sfn2010

Moore JT, Mccarren HS, Beck SG, Kelz MB (2010) Lesioning of the ventrolateral preoptic nucleus alters isoflurane-induced hypnosis in a time-dependent fashion. Neuroscience 2010 Abstracts 300.28/KKK36. Society for Neuroscience, San Diego, CA.

Summary: Despite 160 years of clinical use, the neural mechanisms through which general anesthetics act remain unknown. One possibility is that anesthetics exert their hypnotic effects by acting on the endogenous arousal neural circuitry, including the wake-promoting orexinergic neurons of the hypothalamus and the sleep-promoting GABAergic and galaninergic neurons of the ventrolateral preoptic nucleus (VLPO). We have previously demonstrated that orexinergic neurons play an essential role during emergence from general anesthesia but not during anesthetic induction (Kelz et al., 2008). Here, we present evidence that the VLPO exerted a modulatory role in the induction of anesthetic hypnosis. We used c-Fos immunohistochemistry to analyze the activity of VLPO neurons in brain slices of mice sacrificed after two hours of anesthetic exposure. Whereas anesthetic exposure produced a decrease in the number of c-Fos-positive nuclei in most brain areas, this was not true for the VLPO: exposure to the volatile anesthetics isoflurane or halothane produced a rapid, dose-dependent increase in the number of c-Fos-positive nuclei in the VLPO, implying that hypnotic doses of volatile anesthetics increased the firing rates of VLPO neurons. To determine whether activation of the VLPO was necessary for anesthetic-induced hypnosis, galanin-saporin was used to produce targeted lesions of VLPO neurons. Six days following surgery, the bilaterally lesioned mice were more resistant to induction with isoflurane than control animals in a loss of righting reflex assay. However, 24 days following surgery the lesioned animals were more sensitive to isoflurane than controls. This time-dependent effect was likely due to the build-up of sleep debt–which is known to reduce the anesthetic dose needed to induce hypnosis–as a result of the insomnia-producing VLPO lesions (Lu et al., 2000). These findings are consistent with the VLPO playing a key role in the induction of volatile anesthetic-induced hypnosis, though formal proof will require acute manipulations of VLPO activity that do not produce a sleep debt confound.

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Zheng H, Rinaman LM (2010) Anxiety-like behavior in the elevated plus maze (EPMZ) depends on noradrenergic (NA) inputs to the anterolateral bed nucleus of the stria terminalis (alBST) in rats. Neuroscience 2010 Abstracts 90.7/FFF13. Society for Neuroscience, San Diego, CA.

Summary: The a2 adrenoceptor antagonist yohimbine (YO) increases transmitter release from NA neurons, activates the HPA stress axis, and increases anxiety-like behavior in rats. YO-induced HPA axis activation depends on collateralized projections from caudal brainstem NA neurons that innervate both the alBST and the medial parvocellular paraventricular nucleus of the hypothalamus (mpPVN) [Banihashemi & Rinaman, J. Neurosci., 2006]. The current study examined whether the same NA projections underlie the anxiogenic behavioral effects of YO. Adult male Sprague-Dawley rats were tested for baseline anxiety-like behavior in the EPMZ. Subsequently, anesthetized rats received bilateral microinjections of saporin toxin conjugated to an antibody against dopamine beta hydroxylase (DSAP) into the alBST to remove sources of NA input; sham control rats were similarly microinjected with vehicle. Two weeks after surgery, rats were re-tested in the EPMZ on three different days, with the first test conducted 30 min after i.p. YO (1.0 mg/kg BW), the second test conducted 30 min after i.p. saline, and the final test conducted without injection. As expected, the number of “anxiogenic” open arm entries was significantly reduced in sham control rats after YO compared to pre-surgery baseline behavior (P<0.01). Conversely, open arm entries were unaffected by YO in DSAP rats, and the YO-induced reduction of time spent in the open arms was significantly attenuated in DSAP rats vs. sham controls (P<0.01). Interestingly, in the final EPMZ test with no i.p. injections, sham control rats but not DSAP rats displayed increased anxiety-like behavior compared to their pre-surgery baseline (sham controls P<0.01; DSAP rats P=0.3). These findings support the view that caudal brainstem NA neurons projecting to the alBST are important for anxious behavior in the EPMZ, consistent with an earlier study utilizing pharmacological blockade of BST NA receptors [Cecchi et al., Neurosci., 2002]. Our ongoing studies are examining whether similar DSAP lesions attenuate conditioned and unconditioned fear and anxiety responses in rats under more ethologically relevant experimental conditions.

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Weeden CS, Morris AM, Rossi CA, Roberts JM, Kesner RP (2010) The role of GABA-ergic interneurons in CA1 and dentate gyrus for sequence learning. Neuroscience 2010 Abstracts 99.26/KKK12. Society for Neuroscience, San Diego, CA.

