Antinociceptive effect of calcitonin gene-related peptide in the central nucleus of amygdala: activating opioid receptors through amygdala-periaqueductal gray pathway

The central nucleus of amygdala (CeA) plays an important role in pain regulation. Calcitonin gene-related peptide (CGRP)-like immunoreactive fibers and CGRP receptors are distributed densely in CeA. The present study was performed to elucidate the role of CGRP in nociceptive regulation in the CeA of rats. Intra-CeA injection of CGRP induced dose-dependent increases in the hind-paw withdrawal latency tested by hotplate test and Randall Selitto Test, indicating an antinociceptive effect of CGRP in CeA. Furthermore, the antinociceptive effect of CGRP was blocked by intra-CeA administration of the CGRP receptor antagonist CGRP8-37, suggesting that CGRP receptor1 is involved in the CGRP-induced antinociception. The CGRP-induced antinociception was attenuated by s.c. injection of the opioid antagonist naloxone, suggesting an involvement of endogenous opioid systems in CGRP-induced antinociception. Moreover, it was demonstrated that opioid receptors in the periaqueductal gray, but not in CeA, contributed to the CGRP-induced antinociception, indicating the importance of the pathway between CeA and the periaqueductal gray in CGRP-induced antinociception. Combining retrograde fluorescent tracing with immunohistochemistry, we found that met-enkephalinergic neurons were innervated by CGRP-containing terminals in CeA. Furthermore, most neurons in the CeA retrogradely traced from the periaqueductal gray were contacted by CGRP-containing terminals and some of them were surrounded by characteristic basket-like structures formed by the terminals, suggesting that CGRP innervates the neurons which project from CeA to the periaqueductal gray. The results indicate that CGRP activates the met-enkephalinergic neurons, which project from CeA to the periaqueductal gray, producing antinociceptive effect in rats.     

Synaptic plasticity in the amygdala in a visceral pain model in rats

The amygdala plays a key role in the emotional-affective component of pain. This study is the first to analyze synaptic plasticity in the central nucleus of the amygdala (CeA) in a model of visceral pain. Whole-cell patch-clamp recordings were made from neurons in the latero-capsular part of the CeA in brain slices from control rats and rats with zymosan-induced colitis (>6 h postinduction). Monosynaptic responses were evoked by electrical stimulation of afferents from the pontine parabrachial area (PB) and from the basolateral amygdala (BLA). Enhanced synaptic transmission was observed at the nociceptive PB-CeA synapse, but not at the polymodal BLA-CeA synapse, in rats with colitis. The frequency of action potentials evoked by direct current injection was increased in CeA neurons from colitis rats, suggesting enhanced neuronal excitability. Our results provide novel evidence for an important role of the CeA in visceral pain.     

Vasopressin- and neurophysin-immunoreactive neurons in the septal region, medial amygdala and locus coeruleus in colchicine-treated rats

The distribution and morphology of neurons containing vasopressin, oxytocin and their associated neurophysins were examined immunohistochemically in rats given intracerebroventricular injections of colchicine. Under these conditions, numerous neurons containing vasopressin and neurophysin were found in several brain areas in addition to those previously described in the hypothalamus. Individual parvocellular vasopressin neurons were scattered in the medial and lateral septum and vertical limb of the nucleus of the diagonal band, while a large number of such neurons were found throughout both the bed nucleus of the stria terminals and the dorsal portion of the medial amygdala. In addition a small cluster of parvocellular vasopressin neurons was present adjacent to the top of the third ventricle in the posterior dorsal hypothalamic area and a number of such neurons were found in the ventral locus coeruleus and sub coeruleus. The mean diameters of these parvocellular vasopressin neurons ranged from 16.6 to 19.8 micron in the different regions, in contrast to the 25.4 micron mean diameter of hypothalamic magnocellular vasopressin neurons, or the 13.7 micron mean diameter of parvocellular vasopressin neurons in the suprachiasmatic nucleus. No vasopressin neurons were found in other brain and spinal cord regions under the conditions used in this study, although all regions were examined. No oxytocin neurons other than those previously described in the hypothalamus and immediately contiguous regions were found. Measurement of the mean diameter of oxytocin neurons showed that neurons in the caudal paraventricular nucleus were clearly smaller (18.9 micron) than magnocellular oxytocin neurons (24.8 micron) in other parts of the hypothalamus. These parvocellular oxytocin neurons with experimentally documented central connections were similar in both size and appearance to the parvocellular vasopressin neurons seen after colchicine treatment, which are potential sources of certain central vasopressin pathways. These findings indicate that there are at least two types of oxytocin neurons in the hypothalamus and several types of vasopressin neurons in a variety of different areas in the brain, many of which are outside of the hypothalamus.     

