Irena Nalepa

Increased responsiveness of the cerebral cortical phosphatidylinositol system to noradrenaline and carbachol in senescent rats

The responsiveness of cerebral cortical alpha 1-adrenoceptors and cholinergic muscarinic M1 receptors was assessed in young (3 months) and aged (24 months) male Sprague-Dawley rats. The measure of responsiveness was the accumulation of inositol phosphate (IP) formed in [3H]myo-inositol-preloaded cerebral cortical slices in the presence of lithium, following stimulation with various concentrations of noradrenaline (1-300 microM) and carbachol (5-1000 microM). In old rats the maximum response to noradrenaline was higher by 80%, and that to carbachol by 33%, indicating an increased responsiveness of the investigated receptors in senescence.

Behavioural and biochemical studies of citalopram and WAY 100635 in rat chronic mild stress model

Reversal of chronic mild stress (CMS)-induced decrease of sucrose consumption has been studied in rats after 2, 7, 14, and 35 days treatment with imipramine, citalopram (both 10 mg/kg per day, i.p.), WAY 100635 (0.2 mg/kg sc, b.i.d.), and citalopram plus WAY 100635. Bmax, Kd, and functional status [cyclic AMP (cAMP) generation] of beta1-adrenoceptors were assessed in cortical tissue at the same time points. Citalopram reversed CMS-induced reduction of sucrose intake at an earlier time point than imipramine. WAY 100635 was not effective and did not potentiate the effect of citalopram. CMS produced increase of Bmax. Imipramine decreased Bmax in controls (Days 2, 7, 14, and 35) and normalised Bmax in stressed animals (Day 35). Citalopram, WAY 100635, and the combination increased Bmax in stressed animals and controls (Days 14 and 35). Inconsistent changes of Kd values and of cAMP responses to noradrenaline (NA) stimulation were observed. Thus stress- and drug-induced effects on beta1-adrenoceptors do not appear to be a common biochemical marker of antidepressant-like activity in the CMS model.

Pharmacological actions of the antidepressant venlafaxine beyond aminergic receptors

The present study examines the effects of the antidepressant venlafaxine, a dual amine reuptake inhibitor, on (a) in vivo regulation of the densities of high- and low-affinity dihydroalprenolol (DHA) binding sites in the cortex of normal and reserpinized Sprague-Dawley rats and (b) targets beyond the beta adrenoceptor. While venlafaxine (30 mg/kg i.p. b.i.d.) administered for 4 d did not alter the DHA-binding parameters in the cortex of normal rats, it significantly reduced, in reserpinized animals, the number of up-regulated low-affinity sites (R(L)) which have been tentatively identified as serotonin(1B) sites. The drug did not influence the up-regulated high-affinity (R(H)) DHA-binding sites (beta-adrenoceptor sites). Venlafaxine failed to alter the up-regulated R(L) sites in brains of rats depleted of serotonin (5-HT) by p-chlorophenylalanine (PCPA) indicating that the normalization by venlafaxine of the up-regulated R(L) receptor population is mediated by increased synaptic 5-HT. Venlafaxine, given for a short period of time, thus mimicked the action of fluoxetine. While venlafaxine (20 mg/kg i.p. b.i.d.) given for 10 d did not change protein kinase A activity as assessed by the phosphorylation of kemptide in the 900 g supernatant or particulate fractions, the drug significantly reduced phosphorylated cAMP response-element binding protein (CREB-P) in nuclear lysates of cortex after chronic but not acute administration. Depletion of 5-HT by PCPA did not alter the venlafaxine-induced change in nuclear CREB-P. Lastly, analysis of reverse transcribed cortical CREB mRNA by competitive PCR indicated that the mean steady-state levels of CREB mRNA in venlafaxine vs. saline-treated animals were not significantly different. Therefore, since the phosphorylation status of CREB determines its transcriptional activity the reduction of nuclear CREB-P may be venlafaxines most relevant action beyond the adrenoceptor.

Enhancement of the responsiveness of cortical adrenergic receptors by chronic administration of the 5-hydroxytryptamine uptake inhibitor citalopram.