Summary: The hippocampus (HPP) plays an important role in temporal and spatial memory. Lesion investigations of the CA1 region of HPP indicate the region’s importance in temporal processing and lesions of the dentate gyrus (DG) demonstrate an important role in spatial processing. It has been suggested that a subset of GABAergic interneurons that express Substance P mediate the inhibition of pyramidal and granule cells, which further affects the pattern of their output. This synchronizing action may directly affect information processing of CA1 pyramidal and DG granule cells. A form of temporal processing involves learning specific sequences of events for spatial locations, which incorporates both temporal and spatial qualities attributed to CA1 and DG, respectively. In order to investigate whether interneurons mediate CA1 and DG processing of newly learned locations of sequential patterns, Long-Evans male rats were randomly assigned to the following surgical groups: CA1 pyramidal cell (ibotenic acid), CA1 interneuron (peptidase-resistant substance P analog conjugated to the neurotoxin saporin) (SSP-Saporin), DG granule cell (colchicine), DG interneuron (SSP-Saporin) lesions and controls (PBS). Following recovery from surgery, rats were tested on a sequential learning task for spatial locations using an eight-arm radial maze. Six arm locations were pseudo-randomly assigned to a sequence; each of the arms was baited with a food reward. Doors remained closed until the rat oriented in front of the correct door in the sequence, at which time the door was opened and the rat was allowed access to the reward; the choice was scored as a correct response. However, if the rat oriented to an incorrect door in the sequence, the choice was scored as incorrect and the animal was allowed to reorient to the correct door. The same sequence was repeated ten times per day for a total of ten consecutive days. The percentage of correct choices per day was compared across all ten days. The results indicate that subjects with CA1 pyramidal cell, CA1 interneuron, and DG interneuron, but not DG granule cell lesions, had difficulty acquiring the sequential task when compared to controls. These results suggest an important role for CA1 pyramidal cells, and for interneurons in both CA1 and DG subregions of the HPP in temporal processing of spatial locations.

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Easton A, Phil D, Fitchett A, Eacott MJ, Baxter MG (2010) Cholinergic innervation of the hippocampus is not neccesary for episodic memory, but is required for context-place learning in rats. Neuroscience 2010 Abstracts 99.27/KKK13. Society for Neuroscience, San Diego, CA.

Summary: Loss of cholinergic cortical input is associated with diseases in which episodic memory impairment is a prominent feature, but the degree to which this neurochemical lesion can account for memory impairment in humans with neurodegenerative diseases remains unclear. Removal of cholinergic input to hippocampus impairs some of its functions in memory, perhaps by reducing the plasticity of information representation within the hippocampus, but the role of cholinergic hippocampal input in episodic-like memories has not been investigated. To address this question we tested rats with selective lesions of basal forebrain neurons in the medial septum and vertical limb of the diagonal band (MS/VDB), which contains hippocampal-projecting cholinergic neurons, on a task of integrated memory for objects, places, and contexts (“what-where-which” memory). This task serves as a rodent model of human episodic memory (episodic-like memory) and is sensitive to damage to the hippocampal system. Rats with lesions of cholinergic MS/VDB neurons performed as well on the what-where-which task as controls, but were impaired in a task that simply required them to associate places with contexts (“where-which” memory). Thus, episodic-like memories that rely on the hippocampus do not require cholinergic neuromodulation to be formed. Nevertheless, some more specific aspects of where-which memory, which may be more dependent on the plasticity of hippocampal spatial representations, require acetylcholine. These results suggest that cholinergic projections to hippocampus are not necessary for episodic memory, and furthermore, that hippocampal spatial representations may be to some extent dissociable from episodic memory function.

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Ramanathan D, Conner JM, Anilkumar AA, Tuszynski MH (2010) Early post-natal cholinergic lesion impairs normal development and maturation of the motor cortex in rats. Neuroscience 2010 Abstracts 32.14/D20. Society for Neuroscience, San Diego, CA.

Summary: Prior studies have indicated that sensory and motor representations develop over a defined postnatal period and are dependent upon behavioral experience to achieve appropriate adult patterns. In adult animals, behaviorally driven forms of cortical map plasticity are critically dependent upon the basal forebrain cholinergic system. Based on the critical role cholinergic mechanisms play in mediating experience-dependent plasticity in adulthood, we postulated that cholinergic mechanisms may also play a critical role in shaping initial cortical map formation during development. In this study, using 25 male Fisher rats between the ages of 15 days and 60 days, we first characterized the normal motor map development in the rat. We found that motor maps underwent a significant change in overall size and refinement over time, with more mature animals having larger overall maps (p < 0.001) and an increase in the size of distal forelimb representations (p < 0.01). Following the initial characterization of normal motor map development in the rat, we used 192-IgG-saporin (SAP) to create selective cholinergic lesions early in map development (PND 24), in 5 animals (with 6 animals receiving ACSF as controls). This early cholinergic depletion impaired the normal maturation and refinement of cortical motor representations: the total caudal forelimb area (comprising elbow and wrist) was decreased by 33% in cholinergically depleted animals, from 5.1 ± 0.3 mm2 to 3.4 ± 0.3 mm2 (t-test p < 0.01). This decrease in caudal forelimb area in cholinergically-depleted animals was primarily driven by a significant 37% reduction in the size of the distal forelimb (wrist) representation, from 3.1 ± 0.1 mm2 to 2.0 ± 0.1 mm2 (p < 0.001). In a follow-up experiment with 12 additional animals (6 with cholingeric lesions and 6 controls), we found that early (PND 24) cholinergic depletions resulted in long-term impairments in skilled motor learning, with significant differences in daily motor performance beginning at day 3 of training (repeated measures ANOVA < 0.05). These results suggest a novel role for the basal forebrain cholinergic system in establishing normal cortical map formation during development.

