Alterations of muscarinic cholinergic receptors in the hippocampal formation of stressed rat: in vitro quantitative autoradiographic analysis

Geniposide promotes splenic Treg differentiation to alleviate colonic inflammation and intestinal barrier injury in ulcerative colitis mice

Geniposide has been proven to have a therapeutic effect on ulcerative colitis (UC) in animals, but its potential mechanism in UC remains to be clarified. The purpose of this study was to confirm the efficacy of geniposide in UC and to investigate the possible mechanism of geniposide in UC treatment. In vivo, geniposide relieved weight loss and reduced intestinal tissue damage in UC mice. Geniposide decreased the levels of IL-1β and TNF-α and increased IL-10 levels in the colon and serum of UC mice. Geniposide increased FOXP3 expression in the colon and the number of CD4+ FOXP3+ cells in the spleen of UC mice. BD750 abolished the above regulatory effect of GE on UC mice. In vitro, geniposide increased the number of CD4+ FOXP3+ cells in spleen cells from normal mice, decreased the levels of IL-1β, CCL2 and TNF-α in the supernatant of LPS-treated Caco-2 cells, and decreased the protein expression of Beclin-1 and Occludin in cacO-2 cells. Epirubicin inhibited the effect of geniposide on increasing the number of CD4+ FOXP3+ cells in spleen cells, attenuated the inhibitory effect of geniposide on proinflammatory factors and attenuated the upregulation of geniposide on tight junction proteins in LPS-treated Caco-2 cells in the coculture system. In conclusion, geniposide has an effective therapeutic effect on UC. Increasing Treg differentiation of spleen cells is the mechanism by which geniposide alleviates intestinal inflammation and barrier injury in UC.

Acute restraint stress decreases c-fos immunoreactivity in hilar mossy cells of the adult dentate gyrus

Although a great deal of information is available about the circuitry of the mossy cells (MCs) of the dentate gyrus (DG) hilus, their activity in vivo is not clear. The immediate early gene c-fos can be used to gain insight into the activity of MCs in vivo, because c-fos protein expression reflects increased neuronal activity. In prior work, it was identified that control rats that were perfusion-fixed after removal from their home cage exhibited c-fos immunoreactivity (ir) in the DG in a spatially stereotyped pattern: ventral MCs and dorsal granule cells (GCs) expressed c-fos protein (Duffy et al., Hippocampus 23:649-655, 2013). In this study, we hypothesized that restraint stress would alter c-fos-ir, because MCs express glucocorticoid type 2 receptors and the DG is considered to be involved in behaviors related to stress or anxiety. We show that acute restraint using a transparent nose cone for just 10 min led to reduced c-fos-ir in ventral MCs compared to control rats. In these comparisons, c-fos-ir was evaluated 30 min after the 10 min-long period of restraint, and if evaluation was later than 30 min c-fos-ir was no longer suppressed. Granule cells (GCs) also showed suppressed c-fos-ir after acute restraint, but it was different than MCs, because the suppression persisted for over 30 min after the restraint. We conclude that c-fos protein expression is rapidly and transiently reduced in ventral hilar MCs after a brief period of restraint, and suppressed longer in dorsal GCs.

Ventral tegmental area cholinergic mechanisms mediate behavioral responses in the forced swim test

Recent studies revealed a causal link between ventral tegmental area (VTA) phasic dopamine (DA) activity and pro-depressive and antidepressant-like behavioral responses in rodent models of depression. Cholinergic activity in the VTA has been demonstrated to regulate phasic DA activity, but the role of VTA cholinergic mechanisms in depression-related behavior is unclear. The goal of this study was to determine whether pharmacological manipulation of VTA cholinergic activity altered behavioral responding in the forced swim test (FST) in rats. Here, male Sprague-Dawley rats received systemic or VTA-specific administration of the acetylcholinesterase inhibitor, physostigmine (systemic; 0.06 or 0.125mg/kg, intra-cranial; 1 or 2μg/side), the muscarinic acetylcholine receptor (AChR) antagonist scopolamine (2.4 or 24μg/side), or the nicotinic AChR antagonist mecamylamine (3 or 30μg/side), prior to the FST test session. In control experiments, locomotor activity was also examined following systemic and intra-cranial administration of cholinergic drugs. Physostigmine administration, either systemically or directly into the VTA, significantly increased immobility time in FST, whereas physostigmine infusion into a dorsal control site did not alter immobility time. In contrast, VTA infusion of either scopolamine or mecamylamine decreased immobility time, consistent with an antidepressant-like effect. Finally, the VTA physostigmine-induced increase in immobility was blocked by co-administration with scopolamine, but unaltered by co-administration with mecamylamine. These data show that enhancing VTA cholinergic tone and blocking VTA AChRs has opposing effects in FST. Together, the findings provide evidence for a role of VTA cholinergic mechanisms in behavioral responses in FST.