Activity in the hypothalamus, amygdala, and cortex generates bilateral and convergent modulation of pontine gustatory neurons

Evidence suggests that centrifugal modulation of brain stem gustatory cells might play a role in the elaboration of complex taste-guided behaviors like conditioned taste aversion and sodium appetite. We previously showed that activity in one forebrain area, the central nucleus of the amygdala (CeA), increased the chemical selectivity of taste cells in the parabrachial nucleus (PBN). The present study investigates how activity in 2 other similarly interconnected forebrain sites, the lateral hypothalamus (LH) and gustatory cortex (GC), might influence PBN gustatory processing in rats. The potential convergence of descending inputs from these sites, as well as the CeA, was also evaluated. After anesthesia (35 mg/kg Nembutal ip), 70 PBN gustatory neurons were tested before, during, and after electrical stimulation of these forebrain sites, while responding to 0.3 M sucrose, 0.1 M NaCl, 0.01 M citric acid, and 0.003 M QHCl. Although each forebrain site modulated taste-evoked responses, more PBN neurons were influenced by stimulation of the GC (67%) and CeA (73%) than of the LH (48%). Activation of cortex (71%) and amygdala (85%) most often produced inhibition, whereas inhibition and excitation occurred equally often during hypothalamic stimulation. Of the neurons tested for convergence (n = 60), 88% were influenced by > or =1 of the 3 sites. Twenty were modulated by stimulation at all 3 sites and another 17 by 2 of the 3 sites. The net effect of centrifugal modulation was to sharpen the across-stimulus response profiles of PBN cells, particular with regard to the NaCl- and citric acid-best cells.     

The rodent amygdala contributes to the production of cannabinoid-induced antinociception

The amygdala is a temporal lobe region that is implicated in emotional information processing. The amygdala also is associated with the processing and modulation of pain sensation. Recently, we demonstrated that in nonhuman primates, the amygdala is necessary for the full expression of cannabinoid-induced antinociception [J Neurosci 21 (2001) 8238]. The antinociceptive effect of the cannabinoid receptor agonist (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo(1,2,3-de)-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone (WIN55,212-2) was significantly reduced in rhesus monkeys with large bilateral lesions of the amygdaloid complex. In the present study, we investigated the contribution of the amygdala to cannabinoid-induced antinociception in the rat. Using bilateral local microinjections of the GABA_A receptor agonist muscimol, we inactivated neurons originating from the central nucleus of the amygdala (CeA) or basolateral nucleus of the amygdala (BLA). In rats injected with intra-CeA saline, the cannabinoid receptor agonist WIN55,212-2 produced dose-dependent antinociception on the noxious heat-evoked tail flick assay. In rats treated with intra-CeA muscimol, however, the antinociceptive effect of WIN55,212-2 was significantly reduced. Rats treated with intra-BLA muscimol showed no deficit in WIN55,212-2-induced antinociception. The effect of CeA inactivation on WIN55,212-2-induced suppression of prolonged pain in the formalin test also was tested. In rats treated with intra-CeA saline, WIN55,212-2 reduced the incidence of formalin-induced nociceptive behaviors and also reduced formalin-evoked c-fos expression in both superficial and deep laminae of the spinal cord dorsal horn. In rats treated with intra-CeA muscimol, however, these effects of WIN55,212-2 were significantly reduced.

