Ruth Rabinowitz

Autonomic function in mice lacking α5 neuronal nicotinic acetylcholine receptor subunit

Neuronal acetylcholine nicotinic receptors (nAChR) are composed of 12 subunits (α2‐10, β2‐4), of which α3, α5, α7, β2 and β4 subunits are known to exist in the autonomic nervous system (ANS). α5 subunits possess unique biophysical and pharmacological properties. The present study was undertaken to examine the functional role and pharmacological properties of the nAChR α5 subunits in the ANS using mice lacking α5 nAChR subunits (α5‐/‐). These mice grew to normal size showing no obvious physical or neurological deficit. They also showed normality in thermoregulation, pupil size and resting heart rate under physiological conditions. The heart rate and rectal temperature did not differ between α5‐/‐ and wild‐type mice during exposure to cold stress. An impairment of cardiac parasympathetic ganglionic transmission was observed during high frequency vagal stimulation, which caused cardiac arrest in all wild‐type animals while α5‐/‐ mice were more resistant. Deficiency of α5 subunits strikingly increased the sensitivity to a low concentration of hexamethonium, leading to a nearly complete blockade of bradycardia in response to vagal stimulation. Such a concentration of hexamethonium only slightly depressed the effects of vagal stimulation in control mice. Deficiency of α5 subunits significantly increased ileal contractile responses to cytisine and epibatidine. These results suggest that α5 subunits may affect the affinity and sensitivity of agonists and antagonists in the native receptors. Previous studies revealed that α5 subunits form functional receptors only in combination with other α and β subunits. Thus, the data presented here imply that α5 subunits modulate the activity of nAChR in autonomic ganglia in vivo.

Autonomic impairment in a transgenic mouse model of amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by progressive loss of motor neurons, however it is increasingly recognized that nonmotor manifestations may occur, including autonomic nervous system dysfunction. To better understand the autonomic involvement in ALS we measured autonomic functions in transgenic (TG) mice carrying an SOD1 (G93A) mutation and wild-type (WT) control mice. TG mice had a higher heart rate at rest and following stress than WT mice at all ages except for the advanced stages of the disease (19-20weeks of age). The mean pupil diameter at rest was similar in WT and TG mice; however, TG mice had decreased mydriasis following administration of morphine. The rectal temperature did not differ between TG and WT mice at rest, during exposure to cold stress and following administration of morphine (30mg/kg) except for the advanced stages of the disease in which TG mice had significantly lower temperatures than WT mice during cold stress and following morphine administration. The results suggest autonomic nervous system impairment in this ALS model, consistent with clinical data in humans.

Assessment of experimental autoimmune neuritis in the rat by electrophysiology of the tail nerve

The assessment of experimental autoimmune neuritis (EAN) by electrophysiological studies of the sciatic innervation of the plantar muscle may be complicated by local inflammation. We therefore utilized the tail nerve–muscle system to monitor disease progression in 20 rats with EAN and 10 control rats. Early changes were detected in motor nerve conduction velocity (32.06 ± 1.85 m/s versus 43.57 ± 3.98 m/s in controls, P < 0.001) at 15 days postimmunization (DPI), and conduction block (70.6 ± 9.4% compared to 12.4 ± 3.4%, P < 0.001) at 22 DPI. No consistent conduction block (22.4 ± 10.4%) was found in the plantar muscle measurements. The tail nerve response of EAN rats demonstrated severe temporal dispersion at 43 DPI, which returned to normal at 135 DPI, although motor nerve conduction velocity values were still lower than in controls (24.4 ± 0.9 m/s, P < 0.001). The tail nerve may be a useful addition to electrophysiological studies in this model of the Guillain–Barré syndrome.

Nicotinic acetylcholine receptor α5 subunits modulate oxotremorine-induced salivation and tremor

Neuronal nicotinic acetylcholine receptors (nAChRs) are composed of 12 subunits (alpha2-alpha10 and beta2-beta4). alpha5 Subunits, expressed throughout the central nervous system (CNS) and the autonomic nervous system (ANS), possess unique pharmacological properties. The effects of oxotremorine (OXO) on autonomic functions and tremor were examined in mice lacking alpha5 nAChR subunits (alpha5-/-) and compared with those in wild-type (WT) control mice. The alpha5-/- mice showed significantly increased salivation and tremor responses to OXO. The hypothermia, bradycardia and defecation induced by OXO were of similar magnitudes in the two mouse strains. The enhanced OXO effects in alpha5-/- mice indicate inhibitory effects of alpha5 subunits in autonomic ganglia, and support the participation of these subunits in cholinergic transmission in autonomic ganglia.

The stability of dopamine-β-hydroxylase activity in blood samples

Abstract Dopamine-β-hydroxylase activity was measured in serum samples that were incubated at 37°C for up to seven days and were compared with preincubation values. No change of activity was observed.