The effects of stress on muscarinic receptors. Heterologous receptor regulation: yes or no?

1 Stress is usually comprehended as an event affecting mainly the catecholaminergic system, the hypothalamo-pituitary-adrenocortical (HPA) axis and the receptor systems connected to these neurotransmitters/hormones. Other neurotransmitter/hormone systems can be affected too. Here we review the available data on the effects of different stressful stimuli (physical, chemical, psychological/social, cardiovascular, affecting multiple system) on muscarinic receptors (MR). 2 The data suppose the existence of specific mechanisms that regulate the signalization through MR during different type of stress. 3 Physical stressors (cold vs. heat) reveal opposite type of changes on peripheral-tissue MRs. Chemical stressors (oxidative stress) are tightly connected with MR and it is especially interesting that the sensitivity of MR to oxidative stress is subtype-specific. It is also suggested that heterologous regulation can occur with psychological/social stressors on the organism. Cardiovascular system-disturbing stressors cause imbalance between autonomic receptors or down-regulate MR in the peripheral tissue. Immobilization caused opposite effects on MR in the central nervous system and periphery, where the changes are supposed to be due to heterologous regulation between receptor systems. 4 In conclusion, some data indicate that in specific conditions MR are regulated as a consequence of other changes rather than as a primary effect of stress. On the contrary, in some situations, MR are the first targets to respond to the stress. 5 These findings on stress-induced activity of the cholinergic system and changes in muscarinic receptors support the view that stress is a specific response of the organism.

Anxiety and panic: from human studies to animal research and back

The role of learning and conditioning varies across human anxiety disorders, and distinguishing between fear and panic is important to guide investigation in panic disorder. By reminding that some psychological and psychobiological theories view panic attacks as false alarms of unconditioned biological origin, we suggest that employing endophenotypes of biological and evolutionary relevance--such as the respiratory responses to suffocative stimuli--can be fruitful for both human research and animal models of panic, and can help keeping unconditioned components of the clinical picture separate from the conditioned components in the experimental setting. We present a review of a model of panic disorder by which idiosyncratic environmental adverse events can promote unconditioned and unexpected spells of physical alarm. Along the proposed causal pathway the alternative splicing expression of polymorphic genes of the cholinergic system play an important role. The overproduction of the Acetylcholinesterase readthrough splice variant after minor stress can promote passive avoidance and learning through action at the level of the corticolimbic circuitries, as well as heightened sensitivity to suffocative stimuli by action upon the cholinergic components of chemoception. When a component of anticipatory anxiety complicates the clinical picture of recurrent panic attacks, and the HPA becomes activated, the glucocorticoid response element 17 kb upstream of the Acetylcholinesterase gene transcription initiation site may sustain sensitivity to suffocative stimuli for prolonged time. Finally, we review how animal models of human panic based on unconditioned provocation of alarm reactions by the same respiratory panicogens that are employed in man are viable and promising.

Effects of isolation-rearing on serotonin-1A and M1-muscarinic receptor messenger RNA expression in the hipocampal formation of rats

The aim of the present work was to investigate if isolation rearing could change 5-HT1A or M1 muscarinic receptors messenger RNA (mRNA) expression in the hippocampal formation. Male Wistar rats were isolated either in single cages or in groups of six per cage soon after wearing during 30 days. After this period they were sacrificed and their brains removed for 'in situ' hybridization study using 32P-labeled oligonucleotide probes complementary to 5-HT1A or M1 muscarinic receptor mRNA. The results were analyzed by computerized densitometry. They showed a significant (P < 0.05, Mann-Whitney test) serotonin 1A (5-HT1A) mRNA expression increase in the dentate gyrus and CA3 areas of isolated animals. The signal also tended to be higher (P < 0.10) in CA1 and CA4 regions. No significant change on M1 mRNA expression was found. These results may reflect up-regulation of 5-HT1A gene transcription in response to deficits in hippocampal serotonin neurotransmission induced by social isolation.