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Sheikh A, Kanold PO (2010) Subplate neurons promote the formation of barrels within rat primary somatosensory cortex. Neuroscience 2010 Abstracts 33.1/E1. Society for Neuroscience, San Diego, CA.

Summary: Subplate neurons are a transient neuronal population present in the neonatal cortex. Subplate neurons receive thalamic afferents and project into the developing cortical plate. Selective removal of subplate neurons in cat visual cortex prevents the normal development of ocular dominance columns and the functional maturation of thalamocortical connections (Ghosh & Shatz 1992, Kanold et al. 2003) . A role of subplate neurons in the development of other sensory cortices is unknown. In rodents, thalamocortical afferents representing the whiskers segregate into barrels in the primary somatosensory cortex (S1). This segregation occurs postnatally and can be disrupted by manipulations of neuronal activity. We previously showed that subplate removal disrupts the development of patterned cortical activity in S1 (Tolner, Yukin, Kaila, Kanold, Abstr. SFN 2009). Thus we hypothesized that disruption of patterned activity in S1 alters the development of barrels. Thus here we investigated if subplate neurons play a role in the development of barrels in rat S1. Subplate neurons were ablated in the somatosensory cortex of rat pups at postnatal day (P) 0 by immunotoxin injections. 10-14 days later we investigated the pattern of barrels in S1 via cytochrome oxidase staining. After subplate ablation there was a disturbance in the barrel patterning when compared to the un-manipulated or control-toxin injected hemispheres. Therefore, subplate neurons are involved in the formation of barrels in S1.

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Sorkin LS, Choi J-I, Koehrn FJ (2010) Carageenan evoked P-Akt in deep dorsal horn neurons is prevented by loss of neurokinin1 positive neurons in superficial dorsal horn. Neuroscience 2010 Abstracts 81.21/VV19. Society for Neuroscience, San Diego, CA.

Summary: P-Akt expression increases in dorsal horn after prolonged noxious stimulation and participates in synaptic strengthening. Recent work from our lab, showed separate p-Akt peaks in superficial (45 min) and deep dorsal horn (DH) neurons (2 hrs) after paw carrageenan. It has been suggested that NK1 receptor-expressing projection neurons (NK1+) in superficial DH are necessary for deep DH neuronal sensitization, possibly via a spino-bulbo-spinal loop. In this study, we examined whether the pattern of p-Akt expression was modulated by elimination of superficial DH NK1(+) neurons. Male Holtzman rats (250-275 g) were injected over the lumbar enlargement with substance P-saporin conjugate (SSP-SAP ([Sar9Met(O2)11] 100 ng/µl, n=8), SAP (n=8), or BSA vehicle (n=3). Catheters were removed 20 min post-injection. Two weeks later, carrageenan (2%, 100 µl) was injected into the hindpaw. Animals were perfused 45 min or 2 hrs after carrageenan (or sham) injection. Immunohistochemistry was performed on frozen sections (20mm). After correction for background density, NK-1 immunoreactivity was measured as number of bright pixels (intensity value >50 of 256)/total pixels within user-defined boxes in laminae I-III and IV-V. Neuronal p-Akt was measured using double labeling with rabbit anti-p-Akt ser 473 and mouse anti-NeuN; cells immunopositive for both were counted separately for lamina I-III and IV-V. For both measures, values from four random sections taken from segments L4 and 5 were averaged for each animal. The histologist was blinded as to spinal treatment. Density of NK-1 immunoreactivity was markedly reduced in laminae I-III in rats treated with SSP-SAP compared to SAP or BSA (24.7± 5.6% vs 78.3 ± 3.2%, 76.9 ± 2.0% respectively; p<0.01) with no differences in lamina IV-V (72.2 ± 3.4% vs 75.9 ± 1.7%, & 76.5 ± 3.4%. Counts of p-Akt neurons did not differ at any time point among animals with no pretreatment, BSA or SAP prior to carrageenan. However, the carrageenan-evoked increases in p-Akt neurons seen in laminae I-III at 45 min (9.3 ± 1.0 SAP and 2.4 ± 1.6 SSP-SAP at 45 min) and in laminae IV-V at 2 hour (11.3±1.0 SAP and 3.5± 0.9 SSP-SAP) were totally blocked by loss of NK1 neurons. Selective ablation of NK1+ neurons in superficial DH blocked peripheral inflammation-induced increase of p-Akt expression in both superficial and deep DH neurons. While some p-Akt reduction in laminae I-III was probably due to neuronal loss, i.e. NK1 receptor bearing neurons become p-AKT positive, we propose that reduction in deeper laminae was due to elimination of the first leg of a facilitatory spino-bulbo-spinal loop although loss of local NK+ interneurons could also have contributed.

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