sfn2007

Haller J, Toth M, Zelena D, Halasz J (2007) Molecular basis of violent behavior: The role of NK1 receptors. Neuroscience 2007 Abstracts 531.22/GGG24. Society for Neuroscience, San Diego, CA.

Summary: Background. Neurons expressing Neurokinin1 receptor (NK1 or Substance P receptor) are abundant in limbic areas crucial for different emotional behaviors. In recent years, NK1 receptor blockers were proposed for the treatment of anxiety and depression. Moreover, in two different laboratory models, NK1 receptor blockade was successfully used to decrease violent components of aggression related behaviors in Wistar rats (Biol. Psychiatry, 2007, in press). In the above study, the NK1 receptor blockade reduced the number of more violent hard bites, while the number of soft bites was unaltered. Aggressive encounters were accompanied by a marked activation of neurons expressing NK1 receptors in the medial amygdala and in the hypothalamic attack area, where the highest number and proportion of activated NK1 positive neurons were found. Aim / Methods. We evaluated the precise role of neurons expressing NK1 receptors in the hypothalamic attack area during resident/intruder test. These neurons were selectively eliminated by a Substance P conjugated saporin bilateral microinjection into the hypothalamic attack area. After a week recovery, lesioned and vehicle treated control residents were faced with a smaller untreated opponent in their home cages for 20 min. The brains of the residents were later removed to assess the site of injection and the extent of the lesion. Results. In lesioned Wistars, the bilateral microinjection resulted in a complete and selective disruption of NK1 positive neurons in the hypothalamic attack area. Compared to vehicle injected controls, the number of hard bites toward unfamiliar residents showed a marked decrease (almost a complete abolition) in the lesioned group. The latency of hard bites was significantly increased compared to vehicle injected controls. The number of bite attacks was also reduced, but this reduction was mainly secondary to the dramatic reduction in the number of hard bites. Conclusions. Our data show that hypothalamic neurons expressing NK1 receptors are involved in the control of aggressiveness, especially in the expression of violent attacks. These data confirm and support earlier results that NK1 antagonists – beyond anxiety and depression – may also be useful in the treatment of aggressiveness and violence.

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Gaffan D, Baxter MG, Browning PGF (2007) Intact delayed nonmatching-to-sample in monkeys with combined lesions of the temporal cortical cholinergic system and the fornix. Neuroscience 2007 Abstracts 341.11. Society for Neuroscience, San Diego, CA.

Summary: Rhesus monkeys were pre-operatively trained in truly trial-unique delayed nonmatching-to-sample (DNMS) in an automated apparatus. They were then divided into a control group (n=3) and an experimental group (n=3) and received injections into the inferior temporal cortex of either saline (controls) or the selective cholinergic immunotoxin ME20.4-saporin (experimentals). A postoperative DNMS test showed no significant impairment in the experimental group, both groups performing at their pre-operative level. Both groups then underwent a second surgery to transect the fornix. Again, there was no significant impairment in DNMS, both groups performing at their pre-operative level. If the lesions are confirmed histologically then these results are in marked contrast to our findings with scene learning, in which monkeys with the same combined lesion as those in the present experimental group were severely impaired. However, a number of recent studies have shown that tasks with temporally complex events extended over trials, like DNMS, discrimination learning set, and serial reversal set, depend on a short-term prospective memory strategy that is supported by the interaction of temporal cortex with prefrontal cortex. Thus, the performance of DNMS does not require the laying down of new long-term memories.

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Browning PG, Gaffan D, Baxter MG (2007) Severe visual learning impairments in monkeys with combined but not separate lesions of the temporal cortical cholinergic system and the fornix. Neuroscience 2007 Abstracts 341.7. Society for Neuroscience, San Diego, CA.

