sfn2008

Rapp KL, Watts AG (2008) Interactions between corticosterone and catecholaminergic afferents in the regulation of neuropeptide gene expression in neuroendocrine CRH neurons in the paraventricular nucleus of the hypothalamus. Neuroscience 2008 Abstracts 782.2/RR7. Society for Neuroscience, Washington, DC.

Summary: Neurons in the medial parvicellular part of the paraventricular nucleus of the hypothalamus (PVH) are responsible for neuroendocrine activation of corticotropes in the anterior hypophysis. While corticotropin-releasing hormone (CRH) is the primary peptide responsible for synthesis and release of adrenocorticotropin hormone (ACTH), vasopressin (AVP) is also effective in stimulating ACTH, which stimulates synthesis & secretion of corticosterone (CORT) from the adrenal cortex. This descending pathway, the HPA axis, is part of the stress axis, as its output of CORT facilitates adaptation to changes in energy. While AVP is synthesized in both parvicellular and magnocellular populations of the PVH, it is the AVP in the parvicellular PVH that colocalizes with CRH and increases after adrenalectomy (ADX). The underlying mechanisms contributing to the CORT regulation of Crh and Avp expression still remain elusive, particularly with regard to the role of neural afferents. A major afferent projection system to the PVH originates from hindbrain catecholaminergic (CA) neuron subpopulations. Using saporin-anti-dopamine beta hydroxylase (DSAP) immunotoxin conjugate, to specifically eliminate CA afferents has revealed the importance of CA projections to PVH for both increased Crh expression, and elevated levels of circulating ACTH & CORT following glycemic challenges. We utilized DSAP-mediated deafferentation, followed by ADX and CORT replacement, to determine the role of CA afferents in mediating effects of circulating CORT on Crh and Avp regulation. Male Sprague Dawley rats (~315g) received acute bilateral microinjections of DSAP stereotaxically delivered into the PVH. A control group received bilateral microinjections of saporin conjugated to a non-targeting mouse IgG (SAP). One week later, rats received ADX and timed-release CORT pellet implants (25, 50 or 100 mg). Seven days post-ADX, rats were killed, and radioimmunoassay of plasma from terminal blood samples revealed significantly higher CORT levels in DSAP- vs. SAP-treated rats in CORT replaced groups: 25 mg (p < 0.001), 50 mg (p < 0.01). In contrast, in situ hybridization revealed significantly increased CRH mRNA levels (p < 0.001) and AVP hnRNA levels (p < 0.02) in DSAP- vs. SAP-treated rats with comparable plasma CORT levels. These results suggest that loss of hindbrain CA afferents contributes to the ability of circulating CORT to regulate Crh and Avp expression. The data implicate synergistic interactions between CORT & PVH neural afferents that provide critical metabolic information from the periphery in the regulation of CRH neuroendocrine neurons. Supported by NINDS. (NS029728)

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Pedersen NP, Anaclet C, Vetrivelan R, Saper CB, Lu J (2008) The retroabducens region is necessary for rapid eye movement (REM) during REM sleep in the rat. Neuroscience 2008 Abstracts 784.15/RR66. Society for Neuroscience, Washington, DC.

Summary: REM sleep is characterized by REMs, atonia of the non-respiratory musculature, and active dreaming during which the electroencephalogram (EEG) is desynchronized in humans and shows increased theta activity in rodents. Surprisingly, the source of the actual REMs during REM sleep is not known, although Pompeiano and Morrison (1965) described the reduction or absence of phasic REM phenomena after electrolytic lesion of the medial and spinal vestibular nuclei in the cat. Using the neurotoxins ibotenic acid and saporin-conjugated anti-orexin B IgG, we systematically placed cell-specific lesions in brainstem candidate structures for the generation of REMs in rats equipped for chronic recording of EEG, electrooculogram, and electromyogram. Lesion of a ‘retroabducens’ area, located immediately caudal and extending ventrally from the abducens nucleus, although leaving the abducens nucleus intact, abolished REMs (as well as waking saccades), without affecting other aspects of REM sleep. Animals with retroabducens lesions showed maintenance of slow oscillations in eye position, characteristic of non-REM or slow wave sleep, throughout REM sleep. Lesions of the medial vestibular nucleus, nucleus prepositus hypoglossi and immediately rostral to abducens did not affect REMs. We hypothesize that the retroabducens area may be required for the generation of saccadic eye movements, similar to the paramedian pontine reticular formation as described in cats and monkeys. The retroabducens region appears to be critical for generating the REMs that characterize REM sleep, but most likely downstream from the REM sleep generator.

