Innervation both of peri-orbital structures and of the heart by the cervical sympathetic nerves in mouse, rat, guinea-pig, rabbit and cat

Establishment of stellate ganglion block in mice

BACKGROUND

There have been no reports on the successful implementation of stellate ganglion block (SGB) in mice.

OBJECTIVES

This study aims to investigate a new method for implementing SGB in mice by placing them in a supine position with abducted upper limbs and touching the trachea and sternoclavicular joint with the hand.

METHODS

Fifty BABL/C mice, 8-10 weeks, were selected and randomly divided into four groups: control group (n = 5); SGB-R group (n = 15); SGB-L group (n = 15); and SGB-L + R (group n = 15). SGB was administered with 0.15% ropivacaine solution in a volume of 0.1 mL. The control group received equal volumes of saline. Horner's syndrome, heart rate, and complications such as brachial plexus block, vascular injury, pneumothorax, local anesthetic toxicity, and death were observed.

RESULTS

Horner's syndrome developed in 100% of SGB surviving mice; no difference was seen in the time to onset (100.4 ± 13.4 vs 96.7 ± 12.4, mean ± SD, seconds) and duration (264.1 ± 40.5 vs 296.3 ± 48.0, mean ± SD, min) of Horner's syndrome in the left and right SGB (P > 0.05). Compared with the control group (722 [708-726], median [IQR], bpm), the heart rate was significantly slowed down in the right SGB (475 [451.5-491], median [IQR], bpm) (P < 0.05). While the heart rate was slowed down after performing the left SGB, the difference was not statistically significant (P > 0.05). The overall complication rate was 18.4%, with a brachial plexus block rate of 12.3%, a vascular injury rate of 4.6%, and a mortality rate of 1.5%, as well as no local anesthetic toxicity (includes bilateral implementation of SGB) or pneumothorax manifestations were found.

CONCLUSIONS

This method allows for the successful implementation of SGB in a mouse model.

Megacystis, mydriasis, and ion channel defect in mice lacking the alpha3 neuronal nicotinic acetylcholine receptor

The alpha3 subunit of the neuronal nicotinic acetylcholine receptor is widely expressed in autonomic ganglia and in some parts of the brain. The alpha3 subunit can form heteromultimeric ion channels with other alpha subunits and with beta2 and beta4 subunits, but its function in vivo is poorly understood. We prepared a null mutation for the alpha3 gene by deletion of exon 5 and found that homozygous (-/-) mice lacked detectable mRNA on Northern blotting. The -/- mice survive to birth but have impaired growth and increased mortality before and after weaning. The -/- mice have extreme bladder enlargement, dribbling urination, bladder infection, urinary stones, and widely dilated ocular pupils that do not contract in response to light. Detailed histological studies of -/- mice revealed no significant abnormalities in brain or peripheral tissues except urinary bladder, where inflammation was prominent. Ganglion cells and axons were present in bladder and bowel. Bladder strips from -/- mice failed to contract in response to 0.1 mM nicotine, but did contract in response to electrical field stimulation or carbamoylcholine. The number of acetylcholine-activated single-channel currents was severely reduced in the neurons of superior cervical ganglia in -/- mice with five physiologically distinguishable nicotinic acetylcholine receptor subtypes with different conductance and kinetic properties in wild-type mice, all of which were reduced in -/- mice. The findings in the alpha3-null mice suggest that this subunit is an essential component of the nicotinic receptors mediating normal function of the autonomic nervous system. The phenotype in -/- mice may be similar to the rare human genetic disorder of megacystis-microcolon-intestinal hypoperistalsis syndrome.

Pronounced facilitation of endogenous noradrenaline release by presynaptic beta 2-adrenoceptors in the vasculature of freely moving rats

The facilitation of the noradrenaline (NA) overflow by stimulation of the presynaptic beta-adrenoceptor of the rat portal vein was investigated, using the freely moving unanesthetized permanently cannulated rat as a model. The beta 2-selective agonist fenoterol caused a maximal enhancement of about 300% of the basal NA level at a dose of 0.5 mg/kg. Following administration of cocaine (2.5 mg/kg plus 0.05 mg/kg/min) basal NA levels increased to 150% whereas combination of cocaine and fenoterol results in a dose dependant rise up to over 560% of the basal level (at a fenoterol dosage of 0.5 mg/kg). Blockade of the alpha 2-adrenoceptors with yohimbine (0.5 mg/kg) which enhances the NA level to 486%, followed by 0.125 mg/kg fenoterol results in a further 2.53-fold rise to more than 1,200% of the basal level, indicating the pronounced counterregulatory role of the presynaptic alpha 2-adrenoceptor. After ganglionic blockade with hexamethonium (3 mg/kg plus 6 mg/kg/h) the effect of yohimbine (0.5 mg/kg) alone was diminished to 162%, but the additional facilitatory effect of 0.125 mg/kg fenoterol still was 1.82-fold, to 294% of the basal level. Combination of cocaine (2.5 mg/kg plus 0.05 mg/kg/min), yohimbine (0.5 mg/kg) and fenoterol (0.125 mg/kg) induced a rise to over 9,000 pg/ml NA (about 40-fold of the basal NA level). During electrical stimulation (2 Hz, 3 ms, 5 mA) of the local portal vein nervous plexus, the role of the inhibitory alpha 2-adrenoceptor becomes even more pronounced.(ABSTRACT TRUNCATED AT 250 WORDS)

Method for stimulating the adrenergic system of an isolated perfused rat heart

A method is presented whereby isolated perfused rat hearts can be rapidly prepared for the stimulation of chronotropic activity by electrical pulses or exogenous noradrenaline. The mediation of the response by sympathetic nerves is demonstrated through modulation of the response by compounds with established pharmacological actions. Propranolol inhibits the increase in heart rate to both electrical stimulation and exogenous noradrenaline, whereas bretylium inhibits only electrically induced increases. Chronic pretreatment with 6-hydroxydopamine decreases the response to electrical stimulation but increases that to exogenous noradrenaline.