Summary: A dense amnesia can be produced in the monkey by sectioning the anterior temporal stem, amygdala and fornix, a procedure which deafferents temporal cortex from modulatory inputs from the midbrain and basal forebrain. The present experiment investigated the neurochemical specificity of these severe learning impairments by selectively destroying cholinergic projections to the entire inferior temporal cortex by making multiple injections of the immunotoxin ME20.4-saporin into the inferior temporal cortex bilaterally. Six male macaque monkeys were preoperatively trained to learn new object-in-place discrimination problems each day until they could rapidly learn many such problems within a testing session. The monkeys then underwent surgery and received either injections of immunotoxin (n=3) or injections of saline (n=3). Both groups of monkeys were unimpaired when postoperative and preoperative performance were compared. Each monkey then underwent a second surgery to transect the fornix. After this surgery monkeys who had previously received injections of immunotoxin into temporal cortex showed a severe learning impairment, whereas monkeys who had previously received injections of saline showed a mild impairment. Monkeys with the combined immunotoxin plus fornix lesion were also severely impaired at concurrent object discrimination learning. These results suggest that different neuromodulatory inputs to inferior temporal cortex may act in concert to support cortical plasticity in visual learning such that the loss of acetylcholine only is not sufficient to disrupt normal learning behavior. The results also suggest that in monkeys, as in humans with Alzheimer’s disease, severe memory impairments occur only when a loss of acetylcholine projections to cortex is accompanied by organic tissue damage.

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Baxter MG, Kyriazis DA, Croxson PL (2007) Cholinergic depletion of prefrontal cortex does not impair episodic memory or strategy implementation in rhesus monkeys. Neuroscience 2007 Abstracts 341.9. Society for Neuroscience, San Diego, CA.

Summary: The prefrontal cortex is involved in regulating multiple aspects of memory, decision-making, and cognitive control. Cholinergic input to prefrontal cortex is thought to be involved in supporting its functions. To examine this hypothesis we tested 4 rhesus monkeys (3 male) with cholinergic depletion of ventrolateral prefrontal cortex (N=2) or the entire prefrontal cortex, excluding its medial aspect (N=2). Selective cholinergic depletion was produced by multiple injections of the immunotoxin ME20.4-saporin (0.02 ug/ul) into the prefrontal cortex. These monkeys were tested on two tasks that each require frontal-inferotemporal interaction, as well as an intact ventrolateral prefrontal cortex. The first, strategy implementation, requires monkeys to apply different choice strategies to different categories of objects in order to maximize the rate of reward delivery, and engages decision-making and cognitive control. The second, scene memory, is a test of episodic memory in which monkeys rapidly learn 20 new object-in-place scene discrimination problems within a single test session. Cholinergic depletions of prefrontal cortex, whether they were limited to ventrolateral prefrontal cortex or included the whole of lateral and orbital prefrontal cortex, were without effect on either strategy implementation or new scene learning relative to each monkey’s preoperative performance. Thus, episodic memory and strategy implementation can proceed normally even with severely disrupted cholinergic input, so loss of cholinergic input on its own cannot explain impaired prefrontal function in conditions such as Alzheimer’s disease. Acetylcholine may work in tandem with other neuromodulators to affect prefrontal cortex function; alternatively, it may only be involved in very specific aspects of cortical function, for example representational plasticity.

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Masawaki A, Sugiyo S, Shimoda T, Sakai Y, Ohyamaguchi A, Uehashi D, Moritani M, Yoshida A, Niwa H, Takemura M (2007) Effects of systemic bicuculline on the formalin-induced nociceptive response in the lip and c-Fos expression in the SP-Saporin-treated rats. Neuroscience 2007 Abstracts 186.16/RR16. Society for Neuroscience, San Diego, CA.

