New York, Jan 13 (IANS) Researchers have discovered that SARS-CoV-2 can directly infect the central nervous system and have begun to unravel some of the virus's effects on brain cells.The study, that used both mouse and human brain tissue, indicates that SARS-CoV-2 can affect many other organs in the body, including, in some patients, the central nervous system, where infection is associated with a variety of symptoms ranging from headaches and loss of taste and smell to impaired consciousness, delirium, strokes and cerebral haemorrhage."Understanding the full extent of viral invasion is crucial to treating patients, as we begin to try to figure out the long-term consequences of Covid-19, many of which are predicted to involve the central nervous system," said researcher Akiko Iwasaki, a professor at Yale University.For the study, published on Wednesday in the Journal of Experimental Medicine (JEM), the team analysed the ability of SARS-CoV-2 to invade human brain organoids (miniature 3D organs grown in the lab from human stem cells). The researchers found that the virus was able to infect neurons in these organoids and use the neuronal cell machinery to replicate. The virus appears to facilitate its replication by boosting the metabolism of infected cells, while neighbouring, uninfected neurons die as their oxygen supply is reduced.SARS-CoV-2 enters lung cells by binding to a protein called ACE2, but whether this protein is present on the surface of brain cells is unclear. The team determined that the ACE2 protein is, in fact, produced by neurons and that blocking this protein prevents the virus from human brain organoids.SARS-CoV-2 was also able to infect the brains of mice genetically engineered to produce human ACE2, causing dramatic alterations in the brain's blood vessels that could potentially disrupt the organ's oxygen supply, the team said. Central nervous system infection was much more lethal in mice than infections limited to the lungs, they added.The researchers also analysed the brains of three patients who succumbed to Covid-19. SARS-CoV-2 was detected in the cortical neurons of one of these patients, and the infected brain regions were associated with ischemic infarcts in which decreased blood supply causes localized tissue damage and cell death. Microinfarcts were detected in the brain autopsy of all three patients.--IANSvc/vd
New York- Scientists have given physiological evidence that a pervasive neuromodulation system - a group of neurons that regulate the functioning of more specialized neurons - strongly influences sound processing in an important auditory region of the brain.
The neuromodulator -- acetylcholine -- may even help the main auditory brain circuitry distinguish speech from noise.
"While the phenomenon of these modulators' influence has been studied at the level of the neocortex, where the brain's most complex computations occur, it has rarely been studied at the more fundamental levels of the brain," said study author R Michael Burger from the Lehigh University in the US.
The study, published in the JNeurosci: The Journal of Neuroscience, will likely bring new attention in the field to the ways in which circuits like this, widely considered a 'simple' one, are in fact highly complex and subject to modulatory influence like higher regions of the brain.
The team conducted electrophysiological experiments and data analysis to demonstrate that the input of the neurotransmitter acetylcholine, a pervasive neuromodulator in the brain, influences the encoding of acoustic information by the medial nucleus of the trapezoid body (MNTB), the most prominent source of inhibition to several key nuclei in the lower auditory system.
MNTB neurons have previously been considered computationally simple, driven by a single large excitatory synapse and influenced by local inhibitory inputs.
The team demonstrated that in addition to these inputs, acetylcholine modulation enhances neural discrimination of tones from noise stimuli, which may contribute to processing important acoustic signals such as speech.
Additionally, they describe novel anatomical projections that provide acetylcholine input to the MNTB.
Burger studies the circuit of neurons that are "wired together" in order to carry out the specialized function of computing the locations from which sounds emanate in space.
He described neuromodulators as broader, less specific circuits that overlay the more highly-specialized ones.
"This modulation appears to help these neurons detect faint signals in noise. You can think of this modulation as akin to shifting an antenna's position to eliminate static for your favourite radio station," Burger said.
"In this paper, we show that modulatory circuits have a profound effect on neurons in the sound localization circuitry, at the very low foundational level of the auditory system," the authors wrote. (IANS)