The contribution of the amygdala and hypothalamus to the shaping of hippocampal theta activity

Under chronic experiment of 15 rabbits the hippocampal electrogram character has been studied under electrical, cholinergic, monoaminergic stimulation of the hypothalamus before and after unilateral electrocoagulation of stria terminalis. The synchronizing hypothalamic influence caused by the given stimuli on hippocampal theta-rhythm has been shown to be completely and irreversibly blocked up by the stria terminalis lesion. A leading role of the amygdala-hypothalamic interrelations in hippocampal theta activity formation is suggested.     

Multimodal cross-talk of olfactory and gustatory information in the endopiriform nucleus in rats

The endopiriform nucleus (EPN) is a large group of multipolar cells located in the depth of the piriform cortex (PC). Although many studies have suggested that the EPN plays a role in temporal lobe epilepsy, the normal function of the EPN remains to be elucidated. By using optical imaging of coronal brain slice preparations with voltage-sensitive dye, we found signal propagation from the PC or gustatory cortex (GC) to the EPN in normal medium. In our previous research, we failed to elicit a reliable signal reproducibly in the EPN by single stimulation either to the PC or GC. In our current research, we found that a double-pulse stimulation to either the PC or GC (interpulse interval: 20-100 ms) induced robust signal propagation to the EPN through excitation in the agranular division of the insular cortex (AI), with further extension to the claustrum. Finally, double site paired-pulse stimulation to the PC and GC also evoked excitation in the AI, claustrum, and EPN. These results suggest that the EPN has dual roles: 1) further processing of modality-specific olfactory and gustatory information from the PC and GC, respectively and 2) synergistic integration of PC-derived olfactory information and GC-derived gustatory information.     

Identification of a platyhelminth neuropeptide receptor

We report the characterisation of the first neuropeptide receptor from the phylum Platyhelminthes, an early-diverging phylum which includes a number of important human and veterinary parasites. The G protein-coupled receptor (GPCR) was identified from the model flatworm Girardia tigrina (Tricladida: Dugesiidae) based on the presence of motifs widely conserved amongst GPCRs. In two different assays utilising heterologous expression in Chinese hamster ovary cells, the Girardia GPCR was most potently activated by neuropeptides from the FMRFamide-like peptide class. The most potent platyhelminth neuropeptide in both assays was GYIRFamide, a FMRFamide-like peptide known to be present in G. tigrina. There was no activation by neuropeptide Fs, another class of flatworm neuropeptides. Also active were FMRFamide-like peptides derived from other phyla but not known to be present in any platyhelminth. Most potent among these were nematode neuropeptides encoded by the Caenorhabditis elegans flp-1 gene which share a PNFLRFamide carboxy terminal motif. The ability of nematode peptides to stimulate a platyhelminth receptor demonstrates a degree of structural conservation between FMRFamide-like peptide receptors from these two distinct, distant phyla which contain parasitic worms.     

Dopaminergic innervation of the amygdala is highly responsive to stress

The amygdala has been implicated in the neuronal sequelae of stress, although little is known about the neurochemical mechanisms underlying amygdala transmission. In vivo microdialysis was employed to measure extracellular levels of dopamine in the basolateral nucleus of the amygdala in awake rats. Once it was established that impulse-dependent release of dopamine could be measured reliably in the amygdala, the effect of stress, induced by mild handling, on amygdala dopamine release was compared with that in three other dopamine-innervated regions, the medial prefrontal cortex, nucleus accumbens, and caudate nucleus. The magnitude of increase in dopamine in response to the handling stimulus was significantly greater in the amygdala than in the nucleus accumbens and prefrontal cortex. This increase was maximal during the application of stress and diminished after the cessation of stress. In contrast, the increases in extracellular dopamine levels in other regions, in particular the nucleus accumbens, were prolonged, reaching maximal values after the cessation of stress. These results suggest that dopaminergic innervation of the amygdala may be more responsive to stress than that of other dopamine-innervated regions of the limbic system, including the prefrontal cortex, and implicate amygdalar dopamine in normal and pathophysiological processes subserving an organism's response to stress.     

