The effects of postmortem delay on mu, delta and kappa opioid receptor subtypes in rat brain and guinea pig cerebellum evaluated by radioligand receptor binding

Fundamental features of receptor-mediated Gαi/o activation in human prefrontal cortical membranes: A postmortem study

To elucidate possible abnormalities in transmembrane signal transduction in psychiatric diseases, use of autopsy brain is a feasible approach. However, postmortem studies should be interpreted with caution concerning such factors as age, gender, psychotropic drug history, agonal state, postmortem delay (PMD), and storage period. In this study, agonist-induced [³⁵S]GTPγS binding was performed in postmortem dorsolateral prefrontal cortical membranes of 40 control subjects. In addition to the previously reported G protein-coupled receptor (GPCR)-mediated G_i/o activation, κ-opioid receptor-mediated [³⁵S]GTPγS binding was detected by using U-50,448. The responses elicited by 16 different agonists were determined, and the effects of several factors were investigated. Gender difference was negligible. Concentration-response curve of histamine H₃ receptor-mediated [³⁵S]GTPγS binding was shifted rightward in the subjects with some drugs detected at toxicological screening. Age-related alterations were minimal, except for the age-dependent supersensitivity of μ-opioid receptor-mediated Gα_i/o activation, revealed by endomorphin-1- and DAMGO-stimulated [³⁵S]GTPγS binding. Age-related increase in %E_max values was also detected as to DPDPE-induced [³⁵S]GTPγS binding through δ-opioid receptors. With an exception of NOP receptor/G-protein coupling, GPCR-mediated [³⁵S]GTPγS binding is relatively stable irrespective of PMD or storage period. There were many positive correlations among the %E_max values for different receptor subtypes, which might reflect formation of heterodimer complex of such GPCRs coupled to the same G_i/o proteins. These results provide us with important fundamental data in the future project using human postmortem brains from patients with psychiatric disorders.

Functional coupling between adenosine A1 receptors and G-proteins in rat and postmortem human brain membranes determined with conventional guanosine-5'-O-(3-[35S]thio)triphosphate ([35S]GTPγS) binding or [35S]GTPγS/immunoprecipitation assay

Adenosine signaling plays a complex role in multiple physiological processes in the brain, and its dysfunction has been implicated in pathophysiology of neuropsychiatric diseases such as schizophrenia and affective disorders. In the present study, the coupling between adenosine A₁ receptor and G-protein was assessed by means of two [³⁵S]GTPγS binding assays, i.e., conventional filtration method and [³⁵S]GTPγS binding/immunoprecipitation in rat and human brain membranes. The latter method provides information about adenosine A₁ receptor-mediated Gα_i-3 activation in rat as well as human brain membranes. On the other hand, adenosine-stimulated [³⁵S]GTPγS binding determined with conventional assay derives from functional activation of Gα_i/o proteins (not restricted only to Gα_i-3) coupled to adenosine A₁ receptors. The determination of adenosine concentrations in the samples used in the present study indicates the possibility that the assay mixture under our experimental conditions contains residual endogenous adenosine at nanomolar concentrations, which was also suggested by the results on the effects of adenosine receptor antagonists on basal [³⁵S]GTPγS binding level. The effects of adenosine deaminase (ADA) on basal binding also support the presence of adenosine. Nevertheless, the varied patterns of ADA discouraged us from adding ADA into assay medium routinely. The concentration-dependent increases elicited by adenosine were determined in 40 subjects without any neuropsychiatric disorders. The increases in %E_max values determined by conventional assay according to aging and postmortem delay should be taken into account in future studies focusing on the effects of psychiatric disorders on adenosine A₁ receptor/G-protein interaction in postmortem human brain tissue.