Summary: This study examines the effect of systemic bicuculline (2 mg/kg, ip) on formalin-induced pain-related behavior in the lip (PRB; face scrubbing behavior) and c-Fos expression in the trigeminal nucleus caudalis (SpVc) 2hrs after formalin injection and 2-4 weeks after intra cisterna magna (i.c.m.) injection of substance P (SP) conjugated to neurotoxin, saporin (SP-Sap; 3 µM, 5 µl), blank-Sap- or saline-treatment. In SP-Sap-treated rats, the number of NK-1- immunoreactive (NK-1-IR) neurons in lamina I of the SpVc decreased compared with that of saline- or blank-Sap-treated rats. In SP-Sap-treated rats, PRB at phase 2 decreased compared with that of saline- or blank-Sap-treated rats. In SP-Sap-treated rats, the number of c-Fos-IR cells in the VcI/II decreased compared with that in the saline- or blank-Sap-treated rats. In saline- and blank-Sap- treated rats but not SP-Sap-treated rats, systemic bicuculline decreased the number of PRB at phase 2. These results indicate that i.c.m. injection of SP-Sap eliminates NK-1-bearing neurons in L1 of SpVc, and that NK-1-bearing neurons in the SpVc have pivotal role in formalin-induced PRB at phase 2 and c-Fos expression in the SpVc. The decremental effects of systemic bicuculline on the formalin-induced nociceptive responses at phase 2 and c-Fos expression in the VcI/II are secure in the presence of NK-1 receptor bearing neurons in the Vc.

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Gray PA, Vandunk C (2007) Developmental origins of ventral medullary NK1r neurons. Neuroscience 2007 Abstracts 187.15/SS7. Society for Neuroscience, San Diego, CA.

Summary: Breathing is a fundamental neural behavior generated by neurons within the brainstem. In the adult rat, bilateral injection of substance P conjugated to saporin (SSP) in the preBötzinger Complex (preBötC) eliminates normal breathing. Unilateral injection produces sleep disordered breathing and eliminates the effects of excitatory amino acid injection on breathing and blood pressure. SSP injection in the RTN region, in contrast, blunts chemosensitivity. The extent these different effects are due to ablation of anatomically, functionally, or genetically distinct populations are unknown. Further, the extent NK1R expression identifies unique populations in neonatal mice is unknown. Transcription factors are fundamental to determining the properties of neurons and it has been proposed a “combinatorial code” of transcription factor expression defines each distinct functional population. From a genome-scale analysis of over 1000 transcription factors and transcriptional co-factors we identified several genes expressed in respiratory regions of the brainstem. Using immunohistochemistry, we analyzed gene expression patterns of NK1R expressing neurons of the ventral medulla in embryonic and neonatal mice. We find there are at least four genetically distinct, partially overlapping populations of NK1R expressing neurons in the ventral medulla. These differ in the transcription factors they express, their onset of NK1R expression, and their co-expression of peptides and g-protein coupled receptors. At the level of the preBötC, there are two populations of NK1R expressing neurons derived from distinct developmental progenitor populations. One population corresponds to the preBötC as defined in rats and co-expresses the peptide somatostatin. A second population is continuous with, and genetically identical to the subCVLM population important for respiratory-cardiovascular coordination. Both populations co-express the somatostatin 2a receptor (SST2aR). At the level of the RTN/pFRG, there are also two populations of NK1R expressing neurons that are derived from similar developmental precursors as the preBötC. Neither of these populations expresses SST2aR. Whether either of these populations corresponds to the RTN or pFRG is currently unknown. These data suggest both the preBötC and RTN/pFRG regions contain developmentally related NK1R expressing populations. Further, they identify the developmental origin of preBötC neurons known to be essential for normal breathing and provide a foundation for understanding the genetic origin of an important neural circuit.

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Radley JJ, Sawchenko PE (2007) Noradrenergic denervation of dorsal medial prefrontal cortex (mPFC) modulates paraventricular hypothalamic responses to acute restraint stress. Neuroscience 2007 Abstracts 198.4/ZZ13. Society for Neuroscience, San Diego, CA.