Identification of a signaling network in lateral nucleus of amygdala important for inhibiting memory specifically related to learned fear

We identified the Grp gene, encoding gastrin-releasing peptide, as being highly expressed both in the lateral nucleus of the amygdala, the nucleus where associations for Pavlovian learned fear are formed, and in the regions that convey fearful auditory information to the lateral nucleus. Moreover, we found that GRP receptor (GRPR) is expressed in GABAergic interneurons of the lateral nucleus. GRP excites these interneurons and increases their inhibition of principal neurons. GRPR-deficient mice showed decreased inhibition of principal neurons by the interneurons, enhanced long-term potentiation (LTP), and greater and more persistent long-term fear memory. By contrast, these mice performed normally in hippocampus-dependent Morris maze. These experiments provide genetic evidence that GRP and its neural circuitry operate as a negative feedback regulating fear and establish a causal relationship between Grpr gene expression, LTP, and amygdala-dependent memory for fear.     

Neuropeptide S inhibits release of 5-HT and glycine in mouse amygdala and frontal/prefrontal cortex through activation of the neuropeptide S receptor

Neuropeptide S (NPS) is a neurotransmitter/neuromodulator that has been identified as the natural ligand of G protein-coupled receptors termed NPS receptors (NPSRs). The NPS-NPSR system is involved in the control of numerous centrally-mediated behaviours, including anxiety. As several classical transmitters play a role in fear/anxiety, we here investigated the regulation by NPS of the exocytotic release of 5-hydroxytryptamine (5-HT) and glycine in nerve terminals isolated from mouse frontal/prefrontal cortex and amygdala. Synaptosomes, prelabelled with the tritiated neurotransmitters, were depolarized in superfusion with 12–15 mM KCl and exposed to varying concentrations of NPS. The evoked release of [³H]5-HT in frontal/prefrontal cortex was potently inhibited by NPS (maximal effect about 25% at 0.1 nM). Differently, the neuropeptide exhibited higher efficacy but much lower potency in amygdala (maximal effect about 40% at 1 μM). NPS was an extremely potent inhibitor of the K⁺-evoked release of [³H]glycine in frontal/prefrontal nerve endings (maximal effect about 25% at 1 pM). All the inhibitory effects observed were counteracted by the NPSR antagonist SHA 68, indicating that the neuropeptide acted at NPSRs. In conclusion, NPS can inhibit the exocytosis of 5-HT and of glycine through the activation of presynaptic NPSRs situated on serotonergic and glycinergic terminals in areas involved in fear/anxiety behaviours. The possibility exists that the NPSRs in frontal/prefrontal cortex are high-affinity receptors involved in non-synaptic transmission, whereas the NPSRs on amygdala serotonergic terminals are low-affinity receptors involved in axo-axonic synaptic communication.     

Increased in vivo release of neuropeptide S in the amygdala of freely moving rats after local depolarisation and emotional stress

Intracerebral microdialysis in conjunction with a highly sensitive radioimmunoassay was used to study the in vivo release of neuropeptide S (NPS) within the amygdala of freely moving rats. NPS was consistently detected in basolateral amygdala dialysates and the release considerably enhanced in response to local depolarisation as well as exposure to forced swim stress. Thus, our data demonstrate for the first time emotional stress-induced release of NPS in the amygdala supporting a functional role of endogenous NPS in stress/anxiety-related phenomena.     

Median preoptic nucleus and subfornical organ drive renal sympathetic nerve activity via a glutamatergic mechanism within the paraventricular nucleus

The paraventricular nucleus (PVN) of the hypothalamus is involved in the neural control of sympathetic drive, but the precise mechanism(s) that influences the PVN is not known. The activation of the PVN may be influenced by input from higher forebrain areas, such as the median preoptic nucleus (MnPO) and the subfornical organ (SFO). We hypothesized that activation of the MnPO or SFO would drive the PVN through a glutamatergic pathway. Neuroanatomical connections were confirmed by the recovery of a retrograde tracer in the MnPO and SFO that was injected bilaterally into the PVN in rats. Microinjection of 200 pmol of N-methyl-d-aspartate (NMDA) or bicuculline-induced activation of the MnPO and increased renal sympathetic activity (RSNA), mean arterial pressure, and heart rate in anesthetized rats. These responses were attenuated by prior microinjection of a glutamate receptor blocker AP5 (4 nmol) into the PVN (NMDA - ΔRSNA 72 ± 8% vs. 5 ± 1%; P < 0.05). Using single-unit extracellular recording, we examined the effect of NMDA microinjection (200 pmol) into the MnPO on the firing activity of PVN neurons. Of the 11 active neurons in the PVN, 6 neurons were excited by 95 ± 17% (P < 0.05), 1 was inhibited by 57%, and 4 did not respond. The increased RSNA after activation of the SFO by ANG II (1 nmol) or bicuculline (200 pmol) was also reduced by AP5 in the PVN (for ANG II - ΔRSNA 46 ± 7% vs. 17 ± 4%; P < 0.05). Prior microinjection of ANG II type 1 receptor blocker losartan (4 nmol) into the PVN did not change the response to ANG II or bicuculline microinjection into the SFO. The results from this study demonstrate that the sympathoexcitation mediated by a glutamatergic mechanism in the PVN is partially driven by the activation of the MnPO or SFO.     

