Histaminerjik sistem, beyinde posterior hipotalamusun tuberomammilary merkezinden başlayarak merkezi sinir sistemine dağılır. Bu araştırmada histaminin hippocampusun CA1 bölgesi üzerindeki etkisi sıçan beyni canlı kesitlerinde çalışılmıştır. Histaminin bilinen reseptörlerinin etkileri bir kez daha gözlenmiş, bunun yanısıra N-Methyl D-Aspartik asit (NMDA) akımı üzerinde bağımsız, yeni etkisi gösterilmiştir. Bu etki,
1. Hippocampal kesitlerde magnezyum iyonunun olmadığı ortamda NMDA reseptörü kaynaklı epileptiform alan aktivitesi ile
2. Hippocampal ince kesitlerde, NMDA akımının uyarıcı sinaptik iletimi üzerinde patch-clamp yöntemi ile gösterilmiştir.
Alan aktivitesi yanıtı Schaffer collateral-commisural sinir bağı uyarımı ile CA1 stratum pyramidale ve stratum radiatum bölgelerinden kayıt edilmiştir. Sıçan beyni hippocampal kesitlerinin CA1 bölgesinde, glutamik asitin salgılanmasıyla oluşan NMDA akımı üzerinde histaminin oluşturduğu etki patch-clamp tight seal whole cell kayıt alma yöntemi ile hücre akımları, kayıt elektrodu ve hücre zarı arasında oluşan yüksek dirençli etkileşim ile düşük gürültü ortamında kayıt edilmektedir. Beyin kesitleri yapay beyin sıvısı banyosu içinde 250mm kalınlığında alınıp karbojen (yüzde 95 O2, yüzde 5 CO2 karışımı) akışı destekli beyin sıvısı içinde on saat yaşatılabilmektedir. Bu çalışmada, histaminin NMDA reseptörlerinden oluşan piramidal hücre akımını hidrojen iyon konsantrasyonuna bağlı olarak etkilediği gösterilmiştir. Histamin NMDA reseptör kaynaklı olmayan (non-NMDA) akımı değiştirmemiştir. Histamin, NMDA akımını pH 7.2'de arttırırken pH 7.6'da azaltmıştır. Histaminin NMDA akımı üzerindeki etkisi klasik H1, H2 ve H3 reseptörlerinden kaynaklanmamaktadır. Gözlenen bu etki NMDA reseptörü ile polyaminlerin etkileşmesine benzemektedir. Bu çalışmadan elde edilen sonuç, izole piramidal hücreden kayıt edilen konsantrasyon-clamp deneyleri sonucu ile uyumludur. Histaminin NMDA akımı üzerindeki etkisi fizyolojik ve patofizyolojik ortamlarda oluşabilecek olayları vurgulamaktadır. Bu çalışmada gösterildiği gibi histaminin etkisini büyük ölçüde etkileyebilen pH değerindeki küçük sapmalar, yoğun sinir sistemi aktivitesi, tetanik uyarı ve anoxia şartlarında oluşabilir. Bu şartlar altında da beyindeki histaminerjik sistemin etki hedefi sinaptik plastisite aktiviteleri olacaktır.
The histaminergic system in the brain emanates from the tuberomammilary nucleus of the posterior hypothalamus and projects to the whole central nervous system. In this research, the effect of histamine was investigated in the CA1 region of the hippocampus of rats in vitro.The enhancement of activity mediated by classical histamine receptors has been confirmed and a new independent action of histamine on N-Methyl D-Aspartatic acid (NMDA) receptors has been described in,
1. hippocampal slices as an epileptiform field activity in magnesium free medium, representing NMDA receptor mediated extracellular activity ,
2. thin hippocampal slices with patch-clamp technique as an effect on the NMDA components of excitatory postsynaptic currents.
The extracellular activity evoked by the stimulation of Schaffer collateral-commisural pathway was recorded from CA1 stratum pyramidale and stratum radiatum The NMDA components of excitatory currents evoked by glutamate in the CA1 region of rat hippocampal slices and their modification by histamine were investigated by using the patch-clamp tight seal whole cell recording technique. In this study it has been found that histamine has no influence on non-NMDA current but effects the NMDA current in a pH dependent way. Histamine potentiates the NMDA current at pH 7.2 while it depresses the current at pH 7.6. The NMDA current modification by histamine was not mediated by the activation of known histamine receptors of H1, H2 or H3 type. The effect resembles the known interaction of polyamines with the NMDA receptor-ionophore complex. This work is consistent with the concentration clamp experiments in isolated hippocampal pyramidal cells and emphasizes the physiological and pathophysiological implications: Slight shifts in pH as shown here to profoundly influence the histamine action occur locally during intense nervous activity, tetanic stimulation and globally during anoxia. The modulating action of the histaminergic system in the brain will be specifically targeted towards plasticity under these conditions.
Atrial fibrillation/flutter is a heart rhythm disorder (arrhythmia). It usually involves a rapid heart rate, in which the upper heart chambers (atria) are stimulated to contract in a very disorganized and abnormal manner.
Causes, incidence, and risk factors
Arrhythmias are caused by a disruption of the normal ********ing of the electrical conduction system of the heart. Normally, the atria and ventricles contract in a coordinated manner.
In atrial fibrillation and flutter, the atria are stimulated to contract very quickly and differently from the normal activity originating from the sinoatrial node. This results in ineffective and uncoordinated contraction of the atria in atrial fibrillation, and in a peculiarly organized contraction pattern in atrial flutter.
