Parallel circuits mediating distinct emotional coping reactions to different types of stress

Nociceptive flexion reflex thresholds and pain during rest and computer game play in patients with hypertension and individuals at risk for hypertension

Supraspinal pain modulation may explain hypertensive hypoalgesia. We compared nociceptive flexion reflex (NFR) thresholds and pain during rest and computer game play in hypertensives and normotensives (Experiment 1) and normotensives with and without hypertensive parents (Experiment 2). The game was selected to modulate activity in pain pathways. NFR thresholds did not differ between groups during rest or game play. Pain ratings never differed between hypertensives and normotensives, whereas individuals with hypertensive parents reported less pain during the first two NFR assessments, compared to those without. NFR thresholds and pain were reduced by game play compared to rest. The failure of game play to differentially modulate NFR thresholds or associated pain reports between groups argues against enhanced supraspinal modulation of nociception and pain in hypertensives and those at increased risk for hypertension.

Cardiovascular responses to cognitive stress in patients with migraine and tension-type headache

BACKGROUND

The purpose of this study was to investigate the temporal relationship between autonomic changes and pain activation in migraine and tension-type headache induced by stress in a model relevant for everyday office-work.

METHODS

We measured pain, blood pressure (BP), heart rate (HR) and skin blood flow (BF) during and after controlled low-grade cognitive stress in 22 migraineurs during headache-free periods, 18 patients with tension-type headache (TTH) and 44 healthy controls. The stress lasted for one hour and was followed by 30 minutes of relaxation.

RESULTS

Cardiovascular responses to cognitive stress in migraine did not differ from those in control subjects. In TTH patients HR was maintained during stress, whereas it decreased for migraineurs and controls. A trend towards a delayed systolic BP response during stress was also observed in TTH. Finger BF recovery was delayed after stress and stress-induced pain was associated with less vasoconstriction in TTH during recovery.

CONCLUSION

It is hypothesized that TTH patients have different stress adaptive mechanisms than controls and migraineurs, involving delayed cardiovascular adaptation and reduced pain control system inhibition.

CRF type 1 receptors in the dorsal periaqueductal gray modulate anxiety-induced defensive behaviors

The dorsal periaqueductal gray (dPAG) is involved in defensive coping reactions to threatening stimuli. Corticotropin releasing factor (CRF) is substantially implicated as a direct modulator of physiological, endocrine and behavioral responses to a stressor. Previous findings demonstrate a direct role of the central CRF system in dPAG-mediated defensive reactions toward a threatening stimulus. These include anxiogenic behaviors in the elevated plus maze (EPM) in rats and defensive reactions in both the mouse defense test battery (MDTB) and rat exposure test (RET) paradigms in mice. Furthermore, CRF was shown to directly and dose-dependently excite PAG neurons in vitro. The aim of the present series of experiments was to directly evaluate the role of the CRF1 receptor (CRF1) in dPAG-induced defensive behaviors in the MDTB and the RET paradigms. For this purpose, cortagine, a novel CRF1-selective agonist, was directly infused into the dPAG. In the RET the high dose of cortagine (100 ng) significantly affected spatial avoidance measures and robustly increased burying behavior, an established avoidance activity, while having no effects on behaviors in the MDTB. Collectively, these results implicate CRF1 in the dPAG as a mediator of temporally and spatially dependent avoidance in response to controllable and constant stimuli.

Distinct Fos expression in the brain following freezing behavior elicited by stimulation with NMDA of the ventral or dorsal inferior colliculus

The inferior colliculus (IC) is an important relay station for ascending auditory information to the medial geniculate nucleus (MGN) and temporal cortex. It has been reported that the ventral (ICv) and dorsal (ICd) regions of the IC are involved with the defensive reaction and audiogenic seizures, respectively. As freezing is the first response induced by stimulation of these IC nuclei with increasing doses of N-methyl-d-aspartate (NMDA), a question that arises is whether or not fear and audiogenic seizures generated at the IC level are interrelated processes. To address this issue, the Fos distribution in selected limbic structures following injections of NMDA into the ICv or ICd at freezing (7 nmol)- and escape (20 nmol)-producing doses was examined. Freezing behavior induced by intra-ICd NMDA caused an increase of Fos expression in the MGN, superior colliculus, dorsal columns of the periaqueductal gray and locus coeruleus while freezing induced by intra-ICv NMDA caused a significant Fos immunoreactivity in the prelimbic (PrL) and cingulate (Cg) cortices, basolateral and medial nuclei of the amygdala, ventrolateral periaqueductal gray, cuneiform nucleus and locus coeruleus. Escape behavior induced by NMDA injections into both nuclei caused a widespread Fos labeling in all limbic structures examined in this study. These results suggest that distinct circuits underlie the freezing behavior generated at the level of ICd and ICv. This is the first study to map Fos distribution associated with the stimulation of the ICv and ICd, regions supposed to be involved with fear and audiogenic seizures, respectively.

Regional cerebral perfusion differences between periventricular grey, thalamic and dual target deep brain stimulation for chronic neuropathic pain

Regional cerebral blood flow changes were evaluated in different subcortical brain targets following deep brain stimulation (DBS) for chronic pain. Three patients with intractable neuropathic pain were assessed; one had stimulating electrodes in the ventroposterolateral thalamic nucleus (VPL), one in the periventricular grey (PVG) area, and one had electrodes in both targets. Pain relief was achieved in all patients. Cerebral perfusion was measured by single-photon emission computed tomography to determine the effects of DBS. Comparison was made between individual scans using subtraction analysis. DBS consistently increased perfusion in the posterior subcortical region between VPL and PVG, regardless of the site of stimulation. Furthermore, thalamic and dual target DBS increased thalamic perfusion, yet PVG DBS decreased perfusion in the PVG-containing midbrain region and thalamus. Dual target stimulation decreased anterior cingulate and insular cortex perfusion. The study demonstrates regional differences in cerebral perfusion between three accepted and efficacious targets for analgesic DBS.

Altered brain activation pattern associated with drug-induced attenuation of enhanced depression-like behavior in rats bred for high anxiety

BACKGROUND

The enhanced depression-like behavior in the forced swim test displayed by rats selectively bred for high anxiety-related behavior (HAB) as compared with their low anxiety counterparts (LAB) is abolished by chronic paroxetine treatment. The aim of the present study was to identify neuronal substrates underlying this treatment response in HABs.

METHODS

The HAB rats received paroxetine (10 mg/kg/day) for 24 days via drinking water, and drug-induced modulation of neuronal activation patterns in response to forced swimming was mapped with the expression of the immediate early gene c-Fos as marker.

RESULTS

Chronic paroxetine treatment reduced the immobility scores during forced swimming, confirming the previously observed antidepressant-like effect in these animals, and attenuated the forced swim-induced c-Fos response in a restricted set (11 of 70) of brain areas. These included limbic areas such as the prelimbic cortex, parts of the amygdala, the bed nucleus of the stria terminalis, dorsal hippocampus, dorsal lateral septum as well as hypothalamic and hindbrain areas (dorsolateral periaqueductal gray [PAG], locus coeruleus). Untreated LAB rats, which displayed low depression-like behavior comparable to that of treated HABs, also showed low swim stress-induced c-Fos response in most of these same areas, further supporting an association of attenuated neuronal excitability in the identified areas with attenuated depression-like behavior.

CONCLUSIONS

These findings indicate that modulation of neuronal activation in a restricted set of defined, mainly limbic as well as selected hypothalamic and hindbrain areas by paroxetine treatment is associated with the reduction of enhanced depression-like behavior in a psychopathological animal model.

