The telencephalic limbic system and experimental gastric pathology: a review

Neuroinflammation mechanisms of neuromodulation therapies for anxiety and depression

Mood disorders are associated with elevated inflammation, and the reduction of symptoms after multiple treatments is often accompanied by pro-inflammation restoration. A variety of neuromodulation techniques that regulate regional brain activities have been used to treat refractory mood disorders. However, their efficacy varies from person to person and lack reliable indicator. This review summarizes clinical and animal studies on inflammation in neural circuits related to anxiety and depression and the evidence that neuromodulation therapies regulate neuroinflammation in the treatment of neurological diseases. Neuromodulation therapies, including transcranial magnetic stimulation (TMS), transcranial electrical stimulation (TES), electroconvulsive therapy (ECT), photobiomodulation (PBM), transcranial ultrasound stimulation (TUS), deep brain stimulation (DBS), and vagus nerve stimulation (VNS), all have been reported to attenuate neuroinflammation and reduce the release of pro-inflammatory factors, which may be one of the reasons for mood improvement. This review provides a better understanding of the effective mechanism of neuromodulation therapies and indicates that inflammatory biomarkers may serve as a reference for the assessment of pathological conditions and treatment options in anxiety and depression.

Associations between amygdala reactivity to social threat, perceived stress and C-reactive protein in breast cancer survivors

Chronic inflammation in women diagnosed with breast cancer is critically linked with tumor progression, metastasis and survival. C-reactive protein (CRP)—a circulating marker of inflammation—is an important prognostic marker for cancer-related outcomes in breast cancer survivors (e.g. recurrence, fatigue). Psychological stress, which increases circulating markers of inflammation following sympathetic nervous system (SNS) activation, may modulate tumor-relevant inflammatory processes. However, little is known about neural mechanisms that might link stress and downstream SNS-initiated proinflammatory processes, such as elevated CRP. Past work suggests that threat-related neural regions, such as the amygdala, may be key in translating psychological stress into SNS activity and subsequent peripheral inflammation. Thus, we examined amygdala reactivity to socially threatening stimuli in association with perceived stress and plasma CRP levels to further elucidate neuro-immune pathways of social threat processing within breast cancer survivors (N = 37). Significant positive correlations were found between left amygdala reactivity in response to socially threatening stimuli (e.g. angry/fearful faces vs happy faces) and perceived stress in the previous month (r = 0.32, P = 0.025) and between left amygdala reactivity and CRP (r = 0.33, P = 0.025). This work builds on prior research implicating the amygdala as a key structure in crosstalk between threat-related neural circuitries and peripheral inflammation, particularly within cancer survivors.

Selective hippocampal subfield volume reductions in classic trigeminal neuralgia

Trigeminal Neuralgia (TN) is a chronic neuropathic pain syndrome characterized by paroxysmal unilateral shock-like pains in the trigeminal territory most frequently attributed to neurovascular compression of the trigeminal nerve at its root entry zone. Recent advances in the study of TN suggest a possible central nervous system (CNS) role in modulation and maintenance of pain. TN and other chronic pain patients commonly experience alterations in cognition and affect, as well as abnormalities in CNS volume and microstructure in regions associated with pain perception, emotional modulation, and memory consolidation. However, the microstructural changes in the hippocampus, an important structure within the limbic system, have not been previously studied in TN patients. Here, we use grey matter analysis to assess whether TN pain is associated with altered hippocampal subfield volume in patients with classic TN. Anatomical magnetic resonance (MR) images of twenty-two right-sided TN patients and matched healthy controls underwent automated segmentation of hippocampal subfields using FreeSurfer v6.0. Right-sided TN patients had significant volumetric reductions in ipsilateral cornu ammois 1 (CA1), CA4, dentate gyrus, molecular layer, and hippocampus-amygdala transition area – resulting in decreased whole ipsilateral hippocampal volume, compared to healthy controls. Overall, we demonstrate selective hippocampal subfield volume reduction in patients with classic TN. These changes occur in subfields implicated as neural circuits for chronic pain processing. Selective subfield volume reduction suggests aberrant processes and circuitry reorganization, which may contribute to development and/or maintenance of TN symptoms.

•

Selective Hippocampal subfields alteration in trigeminal neuralgia patients

•

Ipsilateral hippocampal volume reduction in TN patients

•

Females but not males show bilateral hippocampal volume reduction.

•

Pain duration correlates with hippocampal volume reduction.

•

Abnormal neurogenesis could explain hippocampal alterations.

The association of brain structure with gait velocity in older adults: a quantitative volumetric analysis of brain MRI

INTRODUCTION

While cortical processes play an important role in controlling locomotion, the underlying structural brain changes associated with slowing of gait in aging are not yet fully established. Our study aimed to examine the relationship between cortical gray matter volume (GM), white matter volume (WM), ventricular volume (VV), hippocampal and hippocampal subfield volumes, and gait velocity in older adults free of dementia.

METHODS

Gait and cognitive performance was tested in 112 community-residing adults, age 70 years and over, participating in the Einstein Aging Study. Gait velocity (cm/s) was obtained using an instrumented walkway. Volumetric MRI measures were estimated using a FreeSurfer software. We examined the cross-sectional relationship of GM, WM, VV, and hippocampal total and subfield volumes and gait velocity using linear regression models. In complementary models, the effect of memory performance on the relationship between gait velocity and regional volumes was evaluated.

RESULTS

Slower gait velocity was associated with smaller cortical GM and total hippocampal volumes. There was no association between gait velocity and WM or VV. Among hippocampal subfields, only smaller presubiculum volume was significantly associated with decrease in gait velocity. Addition of the memory performance to the models attenuated the association between gait velocity and all volumetric measures.

CONCLUSIONS

Our findings indicate that total GM and hippocampal volumes as well as specific hippocampal subfield volumes are inversely associated with locomotor function. These associations are probably affected by cognitive status of study population.

Greater amygdala activity and dorsomedial prefrontal-amygdala coupling are associated with enhanced inflammatory responses to stress

Psychological stress is implicated in the etiology of many common chronic diseases and mental health disorders. Recent research suggests that inflammation may be a key biological mediator linking stress and health. Nevertheless, the neurocognitive pathways underlying stress-related increases in inflammatory activity are largely unknown. The present study thus examined associations between neural and inflammatory responses to an acute laboratory-based social stressor. Healthy female participants (n=31) were exposed to a brief episode of stress while they underwent an fMRI scan. Blood samples were taken before and after the stressor, and plasma was assayed for markers of inflammatory activity. Exposure to the stressor was associated with significant increases in feelings of social evaluation and rejection, and with increases in levels of inflammation. Analyses linking the neural and inflammatory data revealed that heightened neural activity in the amygdala in response to the stressor was associated with greater increases in inflammation. Functional connectivity analyses indicated that individuals who showed stronger coupling between the amygdala and the dorsomedial prefrontal cortex (DMPFC) also showed a heightened inflammatory response to the stressor. Interestingly, activity in a different set of neural regions was related to increases in feelings of social rejection. These data show that greater amygdala activity in response to a stressor, as well as tighter coupling between the amygdala and the DMPFC, are associated with greater increases in inflammatory activity. Results from this study begin to identify neural mechanisms that might link stress with increased risk for inflammation-related disorders such as cardiovascular disease and depression.