Modification of evoked unit activity of the dorsomedial thalamic nucleus following destruction of the basolateral amygdala in rats

Neuronal responses of the dorsomedial thalamic nucleus of anesthetized rats to stimulation of the anterior periamygdalar cortex were compared before and after destruction of the basolateral nuclei of the ipsilateral amygdala. After destruction of the afferent inflow from the nuclei of the amygdala a new type of response appeared, in the form of prolonged generation of bursts of spikes, and also a significant decrease in the number of cells with a phasic activation response and an increase in the number of tonically activated neurons. Destruction of the amygdala was shown to lead to an increase in the number of cells of the dorsomedial nucleus with spontaneous activity. The duration of the tonic spike response in animals undergoing the operation was found to be significantly increased from 142.5±42.4 to 375.4±53.8 msec, whereas the parameters of other types of neuronal responses did not differ statistically significantly.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 16, No. 6, pp. 784–789, November–December, 1984.     

Effect of the administration of 5,6-dihydroxytryptamine to the amygdala and dorsal raphe nucleus on plasma renin activity

The effect of injections of 5,6-dihydroxytryptamine, a potent and selective neurotoxic of serotonin neurons, into amygdala and dorsal raphe mesencephalic nucleus on the plasma renin activity has been studied in male Wistar rats. Plasma renin activity was estimated on 2nd, 4th, Tth and 14th day after injections in both areas. The administration of 5,6-dihydroxytryptamine in amigdala produced a significant decrease in plasmatic renin activity between 2nd and 4th day, but the inverse effect between 7th and 14th day. Similar effects were found after injections in dorsal raphe nucleus. The contents of cerebral 5-HT were simultaneously evaluated in the entire brain when the drug was implanted in dorsal raphe, and only in amygdaloid tissue when the injection was restricted to this area. A significant decrease in serotonin content was produced 7th day in both places, while partial recuperation was found toward 14th day. The results, especially the ones related to the chemical lesion of dorsal raphe nucleus, suggest that serotoninergic brain systems are involved, as stimulators, in the control of the dynamics of renin-angiotensin system.     

Influence of the medial raphe nucleus damage on discharge activity of the central and bazolateral nuclei of the amygdala

It has been revealed pronounced differences between neuronal discharge activity of central and basolateral nuclei of amygdala. After midbrain raphe medial nucleus damage discharge activity of amygdalar nuclei markedly changes, mainly by reciprocal manner. It is suggest that serotonergic afferentations from nucleus raphe to show various influence upon discharge activity of central and lateral nuclei of amygdala.     

Antiinflammatory activity of a COOH-terminal fragment of the neuropeptide alpha-MSH

The endogenous neuropeptide alpha-melanocyte stimulating hormone (alpha-MSH 1-13), previously found to have marked antipyretic activity, inhibits histamine-induced increases in vasopermeability. The primary antipyretic amino acid message sequence is believed to be the COOH-terminal trieptide, lysine-proline-valine. In recent preliminary research this tripeptide inhibited increases in vasopermeability, raising the possibility that this portion of the alpha-MSH molecule has general antiinflammatory activity. To test this idea, the effects of graded doses of alpha-MSH [11-13] on ear swelling induced by picryl chloride in mice were compared with the effects of saline and a large dose of corticosteroid. Alpha-MSH [11-13] inhibited swelling in a dose-related fashion. This result, together with previous findings, suggests that endogenous circulating alpha-MSH and its COOH-terminal fragments may contribute to modulation of physiological responses in host defense. If this is true, it may be possible to develop new peptide drugs or mimetics based on the tripeptide that are useful in treating inflammation.     