The results constitute the first causal data demonstrating the necessity of descending pain-modulatory circuitry (of which the CeA is a component) for the full expression of cannabinoid-induced antinociception in the rat. Furthermore, the results complement previous findings suggesting an overlap in neural circuitry activated by opioids and cannabinoids.     

Ethanol-induced delta-opioid receptor modulation of glutamate synaptic transmission and conditioned place preference in central amygdala

Alcoholism involves compulsive behaviors of alcohol drinking, which is thought to be related at least initially to the rewarding effect of alcohol. It has been shown that mu-opioid receptors play an essential role in drug reward and dependence for many drugs of abuse including alcohol, but the function of delta-opioid receptors (DOR) in drug reward remains largely unknown at present. Previous animal studies using systemic approaches with DOR antagonists or DOR knockout animals have yielded inconsistent results, showing a decrease, an increase or no change in alcohol consumption and behaviors of alcohol reward after DOR inhibition or deletion. In the present study, we used ethanol-conditioned rats to investigate adaptive DOR function in neurons of the central nucleus of the amygdala (CeA), a key brain site for alcohol reward and addiction. We found that functional DOR was absent in glutamate synapses of CeA neurons from control rats, but it emerged and inhibited glutamate synaptic currents in CeA neurons from rats displaying ethanol-induced behavior of conditioned place preference (CPP). Analysis of paired-pulse ratios and miniature glutamate synaptic currents revealed that the recruited DOR was present on glutamatergic presynaptic terminals. Similar induction of functional DOR was also found on GABA synapses. Furthermore, microinjection of a DOR antagonist into the CeA reversed ethanol-induced CPP behavior in rats in vivo. These results suggest that repeated alcohol exposure recruits new functional DOR on CeA glutamate and GABA synapses, which may be involved in the expression or maintenance of ethanol-induced CPP behavior.     

Antinociceptive effects induced by injection of the galanin receptor 1 agonist M617 into central nucleus of amygdala in rats

The present study was performed to explore the antinociceptive effects of M617, a selective galanin receptor 1 agonist, in the central nucleus of amygdala (CeA) of rats. Intra-CeA injection of 0.1 nmol, 0.5 nmol and 1 nmol of M617 induced dose-dependent increases in hindpaw withdrawal latencies (HWLs) to noxious thermal and mechanical stimulations in rats. Furthermore, rats received intra-CeA administration of M617 and galanin. The HWL to noxious thermal and mechanical stimulations increased markedly, and there were no significant differences in HWLs of rats received intra-CeA administration of M617 and galanin. The results demonstrated that intra-CeA injection of M617 induced significant antinociceptive effects in CeA of rats, indicating that galanin receptor 1 may be involved in M617-induced antinociception in the CeA of rats.     

Differential roles of mGluR1 and mGluR5 in brief and prolonged nociceptive processing in central amygdala neurons

The laterocapsular division of the central nucleus of the amygdala (CeA) is now defined as the "nociceptive amygdala" because of its high content of neurons that respond to painful stimuli. The majority of these neurons become sensitized in a model of arthritis pain. Here we address the role of G protein-coupled group I metabotropic glutamate receptor subtypes mGluR1 and mGluR5 in nociceptive processing under normal conditions and in pain-related sensitization. Extracellular single-unit recordings were made from 65 CeA neurons in anesthetized rats. Each neuron's responses to brief mechanical stimuli, background activity, receptive field size, and threshold were measured before and after induction of the kaolin/carrageenan mono-arthritis in one knee and before and during applications of agonists and antagonists into the CeA by microdialysis. All neurons received excitatory input from the knee(s) and responded most strongly to noxious stimuli. Before arthritis, a group I mGluR1 and mGluR5 agonist (DHPG, n = 10) potentiated the responses to innocuous and noxious stimuli. This effect was mimicked by an mGluR5 agonist (CHPG, n = 15). In the arthritis pain state (>6 h after induction), the facilitatory effects of DHPG (n = 9), but not CHPG (n = 7), increased. An mGluR1 antagonist (CPCCOEt) had no effect before arthritis (n = 12) but inhibited the responses of sensitized neurons in the arthritis pain state (n = 8). An mGluR5 antagonist (MPEP) inhibited brief nociceptive responses under normal conditions (n = 19) and prolonged nociception in arthritis (n = 8). These data suggest a change of mGluR1 function and activation in the amygdala in pain-related sensitization, whereas mGluR5 is involved in brief as well as prolonged nociception.     