Participation of NMDA receptors in the lateral hypothalamus in gastric erosion induced by cold-water restraint

The present study investigated whether neurons in the lateral hypothalamus (LH) play a role in the occurrence of gastric ulcerations induced by cold-water restraint. The first experiment indicated that bilateral N-methyl-d-aspartate (NMDA) lesions of the LH (20μg/1μl per side) reduced the amount of gastric ulceration induced by cold-water restraint. In the second experiment, the NMDA antagonist DL-2-amino-5-phosphonovaleric acid (APV; 2.5μg/0.5μl per side) or its vehicle was microinjected bilaterally into the LH prior to the cold-water restraint procedure. APV did not induce gastric ulcerations but reduced the amount of ulceration induced by cold-water restraint. These results indicate that NMDA receptors in the LH play an important role in the occurrence of gastric ulceration induced by cold-water restraint. The participation of the LH and possible neuronal circuitry involved in stress-induced ulceration are discussed.

Hippocampal subfields differentially correlate with chronic pain in older adults

Although previous studies have demonstrated that the hippocampus plays a role in pain processing, the role of hippocampal subfields is uncertain. The goal of this study was to examine the relationship between hippocampal subfield volumes and chronic pain in nondemented older adults. The study sample included 86 community-residing adults age 70 or older who were free of dementia and recruited from the Einstein Aging Study. Chronic pain was defined as pain over the last 3 months, that was moderate or severe (minimum rating of 4 out of 10) most, or all of the time. Hippocampal subfield volumes were estimated using FreeSurfer software. We modeled the association between chronic pain and hippocampal and subfield volume using linear regression. The sample had a mean age of 80 and was 58% female. Chronic pain, present in 55% of the sample, was associated with smaller right and total hippocampal volumes, particularly in women, after adjusting for age, education, and intracranial volume (eTICV). In addition, in women, volume was significantly reduced in participants with chronic pain in right CA2-3 (β=-0.35, p=0.010), right CA4-DG (β=-0.35, p=0.011), left presubiculum (β=-0.29, p=0.030), and left fimbria (β=-0.30, p=0.023). In men, chronic pain was not associated with the volume of any of the hippocampal subfield volumes. Chronic pain in women is associated with a reduction in the volume of right hippocampus and also selected hippocampal subfields. Future studies should clarify the mechanisms underlying the association between regional hippocampal volumes and chronic pain, particularly in women.

An empirical review of the neural underpinnings of receiving and giving social support: implications for health

Decades of research have demonstrated strong links between social ties and health. Although considerable evidence has shown that social support can attenuate downstream physiological stress responses that are relevant to health, the neurocognitive mechanisms that translate perceptions of social ties into altered physiological responses are still not fully understood. This review integrates research from social and affective neuroscience to illuminate some of the neural mechanisms involved in social support processes, which may further our understanding of the ways in which social support influences health. This review focuses on two types of social support that have been shown to relate to health: receiving and giving social support. As the neural basis of receiving support, this article reviews the hypothesis that receiving support may benefit health through the activation of neural regions that respond to safety and inhibit threat-related neural and physiological responding. This article will then review neuroimaging studies in which participants were primed with or received support during a negative experience as well as studies in which self-reports of perceived support were correlated with neural responses to a negative experience. As the neural basis of giving support, this article reviews the hypothesis that neural regions involved in maternal caregiving behavior may be critical for the health benefits of support-giving through the inhibition of threat-related neural and physiological responding. Neuroimaging studies in which participants provided support to others or engaged in other related forms of prosocial behavior will then be reviewed. Implications of these findings for furthering our understanding of the relationships between social support and health are discussed.

Social ties and health: a social neuroscience perspective

Research over the last several decades has shown that the health of the body is intimately tied to the strength of our social connections, but why? This article reviews evidence from affective and social neuroscience suggesting that, because of the importance of social ties for mammalian survival, threats to social connection are processed by some of the same neural regions that process basic threats to survival and consequently trigger physiological threat responses that have negative health implications. Likewise, social support is processed by some of the same neural regions that process safety or protection from basic threats and inhibit these same health-relevant physiological threat responses.

Brainstem neuropeptides and vagal protection of the gastric mucosal against injury: role of prostaglandins, nitric oxide and calcitonin-gene related peptide in capsaicin afferents

Earlier experimental studies indicated that the integrity of vagal pathway was required to confer gastric protection against damaging agents. Several peptides located in the brainstem initially identified to influence vagal outflow to the stomach, as assessed by electrophysiological approach or by vagal dependent alterations of gastric secretory and motor function, were investigated for their influence in the vagal regulation of the resistance of the gastric mucosa to injury. Thyrotropin releasing hormone (TRH), or its stable TRH analog, RX-77368, injected at low doses into the cisterna magna or the dorsal motor nucleus (DMN) was the first peptide reported to protect the gastric mucosa against ethanol injury through stimulation of vagal cholinergic pathways, inducing the release of gastric prostaglandins/nitric oxide (NO) and the recruitment of efferent function of capsaicin sensitive afferent fibers containing calcitonin-gene related peptide (CGRP). Activation of endogenous TRH-TRH1 receptor signaling located in the brainstem plays a role in adaptive gastric protection against damaging agents. Since then, an expanding number of peptides, namely peptide YY, CGRP, adrenomedullin, amylin, glugacon-like peptide, opioid peptides acting on µ, δ1 or δ2 receptors, nocicpetin, nocistatin, ghrelin, leptin and TLQP-21, a peptide derived from VGF prohormone, have been reported to act in the brainstem to afford gastric protection against ethanol injury largely through similar peripheral effectors mechanisms than TRH. Therefore gastric prostaglandins and CGRP/NO pathways represent a common final mechanism through which brain peptides confer vagally mediated gastroprotection against injury. A better understanding of brain circuitries through which these peptides are released will provide new strategies to recruit integrated and multifaceted gastroprotective mechanisms.

Selection for stress-induced analgesia affects the mouse hippocampal transcriptome

Stress responsiveness, including pain sensitivity and stress-induced analgesia (SIA), depends on genotype and, partially, is mediated by hippocampus. The present study examined differences in constitutive gene expression in hippocampus in lines of mice bred for high (HA) and low (LA) swim SIA. Between the lines, we found 1.5-fold or greater differences in expression of 205 genes in the hippocampus in nonstressed animals. The identity of these genes indicates that selective breeding for swim SIA affected many aspects of hippocampal neurons physiology, including metabolism, structural changes, and cellular signaling. Genes involved in calcium signaling pathway, including Slc8a1, Slc8a2, Prkcc, and Ptk2b, were upregulated in LA mice. In HA mice, robust upregulation of genes coding some transcription factors (Klf5) or receptors for neurotensin (Ntsr2) and GABA (Gabard) suggests the genetic basis for a novel mechanism of the non-opioid type of SIA in HA animals. Additional groups of differentially expressed genes represented functional networks involved in carbohydrate metabolism, gene expression regulation, and molecular transport. Our data indicate that selection for a single and very specific stress response trait, swim SIA, alters hippocampal gene expression. The results suggest that individual stress responsiveness may be associated with characteristics of the constitutive hippocampal transcriptome.

