Determination of the endogenous and evoked release of catecholamines from the hypothalamus and caudate nucleus of the conscious and unrestrained rat

Chromatin remodeller CHD7 is required for GABAergic neuron development by promoting PAQR3 expression

Mutations in the chromatin remodeller‐coding gene CHD7 cause CHARGE syndrome (CS). CS features include moderate to severe neurological and behavioural problems, clinically characterized by intellectual disability, attention‐deficit/hyperactivity disorder and autism spectrum disorder. To investigate the poorly characterized neurobiological role of CHD7, we here generate a zebrafish chd7^−/− model. chd7^−/− mutants have less GABAergic neurons and exhibit a hyperactivity behavioural phenotype. The GABAergic neuron defect is at least in part due to downregulation of the CHD7 direct target gene paqr3b, and subsequent upregulation of MAPK/ERK signalling, which is also dysregulated in CHD7 mutant human cells. Through a phenotype‐based screen in chd7^−/− zebrafish and Caenorhabditis elegans, we show that the small molecule ephedrine restores normal levels of MAPK/ERK signalling and improves both GABAergic defects and behavioural anomalies. We conclude that chd7 promotes paqr3b expression and that this is required for normal GABAergic network development. This work provides insight into the neuropathogenesis associated with CHD7 deficiency and identifies a promising compound for further preclinical studies.

Dopamine-mediated actions of ephedrine in the rat substantia nigra

Although ephedrine is a centrally active stimulant, its effect on midbrain dopamine neurons is not known. To study the effect of ephedrine on dopamine-containing cells, current-clamp microelectrode recordings were made from substantia nigra pars compacta (SNC) neurons in horizontal brain slice preparations. Ephedrine (100-1000 microM) slowed spontaneous firing and produced a modest concentration-dependent hyperpolarization of membrane potential (EC50 279 microM), with a concomitant net decrease in membrane resistance. These effects were blocked by the D2-like dopamine antagonist sulpiride (1 microM). Electrically evoked inhibitory synaptic potentials mediated by GABAB receptors were reduced 28% by ephedrine. However, ephedrine did not reduce fast synaptic potentials mediated by GABAA or ionotropic glutamate receptors. Inhibition of the GABAB response appeared to be mediated by a postsynaptic mechanism because ephedrine also reduced baclofen-induced hyperpolarization by 28%. Both ephedrine-induced hyperpolarization and inhibition of baclofen-induced hyperpolarization were abolished when slices were superfused with the tyrosine hydroxylase inhibitor alpha-methyl-para-tyrosine (AMPT). Despite perfusion with AMPT, the ability of ephedrine to cause hyperpolarization was restored after perfusing the slice with dopamine (30 microM). Taken together, these results suggest that ephedrine causes hyperpolarization and suppresses GABAB receptor-mediated effects by releasing endogenous dopamine. However, the high concentrations required to observe these effects in vitro suggest that biologically relevant central effects of ephedrine are more likely to be mediated either by non-dopamine systems, such as those involving noradrenaline, or by dopamine systems outside the SNC.

Ephedrine, but not phenylephrine, increases bispectral index values during combined general and epidural anesthesia

Ephedrine and phenylephrine are used to treat hypotension during combined general and epidural anesthesia, and they may change anesthetic depth. In the current study, we evaluated the effects of ephedrine versus phenylephrine on bispectral index (BIS) during combined general and epidural anesthesia. After injection of ropivacaine through the epidural catheter, general anesthesia was induced with propofol and vecuronium, and was maintained with 0.75% sevoflurane. Approximately 10 min after the intubation, BIS was recorded as a baseline value. Patients with decreases in arterial blood pressure <30% of the preanesthetic values were defined as control group (n = 9). Patients who had to be treated for larger decreases in arterial blood pressure were randomly assigned to receive ephedrine 0.1 mg/kg (n = 17) or phenylephrine 2 micro g/kg (n = 17). BIS values were recorded at 1-min intervals for 10 min. BIS in the ephedrine group was significantly larger from 7 to 10 min than that in the control and phenylephrine groups (P < 0.05). Seven patients in the ephedrine group had BIS >60, whereas no patient in the control and phenylephrine groups had BIS >60 (P < 0.005). Ephedrine, but not phenylephrine, increased BIS during general anesthesia combined with epidural anesthesia.