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Anaclet C, Pedersen NP, Lu J (2008) Medullary circuitry regulating trigeminal motor nucleus phasic activity during rapid eye movement sleep in the rat. Neuroscience 2008 Abstracts 784.16/RR67. Society for Neuroscience, Washington, DC.

Summary: Rapid Eye Movement (REM) sleep or paradoxical sleep is characterized by activation of the cortical and hippocampal EEG, atonia of postural muscles (neck and limbs), and phasic movements of cranial muscles (eyes, chin, ears and whiskers). We have previously established that glutamatergic neurons of the sublaterodorsal tegmentual nucleus (SLD) play a critical role in generating postural muscle atonia during REM sleep. It has been further proposed that the SLD produces REM motor atonia by stimulating spinal inhibitory neurons, which in turn inhibit spinal motor output neurons. It is not known however whether the SLD is also involved in the regulation of tonic and phasic events of cranial muscles during REM sleep (e.g., rapid eye movement, phasic masseter activation). Previous studies have shown that the supraolivary medulla (SOM, dorsal to the inferior olive) and parvocellular reticular (PCRt) nucleus in the medullary reticular formation project to relevant cranial motor nuclei, including: the trigeminal motor nucleus (Mo5), retroabducens region, facial nucleus (Mo7) and hypoglossal nucleus (Mo12). It is therefore possible that either the SOM or the PCRt (or both) may also be involved in regulating cranial muscle activity in REM sleep. To identify the cell groups responsible for REM phasic control of cranial motor nuclei, we examined masseter muscle EMG following cell-specific lesions (anti-orexin B IgG-saporin) of the SLD, SOM or PCRt. Following two weeks of surgical recovery, we recorded the EEG, EMG (neck and masseter muscles) and EOG continuously for two days. Control rats showed significant phasic activation of the masseter muscles, in particular during the second half of REM sleep episodes. This phasic bursting pattern was similar to eye movements during REM sleep. Neither SLD nor PCRt lesions altered the phasic activity of the masseter muscles during REM sleep, although, and as previously reported, SLD lesions did produce REM without atonia in postural muscles. By contrast, lesions in the SOM eliminated phasic activation of the masseter muscles during REM and produced myoclonic twitching of neck muscles. These results indicate that the SOM is involved in the induction of phasic REM activity of masseter muscles, likely via activation of Mo5, whereas SOM projections to the spinal cord are involved in suppression of myoclonic activity of postural muscles.

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Saenz CM, Borowski T, De Lacalle S (2008) Contrasting effects of estrogen on memory tasks in young female rats. Neuroscience 2008 Abstracts 794.17/UU7. Society for Neuroscience, Washington, DC.

Summary: Sleep deprivation may lead to behavioral alterations and it has been associated with a hyperalgesic state in human beings and animal models. The tricyclic antidepressant amitriptyline can be used as an analgesic drug in patients and in chronic pain animal models that are not improved with classical analgesics, such as spinal nerve injury induced model of peripheral neuropathy. The pain hypersensitivity following both paradoxical sleep deprivation (PSD) and peripheral nerve injury shares common spinal mechanisms, which involve at least the glutamate receptors and nitric oxide. In this way, we evaluated the effects of amitriptyline pretreatment in the thermal hyperalgesia observed in paradoxical sleep deprived rats. Amitriptyline (10 and 30 mg/Kg) or saline were administered i.p. during 11 days to male Wistar rats (n = 7/group, 250 – 350 g). In the last 3 or 4 days of treatment the animals were submitted to 72 or 96 hours of PSD, respectively, or remained in home cages, being subsequently evaluated for their thermal sensitivity on a hot plate test (52oC or 46oC), 1 or 24 hours after the last drug administration. In order to verify if the results observed in the highest withdrawal latencies were due to a reduction on the locomotor activity rather than an analgesic effect, the number of squares crossed in an open field arena during 5 minutes, subsequently to the hot plate test was counted. The results demonstrated that paw withdrawal latency response to 52oC was significantly lower in paradoxical sleep deprived rats than controls (-37%, p<0.05). This hyperalgesic effect was also detected in animals pre-treated with 10 mg/kg (-41%, p<0.05) or 30 mg/Kg (-53%, p<0.05) of amitriptyline. At the highest dose, both groups presented a higher withdrawal threshold when compared to their respective saline groups (+185%, p<0.05 and +112%, p<0.05; control and sleep deprived rats, respectively). However, in the open field test a decrease in the number of squares crossed in control animals was observed (-52%, p<0.05), but not in sleep deprived rats (-3%, p>0.05). When the animals were allowed to recover for 24h from sleep deprivation, the pre-treatment with amitriptyline (10 mg/Kg) was not able to prevent the hyperalgesic state (-60%, p<0.05). Even with lower thermal stimulus (46oC) and sleep deprivation period (72h), the difference between control and sleep deprived animals could still be detected (-40%, p<0.05), with no changes after an amitriptyline 10 mg/Kg pre-treatment (-43%, p<0.05). Overall, these findings highlight that thermal pain hypersensitivity induced by PSD was not prevented by amitriptyline pre-treatment, as observed in other models of inductive pain.

