sfn2006

Pasumarthi RK, Fadel J (2006) Anatomical and neurochemical mediators of nicotine-induced activation of orexin neurons. Neuroscience 2006 Abstracts 369.22. Society for Neuroscience, Atlanta, GA.

Summary: Orexin/hypocretin neurons of the lateral hypothalamus and contiguous perifornical area (LH/PFA) are important for state-dependent behavior and metabolic regulation. These neurons are activated-as indicated by Fos expression-by a variety of psychostimulant drugs including nicotine. Previously, we have shown that acute nicotine-induced activation of orexin neurons can be blocked by either the non-selective nicotinic antagonist mecamylamine or the selective α4β2 antagonist dihydro-beta-erythroidine (DHβE). However, the hypothalamic afferents and neurotransmitters mediating nicotine-elicited activation of orexin neurons remain to be established. Since the LH/PFA is rich in glutamatergic and cholinergic inputs, we performed in vivo microdialysis to determine the effect of both systemic and local nicotine on release of glutamate and acetylcholine (ACh) in this region of the hypothalamus. Local nicotine administration (100 μM; 2.0 mM) increased ACh and glutamate release in the LH/PFA. Furthermore, in a separate experiment, nicotine-elicited Fos expression in orexin neurons was reduced by either ibotenic acid lesions of the prefrontal cortex (PFC), which provides a substantial glutamatergic input to the hypothalamus, or by cholino-selective (192 IgG saporin) lesions of the basal forebrain. Collectively, these data suggest that glutamatergic inputs from the PFC and cholinergic inputs from the basal forebrain may act cooperatively to mediate the effect of acute nicotine on orexin neurons. Neural circuitry linking orexin neurons with the basal forebrain, PFC and PVT is likely to contribute to the effects of nicotine on wakefulness and attention.

Related Products: 192-IgG-SAP (Cat. #IT-01)

Frederick-Duus D, Fadel J (2006) Orexin transmission is required for food-related increases in cortical acetylcholine release. Neuroscience 2006 Abstracts 369.23. Society for Neuroscience, Atlanta, GA.

Summary: The hypothalamic orexin/hypocretin neuropeptides (OxA and OxB) are crucial modulators of state-dependent behavior including the regulation of arousal in response to homeostatic challenges. Orexins provide a moderately dense innervation of cholinergic portions of the basal forebrain, including the ventral pallidum/substantia innominata and nucleus basalis magnocellularis. OxA administration in this area also produces robust increases in cortical acetylcholine (ACh) release. Here, we used in vivo microdialysis to test the hypothesis that orexin transmission is required for the increase in cortical ACh release resulting from presentation of stimuli related to palatable food. Rats were mildly food-deprived and trained to associate sudden darkness in the testing room with presentation of sweetened cereal. Stimulated cortical ACh release in these animals was blocked by orexin B-saporin (OxB-SAP) lesions of the perifornical hypothalamus at doses that produced 75-80% loss of orexin neurons, but minimal loss of other neuronal phenotypes in this area. In intact animals, pretreatment with the orexin 1 receptor (Ox1R) antagonist SB334867 similarly abolished food cue-elicited increases in cortical ACh release, indicating the specific involvement of OxA in this phenomenon. Neither OxB-SAP nor SB334867 reduced affected basal ACh release. Finally, in old rats (28-30 months), double-label immunohistochemistry revealed a reduction in orexin-immunoreactive fibers near cholinergic somata and dendrites in the basal forebrain regions, consistent with the deficits in stimulated ACh release seen with old animals in this paradigm. Collectively, these data suggest that phasic orexin activation of the basal forebrain cholinergic system may bias attentional resources toward stimuli related to underlying homeostatic challenges, thus coordinating the processing of interoceptive and exteroceptive cues. Age-related deficits in these capacities may have an orexinergic basis.

Related Products: Orexin-B-SAP (Cat. #IT-20)

Broussard JI, Venugopal S, Sarter M, Givens B (2006) Cholinergic modulation of posterior parietal neuronal activity associated with the detection of signals in attentional task-performing rats. Neuroscience 2006 Abstracts 369.7. Society for Neuroscience, Atlanta, GA.