Noradrenergic agonist administration into the central nucleus of the amygdala increases the tail-flick latency in lightly anesthetized rats

The amygdala is a medial forebrain structure with an established role in nociceptive modulation, including the expression of stress-induced hypoalgesia (SIH). Projections from the locus coeruleus increase levels of noradrenaline in the amygdala during acute stress. alpha(2)-Noradrenergic receptor agonists have significant clinical utility as analgesic agents. We therefore hypothesized that alpha(2)-noradrenergic activation of the amygdala may result in behaviorally measurable hypoalgesia. Lightly anesthetized rats underwent microinjection of the alpha(2)-noradrenergic agonist clonidine into the amygdala and intermittent measurement of thermal nociception using the tail-flick latency (TFL). Bilateral microinjection of clonidine into the central nucleus of the amygdala (CeA) resulted in a significant, dose-dependent increase in TFL. This effect was blocked by systemic pre-treatment with the alpha(2)-antagonist yohimbine or by local pre-injection of the alpha(2)-antagonist idazoxan but not by local pre-injection of the alpha(1)-antagonist WB-4101. When injected alone, no antagonist resulted in a significant change in TFL compared with baseline. Clonidine injection into the amygdala but outside the CeA, including the basolateral nucleus of the amygdala, did not significantly alter TFL. These results demonstrate that anatomically and pharmacologically specific activation of alpha(2)-receptors in the CeA in lightly anesthetized rats results in behaviorally measurable antinociception.     

Subnuclear organization of parabrachial efferents to the thalamus,amygdala and lateral hypothalamus in C57BL/6J mice: a quantitative retrograde double labeling study

The present study investigated the subnuclear organization of collateralized efferent projection patterns from the mouse parabrachial nucleus (PbN), the second taste relay in rodents, to higher gustatory centers, including the ventroposteromedial nucleus of the thalamus (VPMpc), central nucleus of the amygdala (CeA) and lateral hypothalamus (LH). We made injections of the retrograde tracer red and green latex microspheres into the VMPpc and CeA (VPMpc–CeA group), VMPpc and LH (VPMpc–LH group) or CeA and LH (CeA–LH group, n=6 for each group). Injections into these areas preferentially resulted in retrograde labeling in the ipsilateral PbN in all groups. Cells projecting to the VPMpc, CeA, and LH were generally found in all subnuclei, but were differentially distributed. VPMpc-projecting cells predominated in gustatory-related subnuclei, CeA-projecting neurons predominated in the external lateral (el) subnucleus, and concentrated labeling was observed in the dorsal lateral subnucleus (dl) following LH injection. Double-labeled neurons were found for all groups, almost entirely ipsilaterally and primarily in the medial (m), waist area (wa), ventral lateral (vl) and el subnuclei. These results suggest that PbN neurons in different subdivisions have different projection and collateralization patterns to the VPMpc, CeA and LH. Functional implications of these projections are discussed with an emphasis on their roles in taste.     

Separate sets of neurons of the central nucleus of the amygdala project to the substantia innominata and the caudal pontine reticular nucleus in the rat

The central nucleus of the amygdala (CeA) is generally regarded as a control nucleus of subcortical target systems. Due to its widespread projections to different brain areas it is able to modulate emotional behavior of the organism. However, it is still not clear whether single neurons of the CeA project to different areas or to one target area. Injections of the retrograde tracers Fluorogold and True Blue into target regions of the central nucleus of the amygdala, i.e., the substantia innominata (SI) and the caudal pontine reticular nucleus (PNC), revealed overlapping but otherwise distinct neuronal populations within mainly the medial division of the CeA. From our study we conclude that SI and PNC receive input from different subsets of amygdala neurons.     

