Lipopolysaccharides (LPS) are large molecules consisting of a lipid and a polysaccharide that are bacterial toxins. They are composed of an O-antigen, an outer core, and an inner core all joined by a covalent bond, and are found in the outer membrane of Gram-negative bacteria. Today, the term endotoxin is often used synonymously with LPS, although there are a few endotoxins (in the original sense of toxins that are inside the bacterial cell that are released when the cell disintegrates) that are not related to LPS, such as the so-called delta endotoxin proteins produced by Bacillus thuringiensis.Lipopolysaccharides can have substantial impacts on human health, primarily through interactions with the immune system. LPS is a potent activator of the immune system and pyrogen (agent that causes fever). In severe cases, LPS can play a role in causing septic shock. In lower levels and over a longer time period, there is evidence LPS may play an important and harmful role in autoimmunity, obesity, depression, and cellular senescence. Discovery
The toxic activity of LPS was first discovered and termed endotoxin by Richard Friedrich Johannes Pfeiffer. He distinguished between exotoxins, toxins that are released by bacteria into the surrounding environment, and endotoxins, which are toxins "within" the bacterial cell and released only after destruction of the bacterial outer membrane.
Middle cerebral artery syndrome is a condition whereby the blood supply from the middle cerebral artery (MCA) is restricted, leading to a reduction of the function of the portions of the brain supplied by that vessel: the lateral aspects of frontal, temporal and parietal lobes, the corona radiata, globus pallidus, caudate and putamen. The MCA is the most common site for the occurrence of ischemic stroke.Depending upon the location and severity of the occlusion, signs and symptoms may vary within the population affected with MCA syndrome. More distal blockages tend to produce milder deficits due to more extensive branching of the artery and less ischemic response. In contrast, the most proximal occlusions result in widespread effects that can lead to significant cerebral edema, increased intracranial pressure, loss of consciousness and could even be fatal. In such occasions, mannitol (osmotic diuretic) or hypertonic saline are given to draw fluid out of the edematous cerebrum to minimise secondary injury. Hypertonic saline is better than mannitol, as mannitol being a diuretic will decrease the mean arterial pressure and since cerebral perfusion is mean arterial pressure minus intracranial pressure, mannitol will also cause a decrease in cerebral perfusion. Contralateral hemiparesis and hemisensory loss of the face, upper and lower extremities is the most common presentation of MCA syndrome. Lower extremity function is more spared than that of the faciobrachial region. The majority of the primary motor and somatosensory cortices are supplied by the MCA and the cortical homunculus can, therefore, be used to localize the defects more precisely.