Hypothalamic and brainstem sources of pituitary adenylate cyclase-activating polypeptide nerve fibers innervating the hypothalamic paraventricular nucleus in the rat

The hypothalamic paraventricular nucleus (PVN) coordinates major neuroendocrine and behavioral mechanisms, particularly responses to homeostatic challenges. Parvocellular and magnocellular PVN neurons are richly innervated by pituitary adenylate cyclase-activating polypeptide (PACAP) axons. Our recent functional observations have also suggested that PACAP may be an excitatory neuropeptide at the level of the PVN. Nevertheless, the exact localization of PACAP-producing neurons that project to the PVN is not understood. The present study examined the specific contribution of various brain areas sending PACAP innervation to the rat PVN by using iontophoretic microinjections of the retrograde neuroanatomical tracer cholera toxin B subunit (CTb). Retrograde transport was evaluated from hypothalamic and brainstem sections by using multiple labeling immunofluorescence for CTb and PACAP. PACAP-containing cell groups were found to be retrogradely labeled from the PVN in the median preoptic nucleus; preoptic and lateral hypothalamic areas; arcuate, dorsomedial, ventromedial, and supramammillary nuclei; ventrolateral midbrain periaqueductal gray; rostral and midlevel ventrolateral medulla, including the C1 catecholamine cell group; nucleus of the solitary tract; and dorsal motor nucleus of vagus. Minor PACAP projections with scattered double-labeled neurons originated from the parabrachial nucleus, pericoeruleus area, and caudal regions of the nucleus of the solitary tract and ventrolateral medulla. These observations indicate a multisite origin of PACAP innervation to the PVN and provide a strong chemical neuroanatomical foundation for interaction between PACAP and its potential target neurons in the PVN, such as parvocellular CRH neurons, controlling physiologic responses to stressful challenges and other neuroendocrine or preautonomic PVN neurons.

PTSD and stress sensitisation: a tale of brain and body Part 2: animal models

Animal models that are characterised by long-lasting conditioned fear responses as well as generalised behavioural sensitisation to novel stimuli following short-lasting but intense stress have a phenomenology that resembles that of PTSD in humans. These models include brief sessions of shocks, social confrontations, and a short sequence of different stressors. Subgroups of animals with different behavioural traits or coping styles during stress exposure show a different degree or pattern of long-term sensitisation. Weeks to months after the trauma, treated animals on average also show a sensitisation to novel stressful stimuli of neuroendocrine, cardiovascular and gastrointestinal motility responses as well as altered pain sensitivity and immune function. Functional neuroanatomical and pharmacological studies in these animal models have provided evidence for involvement of amygdala and medial prefrontal cortex, and of brain stem areas regulating neuroendocrine and autonomic function and pain processing. They have also generated a number of neurotransmitter and neuropeptide targets that could provide novel avenues for treatment in PTSD.

Altered brain activity processing in high-anxiety rodents revealed by challenge paradigms and functional mapping

Pathological anxiety involves aberrant processing of emotional information that is hypothesized to reflect perturbations in fear/anxiety pathways. The affected neurobiological substrates in patients with different anxiety disorders are just beginning to be revealed. Important leads for this research can be derived from findings obtained in psychopathologically relevant rodent models of enhanced anxiety, by revealing where in the brain neuronal processing in response to diverse challenges is different to that in animals with lower anxiety levels. Different functional mapping methods in various rodent models, including psychogenetically selected lines or genetically modified animals, have been used for this purpose. These studies show that the divergent anxiety-related behavioral response of high-anxiety- vs. normal and/or low-anxiety rodents to emotional challenges is associated with differential neuronal activation in restricted parts of proposed fear/anxiety circuitries including brain areas thought to be important in stress, emotion and memory. The identification of neuronal populations showing differential activation depends in part on the applied emotional challenge, indicating that specific facets of elicited fear or anxiety preferentially engage particular parts of the fear/anxiety circuitry. Hence, only the use of an array of different challenges will reveal most affected brain areas. A number of the neuronal substrates identified are suggested as candidate mediators of dysfunctional brain activation in pathological anxiety. Indeed, key findings revealed in these rodent models show parallels to observations in human symptom provocation studies comparing anxiety disorder patients with healthy volunteers. Work to investigate exactly which of the changed neuronal activation patterns in high-anxiety rodents has to be modulated by therapeutic drugs to achieve effective anxiolysis and via which neurochemical pathways this can be accomplished is at its early stages but has identified a small number of promising candidates. Extending these approaches should help to provide further insight into these mechanisms, revealing new leads for therapeutic targets and strategies.

The polyvagal perspective

The polyvagal theory introduced a new perspective relating autonomic function to behavior, that included an appreciation of the autonomic nervous system as a "system," the identification of neural circuits involved in the regulation of autonomic state, and an interpretation of autonomic reactivity as adaptive within the context of the phylogeny of the vertebrate autonomic nervous system. The paper has two objectives: first, to provide an explicit statement of the theory; and second, to introduce the features of a polyvagal perspective. The polyvagal perspective emphasizes how an understanding of neurophysiological mechanisms and phylogenetic shifts in neural regulation leads to different questions, paradigms, explanations, and conclusions regarding autonomic function in biobehavioral processes than peripheral models. Foremost, the polyvagal perspective emphasizes the importance of phylogenetic changes in the neural structures regulating the autonomic nervous system and how these phylogenetic shifts provide insights into the adaptive function and the neural regulation of the two vagal systems.

Acetylcholinesterase modulates stress-induced motor responses through catalytic and noncatalytic properties

BACKGROUND

Cholinergic neurotransmission notably participates in stress-induced motor responses. Here we report the contribution of alternative splicing of acetylcholinesterase (AChE) pre-mRNA to modulate these responses. More specifically, we induced stress-associated hypofunction of dopaminergic, mainly D2 dopamine receptor-mediated neurotransmission by haloperidol and explored stress induced hyperlocomotion and catalepsy, an extreme form of immobility, induced in mice with AChE deficiencies.

METHODS

Conditional transgenic (Tet/AS) mice were created with tetracycline-induced antisense suppression of AChE gene expression. Locomotion and catalepsy times were measured in Tet/AS and strain-matched control mice, under open-field exposure threat and under home-cage safety.

RESULTS

In vitro, NGF-treated PC12 cells failed to extend neurites upon Tet/AS suppression. In vivo, Tet/AS but not control mice showed stress-associated hippocampal deposits of heat-shock protein 70 and GRP78 (BiP), predicting posttranscriptional changes in neuronal reactions. Supporting this notion, their striatal cholinergic neurons demonstrated facilitated capacity for neurite extension, attributing these in vivo changes in neurite extension to network interactions. Tet/AS mice presented stress-induced hyperlocomotion. Moreover, the dopamine antagonist haloperidol induced longer catalepsy in threatened Tet/AS than in control mice. When returned to home-cage safety, Tet/AS mice showed retarded release from catalepsy.

CONCLUSIONS

Acetylcholinesterase modulates stress-induced motor responses and facilitates resumption of normal motor behavior following stress through both catalytic and noncatalytic features.

Antidepressant treatment reduces Fos-like immunoreactivity induced by swim stress in different columns of the periaqueductal gray matter

Antidepressant treatment attenuates behavioral changes induced by uncontrollable stress. The periaqueductal gray matter (PAG) is proposed to be a brain site involved in the behavioral responses to uncontrollable stress and antidepressant effects. The main goal of the present study was to investigate the effect of antidepressant treatment on the pattern of neural activation of the PAG along its mediolateral and rostrocaudal subregions after a forced swim stress episode. Male Wistar rats were sub-acutely treated with desipramine (a selective noradrenaline re-uptake blocker, three injections of 10 mg/kg in 24 h) or clomipramine (a non-selective serotonin and noradrenaline re-uptake blocker, three injections of 10 mg/kg in 24 h) and submitted to the forced swimming test (FST). Two hours after the test their brain were removed for Fos immunohistochemistry. Fos-like immunoreactivity (FLI) in rostral, intermediate and caudal portions of dorsomedial (dmPAG), dorsolateral (dlPAG), lateral (lPAG) and ventrolateral (vlPAG) PAG were quantified by a computerized system. The FST session increased FLI in most parts of the PAG. Previous treatment with desipramine or clomipramine reduced FLI in all columns of the PAG. FLI in the PAG correlated positively with to the immobility time and negatively with to climbing behavior scored during the test. These results indicate that neurons in the PAG are activated by uncontrollable stress. Moreover, inhibitory action of antidepressants on this activity may be associated with the anti-immobility effects of these drugs in the FST.

Predicting danger: the nature, consequences, and neural mechanisms of predictive fear learning

The ability to detect and learn about the predictive relations existing between events in the world is essential for adaptive behavior. It allows us to use past events to predict the future and to adjust our behavior accordingly. Pavlovian fear conditioning allows anticipation of sources of danger in the environment. It guides attention away from poorer predictors toward better predictors of danger and elicits defensive behavior appropriate to these threats. This article reviews the differences between learning about predictive relations and learning about contiguous relations in Pavlovian fear conditioning. It then describes behavioral approaches to the study of these differences and to the examination of subtle variations in the nature and consequences of predictive learning. Finally, it reviews recent data from rodent and human studies that have begun to identify the neural mechanisms for direct and indirect predictive fear learning.