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Savage ST, Oberg J, Pernold K, Mattsson A (2008) Enhanced sensitivity to phencyclidine following cortical cholinergic denervation. Neuroscience 2008 Abstracts 842.7/X2. Society for Neuroscience, Washington, DC.

Summary: Alterations in cholinergic signaling in the brain have been implicated as a contributing factor in the pathogenesis of schizophrenia. We have recently shown that cholinergic denervation of cortex cerebri by stereotaxic infusion of the immunotoxin 192 IgG-saporin in the nucleus basalis magnocellularis in adult rats, leads to an enhanced sensitivity to amphetamine. Thus, saporin lesioned rats show a marked increase in locomotor activity, as well as a potentiated dopamine release in nucleus accumbens when challenged with amphetamine. We hypothesize that the loss of cortical cholinergic input alters the activity of cortical glutamatergic neurons and in turn, their regulation of subcortical dopamine neurons. We have previously shown that this cortical cholinergic denervation leads to an increased locomotor response to the NMDA receptor antagonist phencyclidine (PCP), suggesting that disruption of cortical cholinergic activity can lead to disturbances of glutamatergic transmission. In current studies we are investigating attention and memory functions of rats with cholinergic denervation of neocortex using the novel object recognition task. Preliminary data from these investigations shows impairment in performance under PCP-challenge in saporin lesioned rats as compared to sham lesioned controls. These results indicate that cortical cholinergic deficits, in addition to leading to a dramatic potentiation of the locomotor response to PCP, can also lead to an enhanced sensitivity to PCP-induced cognitive impairments. Using pharmacological magnetic resonance imaging (MRI) we are investigating possible spatiotemporal differences in brain activation in rats with cortical cholinergic deficits following administration of PCP. Preliminary data have provided indications of a greater activation in cortical areas in saporin lesioned rats as compared to sham lesioned controls following PCP-challenge. Evaluations of possible alterations in social behavior following cortical cholinergic denervation are ongoing. Social interaction will be investigated under normal conditions, as well as after PCP-challenge. Preliminary results from these studies together with our previous results indicate that loss of cortical acetylcholine can lead to alterations in glutamatergic signaling. These observations are compatible with a possible role of cholinergic deficits in schizophrenia, and provide a possible link between different hypotheses of the disorder.

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Khan AM, Rapp KL, Ponzio TA, Sanchez-Watts G, Watts AG (2008) Stimulus-, circuit- and intracellular-level determinants of MAP kinase and CREB activation in parvicellular hypothalamic paraventricular neurons. Neuroscience 2008 Abstracts 865.23/MM24. Society for Neuroscience, Washington, DC.