Differential sensitization of amygdala neurons to afferent inputs in a model of arthritic pain

Pain is associated with negative affect such as anxiety and depression. The amygdala plays a key role in emotionality and has been shown to undergo neuroplastic changes in models of affective disorders. Many neurons in the central nucleus of the amygdala (CeA) are driven by nociceptive inputs, but the role of the amygdala in persistent pain states is not known. This study is the first to address nociceptive processing by CeA neurons in a model of prolonged pain. Extracellular single-unit recordings were made from 41 CeA neurons in anesthetized rats. Each neuron's responses to brief mechanical stimulation of joints, muscles, and skin and to cutaneous thermal stimuli were recorded. Background activity, receptive field size, and threshold were mapped, and stimulus-response functions were constructed. These parameters were measured repeatedly before and after induction of arthritis in one knee by intraarticular injections of kaolin and carrageenan. Multireceptive (MR) amygdala neurons (n = 20) with excitatory input from the knee joint responded more strongly to noxious than to innocuous mechanical stimuli of deep tissue (n = 20) and skin (n = 11). After induction of arthritis, 18 of 20 MR neurons developed enhanced responses to mechanical stimuli and expansion of receptive field size. These changes occurred with a biphasic time course (early peak: 1-1.5 h; persistent plateau phase: after 3-4 h). Responses to thermal stimuli did not change (7 of 7 neurons), but background activity (16 of 18 neurons) and electrically evoked orthodromic activity (11 of 12 neurons) increased in the arthritic state. Nociceptive-specific (NS) neurons (n = 13) showed no changes of their responses to mechanical, thermal, and electrical stimulation after induction of arthritis. A third group of neurons did not respond to somesthetic stimuli under control conditions (noSOM neurons; n = 8) but developed prolonged responses to mechanical, but not thermal, stimuli in arthritis (5 of 8 neurons). These data suggest that prolonged pain is accompanied by enhanced responsiveness of a subset of CeA neurons. Their sensitization to mechanical, but not thermal, stimuli argues against a nonspecific state of hyperexcitability. MR neurons could serve to integrate and evaluate information in the context of prolonged pain. Recruitment of noSOM neurons increases the gain of amygdala processing. NS neurons preserve the distinction between nociceptive and nonnociceptive inputs.     

Differential expression of glycine receptor subunits in the rat basolateral and central amygdala

The amygdalar complex is a limbic structure that plays a key role in emotional processing and fear conditioning. Although inhibitory transmission in the amygdala is predominately GABA-ergic, neurons of the amygdala are also known to express glycine receptors. The subtype and function of these glycine receptors within the synaptic circuits of the amygdala are unknown. In this study, we have investigated the relative expression of the four major glycine receptor subunits (α1–3 and β) in the rat basolateral (BLA) and central amygdala (CeA), using real-time PCR and protein biochemistry. We demonstrate that α1, α2, α3, and β subunits are all expressed in the BLA and CeA with α2 being the predominant α-subunit in both nuclei. Electrophysiological recordings from BLA and CeA neurons in acute brain slices indicated that differences in relative expression of these subunits were correlated with the pharmacological properties of native glycine receptors expressed on these neurons. We conclude that glycine receptors assembled in BLA neurons are largely α1β-containing heteromultimers whereas receptors assembled in neurons of the central amygdala are primarily α2β-, α3β- or α1β-containing heteromultimers, with a minor component of α2 or α3 homomeric receptors also expressed.     

D-Fenfluramine induces serotonin-mediated Fos expression in corticotropin-releasing factor and oxytocin neurons of the hypothalamus, and serotonin-independent Fos expression in enkephalin and neurotensin neurons of the amygdala

