Medulla oblongata

Hosli, L. Haas, H. L. (1971). Effects of histamine, histidine and imidazole acetic acid on neurones of the medulla oblongata of the cat. Experientia 27, 1311-12. 

Six groups of cell bodies of noradrenergic neurons are clustered in the medulla oblongata, pons and midbrain. They are considered part of the reticular formation and extend from the spinal cord to the lateral pontine reticular formation. One of the best-studied of these groups is the locus ceruleus (Fig. 12-5), which has many ascending and descending projections from the pons. 

The abdominal vagus and sympathetic nerves are the most important afferent inputs involved in vomiting induced by chemotherapy and radiation [31]. The input from vestibular nerves and the cerebellum plays an important role in the motion disease [52]. The afferent inputs from vagal, trigeminal and glossopharyngeal nerves terminate eventually in the nucleus solitarius tract located in the medulla oblongata which has neuronal connections with other medullary areas involved in emesis, for example, area postrema [53]. 

Figure 18.10 Characteristic inclusion bodies in neurodegenerative diseases, all labelled with antibodies (except (d)) as indicated, (a) and (b) HD intranuclear inclusion labelled for ubiquitin and huntingtin (cerebral cortex), (c) and (d) AD neuritic plaque labelled with AP (cerebral cortex) and silver stained, (e) and (f) PD, Lewy bodies labelled for ot-synuclein and phosphorylated a-synuclein (substantia nigra), (g) and (h) ALS labelled with ubiquitin and neurofilaments (medulla oblongata). (From Ross and Poirier, 2004. Reproduced by permission of Nature Publishing Group.)...

Alkaloids such as boldine, codeine, narceine and morphine are active factors in their receptors. Boldine has morphine-like properties and is active on opioid receptors. It may be used to treat stomach disorders and as metabolic stimulant. As it is similar to morphine, boldine can also be considered in the possible development of treatments for narcotic dependence. Codeine also binds to opiate receptors, and specifically functions to reduce bronchial secretions. Codeine can also be used as a cough suppressant when acting on the centre of the medulla oblongata and as a sedative agent. 

Another, new group of compounds act via the same central mode of action the imidazoline receptor agonists. The central regulation of sympathetic tone in the medulla oblongata is sensitive not only to 2-adrenoceptors but to so called imidazoline receptors as well. Two drugs with high affinity towards... 

The injection of a vasoconstrictor, which causes an increase in mean arterial blood pressure, results in activation of the baroreceptors and increased neural input to the cardiovascular centers in the medulla oblongata. The reflex compensation for the drug-induced hypertension includes an increase in parasympathetic nerve activity and a decrease in sympathetic nerve activity. This combined alteration in neural firing reduces cardiac rate and force and the tone of vascular smooth muscle. As a consequence of the altered neural control of both the heart and the blood vessels, the rise in blood pressure induced by the drug is opposed and blunted. 

Atropine can be useful in patients with carotid sinus syncope. This condition results from excessive activity of afferent neurons whose stretch receptors are in the carotid sinus. By reflex mechanisms, this excessive afferent input to the medulla oblongata causes pronounced bradycardia, which is reversible by atropine. 

It is generally agreed that clonidine acts in the same general area in the brain as does a-methyldopa, that is, somewhere in the medulla oblongata. The principal difference between clonidine and a-methyldopa is that clonidine acts directly on a2-receptors, whereas a-methyldopa first must be converted by synthetic enzymes to a-methylnorepinephrine. 

The most common peripheral side effects are anorexia, nausea, and vomiting (likely due to dopamine s stimulation of the chemoreceptor trigger zone of the area postrema in the medulla oblongata). 

These events are coordinated by the emetic center, which lies within the lateral reticular formation of the medulla oblongata close to the respiratory and salivary centers. Stimulation of the emetic center may occur... 

Detach the cerebellum and other neural tissue from the unsectioned portion of the head and examine the midbrain, cerebellum, medulla oblongata, cerebral aqueduct, and fourth ventricle. 

---