Central neural responses to restraint stress are altered in rats with an early life history of repeated brief maternal separation

Repeated brief maternal separation (i.e. 15 min daily, MS15) of rat pups during the first one to two postnatal weeks enhances active maternal care received by the pups and attenuates their later behavioral and neuroendocrine responses to stress. In previous work, we found that MS15 also alters the developmental assembly and later structure of central neural circuits that control autonomic outflow to the viscera, suggesting that MS15 may alter central visceral circuit responses to stress. To examine this, juvenile rats with a developmental history of either MS15 or no separation (NS) received microinjection of retrograde neural tracer, FluoroGold (FG), into the hindbrain dorsal vagal complex (DVC). After 1 week, FG-injected rats and surgically intact littermates were exposed to either a 15-min restraint stress or an unrestrained control condition, and then perfused 1 h later. Brain tissue sections from surgically intact littermates were processed for Fos alone or in combination with phenotypic markers to examine stress-induced activation of neurons within the paraventricular nucleus of the hypothalamus (PVN), bed nucleus of the stria terminalis (BNST), and hindbrain DVC. Compared to NS controls, MS15 rats displayed less restraint-induced Fos activation within the dorsolateral BNST (dBNST), the caudal PVN, and noradrenergic neurons within the caudal DVC. To examine whether these differences corresponded with altered neural inputs to the DVC, sections from tracer-injected rats were double-labeled for FG and Fos to quantify retrogradely labeled neurons within hypothalamic and limbic forebrain regions of interest, and the proportion of these neurons activated after restraint. Only the dBNST displayed a significant effect of postnatal experience on restraint-induced Fos activation of DVC-projecting neurons. The distinct regional effects of MS15 on stress-induced recruitment of neurons within hypothalamic, limbic forebrain, and hindbrain regions has interesting implications for understanding how early life experience shapes the functional organization of stress-responsive circuits.

Involvement of the heme oxygenase-carbon monoxide-cGMP pathway in the nociception induced by acute painful stimulus in rats

Heme oxygenase-carbon monoxide-cGMP (HO-CO-cGMP) pathway has been reported to be involved in peripheral and spinal modulation of inflammatory pain. However, the involvement of this pathway in the modulation of acute painful stimulus in the absence of inflammation remains unknown. Thus, we evaluated the involvement of the HO-CO-cGMP pathway in nociception by means the of analgesia index (AI) in the tail flick test. Rats underwent surgery for implantation of unilateral guide cannula directed toward the lateral ventricle and after the recovery period (5-7 days) were subjected to the measures of baseline tail flick test. Animals were divided into groups to assess the effect of intracerebroventricular administration (i.c.v.) of the following compounds: ZnDPBG (HO inhibitor) or vehicle (Na(2)CO(3)), heme-lysinate (substrate overload) or vehicle (l-lysine), or the selective inhibitor of soluble guanilate cyclase ODQ or vehicle (DMSO 1%) following the administration of heme-lysinate or vehicle. Heme overload increased AI, indicating an antinociceptive role of the pathway. This response was attenuated by i.c.v. pretreatment with the HO inhibitor ZnDPBG. In addition, this effect was dependent on cGMP activity, since the pretreatment with ODQ blocked the increase in the AI. Because CO produces most of its actions via cGMP, these data strongly imply that CO is the HO product involved in the antinociceptive response. This modulation seems to be phasic rather than tonic, since i.c.v. treatment with ZnDPBG or ODQ did not alter the AI. Therefore, we provide evidence consistent with the notion that HO-CO-cGMP pathway plays a key phasic antinociceptive role modulating noninflammatory acute pain.

Roles of the hippocampal formation in pain information processing

Pain is a complex experience consisting of sensory-discriminative, affective-motivational, and cognitive-evaluative dimensions. Now it has been gradually known that noxious information is processed by a widely-distributed, hierarchically- interconnected neural network, referred to as neuromatrix, in the brain. Thus, identifying the multiple neural networks subserving these functional aspects and harnessing this knowledge to manipulate the pain response in new and beneficial ways are challenging tasks. Albeit with elaborate research efforts on the cortical responses to painful stimuli or clinical pain, involvement of the hippocampal formation (HF) in pain is still a matter of controversy. Here, we integrate previous animal and human studies from the viewpoint of HF and pain, sequentially representing anatomical, behavioral, electrophysiological, molecular/biochemical and functional imaging evidence supporting the role of HF in pain processing. At last, we further expound on the relationship between pain and memory and present some unresolved issues.

c-Fos expression in the supraoptic nucleus is the most intense during different durations of restraint water-immersion stress in the rat

Restraint water-immersion stress (RWIS) can induce anxiety, hypothermia, and severe vagally-mediated gastric dysfunction. The present work explored the effects of different durations of RWIS on neuronal activities of the forebrain by c-Fos expression in conscious rats exposed to RWIS for 0, 30, 60, 120, or 180 min. The peak of c-Fos induction was distinct for different forebrain regions. The most intense c-Fos induction was always observed in the supraoptic nucleus (SON), and then in the hypothalamic paraventricular nucleus (PVN), posterior cortical amygdaloid nucleus (PCoA), central amygdaloid nucleus (CeA), and medial prefrontal cortex (mPFC). Moreover, body temperature was reduced to the lowest degree after 60 min of RWIS, and the gastric lesions tended to gradually worsen with the prolonging of RWIS duration. These data strongly suggest that these nuclei participate in the organismal response to RWIS to different degrees, and may be involved in the hypothermia and gastric lesions induced by RWIS.

Region- or state-related differences in expression and activation of extracellular signal-regulated kinases (ERKs) in naïve and pain-experiencing rats

BACKGROUND

Extracellular signal-regulated kinase (ERK), one member of the mitogen-activated protein kinase (MAPK) family, has been suggested to regulate a diverse array of cellular functions, including cell growth, differentiation, survival, as well as neuronal plasticity. Recent evidence indicates a role for ERKs in nociceptive processing in both dorsal root ganglion and spinal cord. However, little literature has been reported to examine the differential distribution and activation of ERK isoforms, ERK1 and ERK2, at different levels of pain-related pathways under both normal and pain states. In the present study, quantitative blot immunolabeling technique was used to determine the spatial and temporal expression of ERK1 and ERK2, as well as their activated forms, in the spinal cord, primary somatosensory cortex (SI area of cortex), and hippocampus under normal, transient pain and persistent pain states.