A role for the periaqueductal gray in switching adaptive behavioral responses

Previous studies suggested a role for the rostral lateral periaqueductal gray (PAG) in the inhibition of maternal behavior induced by low doses of morphine in dams with previous morphine experience. In the present study, we first showed that unilateral NMDA lesions placed in this particular PAG region prevented the morphine-induced inhibition of maternal behavior in previously morphine-sensitized dams. As suggested by previous Fos data on the PAG, predatory hunting appears as a likely candidate to replace maternal behavior in the morphine-treated dams. By testing saline- and morphine-treated dams with live cockroaches only, we have presently shown that morphine challenge increased insect hunting. Moreover, morphine- and saline-treated dams were also observed in an environment containing pups and roaches. Although most of the saline-treated animals displayed active nursing and only occasionally presented insect hunting, all of the morphine-treated animals ignored the pups and avidly pursued and caught the roaches. We next questioned whether the rostral lateral PAG would be involved in this behavioral switch. Our results showed that unilateral lesions of the rostral lateral PAG, but not other parts of the PAG, partially impaired predatory hunting and restored part of the maternal response. Moreover, bilateral lesions of the rostral lateral PAG produced even more dramatic effects in inhibiting insect hunting and restoring maternal behavior. The present findings indisputably show that the rostral lateral PAG influences switching from maternal to hunting behavior in morphine-treated dams, thus supporting a previously unsuspected role for the PAG in selecting adaptive behavioral responses.

Periparabigeminal and adjoining mesencephalic tegmental field projections to the dorsolateral periaqueductal grey in cat - a possible role for oculomotor input in the defensive system

The dorsolateral column of the mesencephalic periaqueductal grey (PAGdl) differs from its adjacent columns in terms of afferent and efferent connections and the distribution pattern of different histochemical substances. Functionally, PAGdl is associated with aversive and defensive behaviours, but in an earlier study of this laboratory [E.M. Klop et al. (2005) J. Comp. Neurol., 492, 303-322], it was found that PAGdl specifically receives input from the nucleus prepositus hypoglossi, which plays a role in oculomotor control. In search for other oculomotor-related brainstem structures projecting to PAGdl we studied the projections from the parabigeminal nucleus (PBGN) and its medially adjoining periparabigeminal area (PPBGA). In three cats, injections of wheatgerm agglutinin-horseradish peroxidase involving PAGdl did not, or to only a very limited extent, result in retrogradely labelled neurons in PBGN. When the peripheral parts of PAGdl were involved in the injection site, labelled neurons were located in PPBGA, while after an injection involving only the more central parts of PAGdl they were located in the tegmentum medial to the PPBGA. An anterograde tracing study using [3H]-leucine and biotinylated dextran amine affirmed that neurons in PPBGA project to more peripheral parts of PAGdl, while neurons located in the tegmentum medial to PPBGA project mainly to its central parts. These results provide further evidence for the existence of two different subdivisions of PAGdl. We hypothesize that PAGdl is alerted by sudden changes in the visual field, and that the PAGdl defensive system is inhibited when these changes are caused by eye movements.

The role of the amygdala and olfaction in unconditioned fear in developing rats

Early in ontogeny, young rats must be able to detect dangerous stimuli and to exhibit appropriate defensive behaviors. Different nuclei of the amygdala mediate unconditioned and conditioned fear responses to threat in adult rats. The aim of this study was to determine the role of the amygdala in unlearned fear behavior in young rats. When exposed to an unfamiliar adult male rat, preweaning rat pups freeze, with peak levels on postnatal day 14 and declining levels on day 18. Pups were made anosmic to block olfactory input to the amygdala, and amygdala activation was assessed by quantifying the neuronal marker c-fos. Anosmic pups did not freeze in the presence of the male rat and had decreased c-fos expression in the medial amygdala on day 14 and in the medial and lateral amygdala on day 18. However, the decrease in freezing between days 14 and 18 was not associated with a decrease in c-fos expression in the medial amygdala. The medial and lateral amygdala were then inactivated by local muscimol infusion on day 14. Muscimol infusion into the medial amygdala decreased freezing to the male rat but not to a loud noise, whereas infusion into the lateral amygdala blocked freezing to a loud noise but not to the male. These findings indicate that different nuclei of the amygdala process sensory information of different modalities, mediate unconditioned freezing, and may be involved in developmental changes in the fear response in young rats.

Unitary hypothesis for multiple triggers of the pain and strain of migraine

Migraine headache is triggered by and associated with a variety of hormonal, emotional, nutritional, and physiological changes. The perception of migraine headache is formed when nociceptive signals originating in the meninges are conveyed to the somatosensory cortex through the trigeminal ganglion, medullary dorsal horn, and thalamus. Is there a common descending pathway accounting for the activation of meningeal nociceptors by different migraine triggers? We propose that different migraine triggers activate a wide variety of brain areas that impinge on parasympathetic neurons innervating the meninges. According to this hypothesis, migraine triggers such as perfume, stress, or awakening activate multiple hypothalamic, limbic, and cortical areas, all of which contain neurons that project to the preganglionic parasympathetic neurons in the superior salivatory nucleus (SSN). The SSN, in turn, activates postganglionic parasympathetic neurons in the sphenopalatine ganglion, resulting in vasodilation and local release of inflammatory molecules that activate meningeal nociceptors. Are there ascending pathways through which the trigeminovascular system can induce the wide variety of migraine symptoms? We propose that trigeminovascular projections from the medullary dorsal horn to selective areas in the midbrain, hypothalamus, amygdala, and basal forebrain are functionally positioned to produce migraine symptoms such as irritability, loss of appetite, fatigue, depression, or the quest for solitude. Bidirectional trafficking by which the trigeminovascular system can activate the same brain areas that have triggered its own activity in the first place provides an attractive network of perpetual feedback that drives a migraine attack for many hours and even days.

Stressed-out endogenous cannabinoids relieve pain

A variety of physical and psychological stressors induce analgesia by activating descending systems that project from the brain to the spinal cord. This stress-induced analgesia (SIA) is mediated by distinct opioid- and non-opioid-dependent mechanisms. New evidence suggests that non-opioid SIA is mediated by two independent endocannabinoids within the midbrain. Furthermore, novel agents that disrupt breakdown of these endocannabinoids enhance non-opioid SIA and pave the way for novel therapies.

Increases in Arousal Are Associated with Reductions in the Human Nociceptive Flexion Reflex Threshold and Pain Ratings

The nociceptive flexion reflex has been regarded as an objective correlate of pain perception. This study examined whether the nociceptive flexion reflex is modulated by physiological arousal in the same manner as pain. Cardiovascular activity, nociceptive flexion reflex thresholds, and pain ratings were measured in 40 healthy adults under three conditions that demanded varying degrees of physiological arousal: Rest, number repetition, and mental arithmetic. Heart rates were faster and R-wave to pulse intervals shorter during mental arithmetic than number repetition, whereas heart rates were slower and R-wave to pulse intervals longer during rest compared to number repetition. Both mental arithmetic and number repetition were associated with reduced nociceptive flexion reflex thresholds compared to rest. Although the nociceptive flexion reflex thresholds were the same during mental arithmetic and number repetition, pain ratings were lower during mental arithmetic than number repetition and rest. The results indicate that nociception was facilitated but pain was inhibited by increased physiological arousal. This dissociation suggests that the nociceptive flexion reflex threshold is not a suitable correlate of pain during states of increased arousal.