Summary: Systemic insulin or 2-deoxyglucose (2-DG) rapidly elevate phosphorylated MAP kinases (phospho-ERK1/2) and/or CRH hnRNA in PVHp neurons, and increase circulating ACTH and corticosterone. These neuroendocrine responses are likely driven by hindbrain-originating catecholaminergic (CA) neuron subpopulations, which richly innervate the PVHp and are activated by glycemic challenges. Supporting this, acute in vivo or in vitro PVH delivery of the prototypical catecholamine, norepinephrine (NE), recapitulates these responses (J Neurosci, 2007, 27:7344-7360). Here, we determined whether PVHp ERK/CREB phosphorylation responses require: 1) intact CA afferents, when triggered by three distinct in vivo challenges; and 2) upstream MEK kinase activity, when triggered by NE application in acute hypothalamic slices maintained in vitro. Methods. Rats given PVH microinjections of anti-dopamine-b-hydroxylase (DBH)-saporin antibody-toxin conjugate (DSAP) or mIgG-saporin control conjugate received either normal 0.9% saline vehicle or one of three systemic challenges: insulin (2 U/kg, i.v.); 2-DG (250 mg/kg, i.v.); or hypertonic saline (1.5 M, i.p.) and sacrificed 30 min later. Brains were processed for CRH mRNA/hnRNA hybridization, or DBH, phospho-ERK or phospho-CREB immunocytochemistry. Plasma was collected for hormone determinations at 0 and 30 min. In separate in vitro studies, acute hypothalamic slices received either no treatment (controls), or received bath-applied NE (100 mM) in the presence or absence of the MEK inhibitor, U0126 (10 mM), or the inactive MEK inhibitor analogue, U0124 (10 mM). Ten min later, slices were placed in fixative. Results. 1. Sham-lesioned animals: Relative to vehicle, all challenges elevated phospho-ERK1/2, phospho-CREB, and ACTH/corticosterone levels; and, except for insulin, also increased CRH hnRNA. 2. Lesioned animals: DSAP treatment selectively destroyed hindbrain-originating CA afferents. In insulin- and, to a lesser extent, 2-DG-treated animals, this loss was accompanied by markedly reduced PVH phospho-ERK1/2 and circulating ACTH/corticosterone. In contrast, these responses remained robust in CA-deafferented hypertonic saline-treated rats. Phospho-CREB levels were differentially reduced relative to phospho-ERK in lesioned rats. 3. Slices: NE-induced PVH elevations of phosphorylated ERK1/2 and CREB were reduced markedly by U0126, but not U0124, pre-treatment. Conclusions. PVHp phospho-ERK selectively couples to CA afferents during glycemic challenges and ERK/CREB recruitment appears to require MEK activity.

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ATS Poster of the Year Winner. Read the featured article in Targeting Trends.

Lecourtier L (2008) Involvement of the habenula in cognition through its regulatory role upon monoamine and acetylcholine transmissions. Neuroscience 2008 Abstracts 698.4. Society for Neuroscience, Washington, DC.

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Wiley RG, Moore SA, Kline IV RH (2008) Analysis of inhibitory phase of formalin test: Effects of specific neural lesions. Neuroscience 2008 Abstracts 772.4/MM19. Society for Neuroscience, Washington, DC.

Summary: The formalin test has been widely used as a model of persistent pain. The 90 mins of formalin-induced nocifensive responding can be divided into two phases (phase 1, first ~10 mins; phase 2, last ~60 mins) separated by a period of reduced responding (interphase, IP), that has received relatively little attention. Behavioral inhibition during the IP of the formalin test has been associated with electrophysiological evidence of inhibition of dorsal horn nociceptive neurons (Henry et al, Pain, 82:57, 1999), probably due, at least in part, to local spinal mechanisms. Behavioral inhibition during IP has been shown to be enhanced by morphine and suppressed by naloxone. In the present study, we sought to determine the effect of selective depletion of specific dorsal horn interneurons known to be involved in nociception, i.e. neurons expressing NPY1R, GalR1 or MOR, or selective destruction of cerebral noradrenergic neurons or spinal cord projecting 5-HT neurons on formalin-induced nociceptive behavior, with particular attention to IP. Type-selective lesions were produced by lumbar intrathecal injection of NPY-saporin, galanin-saporin or dermorphin-saporin, respectively. Cerebral noradrenergic neurons and spinally projecting 5-HT neurons were destroyed using the immunotoxins, anti-DBH-saporin (intracerebroventricular) or anti-SERT-saporin (lumbar intrathecal), respectively. Partial loss of dorsal horn interneurons expressing NPY1R or GalR1 decreased nocifensive responding during IP and phase 2 of the formalin test, while partial loss of MOR-expressing dorsal horn interneurons increased nocifensive responding during IP and during phase 2. Both antiDBH-sap and antiSERT-sap decreased responding during IP, without effects on either phase 1 or 2. These results suggest that the apparent anti-nociception during IP and phase 2 produced by loss of NPY1R- and GalR1-expressing dorsal horn neurons is due to increased inhibition over excitation/facilitation of nociceptive projection neurons, whereas depletion of MOR-expressing interneurons produces the opposite effect. The apparent enhanced nociception during IP, but not phase I and II, produced by anti-DBH-sap and anti-SERT-sap suggests that these neural systems serve to enhance the excitability of nociceptive projection neurons during the formalin IP. Electrophysiologic and pharmacologic studies of formalin IP in selectively lesioned animals combined with the above behavioral findings may reveal new insights into endogenous modulation of nocifensive motor responses and/or nociception.