Abstract: The aim of this study was to evaluate the effect of citalopram, a second generation antidepressant agent producing no β‐down‐regulation, on the receptors and second messenger systems related to noradrenergic transmission in the cerebral cortex of the rat. We confirmed that citalopram does not bind to α1‐, α2‐, and β2‐adrenoceptors, but we found that it attenuates the inhibitory action of the protein kinase C activator, 12‐O‐tetradecanoylphorbol 13‐acetate, on the noradrenergic response from α1‐adrenoceptor. In contrast to most antidepressants, chronic treatment with citalopram does not produce β‐down‐regulation, but increases the responses to noradrenaline from β‐adrenoceptors without increasing the β1,‐adrenoceptor density. Chronic treatment with citalopram also increases the maximal response from α1‐adrenoceptor. The results indicate that β‐down‐regulation is not a necessary characteristic of an efficient antidepressant drug.

A possible physiological role for cerebral tetrahydroisoquinolines.

Tetrahydroisoquinolines present in the mammalian brain, 1,2,3,4-tetrahydroisoquinoline (TIQ) and salsolinol, suspected to cause neurodegeneration leading to Parkinsons disease, were investigated to find their possible physiological role. To this aim their behavioral and receptor effects induced after a single dose were tested in mice and rats. Both compounds do not affect significantly the basal locomotor activity, very effectively block hyperactivity induced by apomorphine (rats) and amphetamine (mice), only partially block hyperactivity induced by scopolamine, do not affect locomotor stimulation induced by cocaine, and strongly augment the running fit induced by morphine (mice). They do not produce extrapyramidal symptoms and do not potentiate haloperidol-induced catalepsy (rats). TIQ and salsolinol do not displace antagonists of several receptors (including D1 and D2) from their binding sites, but displace the agonists of α2-adrenoreceptors, [3H] clonidine and of dopamine receptors, [3H] apomorphine. The results indicate that salsolinol and TIQ act as specific antagonists of agonistic conformation of dopamine receptors, and owing to that may play a role of endogenous feed-back regulators of the dopaminergic system. Those properties make tetrahydroisoquinolines potential antidopaminergic drugs devoid of extrapyramidal effects, with possible application in substance addiction disorder as anti-craving agents.

Minocycline influences the anti-inflammatory interleukins and enhances the effectiveness of morphine under mice diabetic neuropathy

A single streptozotocin (STZ) injection in mice can induce significant neuropathic pain along with an increase in plasma glucose levels and a decrease in body weight. Seven days after the administration of STZ, an upregulation of C1q-positive cells was observed. Additionally, interleukins (IL-1beta, IL-3, IL-4, IL-6, IL-9, IL12p70, IL-17); proteins of the tumor necrosis factor (TNF) family, e.g., IFNgamma and sTNF RII, were upregulated. Chronic administration of minocycline increases antinociceptive factors (IL-1alpha, IL-2, IL-10, sTNFRII) in diabetic mice. Minocycline also reduces the occurrence of neuropathic pain and significantly potentiates the antiallodynic and antihyperalgesic effects of morphine.

Opposite effect of simple tetrahydroisoquinolines on amphetamine- and morphine-stimulated locomotor activity in mice.

Summary. Endogenous tetrahydroisoquinolines, such as 1,2,3,4-tetrahydroisoquinoline (TIQ) and 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol), were tested for their interaction with motor effects of amphetamine and morphine in C57BL/6 mice. TIQ binding to cortical adrenergic α1, α2 and β receptors, striatal dopamine D1 and D2 receptors and cortical L-type calcium channels in the Wistar rat was also studied. Both compounds in high doses reduced the mouse locomotor activity, and in doses not affecting activity inhibited the motor stimulation induced by amphetamine, 2 or 3 mg/kg ip, but facilitated the hyperactivity induced by 10 mg/kg of morphine. TIQ did not displace ligands that are antagonists for several receptor sites (including D1 and D2 receptors), but displaced an agonist of α2-adrenoceptor, clonidine. It is proposed that TIQ and salsolinol specifically antagonize the agonistic conformation of dopamine receptor and that endogenous 1,2,3,4-tetrahydroisoquinolines may play a role of natural feedback regulators of the activity of dopaminergic system.