Molecular evolution of the neuropeptide S receptor

The neuropeptide S receptor (NPSR) is a recently deorphanized member of the G protein-coupled receptor (GPCR) superfamily and is activated by the neuropeptide S (NPS). NPSR and NPS are widely expressed in central nervous system and are known to have crucial roles in asthma pathogenesis, locomotor activity, wakefulness, anxiety and food intake. The NPS-NPSR system was previously thought to have first evolved in the tetrapods. Here we examine the origin and the molecular evolution of the NPSR using in-silico comparative analyses and document the molecular basis of divergence of the NPSR from its closest vertebrate paralogs. In this study, NPSR-like sequences have been identified in a hemichordate and a cephalochordate, suggesting an earlier emergence of a NPSR-like sequence in the metazoan lineage. Phylogenetic analyses revealed that the NPSR is most closely related to the invertebrate cardioacceleratory peptide receptor (CCAPR) and the group of vasopressin-like receptors. Gene structure features were congruent with the phylogenetic clustering and supported the orthology of NPSR to the invertebrate NPSR-like and CCAPR. A site-specific analysis between the vertebrate NPSR and the well studied paralogous vasopressin-like receptor subtypes revealed several putative amino acid sites that may account for the observed functional divergence between them. The data can facilitate experimental studies aiming at deciphering the common features as well as those related to ligand binding and signal transduction processes specific to the NPSR.     

Identification of ribosomal protein S3a as a candidate for a novel PI 3-kinase target in the nucleus

Phosphatidylinositol 3,4,5-trisphosphate (PIP₃) is an important lipid second messenger that mediates various cell responses. We have searched for the nuclear PIP₃ binding proteins using PIP₃ analogue beads. A 33 kD protein was detected in this method, which was identified as ribosomal protein S3a by the mass spectrometric analysis. The recombinant S3a protein bound specifically to PIP₃. S3a localized not only in the cytosol but also in the nucleus. Interestingly, not cytosolic but nuclear S3a bound to PIP₃, suggesting different roles of S3a in the cytosol and the nucleus. This revised version was published online in August 2006 with corrections to the Cover Date.     

Involvement of amygdala central nucleus in the regulation of cardiovascular functions

Effects of high frequency stimulation of the amygdala central nucleus involved a selective decrease in the activity: an increase in the activity of the inferior cardiac nerve and a simultaneous decrease in the activity of the vertebral nerve, as well as an obvious BP increase. Bilateral electrolytic lesions of the same amygdala structure accompanied with an overload of the higher nervous activity induced no hypertensions. The role of the amygdala central nucleus in control of cardiovascular functions is discussed.     

Reserpine-induced immunocytochemical change of neuropeptide Y in the hypothalamic arcuate nucleus

The effect of reserpine on neuropeptide Y immunoreactive (NPY-IR) neurons in the rat hypothalamic arcuate nucleus was examined by immunocytochemical techniques. Although only NPY-IR fibers and terminals were distributed in this nucleus in untreated and saline treated rats, single treatment of reserpine (10 mg/kg, i.p.) visualized abundant NPY-IR neuronal cell bodies: the increase began at 12 h of postinjection, reached its maximal level at 48 h, and returned to its normal level at 96 h. Pretreatment of nialamide, a monoamine oxidase inhibitor, prevented these acute reserpine-induced changes, suggesting reserpine acts on NPY neurons through monoaminergic mechanism. Chronic treatment of haloperidol (5 mg/kg, once daily for 5 days) a dopamine receptor antagonist, could induce the similar increase of NPY immunoreactivity. However, interruption of adrenergic and serotonergic neurotransmissions by chronic treatment of propranorol and methysergide, or chemical lesions of ascending noradrenergic and serotononergic pathways by 6-hydroxydopamine and 5,6-dihydroxytryptamine, could not induce any immunoreactive increase of NPY in arcuate neurons. These findings strongly suggest that reserpine-induced NPY increase occurs through dopaminergic afferents in hypothalamic arcuate neurons. Special issue dedicated to Dr. Kinya Kuriyama.