Hemorrhage activates proopiomelanocortin neurons in the rat hypothalamus

Severe blood loss lowers arterial pressure through a central mechanism that is thought to include opioid neurons. In this study, we investigated whether hemorrhage activates proopiomelanocortin (POMC) neurons by measuring Fos immunoreactivity and POMC mRNA levels in the medial basal hypothalamus. Hemorrhage (2.2 ml/100 g body weight over 20 min) increased the number of Fos immunoreactive neurons throughout the rostral-caudal extent of the arcuate nucleus, the retrochiasmatic area and the peri-arcuate region lateral to the arcuate nucleus where POMC neurons are located. Double label immunohistochemistry revealed that hemorrhage increased Fos expression by beta-endorphin immunoreactive neurons significantly. The proportion of beta-endorphin immunoreactive neurons that expressed Fos immunoreactivity increased approximately four-fold, from 11.7+/-1.4% in sham-operated control animals to 42.0+/-5.2% in hemorrhaged animals. Hemorrhage also increased POMC mRNA levels in the medial basal hypothalamus significantly, consistent with the hypothesis that blood loss activates POMC neurons. To test whether activation of arcuate neurons contributes to the fall in arterial pressure evoked by hemorrhage, we inhibited neuronal activity in the caudal arcuate nucleus by microinjecting the local anesthetic lidocaine (2%; 0.1 or 0.3 microl) bilaterally 2 min before hemorrhage was initiated. Lidocaine injection inhibited hemorrhagic hypotension and bradycardia significantly although it did not influence arterial pressure or heart rate in non-hemorrhaged rats. These results demonstrate that hemorrhage activates POMC neurons and provide evidence that activation of neurons in the arcuate nucleus plays an important role in the hemodynamic response to hemorrhage.

Effect of stress on the voluntary intake of a sweetened ethanol solution in pair-housed adolescent and adult rats

BACKGROUND

Data regarding the effects of stressors on ethanol intake are mixed. Previous experiments reporting greater voluntary intake of ethanol in adolescent than adult rats have examined intake in isolate-housed animals. Given that the stress of isolate housing may differ ontogenetically as well as confound interpretation of other stressor effects, the present study examined stressor/ethanol interactions among pair-housed adolescent and adult rats.

METHODS

Sprague-Dawley male rats were implanted with identification tags that allowed individual monitoring of home cage intake of water and either a 10% (v/v) ethanol solution containing 0.1% (w/v) saccharin or saccharin alone over a 14-day access period. Animals were given zero, one, or eight daily 15-min footshock sessions, with shock-induced freezing and pre-, post-, and recovery corticosterone levels determined on the first and last footshock exposure days. After the access period, withdrawal was assessed with a plus maze, and tolerance to ethanol-induced loss of righting reflex was examined.

RESULTS

Nonstressed adolescents drank considerably more sweetened ethanol than did adults, with chronic stress suppressing this adolescent consumption. Ethanol access in adolescents disrupted within-session adaptation to footshock in terms of freezing behavior, although no such disruption was evident at either age when indexed hormonally. Despite relatively high ethanol intakes (up to 6 g/kg/day in the adolescents), no evidence for withdrawal-associated anxiogenesis emerged. Evidence for tolerance was mixed and, to the extent that it was present, was metabolic in nature.

CONCLUSIONS

Previous reports of heightened voluntary ethanol intake among adolescent rats are not a function of isolate stress but are evident in pair-housed animals. Adolescents were more sensitive to ethanol/stress interactions than were adults, with the elevated ethanol intake of pair-housed adolescents selectively disrupted by chronic stress, a stress-induced disruption not evident in adults. Likewise, ethanol disrupted behavioral adaptation to the footshock stressor among adolescents but not adults.

Central autonomic integration of psychological stressors: Focus on cardiovascular modulation

During stress the sympathoadrenal system and the hypothalamo-pituitary-adrenal axis act in a coordinated manner to force changes within an animal's current physiological and behavioral state. Such changes have been described as 'fight flight' or stress responses. The central nervous system may generate a stress response by different neural circuits, this being dependent upon the type of stressor presented. For instance, the central control of the autonomic function during physical stress would seem to be based on existing homeostatic mechanisms. In contrast, with exposure to psychological stress the means by which autonomic outflow is regulated has not been fully established. This review discusses recent observations of autonomic flow, cardiovascular components in particular, during psychological stress and the possible implications these may have for our understanding of the central nervous system. In addition, an update of recent findings concerning several regions thought to be important to the regulation of autonomic function during psychological stress exposure is provided.

Perfusion functional MRI reveals cerebral blood flow pattern under psychological stress

Despite the prevalence of stress in everyday life and its impact on happiness, health, and cognition, little is known about the neural substrate of the experience of everyday stress in humans. We use a quantitative and noninvasive neuroimaging technique, arterial spin-labeling perfusion MRI, to measure cerebral blood flow (CBF) changes associated with mild to moderate stress induced by a mental arithmetic task with performance monitoring. Elicitation of stress was verified by self-report of stress and emotional state and measures of heart rate and salivary-cortisol level. The change in CBF induced by the stress task was positively correlated with subjective stress rating in the ventral right prefrontal cortex (RPFC) and left insula/putamen area. The ventral RPFC along with right insula/putamen and anterior cingulate showed sustained activation after task completion in subjects reporting a high stress level during arithmetic tasks. Additionally, variations of baseline CBF in the ventral RPFC and right orbitofrontal cortex were found to correlate with changes in salivary-cortisol level and heart rate caused by undergoing stress tasks. We further demonstrated that the observed right prefrontal activation could not be attributed to increased cognitive demand accompanying stress tasks and extended beyond neural pathways associated with negative emotions. Our results provide neuroimaging evidence that psychological stress induces negative emotion and vigilance and that the ventral RPFC plays a key role in the central stress response.

Expression of c-Fos in the mouse Edinger-Westphal nucleus following ethanol administration is not secondary to hypothermia or stress

Restraint stress, lipopolysaccharide (LPS), and ethanol (EtOH) administration have all been found to induce c-Fos in the brain, and to cause hypothermia. The present study was designed to assess whether the c-Fos expression that occurs in the Edinger-Westphal nucleus (EW) after EtOH administration is independent of the hypothermia or any stress effects that occur. To test this, we used restraint stress and LPS in addition to EtOH, and also examined two control areas, the dorsal raphe nucleus (DRN) and the periaqueductal gray (PAG), in addition to EW. Male C57BL6/J mice were used. Groups of mice received intraperitoneal (IP) injections of EtOH (2 g/kg), LPS (600 microg/kg or 50 microg/kg), or saline. A separate group of mice received no injection, but were placed in plastic restrainers for the entirety of the experiment. For all groups, core temperatures were monitored rectally every 30 min for 3 h postinjection, after which, the animals were sacrificed. Then, the number of Fos-positive cells in the brain regions of the EW, DRN, and PAG was quantified. Both EtOH and restraint stress induced a transient hypothermia, where core temperature (Tc) declined immediately and then rose again. Both doses of LPS induced a slower developing, longer lasting hypothermia, while saline had no effect on Tc. Only EtOH induced a significant amount of c-Fos in EW, while both doses of LPS and restraint stress induced c-Fos in DRN, and only restraint stress caused induction in PAG. These data demonstrate that activation of EW after EtOH is unrelated to hypothermia or stress.

The psychobiology of PTSD: coping with trauma

Posttraumatic stress disorder (PTSD) is one of the few psychiatric conditions where a specific psychosocial stressor is explicitly tied to etiology. Although a majority of people experience a traumatic event in their life, most of them will not develop PTSD or other mental health problems such as depressive or anxiety disorders. Emotional and neurobiological responses to psychosocial stressors show striking individual variation. In this paper cognitive appraisal and coping factors are explored as potential sources of individual differences in the neuroendocrinological stress response, and subsequently in mental health outcome. Continued study of the psychobiology of trauma and PTSD will enhance our understanding of adaptation to psychosocial stressors and support efforts to treat associated psychological and biological sequelae.

