Hippocampal administration of kappa-opioid receptor antisense exacerbates isolation-induced hypertension

Hippocampal sulcal cavities: prevalence, risk factors and relationship to memory impairment

While hippocampal volumes have been extensively examined in neuropsychiatric disorders and ageing, small areas of signal variation within the hippocampus commonly observed on MRI, described as hippocampal sulcal cavities (HSCs), have received less attention. We review the published literature on HSCs to examine their prevalence, putative aetiological factors such as hypertension, and possible cognitive correlates. HSCs were reported in 77% (66% weighted mean) of patients with memory disorders and 48% (47% weighted mean) of controls, and the prevalence increased with age in healthy subjects (r=0.64, p=0.047). A number of studies reported hypertension as a risk factor, and related their presence to poorer memory function. Further work is needed to fully understand the clinical significance of these lesions.

Endogenous kappa opioids mediate the action of brain angiotensin II to increase blood pressure

The objectives of this study were to determine whether endogenous opioids are operative in modulating the CNS action of angiotensin II (ang II) on blood pressure and to determine whether this is mediated by endogenous mu or kappa opioid receptor agonists. The study design was: unanesthetized Wistar rats, 300-400g, previously instrumented with a cannula in the lateral cerebral ventricle and a catheter in the femoral artery, had ang II, 0.5microg, injected into the lateral cerebral ventricle (ICV). Groups were allocated to receive naloxone, a mu opioid receptor antagonist or MR 2266 a selective kappa opioid receptor antagonist prior to ang II. In other experiments in unanesthetized rats, baroreceptor reflex function was assessed by intravenous injection of phenylephrine or nitroprusside and the interaction of endogenous opioids and ang II ascertained with use of the mu or kappa opioid receptor antagonist .

RESULTS

Ang II significantly (p<0.05) increased systolic and diastolic blood pressure. The kappa opioid antagonist, MR 2266, 25microg/kg ICV, significantly (p<0.05) reduced and MR 2266, 50microg/kg ICV, completely prevented the increase in blood pressure produced by ang II. In contrast, the mu opioid receptor antagonist, naloxone, 50microg/kg, ICV, did not significantly attenuate the blood pressure responses to ang II. Ang II induced alteration in baroreceptor function. The effect of ang II on baroreceptor function was significantly antagonized by the kappa opioid receptor antagonist MR 2266. In conclusion, these data indicate that: (a) endogenous opioids modulate the pressor response to intracerebral ang II, (b) this effect is mediated mainly through endogenous kappa opioid agonists and kappa rather than mu opioid receptors, (c) alteration of baroreceptor sensitivity by ang II is modulated by endogenous kappa opioids.

Ten years of antisense inhibition of brain G-protein-coupled receptor function

Antisense oligonucleotides (AOs) are widely used as tools for inhibiting gene expression in the mammalian central nervous system. Successful gene suppression has been reported for different targets such as neurotransmitter receptors, neuropeptides, ion channels, trophic factors, cytokines, transporters, and others. This illustrates their potential for studying the expression and function of a wide range of proteins. AOs may even find therapeutic applications and provide an attractive strategy for intervention in diseases of the central nervous system (CNS). However, a lack of effectiveness and/or specificity could be a major drawback for research or clinical applications. Here we provide a critical overview of the literature from the past decade on AOs for the study of G-protein-coupled receptors (GPCRs). The following aspects will be considered: mechanisms by which AOs exert their effects, types of animal model system used, detection of antisense action, effects of AO design and delivery characteristics, non-antisense effects and toxicological properties, controls used in antisense studies to assess specificity, and our results (failures and successes). Although the start codon of the mRNA is the most popular region (46%) to target by AOs, targeting the coding region of GPCRs is almost as common (41%). Moreover, AOs directed to the coding region of the GPCR mRNA induce the highest reductions in receptor levels. To resist degradation by nucleases, the modified phosphorothioate AO (S-AO) is the most widely used and effective oligonucleotide. However, the end-capped phosphorothioate AOs (ECS-AOs) are increasingly used due to possible toxic and non-specific effects of the S-AO. Other parameters affecting the activity of a GPCR-targeting AO are the length (mostly an 18-, 20- or 21-mer) and the GC-content (mostly varying from 30 to 80%). Interestingly, one-third of the AOs successfully targeting GPCRs possess a GC/AT ratio of 61-70%. AO-induced reductions in GPCR expression levels and function range typically from 21 to 40% and 41 to 50%, respectively. In contrast to many antisense reviews, we therefore conclude that the functional activity of a GPCR after AO treatment correlates mostly with the density of the target receptors (maximum factor 2). However, AOs are no simple tools for experimental use in vivo. Despite successful results in GPCR research, no general guidelines exist for designing a GPCR-targeting AO or, in general, for setting up a GPCR antisense experiment. It seems that the correct choice of a GPCR targeting AO can only be ascertained empirically. This disadvantage of antisense approaches results mostly from incomplete knowledge about the internalisation and mechanism of action of AOs. Together with non-specific effects of AOs and the difficulties of assessing target specificity, this makes the use of AOs a complex approach from which conclusions must be drawn with caution. Further antisense research has to be carried out to ensure the adequate use of AOs for studying GPCR function and to develop antisense as a valuable therapeutic modality.