Summary: The posterior parietal cortex (PPC) is considered a major component of the brains’ attention systems, specifically of the orientation control network. This network controls the selection of stimuli, especially if stimuli are presented at unpredictable or multiple locations. Thus, mechanisms optimizing stimulus detection are hypothesized to represent fundamental components of the processes mediated via neuronal circuitry involving the PPC. Previous studies indicated the role of basal forebrain cholinergic projections to the cortex in the detection of signals. Furthermore, we demonstrated that performance of an attentional task involving signal detection activates PPC neurons in rat, specifically if signals are followed by a behavioral response indicating successful detection. The present experiment was designed to test the hypothesis that signal detection-related activation of PPC neurons depends on the integrity of cholinergic inputs to the PPC. Animals were trained to perform an operant sustained attention task involving signal detection as well as responding to non-signal events. Animals were equipped with a drivable headstage to insert stereotrodes into the PPC. After recording PPC neuronal activity during several baseline sessions, including the effects of a distractor, cholinergic projections to the PPC were lesioned by infusing 192 IgG-saporin into the recording region. Recordings from control animals prior to and after saline infusions (599 neurons total) indicate that PPC neurons (56 %) display increases in single unit activity evoked by detected visual signals. Presentation of a visual distractor reduced the number of signal detections but did not alter the detection-associated firing characteristics of PPC neurons, and relatively few neurons were modulated by the onset or offset of the distractor (8%). Unilateral, restricted removal of cholinergic inputs to the PPC did not affect the animals’ detection rate but reduced the proportion of neurons showing detection-related increases in neuronal activity (27 %). These data support the hypothesis that cholinergic inputs to the PPC mediates the detection of signals and thus contributes to the fundamental attentional processing mediated via PPC circuitry.

Related Products: 192-IgG-SAP (Cat. #IT-01)

Likhtik E, Apergis-Schoute J, Pare D (2006) A selective lesioning method to probe the role of intercalated (ITC) amygdala neurons in the extinction of classically conditioned fear responses. Neuroscience 2006 Abstracts 370.19. Society for Neuroscience, Atlanta, GA.

Summary: The acquisition of conditioned fear responses (CRs) is thought to involve the potentiation of synapses conveying information about the conditioned stimulus (CS) to the basolateral (BLA) amygdala. Expression of CRs would depend on transfer of potentiated CS inputs by the BLA to the central amygdala (CE). In contrast, the mechanisms of extinction remain controversial. It was proposed that ITC neurons, which receive BLA inputs and generate feedforward inhibition in CE, are in a key position to mediate extinction. In this view, potentiation of BLA inputs to ITC cells during extinction training, would dampen the impact of CS-related BLA activity on CE neurons, inhibiting CRs. However, this idea is difficult to test because ITC cells occur in small, lateromedially dispersed clusters, making conventional lesioning methods inadequate. The present study aimed to find an effective way of eliminating ITC cells, taking advantage of the fact that, compared to the rest of the amygdala, they exhibit strong immunoreactivity for mu opioid receptors (muORs). First, we performed electron microscopic observations to determine whether muORs are expressed by ITC cells vs. afferents to ITC cells. This test revealed that muORs are concentrated in the postsynaptic membrane density of asymmetric synapses found on ITC cells. Next, we tested whether it is possible to obtain selective ITC lesions by injecting the toxin saporin conjugated to the mu opioid agonist dermorphin (DER-SAP) in the proximity of ITC cells. Thus, rats received intra-amygdaloid pressure injections of DER-SAP in one hemisphere and of vehicle on the contralateral side. Seven days later, the animals were perfused and the tissue processed to reveal muOR. DER-SAP injections produced a marked reduction in muOR immunoreactivity at the BLA-CE border, where ITC cells are usually located. Thus, selective lesioning of ITC cells can be achieved using this method. We are currently testing the impact of such ITC lesions on extinction learning.

Related Products: Dermorphin-SAP / MOR-SAP (Cat. #IT-12)

Iacobucci P, Colonnello V, Ricceri L (2006) Detailed analysis of ultrasound vocalizations emitted by 12-d-old rats during homing test: effects of a brief reunion with littermates in neonatal basal forebrain cholinergic lesioned pups. Neuroscience 2006 Abstracts 374.17. Society for Neuroscience, Atlanta, GA.