Serotonergic systems associated with arousal and vigilance behaviors following administration of anxiogenic drugs

Serotonergic systems play important roles in modulating behavioral arousal, including behavioral arousal and vigilance associated with anxiety states. To further our understanding of the neural systems associated with increases in anxiety states, we investigated the effects of multiple anxiogenic drugs on topographically organized subpopulations of serotonergic neurons using double immunohistochemical staining for c-Fos and tryptophan hydroxylase combined with topographical analysis of the rat dorsal raphe nucleus (DR). Anxiogenic drugs with diverse pharmacological properties including the adenosine receptor antagonist caffeine, the serotonin 5-HT2A/2C receptor agonist m-chlorophenyl piperazine (mCPP), the alpha2-adrenoreceptor antagonist yohimbine, and the benzodiazepine receptor partial inverse agonist N-methyl-beta-carboline-3-carboxamide (FG-7142) induced increases in behavioral arousal and vigilance behaviors consistent with an increase in anxiety state. In addition, these anxiogenic drugs, excluding yohimbine, had convergent actions on an anatomically-defined subset of serotonergic neurons within the middle and caudal, dorsal subdivision of the DR. High resolution topographical analysis revealed that at the mid-rostrocaudal level, caffeine and FG-7142 had convergent effects on c-Fos expression in serotonergic neurons that were restricted to a previously undefined region, which we have named the shell region of the dorsal part of the dorsal raphe nucleus (DRDSh), that overlaps the anatomical border between the dorsal part of the dorsal raphe nucleus, the ventral part of the dorsal raphe nucleus (DRV), and the ventrolateral part of the dorsal raphe nucleus (DRVL). Retrograde tracing methods revealed that DRDSh contains large numbers of neurons projecting to the basolateral amygdaloid nucleus, a forebrain structure important for emotional appraisal and modulation of anxiety-related physiological and behavioral responses. Together these findings support the hypothesis that there is a functional topographical organization in the DR and are consistent with the hypothesis that anxiogenic drugs have selective actions on a subpopulation of serotonergic neurons projecting to a distributed central autonomic and emotional motor control system regulating anxiety states and anxiety-related physiological and behavioral responses.

Brain stem excitatory and inhibitory signaling pathways regulating bronchoconstrictive responses

This review summarizes recent work on two basic processes of central nervous system (CNS) control of cholinergic outflow to the airways: 1) transmission of bronchoconstrictive signals from the airways to the airway-related vagal preganglionic neurons (AVPNs) and 2) regulation of AVPN responses to excitatory inputs by central GABAergic inhibitory pathways. In addition, the autocrine-paracrine modulation of AVPNs is briefly discussed. CNS influences on the tracheobronchopulmonary system are transmitted via AVPNs, whose discharge depends on the balance between excitatory and inhibitory impulses that they receive. Alterations in this equilibrium may lead to dramatic functional changes. Recent findings indicate that excitatory signals arising from bronchopulmonary afferents and/or the peripheral chemosensory system activate second-order neurons within the nucleus of the solitary tract (NTS), via a glutamate-AMPA signaling pathway. These neurons, using the same neurotransmitter-receptor unit, transmit information to the AVPNs, which in turn convey the central command to airway effector organs: smooth muscle, submucosal secretory glands, and the vasculature, through intramural ganglionic neurons. The strength and duration of reflex-induced bronchoconstriction is modulated by GABAergic-inhibitory inputs and autocrine-paracrine controlling mechanisms. Downregulation of GABAergic inhibitory influences may result in a shift from inhibitory to excitatory drive that may lead to increased excitability of AVPNs, heightened airway responsiveness, and sustained narrowing of the airways. Hence a better understanding of these normal and altered central neural circuits and mechanisms could potentially improve the design of therapeutic interventions and the treatment of airway obstructive diseases.

Assessing substrates underlying the behavioral effects of antidepressants using the modified rat forced swimming test

Selective serotonin reuptake inhibitors (SSRIs) are the most widely prescribed antidepressant class today and exert their antidepressant-like effects by increasing synaptic concentrations of serotonin (5-HT). The rat forced swim test (FST) is the most widely used animal test predictive of antidepressant action. Procedural modifications recently introduced by our laboratory have enabled SSRI-induced behavioral responses to be measured in the modified FST. The use of this model to understand the pharmacological and physiological mechanisms underlying the role of 5-HT in the behavioral effects of antidepressant drugs is reviewed. Although all antidepressants reduced behavioral immobility, those antidepressants that increase serotonergic neurotransmission predominantly increase swimming behavior whereas those that increase catacholaminergic neurotransmission increase climbing behavior. The 5-HT(1A), 5-HT(1B/1D) and 5-HT(2C) receptors are the 5-HT receptors most important to the therapeutic effects of SSRIs, based on extensive evaluation of agonists and antagonists of individual 5-HT receptor subtypes. Studies involving chronic administration have shown that the effects of antidepressants are augmented following chronic treatment. Other studies have demonstrated strain differences in the response to serotonergic compounds. Finally, a physiological model of performance in the rat FST has been proposed involving the regulation of 5-HT transmission by corticotropin releasing factor (CRF).

Differences in brain responses to visceral pain between patients with irritable bowel syndrome and ulcerative colitis

Patients with mild chronic inflammation of the rectum or ileum have reduced perceptual responses to rectosigmoid distension compared to patients with irritable bowel syndrome (IBS). The current study sought to identify differences in regional cerebral blood flow (rCBF) during rectal distension, which might correspond to these perceptual differences. In 8 male ulcerative colitis (UC) patients with quiescent disease, 7 male IBS patients and 7 healthy male controls, rCBF was assessed using 15O-water positron emission tomography at baseline and during actual and anticipated but undelivered rectal distensions. No group differences were seen in anterior insula and dorsal anterior cingulate cortex (dACC), two regions consistently activated by painful intestinal stimuli. However, IBS patients showed greater activation of the amygdala, rostroventral ACC, and dorsomedial frontal cortical regions. In contrast, no significant differences were observed between UC and controls. When these two non-IBS groups were combined, functional connectivity analyses showed that right lateral frontal cortex (RLFC) activation positively correlated with activation of the dorsal pons/periaqueductal gray, a key region involved in endogenous pain inhibition. According to the connectivity analysis, this effect was mediated by inhibition of medial frontal cortex by the RLFC. Chronic colonic inflammation is not necessarily associated with increased visceral afferent input to the brain during rectal distension. In the sample studied, the primary difference between functional and quiescent inflammatory disease of the colon was in terms of greater activation of limbic/paralimbic circuits in IBS, and inhibition of these circuits in UC and controls by the RLFC.

Mapping the neural circuit activated by alarm pheromone perception by c-Fos immunohistochemistry

We previously reported that the alarm pheromones released from stressed male rats exaggerated both behavioral and autonomic (stress-induced hyperthermia) responses in recipient rats that were introduced into a novel environment. Subsequent experiments provided evidence that these alarm pheromones could be divided into two functionally different categories based on the site specificity and testosterone dependency of their production. However, the neural mechanisms underlying these behavioral and physiological responses remain unknown. In the present study, we examined Fos expression in 26 brain sites of the recipient rat 60 min after the exposure to the pheromone that aggravated stress-induced hyperthermia. The alarm pheromone-exposed rats showed a concurrent increase in Fos expression, in contrast to control odor-exposed rats in the anterior division lateral and medial group of the bed nucleus of the stria terminalis, paraventricular nucleus, dorsomedial hypothalamic nucleus, anterodorsal medial, lateral and basolateral amygdaloid nucleus, ventrolateral periaqueductal gray, laterodorsal tegmental nucleus, and locus coeruleus. These results provide information about the neural mechanisms in response to a non-sexual pheromone, i.e., an alarm pheromone, and suggest that the perception of the alarm pheromone is related to stress-responsive brains structures, including the hypothalamus and brainstem, as well as to the amygdaloid nuclei.

Neural segregation of Fos-protein distribution in the brain following freezing and escape behaviors induced by injections of either glutamate or NMDA into the dorsal periaqueductal gray of rats

Freezing and escape responses induced by gradual increases in the intensity of the electrical current applied to dorsal regions of the periaqueductal gray (dPAG) cause a distinct pattern of Fos distribution in the brain. From these studies, it has been suggested that a pathway involving the dPAG itself, dorsomedial hypothalamus and the cuneiform nucleus (CnF) would mediate responses to immediate danger and another one involving the amygdala and ventrolateral periaqueductal gray (vlPAG) would mediate cue-elicited responses. As electrical stimulation activates body cells and fibers of passage the need of studies with chemical stimulation of only post-synaptic fibers of the dPAG is obvious. To examine further this issue we measured Fos protein expression in brain areas activated by stimulation of the dPAG with glutamate (5 nmol/0.2 microL) and N-methyl-D-aspartate (NMDA) at doses that provoke either freezing (4 nmol/0.2 microL) or escape (7 nmol/0.2 microL) responses, respectively. The results showed that glutamate-induced freezing caused a selective increase in Fos expression in the superior and inferior colliculi as well as in the laterodorsal nucleus of the thalamus. On the other hand, NMDA-induced escape led to widespread increases in Fos labeling in almost all structures studied. Differently from glutamate, NMDA at doses provoking freezing caused significant increase of Fos labeling in the dPAG and CnF. Therefore, the present data support the notion that freezing behavior induced by activation of either non-NMDA or NMDA receptors in the dorsolateral periaqueductal gray (dlPAG) is neurally segregated: glutamate activates only structures that are mainly involved in the sensorial processing and NMDA-induced freezing structures involved in the motor output of defensive behavior. Therefore, the freezing elicited by the activation of non-NMDA receptors seem to be related to the acquisition of aversive information, whereas that resulting from the activation of NMDA receptors could serve as a preparatory response for flight.