Beyond the usual suspects: a cholinergic route for panic attacks

For unknown reasons and through poorly understood mechanisms, people at risk of panic attacks are hypersensitive to suffocative stimuli and experience hyperventilation and anxiety after exposure to heightened concentrations of carbon dioxide. Similarly to the physiological reflex response to hypercapnia in animals and man, the anxious response to carbon dioxide in people with panic disorder is at least partially controlled by the central muscarinic receptors. It is suggested here that some modifications of the cholinergic functions could underlie human individual differences in carbon dioxide sensitivity and proneness to experience panic attacks. The hypothesis is based upon experimental evidence that stressful and potentially harmful stimuli prime relatively long-lasting changes in cholinergic genes expression and cholinergic receptors' regulation. The adaptive sequels of these modifications include protection of the brain from overstimulation, and, at the level of the corticolimbic circuitries, promotion of passive avoidance and learning after stress. The extension of the same modifications to the cholinergic receptors involved in chemoception, however, could lower the threshold for reaction to suffocative stimuli, including carbon dioxide. The exaggerated sensitivity to carbon dioxide observed in humans suffering from panic attacks could then be thought of as an evolutionary cost of the involvement of the cholinergic system in shaping otherwise adaptive responses to stress and threatening stimuli.

Restriction of environmental space attenuates locomotor activity and hippocampal acetylcholine release in male rats

We examined the effects of the restriction of environmental space on hippocampal acetylcholine release and spontaneous locomotor activity. Four days after the housing in a large or small cage, sampling for microdialysis study was begun. The locomotor activity counts exhibited significant daily changes in all rats in either the large or small cage. But, the mean locomotor activity counts in rats in the small cage was significantly less than that in the large cage. In contrast, the amount of acetylcholine collected per 20-min sample exhibited significant diurnal changes in all six rats in the large cage and in 5 of 6 rats in the small cage. The mean acetylcholine release in the rat in the small cage was significantly lower than that in the rat in the large cage during the dark phase, but not during the light phase. In addition, during the dark phase, hippocampal acetylcholine release was closely associated with spontaneous activity in all six rats in the large cage but not in 3 of 6 rats in the small cage. The present study suggests that the restriction of environmental space somehow interfere with the spontaneous locomotor activity and hippocampal acetylcholine release during the dark phase.

Inescapable stress enhances extracellular acetylcholine in the rat hippocampus and prefrontal cortex but not the nucleus accumbens or amygdala

A number of experimental results has pointed to a cholinergic involvement in the stress response. Recently, analytical techniques have become available to measure acetylcholine release in vivo during exposure to various stressors. In these experiments, microdialysis was used to monitor acetylcholine output every 15 min in the dorsal hippocampus, amygdala, nucleus accumbens and prefrontal cortex before, during and after 1 h of restraint, including a 15-min session of intermittent tail-shock (1/min, 1 mA, 1-s duration) in rats. In response to the stressful event, acetylcholine release was significantly increased in the prefrontal cortex (186%; p < 0.01) and hippocampus (168%; P < 0.01) but not in the amygdala or nucleus accumbens. The sole effects observed in the amygdala and nucleus accumbens occurred upon release from the restrainer, at which point acetylcholine levels were significantly elevated in both areas (amygdala: 150%; P < 0.05; nucleus accumbens: 13%; P < 0.05). An enhanced acetylcholine release was also evident during this sample period in the hippocampus and prefrontal cortex. These data demonstrate an enhancement of cholinergic activity in response to stress in two acetylcholine projection systems (hippocampus and prefrontal cortex) but not in the intrinsic acetylcholine system of the nucleus accumbens or the extrinsic innervation of the amygdala. Moreover, the data showed that relief from stress was accompanied by a more ubiquitous acetylcholine response that extended to each site tested.

