Altered Neuronal Activity Research Articles

Time-dependent effects of hyperoxia on the BOLD fMRI signal in primate visual cortex and LGN

Hyperoxia is present in many anaesthesia protocols used in animal blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) studies. However, little data exist on the influence of hyperoxia on the magnitude of stimulus-induced relative changes in BOLD fMRI signal (ΔBOLD%). No study to date has investigated these effects in a time-resolved manner, although cerebral vasoregulation offers sites for a time-dependent interaction of hyperoxia and ΔBOLD%. Here we investigated time-dependent effects of an inspiratory oxygen fraction of 90%. We tightly clamped end tidal CO2 and body temperature and recorded physiological parameters relevant to rCBF in (fentanyl/isoflurane) anaesthetized monkeys while using visual stimulation to elicit ΔBOLD%. To clarify whether changes in ΔBOLD% arose from changes in baseline blood oxygenation or rather altered neuronal or vascular reactivity, we directly measured changes in rCBV using monocrystalline ion oxide nanoparticles (MION) as contrast agent. In visual cortex we found a biphasic modulation of stimulus-induced ΔBOLD% under hyperoxia: We observed first a significant decrease in ΔBOLD% by −24% for data averaged over the time interval of 0–180 min post onset of hyperoxia followed by a subsequent recovery to baseline. rCBV response amplitudes were decreased by 21% in the same time interval (0–180 min). In the LGN, we neither found a significant modulation of ΔBOLD% nor of MION response amplitude. The cerebrovascular effects of hyperoxia may, therefore, be regionally specific and cannot be explained by a deoxyhemoglobin dilution model accounting for plasma oxygenation without assuming altered neuronal activity or altered neurovascular coupling.

Mechanically-Evoked C-Fiber Activity in Painful Alcohol and AIDS Therapy Neuropathy in the Rat

While altered activities in sensory neurons were noticed in neuropathic pain, caused by highly diverse insults to the peripheral nervous system, such as diabetes, alcohol ingestion, cancer chemotherapy and drugs used to treat AIDS, other infections and autoimmune diseases, as well as trauma, our understanding of how these various peripheral neuropathies manifest as altered neuronal activity is still rudimentary. The recent development of models of several of those neuropathies has, however, now made it possible to address their impact on primary afferent nociceptor function. We compared changes in mechanically-evoked C-fiber activity, in models of painful peripheral neuropathy induced by drinking ethanol (alcohol) or administering 2',3'-dideoxycytidine (ddC), a nucleoside reverse transcriptase inhibitor for AIDS therapy, two co-morbid conditions in which pain is thought to be mediated by different second messenger signaling pathways. In C-fiber afferents, ddC decreased conduction velocity. In contrast, alcohol but not ddC caused enhanced response to mechanical stimulation (i.e., decrease in threshold and increase in response to sustained threshold and supra-threshold stimulation) and changes in pattern of evoked activity (interspike interval and action potential variability analyses). These marked differences in primary afferent nociceptor function, in two different forms of neuropathy that produce mechanical hyperalgesia of similar magnitude, suggest that optimal treatment of neuropathic pain may differ depending on the nature of the causative insult to the peripheral nervous system, and emphasize the value of studying co-morbid conditions that produce painful peripheral neuropathy by different mechanisms.

Conditional CRF receptor 1 knockout mice show altered neuronal activation pattern to mild anxiogenic challenge

Regional-specific corticotropin-releasing factor receptor 1 (CRF-R1) knockout mice have been generated recently as a tool to dissociate CNS functions modulated by this receptor. In these mice, CRF-R1 function is postnatally inactivated in the anterior forebrain including limbic brain structures but not in the pituitary leading to normal activity of the hypothalamic-pituitary-adrenocortical (HPA) axis under basal conditions and reduced anxiety-related behavior in the light-dark box and the elevated plus maze (EPM) as compared to wild-type (WT) mice (Müller et al., Nat Neurosci 6:1100-1107, 2003). To identify neurobiological correlates underlying this reduced anxiety-like behavior, the expression of c-Fos, an established marker for neuronal activation, which was examined in response to a mild anxiogenic challenge. Mice were placed for 10 min on the open arm (OA) of the EPM, and regional c-Fos expression was investigated by immunohistochemistry. OA exposure enhanced c-Fos expression in both conditional CRF-R1 knockout and WT mice in a number of brain areas (39 of 55 quantified), including cortical, limbic, thalamic, hypothalamic, and hindbrain regions. The c-Fos response in conditional CRF-R1 knockout animals was reduced in a restricted subset of activated neurons (4 out of 39 regions) located in the medial amygdala, ventral lateral septum, prelimbic cortex, and dorsomedial hypothalamus. These results underline the importance of limbic CRF-R1 in modulating anxiety-related behavior and suggest that reduced neuronal activation in the identified limbic and hypothalamic key structures of the anxiety circuitry may mediate or contribute to the anxiolytic-like phenotype observed in mice with region-specific deletion of forebrain CRF-R1.