Fos-like immunoreactivity in the brain associated with freezing or escape induced by inhibition of either glutamic acid decarboxylase or GABAA receptors in the dorsal periaqueductal gray

GABAergic neurons exert tonic control over the neural substrates of aversion in the dorsal periaqueductal gray (dPAG). It has been shown that electrical stimulation of this region at freezing or escape thresholds activates different neural circuits in the brain. Since electrical stimulation activates cell bodies and fibers of passage, it is necessary to use chemical stimulation that activates only post-synaptic receptors. To investigate this issue further, reduction of GABA transmission was performed with local injections of either the GABA-A receptor antagonist bicuculline or the glutamic acid decarboxylase (GAD) inhibitor semicarbazide into the dorsolateral periaqueductal gray (dlPAG). Local infusions of semicarbazide (5.0 microg/0.2 microl) or bicuculline (40 ng/0.2 microl) into this region caused freezing and escape, respectively. The results obtained showed that freezing behavior induced by semicarbazide was associated with an increase in Fos expression in the laterodorsal nucleus of the thalamus (LD) and ventrolateral periaqueductal gray (vlPAG), while bicuculline-induced escape was related to widespread increase in Fos labeling, notably in the columns of the periaqueductal gray, hypothalamus nuclei, the central amygdaloid nucleus (Ce), the LD, the cuneiform nucleus (CnF) and the locus coeruleus (LC). Thus, the present data support the notion that freezing and escape behaviors induced by GABA blockade in the dlPAG are neurally segregated: freezing activates only structures that are mainly involved in sensory processing, and bicuculline-induced escape activates structures involved in both sensory processing and motor output of defensive behavior. Therefore, the freezing elicited by activation of dlPAG appears to be related to the acquisition of aversive information, whereas most brain structures involved in the defense reaction are recruited during escape.

Effects of appraisal and coping on the neuroendocrine response to extreme stress

Although many people are exposed to extreme stress, only some of them develop psychobiological disturbances that can lead to posttraumatic stress disorder (PTSD) or other posttrauma psychopathology. This paper examines the effects of different types of appraisal and coping to find clues to how individuals differ in their neuroendocrine responses to extreme stress. It proposes a conceptual model for components of the adult response to stressors. Threat appraisal and defensive coping may play crucial roles in determining the neuroendocrine response to trauma with potential mental health consequences, particularly PTSD.

Concurrent nociceptive stimulation impairs the anxiolytic effect of midazolam injected into the periaqueductal gray in mice

This study investigated whether the opportunity to avoid or escape the open arms of an elevated plus-maze (EPM) affects the antinociceptive response observed when mice are subjected to open arm confinement. Furthermore, in order to better characterize the relationship between emotion and antinociception in the EPM, we examined the behavioral effects of midazolam injection into the midbrain periaqueductal gray matter (PAG). As our main aim was to evaluate the relevance of different levels of approach-avoid conflict (i.e. the presence of open and closed arms) to maze-induced antinociception, mice were exposed to one of three types of EPM-a standard EPM (sEPM), an open EPM (oEPM: four open arms) or, as a control condition, an enclosed EPM (eEPM: four enclosed arms). Nociception was assessed using the formalin test. Twenty minutes after formalin injection (50 microl, 2.5% formalin) into the dorsal right hind paw, mice received an intra-PAG injection of saline or midazolam (10-20 nmol). Five minutes later, they were individually exposed to one of the mazes for 10 min (25-35 min after formalin injection). Videotapes of the test sessions were scored for a variety of behavioral measures including time spent licking the formalin-injected paw. To examine whether the effects of midazolam on anxiety-like behavior may have been influenced by concurrent nociceptive stimulation (i.e. formalin pretreatment), naive mice were submitted to a similar procedure to that described above for the sEPM test but without formalin pretreatment. Results showed that mice exposed to the oEPM spent significantly less time licking the injected paw compared to groups exposed to either the sEPM or eEPM. Although exposure to the sEPM induced anxiety-like behaviors (i.e. open arm avoidance), it did not result in antinociception. Intra-PAG infusions of midazolam failed to block oEPM-induced antinociception or to alter sEPM-induced anxiety in mice that had received formalin injection. However, under normal test conditions (i.e. in the absence of formalin-induced nociceptive stimulation), intra-PAG midazolam produced clear anti-anxiety effects in mice exposed to the sEPM. Findings are discussed in terms of different emotional states induced by the oEPM and sEPM and the influence of concurrent nociceptive stimulation on the anti-anxiety effect of intra-PAG midazolam.

Microarrays--the challenge of preparing brain tissue samples

Microarray experiments allow researchers to collect an amazing amount of gene expression data that have the potential to provide unique information to help interpretation of the biological functions of the central nervous system. These experiments are, however, technically demanding and present unique difficulties when used in the context of neuroscience research, in particular. Success or failure of microarray experiments are highly dependent on reproducible target preparations. This involves a relatively long chain of preparation steps, such as removal of tissue from experimental animals or from post-mortem human brains, storage, selection, and excision of brain regions. This is followed by RNA extraction, reverse transcription, and labeling of target cDNAs or cRNAs. Additionally, it is emphasized that the quality of microarray data largely relies on the proper handling of animals throughout experiments and the time of the day when experiments are stopped. This article tries to provide hints for some basic rules to be observed in preparation of samples for expression profiling studies.

Variations of maternal care differentially influence 'fear' reactivity and regional patterns of cFos immunoreactivity in response to the shock-probe burying test

Natural variations in maternal care in the rat influence the development of neuronal systems that regulate endocrine and behavioral responses to stress. Thus, as adults, rats that received higher levels of maternal licking/grooming (LG) in infancy are less 'fearful' in response to novelty, compared with adult offspring of Low LG mothers. The present study examined the influence of maternal care on behavioral and neuronal responses to a more specific, localizable form of threat using an electrified probe in the shock-probe burying test. Even under these conditions, adult offspring of High LG mothers displayed lower levels of fear reactivity (i.e. less shock-induced freezing and probe burying) throughout the test than did offspring of Low LG mothers. These differences in fearfulness were associated with differential patterns of cFos immunoreactivity (cFos-IR), 120 min following test exposure. Relative to control rats exposed to a non-electrified probe, cFos-IR was increased in the offspring of High LG mothers exposed to an electrified probe in the dentate gyrus, ventral subiculum, lateral and medial septum, nucleus accumbens and the dorsal periaqueductal gray. Shock-exposed offspring of Low LG dams displayed a very different pattern of neuronal activation characterized by both increases (area CA1 of the ventral hippocampus and the inferior colliculus) and decreases (paraventricular nucleus of the hypothalamus and the ventrolateral periaqueductal gray) in cFos-IR compared with the no-shock controls. Together these results suggest that maternal care serves to 'program' neuronal circuits that modulate fear-related responding in the rat resulting in qualitatively different neuronal responses to stress.

Gabaergic regulation of the neural organization of fear in the midbrain tectum

In midbrain tectum (MT) structures, such as the dorsal periaqueductal gray (dPAG), the superior colliculus (SC) and the inferior colliculus (IC) GABAergic neurons exert a tonic control on the neural substrates involved in the expression of defensive reactions. In this review, we summarize behavioral, immunohistochemical (brain Fos distribution) and electrophysiological (auditory evoked potentials) data obtained with the reduction of GABA transmission by local injections of a GABA receptor blocker (bicuculline, BIC) or a glutamic acid decarboxylase inhibitor (semicarbazide, SMC) into the MT. Distinct patterns of Fos distribution were obtained following the freezing and escape reactions induced by MT injections of SMC and BIC, respectively. While only the laterodorsal nucleus of the thalamus was labeled after SMC-induced freezing, a widespread increase in Fos expression in the brain occurred after BIC-induced escape. Also, injections of SMC into the IC increased the auditory evoked potentials recorded from this structure. It is suggested that GABAergic mechanisms of MT are also called into play when sensory gating of the MT is activated during different emotional states.