Summary: The dorsal mPFC is implicated in restricting the hypothalamo-pituitary-adrenal (HPA) axis response to acute emotional stress via its influence on neuroendocrine effector mechanisms represented in the paraventricular hypothalamic nucleus (PVH). The afferents that provide for mPFC engagement during stress may include ascending noradrenergic projections from the locus coeruleus (LC), which are known to be stress-responsive and capable of modulating attentional mechanisms and other aspects of mPFC function. Arguing against such a role for LC-mPFC projections is evidence that LC lesions attenuate PVH/HPA responses to acute emotional stress. Here we sought to clarify the role of the noradrenergic innervation of mPFC in acute stress-induced PVH activation. Rats received injections of the axonally transported catecholamine immunotoxin, anti-dopamine-β-hydroxylase (DBH)-saporin, centered in the prelimbic area, or sham injections of IgG-saporin or saline. 14 days later, rats were subjected to 30 min of restraint and perfused 2 h later. Immunohistochemical localization of the immediate-early gene product, Fos, was employed as an index of cellular activation in PVH. Cell counts revealed that acute stress reliably provoked marked increases in the number of Fos-labeled neurons in the PVH of all restrained groups relative to unstressed controls. Among stressed groups, anti-DBH-saporin lesions in the dorsal mPFC decreased activational responses in the PVH by 30%, relative to sham-lesioned animals, that were focused in the hypophysiotropic (dorsal medial parvocellular) subdivision. DBH immunostaining revealed a virtually complete noradrenergic denervation of the prelimbic area in immunotoxin-treated animals, while the ventral mPFC (infralimbic area) remained intact. Cortical fields dorsally and laterally adjoining the target area displayed a partial denervation, consistent with local collateralization of prelimbic-projecting LC neurons. While these data are consistent with a role for LC-mPFC projections in facilitating restraint-induced PVH engagement, it remains to be determined how this perspective may be reconciled with prior evidence indicating that mPFC serves normally to inhibit PVH/HPA responses to acute emotional stress.

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Sparrow AW, Lowery EG, Thiele TE (2007) Amygdalar neuropeptide Y (NPY) signaling modulates stress-induced reductions of food intake in Balb/cJ mice. Neuroscience 2007 Abstracts 270.10/X24. Society for Neuroscience, San Diego, CA.

Summary: The existing literature suggests that NPY signaling in the amygdala modulates anxiety-like behaviors and ethanol consumption in rodents, but does not modulate food intake. On the other hand, NPY signaling within the hypothalamus controls food intake but does not influence anxiety-like behavior. Based on these observations, the current study tested the hypothesis that attenuation of NPY signaling within the amygdala would increase anxiety-like behavior and augment stress-induced increases of ethanol consumption while at the same time have no effect of feeding behavior. To address this hypothesis, male Balb/cJ were given bilateral injection (48 ng/5-min/side) into the central nucleus of the amygdala (CeA) of NPY conjugated to the neurotoxin saporin (NPY-SAP) or saporin alone (Blank-SAP). NPY-SAP is a ribosome inactivating neurotoxin that targets and kills cells expressing NPY receptors. After recovery, mice were first tested for anxiety-like behavior using the zero maze test. They were then given access to 8% (v/v) ethanol versus water in a two-bottle test. After ethanol intake stabilized, half the NPY-SAP and Blank-SAP mice were subjected to a 5-min forced swim stress sessions, once a day over 5-days. Ethanol, water and food consumption were measured for 4-weeks following the forced swim procedures. At the end of the experiment, ethanol was removed for two-weeks and all mice were given a 24-hour open-field locomotor activity test. The results showed that mice treated with NPY-SAP in the CeA spent significantly less time in the open portion of the zero maze reflecting elevated anxiety-like behavior. Contrary to predictions, neither neurotoxin treatment nor stress condition altered ethanol intake. Interestingly, NPY-SAP treated mice that experienced forced swim stress consumed significantly less food than non-stressed NPY-SAP treated mice and stress and non-stressed mice treated with the Blank-SAP. Reduced feeding by NPY-SAP stressed mice was not associated with reduced body weight, suggesting possible alterations of energy metabolism. Further, reduced feeding was not attributable to reductions of activity. This study provides novel evidence that amygdalar NPY signaling modulates feeding/energy balance in mice with a history of stress exposure.

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Hains BC, Zhao P, Waxman S (2007) ERK1/2 regulates microglia-neuron signaling and pain by PGE2 following SCI. Neuroscience 2007 Abstracts 287.16/LL14. Society for Neuroscience, San Diego, CA.

