Delayed arousal from anesthesia: a further similarity between stress and beta-1 adrenoceptor blockade

cAMP and extracellular signal-regulated kinase signaling in response to d-amphetamine and methylphenidate in the prefrontal cortex in vivo: role of beta 1-adrenoceptors

d-Amphetamine and methylphenidate are widely used in the treatment of attention-deficit/hyperactivity disorder. Both drugs increase extracellular norepinephrine and dopamine in the prefrontal cortex, where they are believed to exert their therapeutic effects. However, the molecular mechanisms underlying their action are poorly understood. To investigate the intracellular signaling pathways activated by d-amphetamine and methylphenidate in the prefrontal cortex in vivo in mice, we measured the cAMP-dependent Ser845 phosphorylation of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor GluR1 subunit and the active form of extracellular signal-regulated kinase (ERK). Administration of d-amphetamine (5-10 mg/kg) or methylphenidate (10-20 mg/kg) increased phosphorylation of GluR1. Basal and d-amphetamine-induced GluR1 phosphorylation was reduced by propranolol, a general beta-adrenoceptor antagonist, and betaxolol, a beta1-antagonist, but not by (+/-)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol (ICI-118,515), a beta2-antagonist. The effect of methylphenidate was also blocked by propranolol and betaxolol. The d-amphetamine effect was slightly potentiated by prazosin, an alpha1-adrenoceptor antagonist, and mimicked by yohimbine, an alpha2 antagonist. Blockade of dopamine or N-methyl-d-aspartate (NMDA) receptors or serotonin depletion had no effect on d-amphetamine-induced GluR1 phosphorylation. d-amphetamine but not methylphenidate increased ERK phosphorylation. This effect required multiple signaling pathways because it was blocked by beta1- and alpha1-adrenoceptor antagonists, by dizocilpine maleate (MK801), an NMDA antagonist, and by serotonin depletion. In contrast, blockade of dopamine receptors had no effect on d-amphetamine-induced ERK phosphorylation. Propranolol and betaxolol increased the hyperlocomotion produced by d-amphetamine and methylphenidate. Thus, both d-amphetamine and methylphenidate potently activate the cAMP pathway in the prefrontal cortex through beta1-adrenergic receptors. This activation could have behavioral consequences and contribute to the treatment of attention-deficit/hyperactivity disorder.

Beta-1 adrenoceptor antagonists potentiate the anticonvulsive effect of swim stress in mice

To explore the possible involvement of beta adrenoceptor antagonists in the previously observed anticonvulsive effect of swim stress, the mice were, prior to administration of convulsants, pre-treated with propranolol (a non-selective beta adrenoceptor antagonist), betaxolol (a selective beta-1 adrenoreceptor antagonist), or ICI 118,551 (a selective beta-2 adrenoreceptor antagonist). In control unstressed animals, only propranolol [10 mg/kg, intraperitoneally (ip)] produced a significant change. It enhanced the threshold dose of picrotoxin producing tonic hindlimb extension. However, in swim-stressed animals, propranolol enhanced doses of picrotoxin producing tonic hindlimb extension and death, while betaxolol (20 mg/kg, i.p.) enhanced doses of picrotoxin producing running/bouncing clonus, tonic hindlimb extension and death. Pre-treatment with ICI 118,551 (4 mg/kg, i.p.) failed to affect doses of picrotoxin producing convulsions and death. The results demonstrate that blockade of beta-1 adrenoceptors potentiates the anticonvulsant effect of swim stress against convulsions produced by picrotoxin, a noncompetitive GABA(A) receptor antagonist.

Blockade of effect of stress on risk assessment behavior in mice by a beta-1 adrenoceptor antagonist

Previous studies have shown that acute stress impairs risk assessment behavior in mice. The present study was undertaken to determine the role of beta adrenoceptors, which are known to be stimulated by stress, in this effect. Mice were treated with either a beta-1 antagonist, betaxolol, a beta-2 antagonist, ICI 118551, an alpha-1 antagonist, prazosin, or an alpha-2 antagonist, yohimbine, and 30 min later were subjected to a 1-h session of restraint stress. Thirty minutes after the stress the animals were tested for the entry latency, number of headpokes prior to entry, and the path of entry into a white open field from a small dark box. In agreement with previous findings, stress was found to markedly reduce risk assessment behaviors as reflected by a reduced entry latency, a reduced number of headpokes and a changed entry path from wall hugging to central entry. Betaxolol was found to prevent all of the above effects of stress dose dependently, whereas ICI 118551, prazosin, and yohimbine had no reversal effects. It is concluded that beta-1 receptor activation and possibly brain glycogen depletion is involved in the effects of stress on risk assessment behavior.