Effects of d,l-propranolol on open field behavior of rats

Cerebellar α6GABAA Receptors as a Therapeutic Target for Essential Tremor: Proof-of-Concept Study with Ethanol and Pyrazoloquinolinones

Ethanol has been shown to suppress essential tremor (ET) in patients at low-to-moderate doses, but its mechanism(s) of action remain unknown. One of the ET hypotheses attributes the ET tremorgenesis to the over-activated firing of inferior olivary neurons, causing synchronic rhythmic firings of cerebellar Purkinje cells. Purkinje cells, however, also receive excitatory inputs from granule cells where the α6 subunit-containing GABAA receptors (α6GABAARs) are abundantly expressed. Since ethanol is a positive allosteric modulator (PAM) of α6GABAARs, such action may mediate its anti-tremor effect. Employing the harmaline-induced ET model in male ICR mice, we evaluated the possible anti-tremor effects of ethanol and α6GABAAR-selective pyrazoloquinolinone PAMs. The burrowing activity, an indicator of well-being in rodents, was measured concurrently. Ethanol significantly and dose-dependently attenuated action tremor at non-sedative doses (0.4-2.4 g/kg, i.p.). Propranolol and α6GABAAR-selective pyrazoloquinolinones also significantly suppressed tremor activity. Neither ethanol nor propranolol, but only pyrazoloquinolinones, restored burrowing activity in harmaline-treated mice. Importantly, intra-cerebellar micro-injection of furosemide (an α6GABAAR antagonist) had a trend of blocking the effect of pyrazoloquinolinone Compound 6 or ethanol on harmaline-induced tremor. In addition, the anti-tremor effects of Compound 6 and ethanol were synergistic. These results suggest that low doses of ethanol and α6GABAAR-selective PAMs can attenuate action tremor, at least partially by modulating cerebellar α6GABAARs. Thus, α6GABAARs are potential therapeutic targets for ET, and α6GABAAR-selective PAMs may be a potential mono- or add-on therapy.

A dose-response study of the effects of pre-test administration of beta-adrenergic receptor antagonist propranolol on the learning of active place avoidance, a spatial cognition task, in rats

The involvement of various neurotransmitter receptors in the brain in the regulation of spatial behavior is a focus of interest for many cognitive neuroscientists. Active allothetic place avoidance (AAPA) task have been demonstrated to require spatial mapping and cognitive coordination and is highly dependent upon hippocampus. The present study was designed to evaluate the role of beta-adrenergic receptors in the modulation of locomotor and spatial behavior in this task. Four doses of centrally active beta-adrenergic antagonist propranolol (5, 20, 25 and 30 mg/kg) were administered intraperitoneally 30 min prior to testing in the place avoidance task. Four daily sessions were pursued, each lasting 20 min. A dose of 25 mg/kg was found to induce a deficit in spatial behavior (measured by number of entrances into the shock sector) without altering locomotion; lower doses were without effect. The highest dose (30 mg/kg) impaired both locomotion and avoidance behavior. The results suggest that beta-adrenoceptors are involved in the regulation of behavior in the place avoidance task and that it is possible to dissociate the effect of propranolol on the spatial performance and locomotion in the AAPA using dose-selection.

The neurophysiology of attention-deficit/hyperactivity disorder

Recent reviews of the neurobiology of Attention-Deficit/Hyperactivity Disorder (AD/HD) have concluded that there is no single pathophysiological profile underlying this disorder. Certainly, dysfunctions in the frontal/subcortical pathways that control attention and motor behavior are implicated. However, no diagnostic criteria or behavioral/neuroimaging techniques allow a clear discrimination among subtypes within this disorder, especially when problems with learning are also considered. Two major Quantitative EEG (QEEG) subtypes have been found to characterize AD/HD. Here we review the major findings in the neurophysiology of AD/HD, focusing on QEEG, and briefly present our previous findings using a source localization technique called Variable Resolution Electromagnetic Tomography (VARETA). These two techniques represent a possible objective method to identify specific patterns corresponding to EEG-defined subtypes of AD/HD. We then propose a model representing the distribution of the neural generators in these two major AD/HD subtypes, localized within basal ganglia and right anterior cortical regions, and hippocampal, para-hippocampal and temporal cortical regions, respectively. A comprehensive review of neurochemical, genetic, neuroimaging, pharmacological and neuropsychological evidence in support of this model is then presented. These results indicate the value of the neurophysiological model of AD/HD and support the involvement of different neuroanatomical systems, particularly the dopaminergic pathways.

Effects of dihydroergotoxine on some dopamine-related behaviors in rats

1. The effects of dihydroergotoxine on open-field behavior, apomorphine-induced stereotype and haloperidol-induced catalepsy were studied quantitatively in rats. 2. Dihydroergotoxine decreased the open-field behavior of rats, in a dose-dependent manner; this effect remained at least for 8 hr. 3. Dihydroergotoxine (10.0 mg/kg) caused a 1.40 leftward displacement of the dose-response curve constructed for apomorphine-induced stereotypy; the ED50 for apomorphine was reduced from 0.40 (+/- 0.05) to 0.29 (+/- 0.03). 4. Dihydroergotoxine (10.0 mg/kg) was unable to change haloperidol-induced catalepsy. 5. Results were discussed in the light of a possible interference of central noradrenergic systems with the expression of dopaminergic behaviors.

Effects of d,l-propranolol on apomorphine induced stereotyped behavior in rats

The effects of d,l propranolol on stereotyped behavior induced by apomorphine administration was studied quantitatively. d,l Propranolol caused a 2.5 leftward displacement of the control dose-response curve constructed to apomorphine-induced stereotypy; the ED50 for apomorphine was reduced from 1.87 +/- 0.38 to 0.74 +/- 0.17. The potentiation was dependent on both d,l-propranolol and apomorphine doses. Results are discussed in the light of a possible interference of the central noradrenergic systems with the expression of dopaminergic-induced stereotyped behavior.