Immobilization stress-induced increase of hippocampal acetylcholine and of plasma epinephrine, norepinephrine and glucose in rats

We investigated the role of the hippocampal cholinergic neurons during immobilization stress in rats using a microdialysis technique. Blood levels of glucose, epinephrine and norepinephrine during immobilization stress were also determined. Acetylcholine release was initially increased by immobilization stress, then gradually decreased. Plasma level of epinephrine increased gradually and reached significance at 30 min after the start of immobilization and remained at the elevated level during immobilization. Plasma level of norepinephrine initially increased and reached significance at 30 min after the start of immobilization and remained at the elevated level during immobilization. Plasma level of glucose increased gradually and reached maximum and significance 45 min after the start of immobilization, then decreased. Fifteen min after immobilization, acetylcholine release increased again, while concentrations of epinephrine and norepinephrine were still elevated. Thus the response of acetylcholine and the other responses to immobilization stress were not parallel.

Long-term control of neuronal excitability by corticosteroid hormones

Hippocampal CA1 neurons express both mineralocorticoid and glucocorticoid receptors. Due to the difference in affinity of the two receptor types for corticosterone and variations in endogenous steroid levels, occupation of the receptors will range between a situation of predominant mineralocorticoid receptor activation and conditions where both receptor types are occupied. It was observed that local signal transduction is regulated by activation of the corticosteroid receptors. Particularly, transmission mediated by biogenic amines appears to be sensitive to steroid control. The data indicate that cholinergic and serotonergic responses are small with predominant mineralocorticoid receptor activation, while additional glucocorticoid receptor activation results in large responses; the reverse has been found for noradrenalin. The steroid-dependent control over transmission by biogenic amines will influence local excitability and therefore functional processes in which the hippocampal system is involved.

Decreased muscarinic receptor binding in rat brain after paradoxical sleep deprivation: an autoradiographic study

Previous work demonstrated that paradoxical sleep deprivation (PSD) leads to a decrease in yawning behavior elicited by cholinergic agonists, suggesting that a downregulation of cholinergic muscarinic receptors may occur after PSD. More recent work using intracerebral injections of muscarinic agonists has suggested a critical role for M2 receptors in paradoxical sleep. In this study [3H]AF-DX 384 was used to investigate the effects of PSD on M2-type cholinergic receptors throughout the brain using quantitative autoradiography. After 96 h of paradoxical sleep deprivation, [3H]AF-DX 384 binding was generally reduced throughout the brain, and significantly so in the olfactory tubercle (-20%), n. accumbens (-23%), frontal caudate-putamen (-16%), islands of Callejas (-20%), piriform cortex (-24%), lateral (-26%) and medial (-24%) septum, anteromedial (-19%), ventrolateral (-22%), and lateral geniculate (-15%) nuclei of thalamus, deep layers of the superior colliculus (-15%), entorhinal cortex (-12%) and subiculum (-23%). [3H]AF-DX 384 binding was reduced in pontine structures, but not to a higher degree than in other brain areas. The observed downregulation of M2-type muscarinic receptors after PSD may be causally related to the previously reported decrease in cholinergically induced behaviors after PSD.

Immobilization stress induces alterations of second-messenger systems in the gerbil brain

The effects of immobilization stress on the cerebral second messenger (adenylate cyclase and phosphoinositide) were investigated autoradiographically in mongolian gerbils. After 10 min (10-min stress group, n = 7), or after 6 h (6-h stress group, n = 7) of fixation on a flat board while supine, in vitro autoradiography was performed using [3H]forskolin (3H-FK) and [3H]phorbol-12,13-dibutyrate (3H-PDBu) as specific ligands to identify the distribution of adenylate cyclase and protein kinase C, respectively. In another group of 7 gerbils (control group), the same autoradiographic procedure was performed immediately after the animals were removed from the cage. In the 10-min stress group, FK binding was significantly decreased in the hypothalamus and amygdala, but significantly increased in the basal ganglia including the caudate-putamen and globus pallidus. FK binding in the 6-h stress group tended to increase throughout the brain, rising significantly in the basal ganglia. PDBu binding in either stress group did not change significantly compared to the control group in any region except the hippocampal CA3 region of the 6-h stress group. Under immobilization stress, the adenylate cyclase system may undergo time-dependent and regionally specific changes, while the phosphoinositide system remains relatively stable.