Opioid system and Alzheimer's disease

The opioid system may be involved in the pathogenesis of AD, including cognitive impairment, hyperphosphorylated tau, Aβ production, and neuroinflammation. Opioid receptors influence the regulation of neurotransmitters such as acetylcholine, norepinephrine, GABA, glutamate, and serotonin which have been implicated in the pathogenesis of AD. Opioid system has a close relation with Aβ generation since dysfunction of opioid receptors retards the endocytosis and degradation of BACE1 and γ-secretase and upregulates BACE1 and γ-secretase, and subsequently, the production of Aβ. Conversely, activation of opioid receptors increases the endocytosis of BACE1 and γ-secretase and downregulates BACE1 and γ-secretase, limiting the production of Aβ. The dysfunction of opioid system (opioid receptors and opioid peptides) may contribute to hyperphosphorylation of tau and neuroinflammation, and accounts for the degeneration of cholinergic neurons and cognitive impairment. Thus, the opioid system is potentially related to AD pathology and may be a very attractive drug target for novel pharmacotherapies of AD.

Depletion of glutathione does not affect electron transport chain complex activity in brain mitochondria: Implications for Parkinson disease and postmortem studies

Glutathione is an important antioxidant in the brain that appears to be decreased, in conjunction with mitochondrial complex I activity, in Parkinson disease patients. In postmortem analysis, measurement of glutathione levels and complex I activity can be delayed up to 20h. We investigated whether depletion of glutathione in the preweanling rat induces a reduction in complex I activity in brain mitochondria and the effects that postmortem delay has on glutathione levels and electron transport chain activity. After injection with the glutamate-cysteine ligase inhibitor, buthionine sulfoximine (L-BSO), glutathione levels were decreased by 53% compared to the control values in whole-brain homogenates. During postmortem delay of 24h, in which animals were kept at 4°C, the levels of glutathione decreased in the control group by 58% and in the L-BSO-treated group by 79%. However, during this period, there were no changes in mitochondrial electron transport chain complex I, II-III, or IV activity in either group. These results suggest that a preexisting deficiency of glutathione or a loss of glutathione during postmortem delay does not influence mitochondrial respiratory chain activity in the brain.

Temporal lobe epilepsy causes selective changes in mu opioid and nociceptin receptor binding and functional coupling to G-proteins in human temporal neocortex

There is no information concerning signal transduction mechanisms downstream of the opioid/nociceptin receptors in the human epileptic brain. The aim of this work was to evaluate the level of G-proteins activation mediated by DAMGO (a mu receptor selective peptide) and nociceptin, and the binding to mu and nociceptin (NOP) receptors and adenylyl cyclase (AC) in neocortex of patients with pharmacoresistant temporal lobe epilepsy. Patients with temporal lobe epilepsy associated with mesial sclerosis (MTLE) or secondary to tumor or vascular lesion showed enhanced [3H]DAMGO and [3H]forskolin binding, lower DAMGO-stimulated [35S]GTPgammaS binding and no significant changes in nociceptin-stimulated G-protein. [3H]Nociceptin binding was lower in patients with MTLE. Age of seizure onset correlated positively with [3H]DAMGO binding and DAMGO-stimulated [35S]GTPgammaS binding, whereas epilepsy duration correlated negatively with [3H]DAMGO and [3H]nociceptin binding, and positively with [3H]forskolin binding. In conclusion, our present data obtained from neocortex of epileptic patients provide strong evidence that a) temporal lobe epilepsy is associated with alterations in mu opioid and NOP receptor binding and signal transduction mechanisms downstream of these receptors, and b) clinical aspects may play an important role on these receptor changes.

Opioid receptor binding in parahippocampus of patients with temporal lobe epilepsy: its association with the antiepileptic effects of subacute electrical stimulation