Hidden function of neuronal nicotinic acetylcholine receptor β2 subunits in ganglionic transmission: comparison to α5 and β4 subunits

Neuronal nicotinic acetylcholine receptors (nAChR), which modulate fast excitatory postsynaptic potentials (f-EPSP), are located on both pre- and postganglionic sites in the autonomic nervous system (ANS). The receptor subunits alpha3, alpha5, alpha7, beta2 and beta4 are present in autonomic ganglia in various combinations and modulate acetylcholine (ACh) transmission. In the present study, autonomic functions were systemically examined in mice lacking beta2 subunits (beta2-/-) to further understand the functional role of beta2 subunits in modulating ganglionic transmission. The results show normal autonomic functions, both under physiological conditions and in perturbed conditions, on thermoregulation, pupillary size, heart rate responses and ileal contractile reactions. This suggests that the function of beta2-containing receptors in ganglionic transmission is hidden by the predominant beta4 containing receptors and confirms previous studies which suggest that alpha3alpha5beta4 nAChRs are sufficient for autonomic transmission. On the other hand, beta2-containing receptors have only a minor function on postsynaptic responses to ACh, but may modulate ACh release presynaptically, although there is no evidence for this.

Dopaminergic drugs influence the intensity of catalepsy induced by microinjections of carbachol into the reticular formation.

Carbachol microinjections into the mesencephalic and pontine reticular formation in rats induced intense and long-lasting catalepsy. Systemically administered haloperidol potentiated, while apomorphine and L-DOPA reduced the cataleptogenic effect of carbachol. These results indicate the existence of functional relations between the cholinergic cataleptogenic mechanism in the reticular formation and the dopaminergic system. They are interpreted in the light of known anatomical ascending and descending interconnections between the reticular formation and basal ganglia.

Action of opioid agonist-antagonist drugs on the pupil and nociceptive responses in mice.

Opioid derivatives with mixed agonist-antagonist activities are becoming increasingly more popular in analgesia. We tested the mydriatic and analgesic activity of morphine in mice in comparison with similar effects of three agonist-antagonist agents: buprenorphine, butorphanol and nalbuphine. We also examined the antagonistic action of these three drugs by evaluating the analgesia and mydriasis in animals pretreated with morphine.The analgesic effect was assayed using the hot plate method while the pupillary responses were measured with a binocular operating microscope.Morphine produced dose-dependent mydriasis and analgesia in mice. The morphine-type agent buprenorphine and two nalorphine-type agonistantagonists, butorphanol and nalbuphine, caused agonistic mydriatic and analgesic effects, usually less effective then morphine. Buprenorphine proved to have higher agonist activity than butorphanol and nalbuphine. The difference between butorphanol and nalbuphine was not statistically significant.A correlation between the mydriatic and the analgesic activity, known to exist among oploid derivatives with agonist activity only, was also demonstrated in the three investigated agonist-antagonist agents.Morphine-induced mydriasis and analgesia were reversed by all three agonist-antagonist drugs, but buprenorphine is a significantly weak antagonist in comparison with butorphanol and nalbuphine. An antagonistic property (antimydriatic and antianalgesic effects after pretreatment with morphine) of both nalorphine-type investigated drugs was not statistically significant, except for the antianalgesic effect of nalbuphine in doses 1 and 3 mg·kg−1 which was higher in comparison with butorphanol.

Effect of electroconvulsive treatment on serum dopamine-beta-hydroxylase activity in man.

The activity of dopamine-beta-hydroxylase was measured in the serum before and immediately after electroconvulsive treatments. No significant difference was observed, suggesting that the seizures did not cause an increase in the peripheral sympathetic tone.

Autonomic dysfunction in experimental autoimmune neuritis:: Heart rate

Autonomic nervous system (ANS) dysfunction occurs in more than half of Guillain--Barré syndrome (GBS) patients and is an important cause of death in the disease. In this study we examined heart rate (HR) changes in an animal model of GBS, experimental autoimmune neuritis (EAN), induced by immunization with myelin extracted from bovine spinal roots. The animals developed progressive motor weakness accompanied by significant weight loss and hypothermia. HR was measured in 33 EAN rats at rest (rHR) and followings stressful stimulation (sHR). Average pre-immunization rHR was 341+/-28 beats per minute (b.p.m.) and sHR was 486+/-21 bpm. Although the mean rHR in rats with EAN was not significantly different compared to that at baseline, there was a significant increase of variation of rHR with six rats demonstrating bradycardia (<280 b.p.m.) and 10 tachycardia (>400 b.p.m.) (P<0.01, F-test). sHR in EAN rats was significantly lower (P<0.01), suggesting sympathetic system impairment. These findings may serve as a basis for testing treatments of ANS dysfunction in EAN.