A cerebral ischemia model produced by injection of microspheres via the external carotid artery in freely moving rats

We produced an improved microembolism model of cerebral focal ischemia by injection of 1000-2000 microspheres (50 +/- 5 microns diameter) via a tube retrogradely inserted into the right external carotid artery in freely moving rats. The group injected with 2000 spheres showed a much more severe mortality rate as well as neurological signs than did the 1000-sphere group. Brain water content of the 2000-sphere group was examined and found to show an increase from 4 to 24 h after embolization in the right hemisphere, indicating serious brain edema. Severe neurological signs and individual deaths by embolization were most likely related to the extent of development of brain edema. Examination of learning behavior by shuttle-box avoidance revealed partial but significant impairment of learning in the 1000-sphere group. Autoradiographic studies for muscarinic acetylcholine receptors and protein kinase C binding sites were conducted. Both these binding sites decreased in number, but protein kinase C seems to be more susceptible to ischemic injury than muscarinic acetylcholine receptors. The observation was considered to be closely related with an impairment of learning. The present study suggests that our microembolism model in freely moving rats is useful for investigations of the early phase and late phase of cerebral ischemia.

Ontogenic distribution of muscarinic receptors and acetylcholinesterase in the rabbit hippocampus

Ontogenic development of muscarinic receptors was examined in the hippocampus of rabbits (from P2 to P60) using radioautographic method. Muscarinic sites were labelled with (3H)-quinuclinidyl-benzilate and pharmacologically defined M1 and M2 receptor subtypes with (3H)-pirenzepine and (3H)-oxotremorine, respectively. The distribution of binding sites was compared to acetylcholinesterase (AChE) staining in adjacent hippocampal sections. The two cholinergic components are progressively set up in the hippocampus during the first three postnatal weeks. The AChE staining was very low in all hippocampal fields in P2 rabbits. At P8 and after, the AChE staining was more pronounced in CA3 and CA4 than in CA1 and CA2. On the contrary, the M1 muscarinic binding sites were more abundant in CA1 and CA2 hippocampal fields than in CA3 and CA4 at all ages studied. M2 muscarinic binding sites were only distinguishable at P45 and have a relatively homogeneous distribution. This study shows a differential developmental evolution in the distribution of AChE and muscarinic M1 receptors, and no obvious correspondence between these two cholinergic markers was observed.

The role of cholinergic neurons in stress-induced increase of interictal discharges in hippocampal-kindled rats

This study aims to clarify the role of cholinergic neurons in the occurrence of epileptic seizures when emotional stress is loaded. The effects of stress and drugs on hippocampal interictal discharges were compared among groups of fully kindled male Wistar rats intraperitoneally given atropine, physostigmine and saline with and without immobilization, or pituitary-adrenocortical hormones without immobilization. Hippocampal interictal discharges increased during immobilization, because hippocampal cholinergic neurons were activated by emotional stress. Pituitary-adrenocortical hormones had no effects on the discharges.

Modification of muscarinic acetylcholine receptors in the rat brain following chronic immobilization stress: an autoradiographic study

The modifications of rat brain muscarinic acetylcholine receptors induced by chronic immobilization stress lasting 10 min/daily or 2 h/daily for 3, 7 or 21 days were analyzed by quantitative in vitro autoradiography. [3H]N-Methylscopolamine ([3H]NMS) was used as ligand. Chronic immobilization stress for 10 min/day did not produce any significant change in the properties of [3H]NMS binding sites throughout the rat brain. In contrast, 2 h/day immobilization caused a significant increase in the maximal number of muscarinic receptors (Bmax) in several brain areas such as the cortical layers, the CA1 field of the hippocampus and caudate-putamen, among others. Affinity values (Kd) were not modified. These results suggest that chronic immobilization stress induces supersensitivity of muscarinic receptors in certain cholinergic pathways in rat brain, the pattern of response being different to that previously found for acute stress.