RESULTS

In naïve rats, we detected regional differences in total expression of ERK1 and ERK2 across different areas. In the spinal cord, ERK1 was expressed more abundantly than ERK2, while in the SI area of cortex and hippocampus, there was a larger amount of ERK2 than ERK1. Moreover, phosphorylated ERK2 (pERK2), not phosphorylated ERK1 (pERK1), was normally expressed with a high level in the SI area and hippocampus, but both pERK1 and pERK2 were barely detectable in normal spinal cord. Intraplantar saline or bee venom injection, mimicking transient or persistent pain respectively, can equally initiate an intense and long-lasting activation of ERKs in all three areas examined. However, isoform-dependent differences existed among these areas, that is, pERK2 exhibited stronger response than pERK1 in the spinal cord, whereas ERK1 was more remarkably activated than ERK2 in the S1 area and hippocampus.

CONCLUSION

Taken these results together, we conclude that: (1) under normal state, while ERK immunoreactivity is broadly distributed in the rat central nervous system in general, the relative abundance of ERK1 and ERK2 differs greatly among specific regions; (2) under pain state, either ERK1 or ERK2 can be effectively phosphorylated with a long-term duration by both transient and persistent pain, but their response patterns differ from each other across distinct regions; (3) The long-lasting ERKs activation induced by bee venom injection is highly correlated with our previous behavioral, electrophysiological, morphological and pharmacological observations, lending further support to the functional importance of ERKs-mediated signaling pathways in the processing of negative consequences of pain associated with sensory, emotional and cognitive dimensions.

Antinociceptive effect of intra-hippocampal CA1 and dentate gyrus injection of MK801 and AP5 in the formalin test in adult male rats

Previous research has shown that the hippocampus processes pain related-information, probably through hippocampal neurons that respond exclusively to painful stimulation. In the current experiments we tested whether blocking NMDA receptors in the hippocampal CA1 region and dentate gyrus could reduce nociceptive behaviors in rats. The competitive and noncompetitive NMDA receptor antagonists 2-amino-5-phosphonopentanoic acid (AP5; 3.75 microg/0.75 microl) and MK801 (1.5, 3, 6 microg/0.5 microl) were injected into the dentate gyrus and CA1 area of behaving rats 5 min before subcutaneous injection of formalin irritant. Pain behaviors in both acute and tonic phases of the formalin test were significantly reduced by AP5 (3.75 microg/0.75 microl) and MK801 (3 microg/0.5 microl, but not 1.5 and 6 microg/0.5 microl) injection to the dentate gyrus. In the CA1, injection of AP5 had no effect while injection of the effective dose of MK801 (3 microg/0.5 microl) had a significant antinociceptive effect. This effect was apparent only during the late phase of the formalin test. These results support the hypothesis that NMDA-sensitive mechanisms are involved in acute and persistent pain-related processing in the dentate gyrus and with tonic pain processing in the hippocampal CA1 region.

Microinjection of ritanserin into the dorsal hippocampal CA1 and dentate gyrus decrease nociceptive behavior in adult male rat

Prenatal 5HT depletion causes a significant decrease in the level of nociceptive sensitivity during the second phase of the formalin test behavioral response. These experiments were designed to test whether blocking 5HT2A/2c receptors in the CA1 region of the hippocampus and dentate gyrus would decrease nociceptive behaviors induced by a peripheral noxious stimulus formalin as an animal model of unremitting human being. The 5HT2A/2c receptor antagonist ritanserin (2, 4 and 8 microg/0.5 microl) was injected into the CA1 area and dentate gyrus of behaving rats 5 min before subcutaneous injection of formalin irritant. Nociceptive behaviors in both phases of the formalin test were significantly decreased by ritanserin (4 and 8 microg/0.5 microl) and ritanserin had no effect at 2 microg/0.5 microl. These results support the hypothesis that the hippocampal formation may modify the processing of incoming nociceptive information and that 5HT2A/2c receptor-sensitive mechanisms in the hippocampus may play a role in nociception and/or the expression of related behaviors.

Enhanced responses of the anterior cingulate cortex neurones to colonic distension in viscerally hypersensitive rats

The anterior cingulate cortex (ACC) is critically involved in processing the affective component of pain sensation. Visceral hypersensitivity is a characteristic of irritable bowel syndrome. Electrophysiological activity of the ACC with regard to visceral sensitization has not been characterized. Single ACC neuronal activities in response to colorectal distension (CRD) were recorded in control, sham-treated rats and viscerally hypersensitive (EA) rats (induced by chicken egg albumin injection, i.p). The ACC neurones of controls failed to respond to 10 or 30 mmHg CRD; only 22% were activated by 50 mmHg CRD. Among the latter, 16.4% exhibited an excitatory response to CRD and were labelled 'CRD-excited' neurones. In contrast, CRD (10, 30 and 50 mmHg) markedly increased ACC neuronal responses of EA rats (10%, 28% and 47%, respectively). CRD produced greater pressure-dependent increases in ACC spike firing rates in EA rats compared with controls. Splanchnicectomy combined with pelvic nerve section abolished ACC responses to CRD in EA rats. Spontaneous activity in CRD-excited ACC neurones was significantly higher in EA rats than in controls. CRD-excited ACC neurones in control and EA rats (7 of 16 (42%) and 8 of 20 (40%), respectively) were activated by transcutaneous electrical and thermal stimuli. However, ACC neuronal activity evoked by noxious cutaneous stimuli did not change significantly in EA rats. This study identifies CRD-responsive neurones in the ACC and establishes for the first time that persistence of a heightened visceral afferent nociceptive input to the ACC induces ACC sensitization, characterized by increased spontaneous activity of CRD-excited neurones, decreased CRD pressure threshold, and increased response magnitude. Enhanced ACC nociceptive transmission in viscerally hypersensitive rats is restricted to visceral afferent input.

Excitotoxic lesions of the medial prefrontal cortex attenuate fear responses in the elevated-plus maze, social interaction and shock probe burying tests

Previous research investigating the effects of medial prefrontal cortex (MPFC) lesions on fear- and anxiety-related behavior has yielded an inconsistent body of findings. Behavioral studies have reported increases, decreases, and no effect on anxiety. In addition, many studies are complicated by the use of lesioning techniques that destroy fibers of passage, and the use of conditioned fear tests, which may introduce the confounding effects of learning and memory. Therefore, the present study examined the effects of ibotenic acid lesions of the MPFC (including prelimbic, infralimbic and anterior cingulate) on three wide-ranging and well-validated behavioral assays of anxiety: the elevated plus maze (EPM), social interaction (SI) and the shock-probe tests (SP). In the EPM test, lesioned rats showed a significantly higher percentage of open arm entries and open arm time than controls. In a version of the SI test sensitive to anxiolytic effects, lesioned rats were found to spend a significantly greater amount of time in active interaction with a conspecific; while another version of the SI test sensitive to anxiogenic effects did not show any differences between lesioned and non-lesioned controls. In the SP test, lesioned rats exhibited significantly lower rates of burying. In contrast, retention of shock probe avoidance was not affected. No effects of lesions on measures of locomotor activity or shock reactivity were found. The concordant anxiolytic-like effects found in the three behavioral assays strongly suggests a general reduction in fear responsiveness in MPFC lesioned rats.