Neural mechanisms of freezing and passive aversive behaviors

Cues that predict aversive outcomes often produce marked inhibitions of behavior known as freezing, but it is unknown exactly what neural pathways cause this inhibition. The amygdala and bed nucleus of the stria terminalis, along with their projections to the periaqueductal gray, are strongly implicated in freezing, but it is not known how these structures inhibit motor output. The median raphe nucleus (MRN), which contains a major population of serotonin neurons, has also been implicated in freezing, but the serotonin neurons themselves do not seem to be involved, leaving it uncertain which neurons in this area promote freezing. Our recent work suggests that GABAergic neurons just lateral to the MRN, but not within the MRN, regulate freezing via projections to midbrain dopamine neurons. Because freezing pathways may control a variety of other passive aversive behaviors, their elucidation may help understand the mechanisms of addictions and compulsions, which involve a failure of aversive outcomes to inhibit behavior.

In cat four times as many lamina I neurons project to the parabrachial nuclei and twice as many to the periaqueductal gray as to the thalamus

The spinothalamic tract, and especially its fibers originating in lamina I, is the best known pathway for transmission of nociceptive information. On the other hand, different studies have suggested that more lamina I cells project to the parabrachial nuclei (PBN) and periaqueductal gray (PAG) than to the thalamus. The exact ratio of the number of lamina I projections to PBN, PAG and thalamus is not known, because comprehensive studies examining these three projections from all spinal segments, using the same tracers and counting methods, do not exist. In the present study, the differences in number and distribution of retrogradely labeled lamina I cells in each segment of the cat spinal cord (C1-Coc2) were determined after large wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) injections in either PBN, PAG or thalamus. We estimate that approximately 6000 lamina I cells project to PBN, 3000 to PAG and less than 1500 to the thalamus. Of the lamina I cells projecting to thalamus or PAG more than 80%, and of the lamina I-PBN cells approximately 60%, were located on the contralateral side. In all cases, most labeled lamina I cells were found in the upper two cervical segments and in the cervical and lumbar enlargements.

Two parts of the nucleus prepositus hypoglossi project to two different subdivisions of the dorsolateral periaqueductal gray in cat

The dorsolateral column of the mesencephalic periaqueductal gray (PAG) is a separate part of the PAG. Its afferent sources, efferent targets, and neurochemical properties differ from the adjacent PAG columns. The dorsolateral PAG is thought to be associated with aversive behaviors, but it is not yet understood how these behaviors are brought about. To elucidate the function of the PAG further, in the present study we investigated which brainstem regions project to the dorsolateral PAG. Wheat germ agglutinin-horseradish peroxidase (WGA-HRP) injections involving the dorsolateral PAG, but extending into the lateral part, resulted in many retrogradely labeled cells in the pontine and medullary tegmentum bilaterally. However, it was concluded that these neurons were labeled from the lateral PAG, because no anterograde labeling was found in the dorsolateral PAG after a large injection into the tegmentum. Retrogradely labeled cells were also found in the nucleus prepositus hypoglossi (PPH), mainly contralaterally. Injections of [3H]leucine or WGA-HRP in the PPH resulted in anterogradely labeled fibers in the dorsolateral PAG. Two separate distribution patterns were found. The caudal and intermediate PPH projected to a small region on the dorsolateral edge of the dorsolateral column, whereas the supragenual PPH distributed labeled fibers to all other parts of the dorsolateral PAG, except the area on the dorsolateral edge. These separate PPH projections suggest that two subdivisions exist within the dorsolateral PAG. The present findings suggest a role for the dorsolateral PAG in the oculomotor system.

The Darwinian concept of stress: benefits of allostasis and costs of allostatic load and the trade-offs in health and disease

Why do we get the stress-related diseases we do? Why do some people have flare ups of autoimmune disease, whereas others suffer from melancholic depression during a stressful period in their life? In the present review possible explanations will be given by using different levels of analysis. First, we explain in evolutionary terms why different organisms adopt different behavioral strategies to cope with stress. It has become clear that natural selection maintains a balance of different traits preserving genes for high aggression (Hawks) and low aggression (Doves) within a population. The existence of these personality types (Hawks-Doves) is widespread in the animal kingdom, not only between males and females but also within the same gender across species. Second, proximate (causal) explanations are given for the different stress responses and how they work. Hawks and Doves differ in underlying physiology and these differences are associated with their respective behavioral strategies; for example, bold Hawks preferentially adopt the fight-flight response when establishing a new territory or defending an existing territory, while cautious Doves show the freeze-hide response to adapt to threats in their environment. Thus, adaptive processes that actively maintain stability through change (allostasis) depend on the personality type and the associated stress responses. Third, we describe how the expression of the various stress responses can result in specific benefits to the organism. Fourth, we discuss how the benefits of allostasis and the costs of adaptation (allostatic load) lead to different trade-offs in health and disease, thereby reinforcing a Darwinian concept of stress. Collectively, this provides some explanation of why individuals may differ in their vulnerability to different stress-related diseases and how this relates to the range of personality types, especially aggressive Hawks and non-aggressive Doves in a population. A conceptual framework is presented showing that Hawks, due to inefficient management of mediators of allostasis, are more likely to be violent, to develop impulse control disorders, hypertension, cardiac arrhythmias, sudden death, atypical depression, chronic fatigue states and inflammation. In contrast, Doves, due to the greater release of mediators of allostasis (surplus), are more susceptible to anxiety disorders, metabolic syndromes, melancholic depression, psychotic states and infection.

Individual Differences in the Modulation of Fear-Related Brain Activation by Attentional Control

In this article, we consider the extent to which variations in the neural activation associated with fear-related stimuli are obligatory or optional. More specifically, we investigated modulation of activation according to type of encoding operation, and how this relates to individual differences in fearfulness and attentional control. In an fMRI study, fear-related (relative to neutral) pictures preferentially activated many of the regions involved in a hierarchical system responsible for organizing defensive behavior, and differential activation in some of these areas was related to self-reported individual variations in fearfulness. Preferential activation according to type of stimulus persisted to a limited extent even when attention was diverted from its emotional aspects. Importantly, however, encoding tasks involving attention to emotional versus nonemotional attributes of the same pictures revealed a pattern of greater activation during emotional encoding, similar to that differentiating fear-related from neutral stimuli. Again, the degree of modulation varied according to individual differences. We conclude that fear-related pictures can recruit activation in the defensive system even when attention is directed elsewhere, but that the extent of this activation is modulated by attentional control mechanisms. More critically, both differential activation and its modulation by attentional control are related to individual variations in emotional vulnerability, in a manner that conforms to predictions derived from existing theoretical accounts.

Characterization of basal and re-inflammation-associated long-term alteration in pain responsivity following short-lasting neonatal local inflammatory insult

Recently, several studies have suggested that neonatal noxious insult could alter future responses to painful stimuli. However, the manifestations, mechanisms, and even developmental nature of these alterations remain a matter of controversy. In part, this is due to the lack of detailed information on the neonatal sensitive period(s) during which noxious stimulation influences future nociception, and the time-course and distribution of the resultant abnormalities. The present paper describes these parameters in a rat model of short-lasting ( approximately 24 h) neonatal local inflammation of a hindpaw produced by injection of 0.25% carrageenan (1 microl/g). Examinations of paw withdrawal responses to thermal and mechanical stimulations in adult animals, which as neonates were subjected to this insult, showed that the previously-reported long-term hypoalgesia and hyperalgesia are not mutually exclusive outcomes of early noxious experience. Long-term hypoalgesia was apparent at the basal conditions and was equally strong in the previously injured and uninjured paws, which suggests a globally-driven deficit. In contrast, long-term excessive hyperalgesia had the strongest manifestation in the neonatally-injured paw after re-inflammation, indicating significant segmental involvement in its generation. The differences between mechanisms underlying the observed hypoalgesia and hyperalgesia are further underscored by the finding that, while the former is detectable only after animals reach the second month of life, the latter is elicitable immediately upon cessation of the initial neonatal inflammation. Nevertheless, we detected a significant overlap in the neonatal sensitive periods for generation of these effects (both occurring within the first postnatal week). Also, neither the basal hypoalgesia nor excessive re-inflammation-associated hyperalgesia subsided with age and were detectable in 120-125-day-old rats. These finding provide a framework within which the entire complex of long-term effects of early noxious experience can be understood and examined.