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Flore G, Saba P, Paba S, Gessa G, Pistis M, Devoto P (2008) Effect of noradrenergic denervation on cerebral cortex catecholamines in the rat. Neuroscience 2008 Abstracts 726.3/D6. Society for Neuroscience, Washington, DC.

Summary: Previous studies in rats have indicated that extracellular dopamine (DA) content in cortical areas with scarce or undetectable dopaminergic innervation, such as the occipital (Occ) or parietal cortex, is modestly lower than that present in areas densely innervated such as the medial prefrontal (mPF) cortex, suggesting that extracellular DA may originate, other than from dopaminergic, also from the homogeneously and densely distributed noradrenergic terminals. To further verify such hypothesis cortical noradrenergic neurons were lesioned with the intraventricular injection of the immunotoxin anti-DA-beta-hydroxylase saporin. Extracellular DA and noradrenaline (NA) were measured in the mPF and Occ cortices by microdialysis 15 to 18 days after the lesion when tissue NA content had been reduced by about 95%, with respect to control rats injected with PBS. The lesion reduced extracellular NA in both cortices, but increased extracellular DA in the mPF and Occ cortices. To verify if such increase was due to the impairment of DA uptake into NA terminals, the NA transporter was inhibited with nisoxetine (NIS). While in control rats NIS increased both extracellular NA and DA, in denervated rats it failed to modify extracellular NA and DA in either cortex, confirming that the NA transporter had been inactivated by the lesion. To verify if the lesion modified the output capacity of dopaminergic and noradrenergic neurons, the effect of the alpha2-adrenoreceptor blocker RS 79948 (RS), given alone or in combination with NIS, in control and denervated rats was compared. In control rats, RS increased extracellular NA and DA in both cortices; in combination with nisoxetine RS produced a striking more than tenfold increase in extracellular NA and DA. In lesioned rats RS increased DA levels, failed to modify extracellular NA, while its co-administration with NIS slightly increased NA output. However, after RS plus NIS, extracellular DA was increased by the same extent as after RS alone, indicating that denervation had severely impaired the capacity of neurons to increase DA output after alpha2-adrenoceptor block. The possibility that such neurons might correspond to NA neurons surviving the lesion is discussed.

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Laplante FP, Dufresne M, Lappi DA, Sullivan RM (2008) Depletion of cholinergic neurons in the nucleus accumbens and its possible involvement in schizophrenic symptomatology. Neuroscience 2008 Abstracts 761.18/FF34. Society for Neuroscience, Washington, DC.

Summary: Schizophrenia is a mental disorder characterized by dysfunctions in several neurotransmitter systems including the central cholinergic system. While alterations in cholinergic neurotransmission have been demonstrated in schizophrenic brains, their biological significance remains to be established. Post-mortem studies of schizophrenic patients have shown a reduction in the density of cholinergic interneurons in the striatum, most prominently in the ventral striatum or nucleus accumbens (N. Acc). Intra-accumbens acetylcholine interacts functionally with the mesolimbic dopaminergic system and is believed to dampen the effects of excessive dopamine (DA) release. Therefore, we hypothesize that a reduction in the density of cholinergic neurons in the N. Acc will be behaviorally relevant, if not causal, to the enhanced (ventral) striatal dopaminergic neurotransmission described in schizophrenia and may contribute substantially to the emergence of schizophrenic symptomatology. In this study we aimed to reproduce in rats a selective reduction in N.Acc. cholinergic cell density, and study the neurophysiological and behavioural consequences of these lesions, relevant to the neuropsychopathology of schizophrenia. A novel saporin immunotoxin coupled with an antibody targeting choline acetyltransferase (ChAT) has been developed. We microinjected this immunotoxin bilaterally (0.5 μg/μl; 0.5 μl) into the N. Acc (core and shell) of adult male Srpague-Dawley rats. Using immunohistochemistry to quantify ChAT staining, we have confirmed that this toxin caused a 40-50 % loss in the number of cholinergic neurons in this region within two weeks post-injection. Lesioned rats exhibited significantly higher spontaneous locomotor activity than control rats and were shown to be hypersensitive to the locomotor activating effects of amphetamine and quinpirole. Furthermore, in separate groups of animals, we have observed in lesioned rats, a reduction in the prepulse inhibition of the acoustic startle response. Taken together, it is proposed that reduction of cholinergic neurons in the N. Acc triggers an enhanced DA responsivity in the N.Acc which may prove highly effective in reproducing behavioral abnormalities analogous to those found in schizophrenia. The neurophysiological consequences of these lesions on DA neurotransmission will be further addressed by measuring both pre- and postsynaptic indices of DA function in this region.

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