The condition can be caused by impulses which are transmitted to the ventricles in an irregular fashion or by some impulses failing to be transmitted. This makes the ventricles beat irregularly, which leads to an irregular (and usually fast) pulse in atrial fibrillation.
In atrial flutter, however, the ventricles may beat rapidly, but regularly. If the atrial fibrillation/flutter is part of a condition called sick sinus syndrome, the sinus node may not work properly, and the heart rate may alternate between slow and fast. The result may be not enough blood to meet the needs of the body.
Underlying causes of atrial fibrillation and flutter include dys******** of the sinus node (the "natural pacemaker" of the heart) and a number of heart and lung disorders, including coronary artery disease, rheumatic heart disease, mitral valve disorders, pericarditis, and others.
Hyperthyroidism, hypertension, and other diseases can cause arrhythmias, as can recent heavy alcohol use (binge drinking). Some cases of atrial fibrillation or flutter occur in the setting of a heart attack or soon after surgery on the heart.
Atrial fibrillation can affect both men and women. The pr*******ence of atrial fibrillation increases with age and varies from 1 case out of 200 persons for people younger than 60 years, to almost 9 cases out of 100 persons for people over 80 years.
Symptoms
Sensation of feeling heart beat (palpitations)
Pulse may feel rapid, racing, pounding, fluttering, or it can feel too slow
Pulse may feel regular or irregular
Dizziness, light-headedness
Fainting
Confusion
Fatigue
Shortness of breath
Breathing difficulty, lying down
Sensation of tightness in the chest
Note: Symptoms may begin or stop suddenly.
Signs and tests
Listening to the heart with a stethoscope shows fast heart beat. The pulse may feel rapid, irregular, or both. The normal heart rate is 60 to 100, but in atrial fibrillation/flutter the heart rate may be 100 to 175. Blood pressure may be normal or low.
An ECG shows atrial fibrillation or atrial flutter. Continuous ambulatory cardiac monitoring -- Holter monitor (24 hour test) -- may be necessary because the condition is often sporadic (occurring at some times but not others).
Tests to determine the presence of underlying heart diseases may include:
Echocardiogram
Nuclear imaging tests
Coronary angiography
Exercise treadmill ECG
Electrophysiologic study (EPS) may be needed in some cases
Treatment
In certain cases, atrial fibrillation may require emergency treatment to convert the arrhythmia to normal (sinus) rhythm. This treatment may involve either with electrical cardioversion or intravenous (IV) drugs such as dofetilide, amiodarone, or ibutilide.
Long-term treatment varies depending on the cause of the atrial fibrillation or flutter. Medication may include beta-blockers, calcium channel blockers, digitalis or other medications (such as anti-arrhythmic drugs), which slow the heartbeat or the conduction of the impulse from the atria to the ventricles.
Blood thinners, such as heparin or Coumadin, may be given to reduce the risk of a thromboembolic event such as a stroke.
Some selected patients with atrial fibrillation, rapid heart rates, and intolerance to medication may require a catheter procedure on the atria called radiofrequency ablation.
For some patients with atrial flutter, radiofrequency ablation is the current treatment of choice. Some patients with atrial fibrillation and rapid heart rates may need the radiofrequency ablation done not on the atria, but directly on the AV junction (i.e., the area that normally filters the impulses coming from the atria before they proceed to the ventricles).
Ablation of the AV junction leads to complete heart block. Treatment for this condition requires a permanent pacemaker.
Expectations (prognosis)
The disorder is usually controllable with treatment. The natural tendency of atrial fibrillation, however, is to become a chronic condition.
Complications
A pulse that is too rapid or too slow may reduce the amount of blood the heart can pump and lead to syncope (fainting).
Emboli to the brain (stroke) or elsewhere -- rare, but often treated with anticoagulation to reduce this risk.
Calling your health care provider
Call your health care provider if symptoms indicate atrial fibrillation or flutter may be present.
Prevention
Follow the health care provider's recommendations for the treatment of underlying disorders. Avoid binge drinking.
Alternative names
Ear infection; Infection - ear
Definition
Otitis is a general term for infection or inflammation of the ear.
Causes, incidence, and risk factors
Otitis can affect the inner or outer parts of the ear. The condition is classified according to whether it occurs suddenly and for a short time (acute) or repeatedly over a long period of time (chronic).
Specific types of ear infection include:
Otitis externa - acute
Otitis externa - chronic
Otitis externa - malignant
Otitis media - acute
Otitis media -chronic
Otitis media - with effusion
Symptoms
Any of the following symptoms may develop with otitis:
Earache
Itching or other discomfort in the ear or ear canal
Drainage from the ear
Hearing loss
Ear noise or buzzing
Fever
Chills
Irritability
Malaise (feeling of general illness)
Nausea, vomiting
Diarrhea
Signs and tests
Your health care provider will examine your ears and use an instrument called an otoscope to look inside them. Signs that may be seen during an exam include a red, painful outer ear or redness or swelling of the eardrum.
Treatment
Treatment may include antibiotics, depending on the suspected cause of the infection.
Expectations (prognosis)
Most types of ear infection respond well to treatment. If there is no improvement after 3 days, your doctor may recommend a different antibiotic. In certain uncomplicated cases, a child over 6 months of age who does not have a fever may not be given medicine unless the infection continues after 48-72 hours. For more specific outlooks and recommendations, see the following articles:
Ear infection - acute
Ear infection - chronic
Calling your health care provider
Call for an appointment with your health care provider if you develop symptoms of otitis.