Noradrenergic modulation of ephedrine-induced hypophagia

The hypophagic action of the sympathomimetic amine ephedrine (EPH) in the rat may reflect actions on central dopaminergic (DA) and noradrenergic (NE) systems. EPH indirectly facilitates DA and NE activity and acts as a partial agonist at alpha(1)-adrenergic receptors. Two approaches were used to assess the possible contribution of NE and DA pathways to EPH-induced hypophagia. In the first, regression analyses of published archival data were computed to characterize the relation between the hypophagic potency values of (-)-(EPH) and related sympathomimetic drugs, including (+)-amphetamine, aminorex, mazindol, and phentermine (data derived from Blosser JC et al., 1987) and the most potent action of these drugs on facilitating NE activity or DA activity in rat brain (data derived from Rothman RB et al., 2001). In the NE analyses, the ED(50) values for these drugs for the inhibition of eating in rats were significantly related (r = 0.91, P = 0.03) to the potency of each drug in facilitating NE activity (either release or inhibition of [(3)H]NE reuptake), whereas in the DA analyses the correlation between ED(50) values and DA activity for these drugs was also significant (r = 0.98, P = 0.003). The regression analyses are thus supportive of a role for NE or DA in the hypophagic capacity of EPH. Although an earlier study noted that administration of the putative DA antagonist pimozide in rats attenuated EPH hypophagia, pimozide exerts similar potency in antagonizing DA receptors and alpha(1)-adrenergic receptors. To clarify the role of alpha(1)-adrenoceptors in EPH-induced hypophagia, adult male rats were pretreated with the alpha(1)-adrenergic receptor antagonist prazosin (0.0.5 and 2 mg/kg) prior to the administration of (-)-EPH (0, 5, 10, or 20 mg/kg, IP). Prazosin pretreatment at 2.0 mg/kg significantly attenuated the hypophagia, but not the hypodipsia, induced by administration of 10 mg/kg and by 20 mg/kg (-)-EPH. Collectively, these results confirm a critical contribution of of alpha(1)-adrenoceptors to the hypophagic action of (-)-EPH in rats.

Sensitization of anorexia and locomotion induced by chronic administration of ephedrine in rats

Repeated daily administration of the sympathomimetic agent ephedrine (EPH) leads to an augmentation (sensitization) of locomotor activity in rats. The present experiments examined the impact of repeated administration of the (-)- and (+)-EPH enantiomers on feeding in rats to assess whether the anorexic activity of EPH exhibits tolerance or sensitization during chronic exposure and whether the time course of these effects follows that observed in studies of locomotion. Adult male rats were injected once daily for 12 days with either vehicle or 5, 10 or 20 mg/kg (-)-EPH or with 10 or 20 mg/kg (+)-EPH. Horizontal locomotion and diet consumption were assessed for 60 min in an activity chamber. Suppression of feeding and the induction of locomotion were augmented over the first four days of administration of either 10 mg/kg or 20 mg/kg of the (-)-EPH enantiomer. In contrast, repeated administration of 20 mg/kg (+)-EPH resulted in augmentation of appetite suppression but not locomotion. These results confirm and extend the phenomenon of locomotor and feeding sensitization for ephedrine, but suggest that these effects may differ for the two enantiomers of ephedrine.

Depletion of central catecholamines reduces pressor responses to arginine vasopressin

Previous reports that central administration of arginine vasopressin (AVP) increases turnover of brain catecholamines raise the possibility that the pressor responses which follow central administration of AVP may be mediated, in part, by central catecholamines. To test this hypothesis, rats were given intraventricular injections of vehicle, or of the neurotoxin, 6-hydroxydopamine, which resulted in significant depletions of hypothalamic and medulla oblongata noradrenalin and hypothalamic dopamine, but not of medullary dopamine or of hypothalamic and medullary 5-hydroxytryptamine. Following a one week recovery, these conscious rats, fitted with indwelling arterial catheters, were given intraventricular injections of AVP; the increases in arterial pressure and heart rate were significantly reduced in the catecholamine-depleted animals. These data support the hypothesis that the pressor and tachycardia responses to intraventricular AVP are mediated, in part, by central catecholamine-containing neurons.

Serotonin in cisternal cerebrospinal fluid of the rat: measurement and use as an index of functionally active serotonin

A simple, selective reverse-phase HPLC-fluorometric method is described for the determination of serotonin (5HT) in cisternal CSF of the rat. The mean (+/- SE) value of CSF 5HT observed in control adult rats was 457 +/- 83 pg/ml (N = 16). In an attempt to validate the measure as an index of extracellular, or functionally active, 5HT, groups of animals were treated with fenfluramine, amitriptyline, pargyline, pargyline plus tryptophan, and 5-hydroxytryptophan plus carbidopa. In all cases CSF 5HT appeared to reflect well the presumed effects of the agents on extracellular levels of 5HT. CSF 5HT was superior in this regard to brain 5HT, brain 5HIAA, or CSF 5HIAA levels. The measurement of cisternal CSF 5HT would appear to offer a convenient index of functionally active 5HT.