Summary: To evaluate the role of the developing cholinergic basal forebrain system on neonatal behavioural repertoire, seven day-old rats received lesions using intraventricular injections of 192 IgG-saporin or saline; on postnatal day (pnd) 12 we recorded ultrasonic vocalizations (USVs) emitted during a homing test (an olfactory based test carried out in a T-shaped arena to measure discrimination of home- versus non familiar- nest odors). USVs emitted by isolated 12-day-old pups were recorded during a first exposure to the homing test (4 min) and during a second exposure in the same setting (4 min), after a 1 min reunion with littermates. In all pups (control and 192 IgG-saporin) number of USVs (ranging between 30 and 60 kHz) significantly increased after reunion with littermates. Analysis of the sonographic structure of the pup calls identified 15 different classes of signals and revealed that the increase in USVs after reunion with littermates was due to a selective increase in 4-5 of the 15 classes [namely, constant frequency signals, brief calls (dot-shape), multiple sweeps calls (e.g. M- or W-shape), rising sweeps (/)]. Also time spent over the home-scented area increased during the second exposure to the homing test in all pups, but such increase was more evident in control than in cholinergic lesioned pups. Even if effects of the neonatal cholinergic lesions were limited, from a methodological point of view these results suggest that USV emission can be measured not only in standard neonatal isolation settings, but also while the subject is performing another neonatal behavioral task. Interestingly, the USV emission during the homing test is modulated by the rat pup after a brief reunion with littermates (a phenomenon resembling the “maternal potentiation”). Such modulation affects both quantitative and qualitative USV features, as well as the time spent by the pups over the home-scented area.

Related Products: 192-IgG-SAP (Cat. #IT-01)

McKay LC, Feldman JL (2006) Unilateral ablation of neurokinin-1 receptor-expressing (NK1R) neurons within the preBötzinger complex (preBötC) in adult rats disrupts breathing during sleep but not during wakefulness. Neuroscience 2006 Abstracts 455.4. Society for Neuroscience, Atlanta, GA.

Summary: In adult rats, as the number of ablated preBötC NK1R neurons increases, breathing becomes increasingly disrupted during sleep(1), eventually resulting in an ataxic breathing pattern during wakefulness when cell loss is >80%(1,2). Here we determine whether ablation of fewer preBötC NKIR neurons leads to sleep-disordered breathing (SDB), while breathing during wakefulness remains stable. Adult male Sprague Dawley rats (n=8) were anesthetized (100mg/kg Ketamine, 10mg/kg Xylazine i.p.) and instrumented to record diaphragmatic, abdominal and neck EMG, ECG, and EEG. Fourteen days post-implantation a second surgery was performed to stereotaxically inject unilaterally into the preBötC, the toxin saporin conjugated to substance P (SP-SAP), which selectively ablates NK1R neurons. Rats were kept on a 12-hour light/dark cycle and monitored within a plethysmograph from day 1 post-injection until they were sacrificed (days 21-50). Post-unilateral SP-SAP injection, respiratory pattern remained normal during wakefulness and sleep until ~day 9. At this point, respiratory pattern during sleep, particularly REM sleep, became increasingly disordered. The disruptions in breathing pattern were characterised by an increase in frequency of apneas and hypopnea (~4-6/hour of sleep vs <3 pre-injection control; p<0.05). Rats that were monitored up to 50 days post-SP-SAP injection continued to have SDB, while breathing during resting wakefulness remained stable. Unlike bilateral SP-SAP injected rats, an ataxic breathing pattern did not develop during wakefulness(1,2). Histological analysis of the ventrolateral medulla confirmed that only NKIR neurons within the preBötC on one side of the medulla were ablated (~300 preBötC NK1R neurons/side in the adult rat). Unilateral SP-SAP injection results in SDB, while breathing during resting wakefulness appears normal. Over time, breathing during sleep does not improve. We have previously proposed that in the elderly and in individuals who suffer from various neurodegenerative diseases, gradual loss of preBötC NK1R neurons may explain why SDB is highly prevalent in these populations. We further speculate that SDB can go unnoticed because breathing during wakefulness is relatively stable.

Related Products: SP-SAP (Cat. #IT-07)

Ho N, Han S, Dawe GS (2006) Effect of running on neurogenesis in cholinergic lesioned mice. Neuroscience 2006 Abstracts 318.5. Society for Neuroscience, Atlanta, GA.