Childhood autism: a circuit syndrome?

BACKGROUND

Autism is a disorder that can lead to life-long disability. Currently, the etiology of autism is unknown, and although there are treatments for some of the behavioral abnormalities, there is no cure.

REVIEW SUMMARY

While this article will review the clinical, anatomic, and pathologic features seen in autism, the primary focus will be to present a new and provocative unifying theory regarding the underlying mechanisms causing this disorder. Current research advances, some controversial, will be discussed, and a novel definition of autism as a "circuit syndrome" will be presented. The work elaborated here will tie many of the disparate findings together, based on the idea that autism arises from abnormalities of the cerebellolimbic circuitry. Some of the more alternative theories of autism, such as mercury toxicity, linkage to the measles, mumps, and rubella vaccine, and the use of secretin will be discussed. Finally, pharmacologic treatment options will be reviewed.

CONCLUSIONS

Autism is not single disorder but represents dysfunction of the cerebellolimbic circuitry that can arise from many different etiologies.

Contribution of amygdala neurons containing peptides and calcium-binding proteins to fear-potentiated startle and exploration-related anxiety in inbred Roman high- and low-avoidance rats

The purpose of this study was to investigate amygdala-related fear and anxiety in two inbred rat lines differing in emotionality (RHA/Verh and RLA/Verh), and to relate the behaviour of the animals to neuronal types in different nuclei of the amygdala. The behavioural tests used were the motility test, elevated plus-maze and fear-potentiated startle response. The neurons investigated were immunoreactive for the anxiogenic peptide corticotropin-releasing factor (CRF-ir), the anxiolytic peptide neuropeptide Y (NPY-ir), and the calcium-binding proteins parvalbumin (PARV-ir) and calbindin (CALB-ir). The NPY-ir, PARV-ir and CALB-ir neurons studied were subpopulations of GABAergic neurons. RLA/Verh rats, which showed a significant fear-potentiation of the acoustic startle response, had more CRF-ir projection neurons in the central nucleus of the amygdala. The same RLA/Verh rats were either less or equally anxious in the motility test (similar to open field) and elevated plus-maze as compared with RHA/Verh rats. In accordance with this behaviour, the RLA/Verh rats had more NPY-ir neurons in the lateral, and more PARV-ir neurons in basal nuclei of the amygdala than RHA/Verh rats, but no differences were detected in the number of CRF-ir and CALB-ir neurons of the basolateral complex. In conclusion, the RLA/Verh rats displayed an opposite behaviour in the fear-potentiated startle model and the exploratory tests measuring anxiety based on choice behaviour. Thus, the anxiogenic systems in the central nucleus and anxiolytic systems in the basolateral complex of the amygdala might be differentially involved in the fear-potentiated startle paradigm and exploratory tests in the Roman rat lines.

Blocking NMDA receptors in the hippocampal dentate gyrus with AP5 produces analgesia in the formalin pain test

The hippocampus is an integral component of the "limbic" system and, as such, may contribute to the negative affect and avoidance motivation experienced during pain. A substantial body of evidence indicates that the hippocampus processes pain-related information, that some hippocampal neurons respond exclusively to painful stimulation, and that long-term anatomical changes occur in dentate gyrus neurons, following noxious physical stimulation. NMDA receptor antagonist drugs administered to the hippocampus interfere with long-term potentiation, learning, and memory; these same drugs, when applied to the spinal cord, prevent the long-term neurophysiological changes caused by noxious physical stimulation. This experiment tested whether blocking NMDA receptors in the hippocampal formation reduces nociceptive behaviors in an animal model of persistent human pain. The competitive NMDA receptor antagonist AP5 was injected into the dentate gyrus of alert, unrestrained rats either 5 min before or 15 min following the administration of a subcutaneous injection of formalin irritant. Pain behaviors in both acute and tonic phases of the formalin test were significantly reduced by AP5 treatments. These results support the hypothesis that the hippocampal formation is involved in pain-related neural processing and that NMDA receptor-sensitive mechanisms in the hippocampus are involved in pain perception and/or the expression of pain-related behaviors.

Projections from the central nucleus of the amygdala to the gastric related area of the dorsal vagal complex: a Phaseolus vulgaris-leucoagglutinin study in rat

Electrophysiological and anatomic studies suggest that the amygdala regulates gastrointestinal motility and gastric acid secretion via projections to the dorsal vagal complex. The topography of these projections is poorly understood. Here, these projections were investigated by injecting anterograde tracer, Phaseolus vulgaris-leucoagglutinin, into the different divisions of the central nucleus of the amygdala in 13 rats. The distribution of immunohistochemically labeled terminals in the different portions of the dorsal vagal complex was analyzed. We found that (1) the dorsal aspect of the medial division of the central nucleus provided moderate projections to the dorsal vagal complex; (2) the heaviest projections terminated in the parvicellular and medial divisions of the nucleus of the solitary tract. These data suggest that via topographically organized projections, the amygdala can modulate the vago-vagal gastrointestinal reflexes in emotional and stressful situations.

Gastric mucosal erosion produced by NMDA microinfusions in the lateral hypothalamus: effect of selective knife cuts

Bilateral infusions of N-methyl-D-aspartate (NMDA) into the lateral hypothalamus (LH) produce gastric erosions in rats. The present study attempted to determine the neural pathways that mediate this effect. In order to interrupt axonal transmission, knife cuts (KC) were made in different planes adjacent to the LH. In separate groups of rats, KC were made anterior, posterior or lateral to the LH just prior to bilateral NMDA infusions (20 micrograms/microliter). The incidence of gastric erosions was measured 24 h after NMDA infusions. Animals receiving sham KC and infused with NMDA exhibited significantly more gastric erosions than those infused with vehicle. Lateral parasagittal KC blocked the occurrence of gastric erosions produced by NMDA, whereas anterior coronal KC significantly increased the incidence of erosions produced by NMDA. Posterior coronal KC did not alter the incidence of gastric erosions produced by NMDA infusions into the LH. These results suggest that intrinsic LH neurons with gastric function project axons laterally and probably descend through the internal capsule to brainstem medullary nuclei. The results of the anterior KC suggest that the LH sends and/or receives inhibitory projections from neural structures (possibly the amygdaloid complex) anterior to the plane of the KC.

