reaction and restriction fragment length polymorphism was used to analyze ATr1 A1166C polymorphism, and only polymerase chain reaction was used to analyze functional ACE insertion/deletion polymorphism in 123 patients with PD and in 169 similarly aged disease-free controls.

RESULTS

 There was no significant difference in the genotype distribution between PD patients and controls for each polymorphism (P>0.05). Allele frequency of ACE insertion/deletion was borderline statistically significant between the groups (P=0.055; odds ratio: 1.39; 95% confidence interval: 0.99-1.95), and allele frequency of ATr1 A1166C was not significantly different between the groups (P=0.32; odds ratio: 0.81; 95% confidence interval: 0.53-1.22).

CONCLUSION

This study suggests that polymorphisms of ACE I/D and ATr1 A1166C are not associated with risk of PD in Turkish patients. However, in ACE insertion/deletion polymorphism, the insertion allele was found to be more frequent in the male subgroup of patients (χ²=4.61, P=0.032) than in controls, suggesting a potential male-specific role of the less active ACE insertion allele in the pathogenesis of PD.

Associations between the angiotensin-converting enzyme insertion/deletion polymorphism and monoamine metabolite concentrations in cerebrospinal fluid

Angiotensin II has been suggested to influence central dopamine and serotonin turnover. Since the angiotensin-converting enzyme (ACE) plays a key role in angiotensin regulation by converting inactive angiotensin I to active angiotensin II, we hypothesised that the functional insertion/deletion (I/D) polymorphism in the ACE gene, which has previously been suggested to be associated with, depression and panic disorder, may influence monoamine activity. A well-established technique for assessing brain monoamine turnover in humans is to measure concentrations of monoamine metabolites in the cerebrospinal fluid (CSF). We thus investigated possible associations between the ACE I/D polymorphism and CSF monoamine metabolite concentrations in a population of healthy male subjects. After having found such an association between the ACE I/D polymorphism and CSF levels of the dopamine metabolite homovanillic acid and the serotonin metabolite 5-hydroxyindoleacetic acid in this sample, I carriers displaying lower levels, we tried to replicate this observation in a population of violent male offenders from which also both CSF and DNA were available. Also in this sample, the same associations were found. Our results suggest that the ACE I/D polymorphism may play a role in the modulation of serotonergic and dopaminergic turnover in men.

Renin enhancer is critical for control of renin gene expression and cardiovascular function

The important cardiovascular regulator renin contains a strong in vitro enhancer 2.7 kb upstream of its gene. Here we tested the in vivo role of the mouse Ren-1c enhancer. In renin-expressing As4.1 cells stably transfected with Ren-1c promoter with or without enhancer, expression of linked beta-geo reporter, stable expression, and colony formation were dependent on the presence of the enhancer. We then generated mice carrying a targeted deletion of the enhancer (REKO mice) and found marked depletion of renin in renal juxtaglomerular and submandibular ductal cells, as well as hyperplasia of macula densa cells. Plasma creatinine was increased, but electrolytes were normal. Male REKO mice implanted with telemetry devices had 9 +/- 1 mm Hg lower mean arterial pressure (p < 0.001), which was partly normalized by a high NaCl diet. Locomotor activity was lower, and baroreflex sensitivity was normal. Markedly reduced mean arterial pressure variability in the midfrequency band indicated a contribution of reduced sympathetic vasomotor tone to the hypotension. In conclusion, the renin enhancer is critical for renin gene expression and physiological sequelae, including response to alteration in salt intake. The REKO mouse may be useful as a low renin expression model.

Enhanced activity of central adrenergic neurons in two-kidney, one clip hypertension in Sprague–Dawley rats

The present study was aimed at investigating whether two-kidney, one clip (2K1C) hypertension is associated with an enhanced central adrenergic activity. Rats were made 2K1C hypertensive, and the expression of Fos-like immunoreactivity (FLI) and phenylethanalamine N-methyltransferase (PNMT)-immunoreactivity was determined in the brain areas related to the cardiovascular regulation. In 2K1C hypertension, the basal Fos-immunoreactivity was significantly increased in rostral ventrolateral medulla (RVLM), paraventricular nucleus (PVN), and supraoptic nucleus (SON). PNMT-immunoreactivities were noted in RVLM, but not in PVN or SON. Intracerebroventricular administration of angiotensin II (AII) markedly increased Fos-immunoreactivities, the degree of which was greater in hypertension. Furthermore, AII increased the ratio of PNMT-positive/Fos-positive neurons in RVLM in hypertension. It is suggested that the responsiveness to AII of the central adrenergic system is enhanced in 2K1C hypertension.