Summary: Neurogenesis occurs mainly in two regions of the adult rodent brain, the dentate gyrus of the hippocampus and the subventricular zone. There are many factors which regulate neurogenesis, but voluntary exercise has consistently been shown to enhance neurogenesis. Exercise has been reported to specifically stimulate neural cell proliferation in the hippocampus but not the olfactory bulb. One of the major sources of afferents to the hippocampus are the septohippocampal projections, in which axons from the medial septum and diagonal band of Broca (MSDB) project to the hippocampus. Major components of the septohippocampal pathway that act as ‘pacemakers’ for hippocampal theta rhythm, which increases in conjunction with the voluntary running, are the cholinergic and GABAergic projections rising from cells in the MSDB. This present study investigates the effect of a partial cholinergic lesion in the basal forebrain and MSDB of mice, a partial model of the neurodegeneration that occurs in Alzheimer’s disease, on neural cell proliferation and neurogenesis. Murine p75-SAP, a conjugate of a p75 antibody that targets selectively cholinergic cells and cytotoxic saporin, was injected into the ventricles of female adult Swiss mice. After recovery from surgery mice were then administered bromodeoxyuridine (BrdU). BrdU immunopositive cells were quantified 24 hours and 4 weeks to assess for neural cell proliferation and survival of newly generated cells. Partial cholinergic denervation led to a decrease in the survival of new born cells in the dentate gyrus. We compared the effects of voluntary running for a period of 12 days in non-lesioned and lesioned mice under similar experimental conditions. Running resulted in an increase in neural cell proliferation for both the non-lesioned and lesioned groups. Running led to a marked increase in cell proliferation in lesioned mice compared to the controls, and also enhanced neurogenesis, as determined by the colocalization of BrdU and the neuronal nuclei marker NeuN in cells within the dentate gyrus. The present study suggests that voluntary running may have a positive effect on neurogenesis in neurodegenerative models in rodents. Further work needs to be done to elucidate the underlying mechanisms of exercise-induced neurogenesis.

Related Products: mu p75-SAP (Cat. #IT-16)

Li A, Nattie EE (2006) Lesions of neurokinin-1 receptor immunoreactive (NK1R-ir) neurons in the ventral medulla decrease chemoreception and ventilation. Neuroscience 2006 Abstracts 455.5. Society for Neuroscience, Atlanta, GA.

Summary: We injected SSP-saporin, a toxin specific for NK1R-ir neurons, into the cisterna magna in order to lesion a wide aspect of the ventral medulla. NK1R-ir loss after 21 days was 79% in the retrotrapezoid nucleus, 65% in the A5 region, 38% in the medullary raphe and 49% in the pre-Botzinger complex. This resulted in a large reduction in the ventilatory response to 7% CO2 during wakefulness (-61%) and NREM sleep (-57%). The response to 12% O2 was reduced by 35-40% at 8 days but partially recovered by 22 days. We did not measure chemoreception in REM sleep. Ventilation in wakefulness, NREM and REM sleep measured over 4 hrs of air breathing decreased by 12-13% at 21 days compared to baseline values (P< 0.005, one-way repeated measures ANOVA; P< 0.05 post hoc comparison, Dunnett’s test). In REM sleep compared to awake and NREM sleep, the rats breathed with a higher frequency and smaller tidal volume, a pattern that was unaffected by the lesion, and with a greater coefficient of variability, which was further increased by the lesion (71 +/- 4 % vs 34 +/- 6 %). We did not observe any severe rhythm disturbances. We attribute the effect of these lesions, which are greatest in the ventral medullary regions including the retrotrapezoid nucleus and the medullary raphe, to loss of tonic chemoreceptor input. This input seems to have equal weight in wakefulness and in NREM and REM sleep and it seems to minimize the variability of frequency observed in REM sleep.

Related Products: SSP-SAP (Cat. #IT-11)

Rapp KL, Khan AM, Watts AG (2006) Catecholaminergic afferents are required for hypothalamic parvicellular paraventricular neurons to transduce signals associated with hypoglycemia into p44/42 MAP kinase phosphorylation events. Neuroscience 2006 Abstracts 355.9. Society for Neuroscience, Atlanta, GA.

