Chronic antidepressant counteracts the conditioned analgesia induced by a context previously associated with inescapable shock

Blockade of voltage-dependent K+ current in rabbit coronary arterial smooth muscle cells by the tricyclic antidepressant clomipramine

We investigated the effect of the tricyclic antidepressant clomipramine on voltage-dependent K⁺ (Kv) channels in native rabbit coronary arterial smooth muscle cells. Our results showed that clomipramine inhibited vascular Kv channels in a concentration-dependent manner, with an IC₅₀ value of 8.61 ± 4.86 μM and a Hill coefficient (n) of 0.58 ± 0.07. The application of 10 μM clomipramine did not affect the activation curves of the Kv channels; however, the inactivation curves of the Kv channels were shifted toward a more negative potential. The clomipramine-induced inhibition of Kv currents was not changed by the application of train pulses (1 or 2 Hz), which demonstrated that clomipramine inhibited Kv current in a state (use)-independent manner. Pretreatment with the Kv1.5 and Kv2.1 inhibitors, DPO-1 and guangxitoxin, respectively, partially reduced the clomipramine-induced inhibition of Kv currents. Therefore, we concluded that clomipramine inhibited vascular Kv channels in a concentration-dependent, but state (use)-independent manner, regardless of its own function.

Involvement of potassium channels in amitriptyline and clomipramine analgesia

The effect of the administration of modulators of different subtypes of K(+) channels on antinociception induced by the tricyclic antidepressants amitriptyline and clomipramine was evaluated in the mouse hot plate test. The administration of the voltage-gated K(+) channel blocker tetraethylammonium (0.01-0.5 microg per mouse i.c.v. ) prevented antinociception induced by both amitriptyline (15 mg kg(-1) s.c.) and clomipramine (25 mg kg(-1) s.c.). The K(ATP) channel blocker gliquidone (0.1-1.0 microg per mouse i.c.v.) prevented antinociception produced by amitriptyline and clomipramine whereas the K(ATP) channel openers minoxidil (10 microg per mouse i. c.v.) and pinacidil (25 microg per mouse i.c.v.) potentiated tricyclic antidepressant-induced analgesia. The administration of the Ca(2+)-gated K(+) channel blocker apamin (0.1-1.0 ng per mouse i. c.v.) completely prevented amitriptyline and clomipramine analgesia. At the highest effective doses, none of the drugs used induced behavioural side effects or impaired motor coordination, as revealed by the rota-rod test, spontaneous motility or inspection activity, as revealed by the hole board test. The present results demonstrate that central antinociception induced by amitriptyline and clomipramine involves the opening of different subtypes of K(+) channels (voltage-gated, K(ATP) and Ca(2+)-gated) which, therefore, represent a step in the transduction mechanism of tricyclic antidepressant analgesia.

Prior electrical stimulation of the inferior colliculus sensitizes rats to the stress of the elevated plus-maze test

Besides its primary function in the transmission of acoustic signals, the inferior colliculus (IC) is involved in conveying auditory information of aversive nature to higher cortical structures. In the field of anxiety research, one widely used animal model is the electrical stimulation of a given structure supposed to be involved in the neural circuitry underlying emotional behavior. Indeed, electrical stimulation of the inferior colliculus produces fear-like responses. Moreover, prior exposure to stressful events sensitizes rodents' responsivity to fearful stimuli when they are subsequently tested in the elevated plus-maze. Based on these evidence it seems to be important to know whether animals stimulated in the inferior colliculus would show a heightened behavioral responsivity to subsequent stressful events. To this end, we examined the temporal course of the effects of the electrical stimulation of this midbrain region (5, 10 and 15 min afterward) on the conventional and ethological measures of the behavior of rats exposed to the elevated plus-maze test. Prior electrical stimulation of the inferior colliculus produced an 'anxiogenic' profile in the elevated plus-maze, i.e. a significant reduction in the number of entries and time spent into the open arms. Still, previous electrical stimulation of the inferior colliculus caused a significant decrease in rearing, scanning, peeping out, head dipping and end-arm activity while increased immobility. All these changes occurred after 5 min of inferior colliculus electrical stimulation. Therefore, stimulation of the inferior colliculus causes a heightened responsivity to anxiogenic stimuli inherent to the elevated plus-maze test. These findings bring additional support to the proposed role of this midbrain structure in the elaboration of adaptive responses to stressful situations.

Antinociception induced by amitriptyline and imipramine is mediated by alpha2A-adrenoceptors

The involvement of alpha2-adrenoceptors in the antinociception induced by the tricyclic antidepressants amitriptyline and imipramine was investigated in mice by using the hot-plate and abdominal constriction tests. The antinociception produced by amitriptyline (15 mg/kg, i.p.) and imipramine (15 mg/kg, i.p.) was prevented by reserpine (2 mg/kg, i.p.) and yohimbine (3-10 mg/kg, i.p.) but not by naloxone (1 mg/kg, i.p.), atropine (5 mg/kg, i.p.), CGP 35348 (100 mg/kg, i.p.) and prazosin (1 mg/kg, i.p.). On the basis of the above data, it can be postulated that amitriptyline and imipramine exerted their antinociceptive effect by activation of alpha2-adrenoceptors. Administration of the alpha2A-adrenoceptor antagonist BRL 44408 (1 mg/kg, i.p.) prevented amitriptyline and imipramine antinociception, whereas the alpha2B/C-adrenoceptor antagonist ARC 239 (10 mg/kg, i.p.) was ineffective. These data indicate that the enhancement of the pain threshold produced by amitriptyline and imipramine is mediated by activation of alpha2A-adrenoceptors. Neither tricyclic antidepressants nor the antagonists used impaired mouse performance evaluated by the rota-rod and hole-board tests.

Blockade of clomipramine and amitriptyline analgesia by an antisense oligonucleotide to mKv1.1, a mouse Shaker-like K+ channel

The effect of an antisense oligonucleotide to the K+ channel coding mKv1.1 mRNA on antinociception induced by the tricyclic antidepressants, clomipramine (20-35 mg kg(-1) s.c.) and amitriptyline (10-25 mg kg(-1) s.c.), was investigated in the mouse hot-plate test. Antisense oligonucleotide (0.5-1.0-2.0-3.0 nmol per i.c.v. injection) produced a dose-dependent inhibition of clomipramine and amitriptyline antinociception 72 h after the last i.c.v. injection. The sensitivity to both analgesic drugs returned 7 days after antisense oligonucleotide injection, indicating the absence of irreversible damage or toxicity. Treatment with a degenerated oligonucleotide did not modify the clomipramine- and amitriptyline-induced antinociception in comparison with that in naive (unpretreated controls), vector and saline i.c.v.-injected mice. A quantitative reverse transcription-polymerase chain reaction (RT-PCR) study demonstrated a reduction in mRNA levels only in the antisense oligonucleotide treated group. Antisense oligonucleotide, degenerated oligonucleotide or vector pretreatment, in the range of doses used, did not produce any behavioural impairment as revealed by the mouse rotarod and hole-board tests. The present results indicate that modulation of the mKv1.1 K+ channel plays an important role in the central analgesia induced by the tricyclic antidepressants, clomipramine and amitriptyline.