Cardiovascular responses in spontaneously hypertensive rats with acute renal failure

Cardiovascular status and reactivity have been investigated in spontaneously hypertensive rats (SHR) with glycerol-induced acute renal failure. SHR with acute renal failure had significantly lower mean arterial blood pressures and heart rates. The pressor responses to noradrenaline and the chronotropic responses to right cervical sympathetic and vagal nerve stimulation were diminished in uraemic SHR compared to control SHR. The cardiovascular depression observed in SHR with acute renal failure was similar to that previously noted in normotensive rats with acute renal impairment.

Cardiovascular responses in rats with glycerol-induced acute renal failure

Autonomic and cardiovascular function were assessed in rats with glycerol-induced acute renal failure (ARF). Rats with ARF had significantly lower mean arterial blood pressure and heart rates and significantly elevated plasma noradrenaline concentrations. The chronotropic responses to right cervical sympathetic and vagal stimulation were diminished in rats with ARF. The pressor and depressor responses to noradrenaline and nitroprusside respectively when expressed as a change in mmHg pressure were significantly reduced in rats with ARF when compared to controls. However, when the depressor responses to nitroprusside were expressed as a percentage fall in basal mean arterial pressure, with the exception of the response to a dose of 10 micrograms kg-1, there were no significant differences between control and uraemic rats. The present findings show that in the rat, changes in cardiovascular responsiveness occur after a brief period of uraemia which are similar to those observed in patients and rats with chronic renal failure.

Absence of a cholinergic component in noradrenergic transmission in the cervical sympathetic nerve of the rat

1 In rats anaesthetised with chloralose and pentobarbitone, frequency-dependent tachycardia and contraction of the ipsilateral inferior eyelid occurred when the intact right cervical sympathetic nerve was stimulated. 2 After successive doses of 5, 12.5 and 30 micrograms.kg-1 neostigmine sulphate (i.v.) a progressive reduction was seen in the tachycardias to low frequency stimulation (0.2 to 2 Hz) but either no effect, or an augmentation after 30 micrograms.kg-1, was evident at higher frequencies (up to 20 Hz). Atropine sulphate (i.v., 100 micrograms.kg-1) abolished the augmentatory effect of neostigmine on the high-frequency responses and offset partially the depressant effect of neostigmine on the responses to 0.2 and 0.5 Hz. By contrast, contractions of the eyelid were unaltered by neostigmine and atropine. 3 Reserpinised rats (8 mg.kg-1 i.p., 24 h earlier) were quite refractory to stimulation and remained so after neostigmine and atropine. 4 The effectiveness of neostigmine (enhancing responses) and atropine (inhibiting them) was demonstrated on endogenous acetylcholine (ACh) by measuring bradycardia to right efferent vagal stimulation, and on exogenous ACh by measuring inferior eyelid retraction in both reserpinised and control rats. These groups were equally sensitive to either ACh or noradrenaline and cocaine potentiated the tachycardia to noradrenaline in both groups. 5 Propranolol reduced the tachycardia and phentolamine the eyelid contraction induced by sympathetic nerve stimulation. 6 The findings offer no support to a theory implying an obligatory cholinergic-link in noradrenergic transmission.

The influence of the frequency and pattern of sympathetic nerve activity on serotonin N-acetyltransferase in the rat pineal gland

The activity of the pineal enzyme arylamine: N-acetyltransferase (NAT) was determined following direct stimulation of the preganglionic or post-ganglionic nerves of the superior cervical ganglia. 1. Stimulation of the preganglionic trunks at 10 c/sec during the day or night was sufficient to increase NAT activity approximately 50-fold, to levels comparable to those observed at night in the intact animal. The time course of this effect of nerve stimulation differed between day and night. 2. The responses of pineal NAT to certain frequencies of stimulation were similar for preganglionic and post-ganglionic stimulation. In both cases the responses to stimulation at 5 c/sec appeared to be maximal, 10 c/sec causing no further increase. However, at 10 c/sec, stimulation was more effective post-ganglionically than preganglionically. 3. Various patterns of preganglionic stimulation, having the same average frequency, differed in their ability to increase the activity of NAT. Some, though not all, of these differences between patterns were observed during post-ganglionic stimulation. 4. Unilateral stimulation of the preganglionic nerves produced an increase in NAT activity that was less than half the increase produced by bilateral stimulation, suggesting that the innervation from the two ganglia interact within the pineal gland. 5. These data indicate that changes in the firing rates of sympathetic nerves innervating the pineal gland, within the range of frequencies typically observed for sympathetic neurones, would be sufficient to account for the circadian rhythm in NAT activity observed in the intact rat. Changes in the over-all pattern of sympathetic activity, in addition to changes in the total number of stimuli, could play a significant role in the pineal response.

The effects of prostaglandins E1, E2 and F2alpha on vagal bradycardia in the anaesthetized mouse

1 In anesthetized mice prostaglandins E1 and E2 reduced the bradycardia caused by electrical stimulation of the sectioned peripheral vagus nerve; prostaglandin F2alpha produced only a slight inhibition of the vagal response. 2 None of the prostaglandins studied affected acetylcholine-induced bradycardia. 3 Prostaglandins modify parasympathetic nerve activity in vivo presumably by a pre-synaptic action.