Summary: Hypoglycemia activates CRH neuroendocrine neurons in the hypothalamic paraventricular nucleus (PVH), thereby rapidly elevating plasma ACTH and corticosterone concentrations. Hindbrain-originating catecholaminergic (CA) neurons projecting to the PVH facilitate ACTH release after insulin-induced hypoglycemia; however, the intracellular signaling mechanisms that CRH neurons use to transduce CA signals into secretogogue function are unknown. We have previously shown that p44 and/or p42 MAP kinases (ERK1/2) are phosphorylated in CRH neurons after 2-deoxy-D-glucose challenge (Endoc. v145:351, 2004). We now ask: Are hindbrain-originating CA projections to the PVH essential for ERK1/2 phosphorylation in response to insulin-induced hypoglycemia? Male Sprague-Dawley rats received acute bilateral PVH microinjections of either saporin toxin conjugated (DSAP) to an antiserum against dopamine beta hydroxylase (DBH) or conjugated to a non-targeted mouse IgG (control mIgG-SAP), were fitted with jugular catheters, and allowed to recover. On the day of testing, plasma glucose was measured just before the onset of hypoglycemia (induced via insulin bolus [2U/kg, i.v.]) and then 10 and 30 min thereafter. Rats were then anesthetized and transcardially perfused. Brain tissue processed for dual immunofluorescence using antibodies raised against DBH and phospho-ERK1/2 was visualized by confocal microscopy. Baseline plasma glucose levels did not differ significantly between groups (5.66 ± 0.26 mM), but were significantly reduced in each group when compared to baseline after 10 (1.48 ± 0.12 mM) and 30 (1.92 ± 0.12 mM) minutes. DSAP rats displayed marked loss of DBH immunostaining in the PVH relative to controls, with concomitant loss of phospho-ERK1/2 immunostaining within the parvicellular PVH. Further analysis was performed to address the effect of DSAP on DBH staining and ERK1/2 recruitment in the hindbrain and arcuate nucleus. Our results confirm that phosphorylation of ERK1/2 in parvicellular PVH after insulin-induced hypoglycemia requires intact CA afferent innervation. These data contribute to our understanding of how intracellular signaling is regulated in parvicellular PVH neurons. They also underscore an emerging importance of CA afferents for mediating neuroendocrine responses to systemic alterations in glucose.

Related Products: Anti-DBH-SAP (Cat. #IT-03)

Shiromani PJ, Blanco-Centurion C, Xu M, Murillo-Rodriguez E, Gerashchenko D, Hof PR (2006) Adenosine and sleep debt in the basal forebrain. Neuroscience 2006 Abstracts 458.13. Society for Neuroscience, Atlanta, GA.

Summary: The waxing and waning of the sleep drive is hypothesized to be regulated by endogenous sleep factors acting on specific neurons in the brain. One such factor, adenosine (AD), accumulates during wake and begins to inhibit neural activity in wake-promoting brain regions. The current version of the AD hypothesis (Strecker et al., Sleep, 2006) postulates that the adenosine A1 receptor activation on cholinergic neurons in the basal forebrain (BF) is key to sleep debt. Here we directly test this by administering 192-IgG-saporin to lesion the BF cholinergic neurons and then measuring AD levels in the BF via microdialysis. 46 Sprague-Dawley rats were administered either saline (n=21) or 192-IgG-SAP (n=25) (under anesthesia) and two weeks later when it is known that the cholinergic neurons have died, experiments were started. Rats were maintained on 12:12 light-dark schedule and given food and water ad-libitum. In rats with 95% lesion of the BF cholinergic neurons (n=7) AD levels in the BF did not increase with 6 h of prolonged waking but consistent with established findings it increased in non-lesioned rats (n=6). The lesioned rats had intact sleep drive after 6 and 12 h of prolonged waking, including a robust increase in delta power, indicating that the AD accumulation in the BF is not necessary for sleep drive. Next we determined that in the absence of the BF cholinergic neurons the selective adenosine A1 receptor agonist, CHA, administered to the BF continued to be effective in inducing sleep in a concentration-dependent manner, indicating that the BF cholinergic neurons are not essential to sleep induction. Basal sleep-wake levels and the amplitude of the diurnal rhythm of sleep-wake were not different between lesioned and non-lesioned rats. Thus, the hypothesis that basal forebrain cholinergic neurons are central to the AD regulation of sleep debt is rejected since neither the activity of the BF cholinergic neurons nor the accumulation of AD in the BF during wake is necessary for accumulating sleep debt.

Related Products: 192-IgG-SAP (Cat. #IT-01)