The role of paraventricular nucleus of hypothalamus in stress-ulcer formation in rats

The rat stress model of restraint and cold water immersion was used to investigate the effect of stimulating the paraventricular nucleus (PVN) of hypothalamus on the development of stress-induced gastric ulceration. The results were (1) electric stimulation of the PVN increased the stress ulceration, while electrolytic lesion of the PVN decreased it; (2) intracerebroventricular injection (i.c.v.) of acetylcholine (Ach) enhanced the effect of PVN stimulation on stress ulcers, and the M-receptor was involved; (3) i.c.v. norepinephrine (NE) attenuated the effect of PVN stimulation on stress ulcers in a dose-dependent manner, and the beta-receptor was involved; (4) i.c.v. 5-hydroxytryptamine (5-HT) enhanced the effect of PVN stimulation on stress ulcers; (5) electrolytic lesions of dorsal raphe nucleus (DR) attenuated the effect of PVN stimulation on stress ulcers, while electrolytic lesions of the locus ceruleus (LC) aggravated the effect; (6) thyroidectomy, adrenalectomy, ovariectomy, vagotomy and sympathectomy all attenuated the effect of PVN stimulation on stress ulcers; (7) electric stimulation of the PVN produced no effect on gastric juice volume, acidity, total acid output, pepsin activity or the gastric barrier mucus; but greatly reduced gastric mucosal blood flow. These results indicate that the PVN is an important brain site regulating the development of stress-induced gastric ulcers, that the classical neurotransmitters Ach, NE and 5-HT are involved, and that in the periphery, both the parasympathetic and sympathetic nervous systems and the three endocrine glands (thyroid, adrenal and gonad) take part in the effect.

Anti-ulcer activity of cromakalim (BRL 34915), a potassium-channel opener, against experimentally induced gastric and duodenal ulcers in rats and guinea-pigs

The effect of cromakalim, a potassium-channel opener, was studied on pylorus ligation-induced, aspirin-induced and water-immersion plus restraint stress-induced gastric ulcers in rats and on histamine-induced duodenal ulcer in guinea-pigs. Pretreatment with cromakalim (50-500 micrograms kg-1, p.o.) resulted in a significant reduction in the incidence of gastric and duodenal ulceration in each model. The anti-ulcer activity of cromakalim was comparable with that of cimetidine. Cromakalim at 100, 250 and 500 micrograms kg-1 caused a reduction in the volume of the gastric content in pylorus-ligated rats, and a dose of 250 micrograms kg-1 resulted in a significant reduction in total acidity (28.81 +/- 11.73 mEq L-1, P < 0.02) in the pylorus ligation model. A significant reduction in total acid output was observed at doses of 250 micrograms kg-1 (84.27 +/- 22.33 mEqH+, P < 0.02) and 500 micrograms kg-1 (120.17 +/- 24.49 mEqH+, P < 0.01) in pylorus-ligated rats. A significant reduction in the ulcer index in pylorus-ligated rats was observed at all cromakalim doses: 50 micrograms kg-1 (0.23 +/- 0.09, P < 0.05), 100 micrograms kg-1 (0.15 +/- 0.09, P < 0.02), 250 micrograms kg-1 (0.12 +/- 0.05, P < 0.01) and 500 micrograms kg-1 (0.14 +/- 0.03, P < 0.02). A significant reduction in the ulcer index of aspirin-treated rats was also observed at all cromakalim dose levels: 50 micrograms kg-1 (0.39 +/- 0.03, P < 0.01), 100 micrograms kg-1 (0.28 +/- 0.06, P < 0.01), 250 micrograms kg-1 (0.22 +/- 0.04, P < 0.001) and 500 micrograms kg-1 (0.28 +/- 0.03, P < 0.01). In the water-immersion plus restraint stress-induced gastric ulcer model, cromakalim significantly reduced gastric ulceration at all the dose levels: 50 micrograms kg-1 (28.2 +/- 2.12, P < 0.001), 100 micrograms kg-1 (20.24 +/- 1.71, P < 0.01), 250 micrograms kg-1 (19.95 +/- 1.46, P < 0.001) and 500 micrograms kg-1 (21.61 +/- 3.00, P < 0.001) but there was no consistent reduction of gastric bleeding. In addition to gastric ulcers, duodenal lesions were also reduced by pretreatment with cromakalim at all dose levels: 50 micrograms kg-1 (97.87 +/- 20.03 mm2, P < 0.02), 100 micrograms kg-1 (70.72 +/- 12.82 mm2, P < 0.02), 250 micrograms kg-1 (48.32 +/- 8.42 mm2, P < 0.01) and 500 micrograms kg-1 (55.50 +/- 12.50 mm2, P < 0.01). Cromakalim at a dose of 100 micrograms kg-1 also reduced total acidity (99.36 +/- 9.12 mEqL-1, P < 0.02) and total acid output (172.22 +/- 45.33 mEq of H+, P < 0.05) in this model. These findings demonstrate the anti-ulcer activity of cromakalim in different experimental models and suggest its potential use in ulcer therapy.

Microinjection of thyrotropin-releasing hormone analogue into the central nucleus of the amygdala stimulates gastric contractility in rats

The effect on gastric contractility following bilateral microinjection of thyrotropin-releasing hormone (TRH) analog, RX 77368, into the central nucleus of the amygdala was examined in fasted, urethane-anesthetized rats. Extraluminal force transducers were used to measure gastric corpus contractility. Bilateral microinjection of RX 77368 (0.5 microgram, 1.0 microgram, n = 6 each) stimulated gastric contractility for up to 120 min post-injection, P < 0.05. Gastric contractility was not significantly stimulated by microinjection of 0.1 microgram RX 77368, 0.1% bovine serum albumin (BSA) into the central nucleus or RX 77368 (0.5 microgram, 1.0 microgram) into sites adjacent to the central nucleus. Peak responses (1.0 microgram) occurred 40 min post-injection and represented a 16-26-fold increase over basal values. The frequency of gastric contraction waves was attenuated for 0-90 min in rats receiving central amygdaloid microinjection of RX 77368 (0.1, 0.5 or 1.0 microgram) versus rats microinjected with the vehicle or RX 77368 into sites adjacent to the central nuclei. The stimulatory effect of RX 77368 (1.0 microgram) on gastric contractility was abolished by subdiaphragmatic vagotomy. These results indicate that the TRH analog, RX 77368, acts within the central amygdala to vagally stimulate gastric contractility.

Gastric and duodenal anti-ulcer activity of SKF 38393, a dopamine D1-receptor agonist in rats

The effect of SKF 38393 (1-phenyl-7,8-diol-2,3,4,5-tetrahydro-1H-3-benzazepine), a specific dopamine D1-receptor agonist, was studied on pylorus-ligation and water immersion plus restraint stress-induced gastric ulcers, and cysteamine-induced duodenal ulcers in rats. Repeated administration of SKF 38393 (5 and 10 mg kg-1, p.o.) for six days was found to be effective in the prevention of gastric ulceration induced by water immersion plus restraint stress in rats. In 19-h pylorus-ligated rats, repeated treatment with SKF 38393 showed a significant reduction in the number and severity of ulcers. SKF 38393 did not alter the total gastric-mucosal carbohydrates:protein ratio; however, the gastric content volume and the free and total acidity were significantly reduced. In cysteamine-induced duodenal ulcers, the treatment with SKF 38393 for 6 days prevented the duodenal lesions. Our data suggests the involvement of dopamine D1 receptors in the anti-ulcer activity of SKF 38393, which could be largely attributed to its anti-secretory effect. Its anti-ulcer activity against water immersion plus restraint, also points towards a central mode of action, but its failure to alter the carbohydrate:protein ratio rules out any protective effect through the strengthening of the gastric mucosal barrier.

