Inhibitory effect reflex

Opiates activate the chemoreceptor trigger zone in the medulla (by disinhibition) to cause nausea and vomiting, and cough suppression also occurs because of the inhibitory effects of opiates on the brainstem nuclei in the cough reflex pathway. Dextromethorphan is the non-opiate isomer of the opiate levorphanol and is an effective cough suppressant. 

Schneider et al. (S6, S7, S8) have demonstrated that wheat gluten and certain gluten fractions cause inhibition of the isolated small intestine of the rat. In the Trendelenburg preparation, as modified by Biilbring et al. (B21), inhibition of the peristaltic reflex occurred if the material was placed outside the intestine so that it could reach the muscle without traversing the mucous membrane. If it was placed inside the lumen no inhibitory effect was seen. If the gluten or gluten fractions were incubated with rat mucous membrane extract, complete inactivation of the inhibitory effect was obtained. This action of mucous... 

Inhibitory effect on peristaltic reflex in isolated rat intestine + + + — + —... 

Pharmacology Benzonatate anesthetizes stretch receptors in respiratory passages, lungs, and pleura, dampening their activity, and reducing the cough reflex. It has no inhibitory effect on the respiratory center in recommended dosage. Onset of action is... 

Some sedative-hypnotics, particularly members of the carbamate (eg, meprobamate) and benzodiazepine groups, exert inhibitory effects on polysynaptic reflexes and internuncial transmission and at high doses may also depress transmission at the skeletal neuromuscular junction. Somewhat selective actions of this type that lead to muscle relaxation can be readily demonstrated in animals and have led to claims of usefulness for relaxing contracted voluntary muscle in muscle spasm (see Clinical Pharmacology). Muscle relaxation is not a characteristic action of zolpidem, zaleplon, and eszopiclone. 

In spite of the well documented inhibitory effects mediated by H3 receptors in electrically-stimulated preparations of the guinea pig intestine, the activation of this receptor subtype does not influence the reflex-evoked peristaltic motility of the guinea pig ileum (Poli et al., 1997 Poli and Pozzoli 1997). Since this experimental model reproduces peristalsis in quasi-physiologic conditions (Holzer, 1989), H3 receptors apparently play a minor role when compared to that of the other prejunctional receptors, such as a2-adrenoceptors and adenosine Ai-receptors, in the control of the physiologic motility of the gut (Figure 8). 

Shimizu S, Honda M, Tanabe M, et al. Endogenous GABA does not mediate the inhibitory effects of gabapentin on spinal reflexes in rats. J Pharmacol Sci. 2004 94 137-143. 

Some of the commonly used antitussives are listed in Table 26-1. As shown in the table, codeine and similar opiate derivatives suppress the cough reflex by a central inhibitory effect.21,124 Other nonopioid antitussives work by inhibiting the irritant effects of histamine on the respiratory mucosa or by a local anesthetic action on the respiratory epithelium. The primary adverse effect associated with most antitussives is sedation. Dizziness and gastrointestinal upset may also occur. 

Diazepam, the most commonly used benzodiazepine in equine medicine, is used as a component of anesthetic protocols (see Ch. 15) and for the treatment of seizures (see Ch. 9). It induces skeletal muscle relaxation by facilitating the action of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) within the central nervous system. It acts primarily within the spinal cord and exerts inhibitory effects on polysynaptic reflexes and intemuncial neuron transmission. 

The primary mechanism of terbutaline is the stimulation of adenylcyclase, which catalyzes cyclic adenosine monophosphate (AMP) from adenosine triphosphate (ATP). In the liver, buildup of cyclic AMP stimulates glycogenolysis and an increase in serum glucose. In skeletal muscle, this process results in increased lactate production. Direct stimulus of sodium/potassium AT-Pase in skeletal muscle produces a shift of potassium from the extracellular space to the intracellular space. Relaxation of smooth muscle produces a dilation of the vasculamre supplying skeletal muscle, which results in a drop in diastolic and mean arterial pressure (MAP). Tachycardia occurs as a reflex to the drop in MAP or as a result of Pi stimulus. )Si-Adrenergic receptors in the locus ceruleus also regulate norepinephrine-induced inhibitory effects, resulting in agitation, restlessness, and tremor. 

Fig. 1 An airway sensory nerve ending, which can be activated by capsaicin and low-pH stimuii to evoke cough, airway hyperresponsiveness, mucus secretion and choUnergic reflex activation. In inflammatory conditions, these nerves may be sensitised so that they respond at lower thresholds. Opioids, nociceptin and cannabinoid ligands have aU been postulated to exert an inhibitory effect on sensory nerve activation...

Golgi tendon organ reflex. When tension on the tendon becomes extreme, the inhibitory effect from the tendon organ can become so great that it causes a sudden relaxation of the entire muscle. This technique is used in active resistive myofascial therapy. 

The major site of action is the recurrent inhibitory interneurons (Renshaw cells) of the reflex arc in the spinal cord and medulla. Inhibitory effects in the reflex arc are lost leading to uncontrolled excitation of the spinal reflex. 

Strychnine causes loss of the inhibitaty efiect of the intemuncial rreurons in the spinal reflex arc. Loss of these inhibitory effects allows excessive reaction to stimuli. The extensor muscles predominate, leading to rigidity and tetarric seizures that are worsened by stimuli because there is no corrtrol over tire spinal reflexes. 

A second current clinical indication of cannabimimetics is their antiemetic and antinausea effects, especially in cancer chemotherapy patients. These effects are mediated above the level of vomiting reflex and possibly through descending inhibitory connections to the lower brain stem centers (Levitt, 1986). 

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