The neurotransmitters expressed by neurons activated by D-fenfluramine (5 mg/kg, i.p.) were identified in the hypothalamus, amygdala and bed nucleus of the stria terminalis. Induction of Fos immunoreactivity following D-fenfluramine injection was used as an index of neuronal activation. To test whether D-fenfluramine activated neurons by releasing serotonin from the serotonergic nerve terminals, rats were pretreated with fluoxetine (10 mg/kg, i.p.), a serotonin reuptake inhibitor that prevents the release of serotonin stimulated by D-fenfluramine, 12 h before D-fenfluramine injection. The approximate percentages of peptidergic neurons that contained Fos immunoreactivity after D-fenfluramine administration were 94% of corticotropin-releasing factor and 22% of oxytocin cells in the paraventricular nucleus of the hypothalamus, 6% of oxytocin cells in the supraoptic nucleus of the hypothalamus, 36% of enkephalin and 15% of neurotensin cells in the central amygdaloid nucleus, and 19% of enkephalin and 9% of neurotensin cells in the bed nucleus of the stria terminalis. Fluoxetine pretreatment blocked Fos expression in corticotropin-releasing factor- and oxytocin-expressing cells in the hypothalamus, but not in enkephalin-and neurotensin-expressing cells located in the bed nucleus of the stria terminalis and central amygdaloid nucleus. D-Fenfluramine did not induce Fos immunoreactivity in vasopressin-, thyrotropin-releasing hormone-, somatostatin- and tyrosine hydroxylase-containing cells in the hypothalamus, and corticotropin-releasing factor-expressing cells in the central amygdaloid nucleus and bed nucleus of the stria terminalis. These results show that D-fenfluramine stimulates corticotropin-releasing factor- and oxytocin-expressing cells in the hypothalamus via serotonin release. The enkephalin- and neurotensin-expressing cells in the amygdala are activated by D-fenfluramine via non-serotonergic mechanisms. Induction of Fos expression by D-fenfluramine in restricted populations of cells suggests a selective activation of neuronal circuitry that is likely to be involved in the appetite suppressant effects of D-fenfluramine.     

Viscerosensory activation of noradrenergic inputs to the amygdala in rats

Norepinephrine (NE) acts in the amygdala to regulate processes underlying acquisition and expression of emotional learning. The present study investigated whether stimulation of gastric vagal sensory afferents activates neurons immunoreactive for the NE synthetic enzyme, dopamine beta hydroxylase (DbetaH), in medullary and pontine cell groups that innervate the central nucleus of the amygdala (CeA) in rats. To identify such neurons, retrograde neural tracers were microinjected bilaterally into the CeA. Seven to 10 days later, rats were injected intraperitoneally with saline vehicle (controls) or cholecystokinin octapeptide (CCK, 10 microgram/kg) to stimulate gastric vagal afferents, then perfused with fixative 60-90 min later. Brain sections were processed for localization of neural tracer and cFos protein (to identify activated cells). Approximately 30% of retrogradely labeled neurons in the nucleus of the solitary tract (NST, A2/C2 region) and 19% of retrogradely labeled neurons in the ventrolateral medulla (VLM, A1/C1 region) were activated in rats after CCK treatment. Triple immunolabeling of cFos, neural tracer, and DbetaH confirmed that the large majority of activated, CeA-projecting neurons were noradrenergic (or adrenergic). Conversely, CCK activated less than 4% of CeA-projecting neurons in the locus coeruleus (LC, A6 cell group), similar to control cases. These findings suggest that vagal afferent stimulation may modify amygdalar processes of emotional learning via direct noradrenergic/adrenergic projections from the caudal medulla to the CeA.     

The expression of corticotropin-releasing factor in the central nucleus of the amygdala, induced by colorectal distension, is attenuated by general anesthesia

Corticotrophin-releasing factor (CRF), a key regulator of the hypothalamic-pituitary axis, is expressed in the central nucleus of the amygdala (CeA) and its expression is upregulated in stress-related disorders. We investigated here the effect of noxious colorectal distension (CRD) on the expression of CRF in the CeA of conscious and unconscious rats. Adult male rats with or without general anesthesia were exposed to visceral pain induced by CRD for 5 min; this procedure was repeated 3 times with 1 min resting after each distension. The rats were sacrificed and sections of the CeA were immunostained for CRF as an indicator for anxiety response, and for phosphorylated extracellular signal-regulated kinase (p-ERK) as a marker for pain-specific activation of neurons; sections of lumbosacral spinal cord were immunostained for c-Fos as a marker for activation of spinal neurons. CRD elicited a significant increase in the expression of CRF and p-ERK in the CeA and of c-Fos in the spinal cord. General anesthesia attenuated the increase in CRF and p-ERK in the CeA, but did not affect the expression of spinal c-Fos. These results suggest that conscious recognition of pain at higher brain centers is an important determinant of CRF expression in the CeA.     