Reversal by imipramine of β-adrenoceptor up-regulation induced in a chronic mild stress model of depression

Male Wistar rats were subjected to a chronic mild stress procedure involving different stress stimuli applied for 8 weeks. During this time the consumption of 1% sucrose solution was monitored at weekly intervals. After the first 3 weeks, when stressed animals displayed a reduction of sucrose consumption, the control and stressed groups were divided into subgroups receiving daily placebo or imipramine (10 mg/kg/day) treatment. After 5 weeks of treatment, 24 h after the last injection, the rats were killed and beta-adrenoceptor density and affinity in cortical membrane preparations and the accumulation of cyclic AMP in cortical slices stimulated with noradrenaline were assessed. While in stressed placebo-treated rats the sucrose consumption remained reduced, in the imipramine-treated group the level of consumption gradually returned to control values. The stressed placebo-treated rats also displayed an increase in cortical beta-adrenoceptor density (by 34%) with no changes in affinity, and an increase (22%) in the cyclic AMP response to noradrenaline in cortical slices. Imipramine, which in non-stressed rats did not affect sucrose intake but depressed the beta-adrenoceptor density and the cyclic AMP response, reversed the stress-induced decrease in sucrose consumption and the increase in the beta-adrenoceptor density; at physiological noradrenaline concentrations it also reduced the enhanced cyclic AMP response. The results suggest that the chronic mild stress procedure produces behavioral and biochemical changes consistent with a realistic model of depression in animals.

Concomitant administration of fluoxetine and amantadine modulates the activity of peritoneal macrophages of rats subjected to a forced swimming test

Recent studies show that administration of a non-competitive NMDA receptor antagonist, amantadine (AMA), potentiates the action of antidepressant drugs. Since antidepressants may modulate functioning of the immune system and activation of a pro-inflammatory response in depressive disorders is frequently reported, the aim of the present study was to examine whether a combined administration of AMA and the antidepressant, fluoxetine (FLU), to rats subsequently subjected to a forced swimming test (FST) modifies the parameters of macrophage activity, directly related to their immunomodulatory functions, i.e., arginase (ARG) activity and synthesis of nitric oxide (NO). We found that 10 mg/kg AMA and 10 mg/kg FLU, ineffective in FST for antidepressant-like activity when administered alone, increased the ARG/NO ratio in macrophages when administered concomitantly. This effect was accompanied by a decrease of cellular adherence. Concurrently, the basal metabolic activity of the cells measured with reduction of resazurin, and intracellular host defense as assessed by a synthesis of superoxide anion, were not affected by such antidepressive treatment. Our data indicate that co-administration of AMA and FLU decreases the pro-inflammatory properties of macrophages and causes a redirection of immune response toward anti-inflammatory activity, as one can anticipate in the case of an effective antidepressive treatment.

Prenatal stress affects insulin-like growth factor-1 (IGF-1) level and IGF-1 receptor phosphorylation in the brain of adult rats

It has been shown that stressful events occurring in early life have a powerful influence on the development of the central nervous system. Insulin-like growth factor-1 (IGF-1) promotes the growth, differentiation and survival of both neurons and glial cells and is thought to exert antidepressant-like activity. Thus, it is possible that disturbances in the function of the IGF-1 system may be responsible for disturbances observed over the course of depression. Prenatal stress was used as a valid model of depression. Adult male offspring of control and stressed rat dams were subjected to behavioural testing (forced swim test). The level of IGF-1 in the blood and the expression of IGF-1, IGF-1R, and IRS-1/2 in the hippocampus and frontal cortex using RT-PCR, ELISA and western blotting were measured. In addition the effect of intracerebroventricularly administered IGF-1 and/or the IGF-1R receptor antagonist JB1 in the forced swim test was studied. Prenatally stressed rats showed depressive like behaviour, including increased immobility time as well as decreased mobility and climbing. Intracerebroventricular administration of IGF-1 reversed these effects in stressed animals, whereas concomitant administration of the IGF-1R antagonist JB1 completely blocked the effects. Biochemical analysis of homogenates from the hippocampus and frontal cortex revealed decreases in IGF-1 level and IGF-1R phosphorylation along with disturbances in IRS-1 phosphorylation. These findings reveal that prenatal stress alters IGF-1 signalling, which may contribute to the behavioural changes observed in depression.