A two-dimensional neuropsychology of defense: fear/anxiety and defensive distance

We present in this paper a picture of the neural systems controlling defense that updates and simplifies Gray's "Neuropsychology of Anxiety". It is based on two behavioural dimensions: 'defensive distance' as defined by the Blanchards and 'defensive direction'. Defensive direction is a categorical dimension with avoidance of threat corresponding to fear and approach to threat corresponding to anxiety. These two psychological dimensions are mapped to underlying neural dimensions. Defensive distance is mapped to neural level, with the shortest defensive distances involving the lowest neural level (periaqueductal grey) and the largest defensive distances the highest neural level (prefrontal cortex). Defensive direction is mapped to separate parallel streams that run across these levels. A significant departure from prior models is the proposal that both fear and anxiety are represented at all levels. The theory is presented in a simplified form that does not incorporate the interactions that must occur between non-adjacent levels of the system. It also requires expansion to include the dimension of escapability of threat. Our current development and these proposed future extensions do not change the core concepts originally proposed by Gray and, we argue, demonstrate their enduring value.

Neural correlates of cat odor-induced anxiety in rats: region-specific effects of the benzodiazepine midazolam

Cat odor elicits a profound defensive reaction in rats that is reduced by benzodiazepine drugs. The neural correlates of this phenomenon were investigated here using Fos immunohistochemistry. Rats received either midazolam (0.75 mg/kg, s.c.) or vehicle and were exposed to pieces of a collar that had been worn by a domestic cat or an unworn (dummy) collar. Cat odor caused midazolam-sensitive defensive behavioral responses, including avoidance of collar contact, inhibition of grooming, and prolonged rearing. Cat odor exposure induced Fos expression in the posterior accessory olfactory bulb (glomerular, mitral, and granule cell layers), with granule cell layer activation attenuated by midazolam. High basal Fos expression, and some cat odor-associated Fos expression, was evident in the main olfactory bulb (glomerular cell layer), and midazolam exerted a strong inhibitory effect in this region. Midazolam inhibited Fos expression in key limbic regions involved in pheromone transduction (medial amygdala and bed nucleus of the stria terminalis) and defensive behavior (prelimbic cortex, lateral septum, lateral and medial preoptic areas, and dorsal premammillary nucleus). However, midazolam failed to affect cat odor-related Fos expression in a range of key defense-related sites, including the ventromedial hypothalamic nucleus, paraventricular nucleus of the hypothalamus, periaqueductal gray, and cuneiform nucleus. These results indicate that midazolam exerts a region-specific effect on the neural substrates activated by predator odor, with effects in the lateral septum and dorsal premammillary nucleus likely to be of major importance. These findings also suggest the intriguing hypothesis that cat odor is processed by rats as a "pheromone-like" stimulus.

Fos-like immunoreactive neurons following electrical stimulation of the dorsal periaqueductal gray at freezing and escape thresholds

Electrical stimulation of the dorsal regions of the periaqueductal gray (PAG) leads to defensive reactions characterized as freezing and escape responses. Until recently it was thought that this freezing behavior could be due to the recruitment of neural circuits in the ventrolateral periaqueductal gray (vlPAG), while escape would be mediated by other pathways. Nowadays, this view has been changing mainly because of evidence that freezing and escape behaviors thus elicited are not altered after lesions of the vlPAG. It has been suggested that there are at least two pathways for periaqueductal gray-mediated defensive responses, one involving the hypothalamus and the cuneiform nucleus (CnF) which mediates responses to immediate danger and another one involving the amygdala and vlPAG which mediates cue-elicited responses, either learned or innate. To examine this issue further we measured Fos protein expression in brain areas activated by electrical stimulation of the dorsolateral PAG (dlPAG) at the freezing and escape thresholds. The data obtained showed that freezing-provoking stimulation caused increases in Fos expression in the dorsomedial PAG (dmPAG), while escape-provoking stimulation led to increases at both dmPAG and dlPAG. Surprisingly, neither escape- nor freezing-provoking stimulations altered Fos expression in the central nucleus of amygdala (CeA). Escape-provoking stimulation caused increased Fos expression in the ventromedial hypothalamus (VMH), dorsal premammilary nucleus (PMd) and in the cuneiform nucleus. Significant increases in Fos labeling were found in the dmPAG and PMd following freezing-provoking stimulation. Therefore, the present data support the notion of a neural segregation for defensive behaviors in the dorsal columns of PAG, with increased Fos expression in the dmPAG following freezing, while dlPAG is affected by both freezing and escape responses. dlPAG, CnF, VMH and PMd are part of a brain aversion network activated by fear unconditioned stimuli. The present data also suggests that the defensive responses generated at the dlPAG level do not recruit the neural circuits of the vlPAG and CeA usually activated by conditioned fear stimuli.

Hemorrhagic sympathoinhibition mediated through the periaqueductal gray in the rat

In response to hemorrhage in the anesthetized rat, an initial renal sympathoexcitation is followed by profound sympathoinhibition and hypotension with increasing blood loss. Microinjection of the gamma-aminobutyric acid(A) agonist muscimol to block neurotransmission through the sympathoinhibitory region of the ventrolateral periaqueductal gray matter (vlPAG) did not alter resting sympathetic nerve activity or blood pressure. However, the response to hemorrhage was converted to a maintained renal sympathoexcitation with a delayed and attenuated accompanying hypotension. These data indicate that neurons in the vlPAG mediate the sympathetic and cardiovascular responses to severe hemorrhage.

Haemodynamic response to haemorrhage: distinct contributions of midbrain and forebrain structures

The haemodynamic response to a fixed volume haemorrhage passes through three distinct phases: a normotensive, compensatory phase; a hypotensive, decompensatory phase; and a post-haemorrhage, recompensatory phase. The role of the forebrain and midbrain in regulating the triphasic response to a 'fast' (1.5%/min) or 'slow' (0.75%/min) rate of blood withdrawal (30% haemorrhage) was evaluated by comparing, in unanaesthetised rats, the effects of pre-collicular (PCD) vs. pre-trigeminal decerebrations (PTD). It was found that pre-trigeminal decerebration attenuated the decompensatory (hypotensive) phase to either a fast or slow haemorrhage. In contrast, pre-collicular decerebration attenuated the compensatory and recompensatory phases of the response to a 'fast' (but not a slow) haemorrhage. These results suggest that the integrity of (i) forebrain structure(s) are critical for compensatory and recompensatory responses to 'rapid' blood loss; and (ii) midbrain structure(s) are critical for the decompensatory response to progressive blood loss irrespective of rate.

Análise crítica dos sistemas neurais envolvidos nas respostas de medo inato

O nosso entendimento das bases neurofisiológicas da reação emocional do medo baseia-se em grande parte nos estudos que envolvem respostas condicionadas a estímulos fisicamente aversivos, como, por exemplo, o choque elétrico nas patas. Enquanto este paradigma parece ser útil para avaliarmos os sistemas neurais envolvidos na resposta do, assim chamado, medo condicionado (que tipicamente tem se limitado à observação da resposta de congelamento), este paradigma parece ter sérias limitações para investigarmos as bases neurais das respostas de medo em circunstancias naturais. Trabalhos recentes utilizando técnicas de lesões neurais bem como de mapeamento funcional em animais expostos a predadores naturais, ou somente ao odor destes predadores, revelam uma série de estruturas neurais como responsáveis pelas respostas de medo inato, bastante distintas daquelas previamente implicadas nas respostas de condicionamento aversivo. Como revisto no presente trabalho, entre estas estruturas temos distritos diferenciados da zona medial do hipotálamo; setores específicos da amídala e do sistema septo-hipocampal, envolvidos, respectivamente no processamento de pistas relacionadas à presença do predador e na análise contextual do ambiente; e setores da matéria cinzenta periaquedutal, já classicamente envolvidos na expressão de respostas de defesa. Estas informações podem ser potencialmente importantes para a análise e terapêutica de psicopatologias relacionadas aos distúrbios da reação emocional de medo.