Ultrastructural relationship between N-methyl-d-aspartate-NR1 receptor subunit and mu-opioid receptor in the mouse central nucleus of the amygdala

The central nucleus of the amygdala (CeA) is an important neuroanatomical substrate of emotional processes that are critically involved in addictive behaviors. Glutamate and opioid systems in the CeA play significant roles in neural plasticity and addictive processes, however the cellular sites of interaction between agonists of N-methyl-d-aspartate (NMDA) and μ-opioid receptors (μOR) in the CeA are unknown. Dual labeling immunocytochemistry was used to determine the ultrastructural relationship between the essential NMDA-NR1 receptor subunit and μOR in the CeA. It was found that over 80% of NR1-labeled profiles were dendrites while less than 10% were axons. In the case of μOR-labeled profiles, approximately 60% were dendritic, and over 35% were axons. Despite their somewhat distinctive patterns of cellular location, numerous dual-labeled profiles were observed. Approximately 80% of these were dendritic, and less than 10% were axonal. Moreover, many dual-labeled dendritic profiles were contacted by axon terminals receiving asymmetric-type synapses indicative of excitatory signaling. These results indicate that NMDA and μORs are strategically localized in dendrites, including those receiving excitatory synapses, of central amygdala neurons. Thus, postsynaptic co-modulation of central amygdala neurons may be a key cellular substrate mediating glutamate and opioid interaction on neural signaling and plasticity associated with normal and pathological emotional processes associated with addictive behaviors.     

Pontine gustatory activity is altered by electrical stimulation in the central nucleus of the amygdala

Visceral signals and experience modulate the responses of brain stem neurons to gustatory stimuli. Both behavioral and anatomical evidence suggests that this modulation may involve descending input from the forebrain. The present study investigates the centrifugal control of gustatory neural activity in the parabrachial nucleus (PBN). Extracellular responses were recorded from 51 single PBN neurons during application of sucrose, NaCl, NaCl mixed with amiloride, citric acid, and QHCl with or without concurrent electrical stimulation in the ipsilateral central nucleus of the amygdala (CeA). Based on the sapid stimulus that evoked the greatest discharge, 3 neurons were classified as sucrose-best, 32 as NaCl-best, and 16 as citric acid-best. In most of the neurons sampled, response rates to an effective stimulus were either inhibited or unchanged during electrical stimulation of the CeA. Stimulation in the CeA was without effect in two sucrose-best neurons, nine NaCl-best neurons, and one citric acid-best neuron. Suppression was evident in 1 sucrose-best neuron, 18 NaCl-best neurons, and 15 citric acid-best neurons. In NaCl-best neurons inhibited by CeA stimulation, the magnitude of the effect was similar for spontaneous activity and responses to the five taste stimuli. Nonetheless, the inhibitory modulation of gustatory sensitivity increased the relative effectiveness of NaCl resulting in narrower chemical selectivity. For citric acid-best neurons, the magnitude of inhibition produced by CeA activation increased with an increase in stimulus effectiveness. The responses to citric acid were inhibited significantly more than the responses to all other stimuli with the exception of NaCl mixed with amiloride. The overall effect was to change these CA-best neurons to CA/NaCl-best neurons. In a smaller subset of NaCl-best neurons (n = 5), CeA stimulation augmented the responsiveness to NaCl but was without effect on the other stimuli or on baseline activity. It appears that electrical stimulation in the CeA modulates response intensity, as well as the type of gustatory information that is transmitted in a subset of NaCl-best neurons. These findings provide an additional link between the amygdala and the PBN in the control of NaCl intake, modulating the response and the chemical selectivity of an amiloride-sensitive Na+ detecting input pathway.     