Affinity changes in muscarinic acetylcholine receptors in the rat brain following acute immobilization stress: an autoradiographic study

The modifications in rat brain muscarinic acetylcholine receptors induced by acute immobilization stress lasting 10 min or 2 h were analyzed by quantitative in vitro autoradiography. [3H]N-Methylscopolamine ([3H]NMS) was used as a ligand. Immobilization stress for 10 min did not produce any significant change in the properties of [3H]NMS binding sites throughout the brain. In contrast, 2 h immobilization caused a significant increase in receptor affinity (Kd) without modification in the maximal number of receptors (Bmax) in several brain areas such as the caudate-putamen, cortical layers and CA1 field of the hippocampus, among others. These results, found even in animals killed immediately after the end of the immobilization sessions, suggest that immobilization stress induces supersensitivity of muscarinic receptors in certain cholinergic pathways in rat brain.

Selective increase of AMPA binding to the AMPA/quisqualate receptor in the hippocampus in response to acute stress

The binding properties of ligands specific for two subclasses of glutamate receptors were studied by quantitative autoradiography after one hour of acute immobilization/shock stress. [3H]N-(1-(2-thienyl)cyclohexyl)-3,4-piperidine (TCP) and [3H]alpha-amino-3-methylisoxazole-4-propionic acid (AMPA) were used to visualize the N-methyl-D-aspartate receptor and the AMPA/quisqualate receptor types, respectively. While no change was observed in the binding properties of the [3H]TCP, [3H]AMPA binding was significantly increased in several areas of the hippocampus of acutely stressed rats relative to naive controls.

Somatostatin receptors in the senescent rat brain: a quantitative autoradiographic study

To examine the effects of aging on the density and distribution of somatostatin receptors (SS-R) in the rat brain, receptor autoradiography for SS-R was carried out in rats aged 3 and 24 months using 125I-labeled Tyr11-SS-14. Autoradiograms were quantitatively assessed by an image analyzer to evaluate changes in the expression of SS-R due to senescence. Statistically significant decreases in SS-R binding were found in specific regions of the brains of senescent rats as compared to young adult rats. The regions affected included the periaqueductal gray matter (73% loss versus young adult rats), the interpeduncular nucleus (73% loss), the pontine nucleus (63% loss), the superior colliculus (46% loss), the ventral tegmental area (46% loss), the temporal cortex (39% loss), the frontal cortex (34% loss), the hippocampus (33% loss), the amygdala (27% loss) and the claustrum (26% loss). There was no significant change in SS-R expression in the spinal cord with aging. Significant reductions in SS-R binding in these brain regions may be involved in the impairment of sensory and cognitive function that can occur with aging.

Reduction of oxotremorine-induced analgesia after chronic but not acute restraint stress

The analgesic response (tail-flick latency) induced by the muscarinic cholinergic agonist oxotremorine was investigated in DBA/2 mice exposed to acute (a single 2 h session) and chronic (2 h once daily for 10 days) restraint stress. While a single exposure to stress did not influence the antinociceptive effects of the cholinergic agonist, chronic stress induced a clear-cut reduction of the oxotremorine-induced analgesia. The results show an involvement of cholinergic mechanisms in the adaptive modulation of nociception after chronic stressful events.

Effects of noise on high-affinity choline uptake in the frontal cortex and hippocampus of the rat are blocked by intracerebroventricular injection of corticotropin-releasing factor antagonist

Acute exposure (20 min) to loud noise (100 dB) decreased sodium-dependent high-affinity choline uptake activities in the frontal cortex and hippocampus of the rat. These effects were blocked by intracerebroventricular (i.c.v.) administration of the corticotropin-releasing factor (CRF) antagonist alpha-helical-CRF9-41 (alpha-HCRF) immediately before noise exposure. Intracerebroventricular injection of CRF (1 microgram) also decreased high-affinity choline uptake in the frontal cortex and the hippocampus of the rat, and these effects of CRF could be blocked by pretreating the animal with the narcotic antagonist naltrexone (1 mg/kg, i.p.). These results indicate that the effects of noise on central cholinergic systems are mediated by CRF and suggest a stressor-CRF-endogenous opioid-acetylcholine sequence of effects in the brain.