Angiotensin-II Modulates GABAergic Neurotransmission in the Mouse Substantia Nigra

Signaling pathways and genetics of brain Renin angiotensin system in psychiatric disorders: State of the art

Along the conventional pathways, Renin-angiotensin system (RAS) plays a key role in the physiology of the CNS and pathogenesis of psychiatric diseases. RAS is a complex regulatory pathway which is composed of several peptides and receptors and comprises two counter-regulatory axes. The classical (ACE1/AngII/AT1 receptor) axis and the contemporary (ACE2/Ang (1-7)/Mas receptor) axis. The genes coding for elements of both axes have been broadly studied. Numerous functional polymorphisms on components of RAS have been identified to serve as informative disease and treatment markers. This review summarizes the role of each peptide and receptor in the pathophysiology of psychiatric disorders (depression, bipolar disorders and schizophrenia), followed by a concise look at the role of genetic polymorphism of the RAS in the pathophysiology of these disorders.

The cannabinoid CB1 receptor interacts with the angiotensin AT2 receptor. Overexpression of AT2-CB1 receptor heteromers in the striatum of 6-hydroxydopamine hemilesioned rats

It is of particular interest the potential of cannabinoid and angiotensin receptors as targets in the therapy of Parkinson's disease (PD). While endocannabinoids are neuromodulators that act through the CB₁ and CB₂ cannabinoid receptors, the renin angiotensin-system is relevant for regulation of the correct functioning of several brain circuits. Resonance energy transfer assays in a heterologous system showed that the CB₁ receptor (CB₁R) can directly interact with the angiotensin AT₂ receptor (AT₂R). Coactivation of the two receptors results in increased G_i-signaling. The AT₂-CB₁ receptor heteromer imprint consists of a blockade of AT₂R-mediated signaling by rimonabant, a CB₁R antagonist. Interestingly, the heteromer imprint, discovered in the heterologous system, was also found in primary striatal neurons thus demonstrating the expression of the heteromer in these cells. In situ proximity ligation assays confirmed the occurrence of AT₂-CB₁ receptor heteromers in striatal neurons. In addition, increased expression of the AT₂-CB₁ receptor heteromeric complexes was detected in the striatum of a rodent PD model consisting of rats hemilesioned using 6-hydroxydopamine. Expression of the heteromer was upregulated in the striatum of lesioned animals and, also, of lesioned animals that upon levodopa treatment became dyskinetic. In contrast, there was no upregulation in the striatum of lesioned rats that did not become dyskinetic upon chronic levodopa treatment. The results suggest that therapeutic developments focused on the CB₁R should consider that this receptor can interact with the AT₂R, which in the CNS is involved in mechanisms related to addictive behaviors and to neurodegenerative and neuroinflammatory diseases.

Can chronic therapeutic drug use by the elderly affect Alzheimer’s disease risk and rate of progression?

There is no approved drug capable of halting the progression of the most prevalent neurodegenerative disorders, namely Alzheimer’s disease (AD) and Parkinson’s disease (PD). Current therapeutic strategies focus mainly on the inhibition of the formation of protein aggregates and their deposition in the central nervous system. However, after almost a hundred years, proper management of the disease is still lacking. The fact of not finding effective management tools in the various clinical trials already carried out suggests that new hypotheses and strategies should be explored. Although vast resources have been allocated to the investigation of protein aggregates and the pathophysiology is now better understood, clues to the actual etiology are lacking. It is well known that brain homeostasis is of paramount importance for the survival of neurons. Drugs that target the periphery are often not subject to evaluation for their potential effect on the central nervous system. While acute treatments may be irrelevant, pills used for chronic conditions can be detrimental to neurons, especially in terms of progressive damage leading to a long-term decline in neuronal survival. Due to the lack of advances in the search for a curative treatment for neurodegenerative diseases, and the lack of new hypotheses about their etiology, a novel hypothesis is here proposed. It consists of assuming that the effects of the drugs most commonly used by the elderly, such as antihypertensive, hypoglycemic, and hypocholesterolemic, could have a negative impact on neuronal survival.

Angiotensin II increases respiratory rhythmic activity in the preBötzinger complex without inducing astroglial calcium signaling

Angiotensin II (Ang II) is the primary modulator of the renin-angiotensin system and has been widely studied for its effect on the cardiovascular system. While a few studies have also indicated an involvement of Ang II in the regulation of breathing, very little is known in this regard and its effect on brainstem respiratory regions such as the preBötzinger complex (preBötC), the kernel for inspiratory rhythm generation, has not been investigated yet. This study reports that Ang II temporarily increases phrenic nerve activity in the working heart-brainstem preparation, indicating higher central respiratory drive. Previous studies have shown that the carotid body is involved in mediating this effect and we revealed that the preBötC also plays a part, using acute slices of the brainstem. It appears that Ang II is increasing the respiratory drive in an AT1R-dependent manner by optimizing the interaction of inhibitory and excitatory neurons of the preBötC. Thus, Ang II-mediated effects on the preBötC are potentially involved in dysregulating breathing in patients with acute lung injury.

Mechanistic Insight and Possible Mechanism of Seizure in Covid-19: The Nuances and Focal Points

Coronavirus disease 2019 (COVID-19) is a primary respiratory disease with an alarming impact worldwide. COVID-19 is caused by severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) and presents various neurological symptoms, including seizures. SARS-CoV-2 shows neuroinvasive and neurotropic capabilities through a neuronal angiotensin-converting enzyme 2 (ACE2), which is also highly expressed in both neuronal and glial cells. Therefore, SARS-CoV-2 can trigger neuroinflammation and neuronal hyperexcitability, increasing the risk of seizures. Olfactory neurons could be an exceptional neuronal pathway for the neuroinvasion of respiratory viruses to access the central nervous system (CNS) from the nasal cavity, leading to neuronal injury and neuroinflammation. Although neuronal ACE2 has been widely studied, other receptors for SARS-CoV-2 in the brain have been proposed to mediate viral-neuronal interactions with subsequent neurological squeals. Thus, the objective of the present critical review was to find the association and mechanistic insight between COVID-19 and the risk of seizures.