Casos relacionados de la judicialización de la prueba material y su

5.4.2.1/ Injection of atipamezole alone

In both brain areas, noradrenaline efflux in animals receiving atipamezole alone was no different, 1 h after the injection, from that in animals destined for BTS 54 354. This reflects findings from an earlier study done in this laboratory in which injection of atipamezole or another az-antagonist, RX 821002, had transient effects only on the noradrenaline efflux in both the frontal cortex and the hypothalamus (Wortley et a l,

1999a; 1999b). After administration of these agents, noradrenaline efflux reached a maximum increase within 20 min and progressively returned to basal levels thereafter.

Also, in the present experiments, in both the frontal cortex and the hypothalamus of animals which received atipamezole only, whether or not noradrenaline efflux was increased transiently by the atipamezole injection, the noradrenaline efflux was stable throughout the experiments.

5.4.2.2/ The effects o f atipamezole on the BTS 54 354 Induced response

Administration of atipamezole (1 mg/kg; i.p.), 2 h before the beginning of infusion of BTS 54 354, increased the response induced by the reuptake inhibitor, in both brain areas. This is supported by findings from a microdialysis study by Gobert and colleagues. They reported that injection of atipamezole (0.16 mg/kg, s.c.) potentiated the effect of duloxetine, another noradrenaline and 5-HT reuptake inhibitor, on noradrenaline efflux in the frontal cortex (Gobert et al. 1997). However, so far, the hypothalamus has not been studied in this way.

Although it is evident that blockade of (Xi-adrenoceptors alone can increase

release of noradrenaline in both the frontal cortex and the hypothalamus (whether given systemically, or via the probe), an increase in noradrenaline ejflux is evident only when

either an uptake inhibitor is co-administered (present results; Wortley et aL, 1999a; 1999b; Gobert et aL 1997) or when animals are aroused, as by the injection procedure, so that reuptake cannot keep pace with release (Dailey and Stanford, 1995).

The present results indicate that there was no difference in the noradrenaline response to infusion of BTS 54 354, following injection of atipamezole, in the frontal cortex and the hypothalamus: i.e. the efflux in noradrenaline was the same after administration of the reuptake blocker despite the absence of regulation of firing rate by blockage of the a2-adrenoceptors. These results, obtained with an g^-antasonist

administered systemically. suggest that the oyerall modulation of noradrenaline efflux by Œz-adrenoceptors does not differ in the two brain areas (at least when the reuptake inhibitor is giyen locally). Howeyer, it is noteworthy that the results presented in Chapter 7 show that 5-HT modulates the noradrenergic response to BTS 54 354 and that the impact of this differs considerably between the frontal cortex and the hypothalamus. Neyertheless, such modulation does not undermine the main conclusions described in the present chapter,

Wortley et al. (1999b) also found that the noradrenergic response to systemic administration of sibutramine was potentiated by treatment with the az-antagonists, RX 821002 or atipamezole, in both the frontal cortex and the hypothalamus. Howeyer, Wortley and colleagues found that, when infused locally into the terminal fields, RX 821002, increased the response to systemic sibutramine (10 mg/kg, i.p.) by 3-fold in the hypothalamus compared to 1.5-fold in the frontal cortex. The authors inferred that terminal a2-adrenoceptors in the hypothalamus had more influence on the noradrenaline

efflux than those in the frontal cortex. Moreover, they also observed that the noradrenaline response to sibutramine (10 mg/kg) declined rapidly after 40 min in the hypothalamus, but that subsequent infusion of RX 821002 restored efflux to its maximum. Altogether, these results suggested that the terminal a2-adrenoceptors play a

major role in the regulation of noradrenaline release in the hypothalamus.

Finally, in the frontal cortex, when atipamezole was administered systemically, the decline in noradrenaline efflux, seen after 2 h in animals that received BTS 54 354 alone, was abolished. This suggests that a2-adrenoceptors were responsible for this

Chapters: The effects of local administration of the SNRI, BTS 54 354, on noradrenaline effiux in the frontai cortex and the hypothaiamus

decline. However, in the hypothalamus, although the noradrenaline response was sustained for longer when animals received atipamezole, noradrenaline efflux declined after 3 h of infusion. Such attenuation of noradrenaline efflux must rely on a mechanism which does not involve a2-adrenoceptors.

In conclusion, the present results show that there is no difference in the amplitude of the noradrenaline response to sibutramine and its metabolite, BTS 54 354, in both the frontal cortex and the hypothalamus. However, the time course of the response to these drugs differed: the delay in the increase seen when sibutramine is infused supports evidence that this drug has to be metabolised in order to potently block reuptake of noradrenaline. Moreover, there is ultimately a decrease in the response to BTS 54 354 despite continued infusion of the drug. This does not happen when sibutramine is infused which seems to indicate that different populations of receptors contribute to the regulation o f noradrenaline efflux.

Finally, there is no difference in the effects of local administration of the reuptake inhibitor, BTS 54 354, in the frontal cortex and the hypothalamus. Since accumulation of extracellular noradrenaline after administration of a reuptake blocker is secondary to its impulse-evoked release, this seems to suggest that there are no regional differences in the net effects of the main factors governing the resting concentrations of extracellular noradrenaline in both brain areas. Moreover, administration of the ai-antagonist, atipamezole, increased the BTS 54 354 induced response in the same extent in both brain regions, although the duration of the effects of BTS 54 354 differed. Therefore, it seems that impulse-evoked release of noradrenaline is normally blunted by activation of a2-adrenoceptors in both the frontal cortex and the hypothalamus.

Key findings:

• The amplitude of the noradrenaline response to local BTS 54 354 (a potent noradrenaline reuptake inhibitor) is the same in the frontal cortex and the hypothalamus.

• The a2-antagonist, atipamezole, increases the noradrenaline

response to local BTS 54 354 to the same extent in the frontal cortex and the hypothalamus.

• The duration of the cumulative effects of atipamezole and local BTS 54 354 is longer in the frontal cortex than in the hypothalamus.

Chapter 6: Effects of local infusion of 6-amphetamlne on noradrenaline efflux In the frontal cortex