Summary: We recently showed that microglia become activated after experimental SCI and dynamically maintain hyperresponsiveness of spinal cord nociceptive neurons and pain-related behaviors. Mechanisms of signaling between microglia and neurons that help to maintain abnormal pain processing are unknown. In this study, adult male Sprague Dawley rats underwent T9 spinal cord contusion injury. Four weeks after injury when lumbar dorsal horn multireceptive neurons became hyperresponsive and when behavioral nociceptive thresholds to mechanical and thermal stimuli were decreased, we tested the hypothesis that prostaglandin E2 (PGE2) contributes to signaling between microglia and neurons. Immunohistochemical data showed specific localization of phosphorylated extracellular signal-regulated kinase 1/2 (pERK1/2), an upstream regulator of PGE2 release, to microglial cells and a neuronal localization of the PGE2 receptor E-prostanoid 2 (EP2). Enzyme immunoassay analysis showed that PGE2 release was dependent on microglial activation and ERK1/2 phosphorylation. Pharmacological antagonism of PGE2 release was achieved with the mitogen-activated protein kinase kinase 1/2 (MEK1/2) inhibitor PD98059 and the microglial inhibitor minocycline. Cyclooxygenase-2 expression in microglia was similarly reduced by MEK1/2 inhibition. PD98059 and EP2 receptor blockade with AH6809 resulted in a decrease in hyperresponsiveness of dorsal horn neurons and partial restoration of behavioral nociceptive thresholds. Selective targeting of dorsal horn microglia with the Mac-1-SAP immunotoxin resulted in reduced microglia staining, reduction in PGE2 levels, and reversed pain-related behaviors. On the basis of these observations, we propose a PGE2-dependent, ERK1/2-regulated microglia-neuron signaling pathway that mediates the microglial component of pain maintenance after injury to the spinal cord.

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Stornetta RL, Takakura AC, Moreira TS, Mulkey DP, Bayliss DA, Guyenet PG (2007) Phox2b-expressing neurons of the retrotrapezoid nucleus (RTN) and central respiratory chemoreception in rats. Neuroscience 2007 Abstracts 230.9. Society for Neuroscience, San Diego, CA.

Summary: The RTN contains glutamatergic interneurons that are strongly activated by CO2 via acidification. These chemosensitive neurons are non-catecholaminergic and they express the transcription factor Phox2b. Although RTN chemoreceptors innervate selectively the brainstem regions that contain the respiratory rhythm and pattern generator (CPG), it is not yet clear whether these neurons drive inspiration or expiration, pump or airway muscles, autonomic circuits or all of the above. To determine whether RTN neurons drive inspiration, we examined whether their selective destruction modifies the CO2 sensitivity of the phrenic nerve discharge (PND) in anesthetized vagotomized rats. Using electrophysiological recordings in vivo and in slices, we found that the chemosensitive neurons of RTN express substance P receptors. We also found that these cells can be destroyed by local injection of a substance P agonist conjugated with saporin (SSP-SAP). The kill rate of RTN chemoreceptors was determined by counting the number of residual Phox2b-expressing non-catecholaminergic neurons present in this structure 15 days after toxin injection. Unilateral injection of 0.6 ng SSP-SAP destroyed 75% of the presumptive chemoreceptors on the injected side only. The lesion was selective because nearby neurons such as facial motoneurons, catecholaminergic and serotonergic cells were spared. SSP-SAP also spared the ventral respiratory column caudal to RTN except for a small amount of damage in the Bötzinger region closest to RTN. Unilateral lesion of the Phox2b-expressing neurons of RTN had no effect on PND and on respiratory chemoreception. However, in such rats, a single injection of the GABA-mimetic muscimol into the contralateral intact RTN instantly eliminated PND. After muscimol, PND did not usually reappear in the presence of hypercapnia up to 10% end-expiratory CO2. However, PND could typically be reactivated by strong stimulation of peripheral chemoreceptors which suggests that the respiratory oscillator had remained functional after muscimol. Unilateral injection of a lower dose of SSP-SAP (0.15 ng) had no effect on the Phox2b-expressing neurons of RTN. In such rats, unilateral injection of muscimol into the contralateral RTN had no detectable effect on PND and central chemoreception.

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