Immunohistochemical study of dopamine in rat gastric mucosa with acute gastric ulcer

Recent studies have shown the presence of dopamine (DA) in gastric and duodenal mucosa, and changes in gastric mucosal DA content have been observed in patient with acute ulcers. Immunohistochemical demonstration of the distribution of DA in gastric mucosa under stress was studied by light and electron microscopy. In the control group, DA was present in the gastric gland proper in the gastric corpus and antrum on light microscopy, and on the surface of mucous granules in chief cells, mucous neck cells, and surface epithelium on electron microscopy. In the stress group, DA in gastric mucosa was almost undetectable on light and electron microscopy. Further, in this group serum DA concentration was significantly higher in the portal vein than in the abdominal aorta. Endogenous DA in gastric mucosal cells may affect gastric mucosa differently from exogenous DA, and stress may release endogenous intracellular DA into extracellular spaces.

Stimulatory effects of the central amygdaloid nucleus on pancreatic exocrine secretion in rats

The effects of electrical stimulation of the central (CE) and basolateral (BL) amygdaloid nuclei on pancreatic exocrine secretion were tested in urethane-anesthetized rats. Electrical stimulation (0.1 mA, 1 ms, 40 Hz) of the CE significantly increased basal and hormone (secretin+cholecystokinin-8)-infused pancreatic exocrine secretion. These increases in pancreatic secretion were abolished by bilateral vagotomy. Electrical stimulation of the BL had no significant effect on basal and hormone-infused secretion. We conclude that the CE plays a stimulatory role in pancreatic exocrine secretion via the vagus nerve but the BL does not affect pancreatic secretion.

Distribution of dopaminergic fibers in the central division of the extended amygdala of the rat

The distribution of dopaminergic fibers in the principal components of the central extended amygdala (central amygdaloid nucleus (Ce), substantia innominata, and bed nucleus of the stria terminalis (BNST)), was studied using immunocytochemistry against tyrosine hydroxylase, dopamine beta-hydroxylase and dopamine. Dopamine fibers were found most densely distributed in the dorsolateral subdivision of the BNST and the lateral part of the Ce. Smaller numbers of dopaminergic fibers were found in the rest of the central extended amygdala. In contrast, dopamine beta-hydroxylase fibers were virtually absent from the dorsolateral bed nucleus of the stria terminalis and lateral part of the central amygdaloid nucleus, but were distributed in a moderate density in the medial part of Ce, dorsal substantia innominata and posterolateral BNST. Our results show that dopamine fibers are most concentration over those regions of the central extended amygdala with large numbers of GABAergic neurons whose projections remain within the central extended amygdala, while noradrenergic fibers are most heavily concentrated over those regions containing a large proportion of brainstem projection neurons. That dopamine fibers are concentrated over regions with GABAergic medium spiny neurons suggests that those regions might be organized as a striatal parallel.

Intracisternal neutral endopeptidase-24.11 inhibitors produce inhibition in gastric acid output: independence from opiate, bombesin, or neurotensin-mediated mechanisms

Intracisternal (ic) injection of the neutral endopeptidase-24.11 inhibitor phosphoramidon (1-100 nmol) produced a dose-dependent inhibition of gastric acid secretion in 2-h pylorus-ligated rats. The response resulted from a reduction in acid concentration and volume. Likewise, ic injection of another neutral endopeptidase-24.11 inhibitor Zincov (200 nmol) produced a 63% inhibition in gastric acid output. In contrast, neither intravenous injection of phosphoramidon (100 nmol) nor ic injection of the aminopeptidase inhibitor amastatin (100 nmol) produced any change in gastric acid secretion. The inhibitory effect of ic phosphoramidon (10 nmol) was not reversed by a dose of naloxone sufficient to antagonize the acid inhibitory effects of ic [D-Ala2-D-met5]enkephalinamide (8.5 nmol). Moreover, phosphoramidon-induced inhibition of acid was not reduced by the centrally effective bombesin antagonist N-acetyl-GRP(20-26)-O-CH3 or by reserpine pretreatment at a dose effective to antagonize ic neurotensin-induced inhibition in acid secretion. These results suggest that an endogenous neutral endopeptidase-24.11 sensitive substrate may act in the brain to inhibit gastric acid output by mechanisms independent of CNS opiate, bombesin or neurotensin activity.

Effects of amygdaloid lesions on gastric erosion formation during exposure to activity-stress

To examine the role of the amygdala in the production of gastric ulcers induced by activity-stress, electrolytic lesions were placed in the centromedial (CENT) and medial (MED) amygdaloid nuclei, as well as in the intra-amygdaloid division of the bed nucleus of the stria terminalis (BNST). As compared to sham-operated controls (CONT), gastric ulceration was attenuated in rats with CENT lesions and exacerbated in rats with lesions located in the BNST or MED. Wheel running did not differ significantly between control animals and lesioned rats, but did differ within lesioned groups. Rats with MED lesions ran more than rats with CENT or BNST lesions. Results support the view that the integrity of the centromedial amygdala is critical for the maintenance of the viscera and demonstrate that neurogenic factors contribute to the development of gastric erosions during exposure to activity-stress.

Nitric oxide inhibition intensifies cold-restraint induced gastric ulcers in rats

Treatment 20 min beforehand with an inhibitor of nitric oxide (NO) synthesis NW-nitro-1-arginine methyl ester (L-NAME) (12.5, 25, 50 or 100 mg/kg, s.c.), dose-dependently intensified gastric glandular mucosal ulceration produced by cold-restraint stress. Hexamethonium (20 mg/kg) or atropine (1 mg/kg) pretreatment s.c. 20 min before stress strongly antagonised stress-evoked ulceration, as well as the ulcer-potentiating effects of L-NAME when either cholinoceptor antagonist was given concurrently with the NO inhibitor. Stress-induced mast cell degranulation was not worsened by L-NAME pretreatment. The findings suggest that NO could confer partial protection against stress-induced gastric ulcer formation; its activity is triggered off by the ulcerogenic mechanism of stress.

Analgesia produced by lidocaine microinjection into the dentate gyrus

The local anesthetic lidocaine was injected into the dentate gyrus (DG) of alert, unrestrained rats 10 min prior to investigation within the formalin test. Regional anesthesia of the DG resulted in a reduction of pain scores when administered contralateral to the site of subcutaneous formalin injection. The analgesic effect was evident 30-50 min after central infusion. These results provide evidence of the involvement of the hippocampal formation (HF) in pain perception.