Opioid receptor binding was evaluated in parahippocampal cortex (PHC) obtained from patients with intractable mesial temporal lobe epilepsy (MTLE) with and without subacute high frequency electrical stimulation (HFS) in this brain area. Mu, delta and nociceptin receptor binding was determined by autoradiography in PHC of five patients (ESAE group) with MTLE history of 14.8 +/- 2.5 years and seizure frequency of 11 +/- 2.9 per month, two of them (40%) with mesial sclerosis. This group demonstrated antiepileptic effects following subacute HFS (130 Hz, 450 micros, 200-400 microA), applied continuously during 16-20 days in PHC. Values were compared with those obtained from patients with severe MTLE (history of 21.7 +/- 2.8 years and seizure frequency of 28.2 +/- 14 per month) in whom electrical stimulation did not induce antiepileptic effects (ESWAE group, n = 4), patients with MTLE in whom no electrical stimulation was applied (MTLE group, n = 4) and autopsy material acquired from subjects without epilepsy (n = 4 obtained from three subjects). Enhanced 3H-DAMGO (MTLE, 755%; ESAE, 375%; ESWAE, 693%), 3H-DPDPE (MTLE, 242%; ESAE, 80%; ESWAE, 346%) and 3H-nociceptin (MTLE, 424%; ESAE, 217%; ESWAE, 451%) binding was detected in the PHC of all epileptic groups. However, tissue obtained from ESAE group demonstrated lower opioid receptor binding (3H-DAMGO, 44.5%, p < 0.05; 3H-DPDPE, 47%, p < 0.05; 3H-nociceptin, 39.3%, p < 0.5) when compared with MTLE group. The present results indicate that a high effectiveness to the antiepileptic effects induced by HFS is associated with reduced opioid peptide binding.

The role of the courts in clinical decision making

With advances in medical technology more can be offered with respect to treatment, for example, in neonates born prematurely. This raises the public's expectations of what medical professionals can offer and puts healthcare professionals under pressure to continue treatment, which may ultimately be futile. The courts may be asked to intervene in those cases where there is disagreement between parents and healthcare professionals. This may occur where doctors refuse to instigate or continue futile treatments or where treatment is not felt to be in the best interests of the patient. Cases may also be referred to the courts where doctors feel treatment options do exist but those with parental responsibility refuse to consent. Disagreement may also occur between parents. The best interests of the child are paramount and their welfare should always be the primary consideration. However, the court's opinion will be increasingly sought as parents' expectations increase and doctors fear litigation if they act against the parents' wishes. This paper reviews the role of the courts, using a number of high profile cases as examples. While the courts generally support the views of the healthcare professional, this cannot be guaranteed.

Influence of age, postmortem delay and freezing storage period on cannabinoid receptor density and functionality in human brain

It has been suggested that cannabimimetic drugs could be of interest in the treatment of several nervous disorders. Thus, it is important to analyse the distribution and properties of cannabinoid (CB) receptors directly in human brain. As postmortem human tissue is subjected to the effects of several biological variables, we have analyzed by autoradiography the influence of age, postmortem delay and freezing storage period (at -25 degrees C) on two parameters corresponding to cannabinoid CB1 receptors in human frontal cortex: receptor density and degree of activation of G-proteins ([35S]GTPgammaS assays). A significant decrease in the amount of both receptor density and agonist-stimulated G-protein activity was observed with age, revealing a mean reduction of about 10% per decade. In contrast, no significant correlations were found with postmortem delay either for CB1 receptors density or functionality. Finally, both parameters (receptor density and [35S]GTPgammaS response) were significantly reduced with freezing storage period at -25 degrees C in frontal cortical layers. Non-linear analysis of these data yielded values between 12 and 24 months of storage for a 50% reduction. In conclusion, when studying CB1 receptor properties in human brain samples, a careful analysis (and matching) for variables such as age and freezing storage period has to be carried out.

Characterization of kappa1-opioid receptor binding in human insular cortex

Mesolimbic dopaminergic neurotransmission is modulated by dynorphin peptides binding to kappa-opioid receptors. The interaction between dynorphin and dopamine systems makes the kappa-opioid receptor a potential drug discovery target for the development of therapeutic agents for schizophrenia and drug abuse. This study reports the specificity and parameters of [3H]U69593 binding in the insular cortex, a representative corticolimbic area of the human brain. The results demonstrate that the radioligand [3H]U69593 labels a single population of receptors in human insular cortex with an affinity in the low nanomolar range. The pharmacological profile for inhibition of [3H]U69593 binding was determined in this brain region using drugs known to bind to mu, kappa and delta opioid receptors. The results show that kappa-opioid selective agonists and antagonists inhibit binding of this ligand in human brain with comparable affinities and rank order as previously described for rat and guinea pig brain and the cloned kappa1-opioid receptor subtype.