Localization of DARPP-32 immunoreactive neurons in the bed nucleus of the stria terminalis and central nucleus of the amygdala: co-distribution with axons containing tyrosine hydroxylase,vasoactive intestinal polypeptide,and calcitonin gene-related peptide

Summary The distribution and morphology of neurons containing the dopamine- and cyclic AMP-regulated phosphoprotein, DARPP-32, were investigated in the bed nucleus of the stria terminalis (BST) and the central nucleus of the amygdala (CeA). DARPP-32 immunoreactive neurons are numerous in both regions, but are restricted to the lateral dorsal and the lateral juxtacapsular subdivisions of the BST, and the central lateral and lateral capsular subdivisions of the CeA. Immunoreactive neurons in the lateral dorsal BST, and the central lateral and lateral capsular CeA are similar morphologically, while those in the juxtacapsular BST appear to be a subpopulation of striatal mediumsized spiny neurons. The distribution of DARPP-32 immunoreactive neurons in the BST and CeA overlaps considerably with axonal plexuses containing tyrosine hydroxylase (TH), vasoactive intestinal polypeptide (VIP), and calcitonin gene-related peptide (CGRP). These studies provide further evidence of the close relationship between the CeA and BST, and also provide anatomical evidence for possible interactions between neurotransmitters, neuropeptides, and phosphoproteins.Abbreviations ac anterior commissure - BLA basolateral amygdaloid nucleus - BST bed nucleus of the stria terminalis - BSTL bed nucleus of the stria terminalis, lateral - BSTLD bed nucleus of the stria terminalis, lateral dorsal - BSTLJ bed nucleus of the stria terminalis, juxtacapsular - BSTM bed nucleus of the stria terminalis, medial - BSTV bed nucleus of the stria terminalis, ventral - CeA central nucleus of the amygdala - CGRP calcitonin gene-related peptide - CL central amygdaloid nucleus, lateral central - CLC central amygdaloid nucleus, lateral capsular - CM central amygdaloid nucleus, medial - CPu caudate-putamen - DARPP-32 dopamine- and cyclic AMP-regulated phosphoprotein with an apparent molecular weight of 32000 Daltons - GP globus pallidus - ic internal capsule - I intercalated mass of the amygdala - IMG intramedullary gray - LA lateral amygdaloid nucleus - LV lateral ventricle - LS lateral septal nucleus - Me medial amygdaloid nucleus - ot optic tract - SHy septohypothalamic nucleus - st stria terminalis - TH tyrosine hydroxylase - VIP vasoactive intestinal polypeptide     

Activation of basolateral amygdala corticotropin-releasing factor 1 receptors modulates the consolidation of contextual fear

The basolateral amygdala complex (BLA) and central amygdala nucleus (CeA) are involved in fear and anxiety. In addition, the BLA contains a high density of corticotropin-releasing factor 1 (CRF₁) receptors in comparison to the CeA. However, the role of BLA CRF₁ receptors in contextual fear conditioning is poorly understood. In the present study, we first demonstrated in rats that oral administration of DMP696, the selective CRF₁ receptor antagonist, had no significant effects on the acquisition of contextual fear but produced a subsequent impairment in contextual freezing suggesting a role of CRF₁ receptors in the fear memory consolidation process. In addition, oral administration of DMP696 significantly reduced phosphorylation of cyclic AMP response element-binding protein (pCREB) in the lateral and basolateral amygdala nuclei, but not in the CeA, during the post-fear conditioning period. We then demonstrated that bilateral microinjections of DMP696 into the BLA produced no significant effects on the acquisition of conditioned fear but reduced contextual freezing in a subsequent drug-free conditioned fear test. Importantly, bilateral microinjections of DMP696 into the BLA at 5 min or 3 h, but not 9 h, after exposure to contextual fear conditioning was also effective in reducing contextual freezing in the conditioned fear test. Finally, microinfusions of either DMP696 into the CeA or a specific corticotropin-releasing factor 2 receptor antagonist in the BLA were shown to have no major effects on disrupting either contextual fear conditioning or performance of contextual freezing in the drug-free conditioned fear test. Collectively, results implicate a role of BLA CRF₁ receptors in activating the fear memory consolidation process, which may involve BLA pCREB-induced synaptic plasticity.