Organization of amygdaloid projections to brainstem dopaminergic, noradrenergic, and adrenergic cell groups in the rat

The distribution of amygdaloid axons in the various brainstem dopaminergic, noradrenergic, and adrenergic cell groups was examined. This was accomplished by means of the Phaseolus vulgaris leucoagglutinin lectin (PHA-L) anterograde tracing technique combined with glucose-oxidase immunocytochemistry to catecholamine markers (i.e., tyrosine hydroxylase, dopamine beta hydroxylase, and phenylethanolamine N-methyltransferase). Injections of PHA-L in the medial part of the central amygdaloid nucleus resulted in axonal and terminal labeling in most catecholamine cell groups in the brainstem. Amygdaloid terminals appeared to contract catecholaminergic cells in several brainstem regions. The most heavily innervated catecholaminergic cells were the A9 (lateral) and A8 dopaminergic cell groups and the C2/A2 adrenergic/noradrenergic cell groups in the nucleus of the solitary tract. The medial part of the A9 and adjacent A10 dopaminergic cell groups was moderately innervated. A moderate innervation by amygdaloid terminals was observed on rostral locus coeruleus noradrenergic cells (A6 rostral) and adrenergic cells of the rostral ventrolateral medulla (C1). Noradrenergic cells of the A5, main body of the locus coeruleus (A6), A7, and subcoeruleus were sparsely innervated. Amygdaloid axons were not observed on noradrenergic neurons of the A4 cell group, area postrema, and A1 cells of the ventrolateral medulla. The results demonstrate that the amygdala primarily innervates the dopaminergic cells of midbrain (i.e., A8 and lateral A9 cells) and the adrenergic cells (C2) and noradrenergic (A2) cells in the nucleus of the solitary tract. The possible functional significance of amygdaloid innervation of catecholaminergic cells is discussed.

Synaptic contacts between CGRP-immunoreactive terminals and enkephalin-immunoreactive neurons in the central amygdaloid nucleus of the rat

An immunoelectron microscopic method combined with immunofluorescence double staining was carried out to examine the relationship between calcitonin gene-related peptide (CGRP)-like immunoreactive (LI) axon terminals and enkephalin (ENK)-LI neurons in the central amygdaloid nucleus (Ce) of the rat. The latter method showed that many ENK-LI cell bodies are densely surrounded by CGRP-LI axons in the lateral subdivision of the Ce (CeL). After taking fluorescence micrographs, the immunoperoxidase technique was used to examine the CGRP-LI axonal profiles under an electron microscope. CGRP-LI terminals were frequently found to form axo-somatic synaptic contacts with ENK-LI neurons in the CeL.

The role of the amygdala in fear-potentiated startle: implications for animal models of anxiety

Over the past several years, major advances have been made in understanding the pharmacology of anxiety, involving three broad classes of experimental approach. One approach studies the mechanism of action of drugs that are known to treat anxiety clinically, such as the benzodiazepines. A second approach uses various animal models of fear or anxiety that are sensitive to known anxiolytic drugs, to see if they will detect new compounds. A third approach involves describing the neural pathways and neurotransmitters that are active in a state of fear or anxiety; importantly, this approach is not derived from the mechanisms of known anxiolytics. In this review, Michael Davis describes such a 'neural systems' approach to the study of fear or anxiety that uses the paradigm of fear-potentiated startle.

The basolateral amygdala, dopamine and gastric stress ulcer formation in rats

Bilateral microinjections of dopamine (DA, 0.3, 3.0 or 30.0 micrograms) or the DA-agonist, bromocriptine (3.0 micrograms) into the basolateral amygdala (BLA) dose-dependently attenuated cold restraint stress (3 h at 4 degrees C)-induced gastric ulcer formation in rats. On the other hand, intra-BLA injections of the neurotoxin, 6-hydroxydopamine (10 micrograms) of the DA-antagonist, haloperidol (0.1 or 1.0 micrograms) aggravated such stress ulcer formation. All these effects were seen only when the injection sites were localized in the posterior (and not the anterior) BLA. Further, pretreatment of rats with haloperidol (0.1 micrograms) clearly antagonized the gastric cytoprotective effects of DA or bromocriptine (both at 3.0 micrograms), when both chemicals were injected in the posterior BLA. The results indicate that DA-ergic mechanisms in the posterior BLA are important for the regulation of gastric mucosal integrity during cold restraint stress.

TRH-enkephalin interactions in the amygdaloid complex during gastric stress ulcer formation in rats

The formation of gastric stress ulcers was studied as a function of interactions between thyrotropin releasing hormone (TRH) and endogenous opioids in the central amygdalar nucleus (CEA) in rats. Bilateral microinjections of TRH (1 or 10 micrograms) into the CEA produced dose-related aggravations in cold restraint stress (CRS, 3 h at 4 degrees C)-induced gastric ulcer formation. Similar stress ulcer facilitating effects were also seen with intra-CEA injections of the opioid antagonists, naloxone (1 or 10 micrograms). On the other hand, the enkephalin analog, D-Ala2-metenkephalinamide (DAMEA, 1, 10 or 20 micrograms) produced dose-dependent attenuations in gastric stress pathology, the effects being most marked with the latter two doses. Pretreatment of rats with intra-CEA naloxone (1 microgram) (a) antagonized the gastric cytoprotective effects of DAMEA (20 micrograms) and (b) further aggravated the ulcerogenic response of TRH (1 microgram), without influencing significantly the TRH (10 micrograms) effect. Further, when DAMEA (20 micrograms) was administered intra-CEA just after TRH (10 micrograms), the stress ulcer facilitating effects of the latter was neutralized. The results indicate that TRH-enkephalin interactions are possible at the level of the CEA during CRS-induced gastric ulcer formation.

The bed nucleus-amygdala continuum in human and monkey

The cytoarchitecture and distributions of seven neuropeptides were examined in the the bed nucleus of the stria terminalis (BST), substantia innominata (SI), and central and medial nuclei of the amygdala of human and monkey to determine whether neurons of these regions form an anatomical continuum in primate brain. The BST and centromedial amygdala have common cyto- and chemo-architectonic characteristics, and these regions are components of a distinct neuronal complex. This neuronal continuum extends dorsally, with the stria terminalis, from the BST and merges with the amygdala; it extends ventrally from the BST through the SI to the centromedial amygdala. The cytoarchitectonics of the BST-amygdala complex are heterogeneous and compartmental. The BST is parcellated broadly into anterior, lateral, medial, ventral, supracapsular, and sublenticular divisions. The central and medial nuclei of the amygdala are also parcellated into several subdivisions. Neurons of central and medial nuclei of the amygdala are similar to neurons in the lateral and medial divisions of the BST, respectively. Neurons in the SI form cellular bridges between the BST and amygdala. The BST, SI, and amygdala share several neuropeptide transmitters, and patterns of peptide immunoreactivity parallel cytological findings. Specific chemoarchitectonic zones were delineated by perikaryal, peridendritic/perisomatic, axonal, and terminal immunoreactivities. The results of this investigation demonstrate that there is a neuronal continuity between the BST and amygdala and that the BST-amygdala complex is prominent and discretely compartmental in forebrains of human and monkey.