The Effect of Flavanol-rich Cocoa on the fMRI Response to a Cognitive Task in Healthy Young People

Flavanols are the main flavonoids found in cocoa and chocolate, and can be especially abundant in certain cocoas. Research over the past decade has identified flavanols as showing diverse beneficial physiologic and antioxidant effects, particularly in context of vascular function. The present study employed functional magnetic resonance imaging based on blood oxygenation level-dependent (BOLD) contrast to explore the effect of flavanols on the human brain. Magnetic resonance imaging was used to measure BOLD responses to a cognitive task in 16 healthy young subjects. The data presented show an increase in the BOLD signal intensity in response to a cognitive task following ingestion of flavanol-rich cocoa (5 days of 150 mg of cocoa flavanols). This may arise either as a result of altered neuronal activity, or a change in vascular responsiveness, or both--the net effect then being dependent on which of the two effects is dominant. No significant effects were evident in behavioral reaction times, switch cost, and heart rate after consumption of this moderate dose of cocoa flavanols. A pilot study evaluated the relationship between cerebral blood flow and a single acute dose (450 mg flavanols) of flavanol-rich cocoa and showed that flavanol-rich cocoa can increase the cerebral blood flow to gray matter, suggesting the potential of cocoa flavanols for treatment of vascular impairment, including dementia and strokes, and thus for maintaining cardiovascular health.

Dendritic spine plasticity: Looking beyond development

Most excitatory synapses in the CNS form on dendritic spines, tiny protrusions from the dendrites of excitatory neurons. As such, spines are likely loci of synaptic plasticity. Spines are dynamic structures, but the functional consequences of dynamic changes in these structures in the mature brain are unclear. Changes in spine density, morphology, and motility have been shown to occur with paradigms that induce synaptic plasticity, as well as altered sensory experience and neuronal activity. These changes potentially lead to an alteration in synaptic connectivity and strength between neuronal partners, affecting the efficacy of synaptic communication. Here, we review the formation and modification of excitatory synapses on dendritic spines as it relates to plasticity in the central nervous system after the initial phase of synaptogenesis. We will also discuss some of the molecular links that have been implicated in both synaptic plasticity and the regulation of spine morphology.

(642): Sustained release of Interleukin-1 receptor antagonist (IL-1ra) prevents tactile allodynia and spontaneous ectopic neuronal activity following nerve injury

Neuropathic pain is a chronic pain state resulting from peripheral nerve injury, characterized by an exaggerated response to painful stimuli (hyperalgesia) and to non-noxious stimuli (allodynia). In our previous experiments we found that impaired IL-1-signaling attenuates neuropathic pain behavior and neuronal activity. In those experiments we used mice with targeted deletion of the IL-1 receptor type I (IL-1rKO) and mice with transgenic overexpression of the IL-1 receptor antagonist (IL-1raTG), and their wild-type (WT) controls. In this study we tried to mimic the IL-1ra overexpression by subcutaneously implantation of osmotic micropumps containing 100μl of IL-1ra (releasing 6ı̀l/day) in WT mice. As a control osmotic micropumps containing vehicle were used. Two days after implantation spinal nerve transaction of L5 (Chung model) was performed. Mechanosensitivity test using von-Frey monofilament was taken for 7 consecutive days after the nerve-injury. By the 7th day post operatively electrophysiological recordings from L5 dorsal root of spontaneous ectopic activity were performed. We found that mice which received the IL-1ra did not display decreased pain threshold in either hind paw, whereas control mice developed significant allodynia in the hind paw ipsilateral to the injury side. Electrophysiological recordings revealed that in mice which received the IL-1ra, only a minimal number of axons exhibited ectopic activity (0.8±0.4%), whereas the control mice showed a significant proportion of spontaneous ectopic activity (4.1±1.1%, p<0.01). These results, as predicted, confirmed our hypothesis that IL-1 signaling plays an important role in the neuropathic pain and in the altered neuronal activity that underlies its development. Neuropathic pain is a chronic pain state resulting from peripheral nerve injury, characterized by an exaggerated response to painful stimuli (hyperalgesia) and to non-noxious stimuli (allodynia). In our previous experiments we found that impaired IL-1-signaling attenuates neuropathic pain behavior and neuronal activity. In those experiments we used mice with targeted deletion of the IL-1 receptor type I (IL-1rKO) and mice with transgenic overexpression of the IL-1 receptor antagonist (IL-1raTG), and their wild-type (WT) controls. In this study we tried to mimic the IL-1ra overexpression by subcutaneously implantation of osmotic micropumps containing 100μl of IL-1ra (releasing 6ı̀l/day) in WT mice. As a control osmotic micropumps containing vehicle were used. Two days after implantation spinal nerve transaction of L5 (Chung model) was performed. Mechanosensitivity test using von-Frey monofilament was taken for 7 consecutive days after the nerve-injury. By the 7th day post operatively electrophysiological recordings from L5 dorsal root of spontaneous ectopic activity were performed. We found that mice which received the IL-1ra did not display decreased pain threshold in either hind paw, whereas control mice developed significant allodynia in the hind paw ipsilateral to the injury side. Electrophysiological recordings revealed that in mice which received the IL-1ra, only a minimal number of axons exhibited ectopic activity (0.8±0.4%), whereas the control mice showed a significant proportion of spontaneous ectopic activity (4.1±1.1%, p<0.01). These results, as predicted, confirmed our hypothesis that IL-1 signaling plays an important role in the neuropathic pain and in the altered neuronal activity that underlies its development.

Genetic impairment of interleukin-1 signaling attenuates neuropathic pain, autotomy, and spontaneous ectopic neuronal activity, following nerve injury in mice

Peripheral nerve injury may lead to neuropathic pain, which is often associated with mechanical and thermal allodynia, ectopic discharge of from injured nerves and from the dorsal root ganglion neurons, and elevated levels of proinflammatory cytokines, particularly interleukin-1 (IL-1). In the present study, we tested the role of IL-1 in neuropathic pain models using two mouse strains impaired in IL-1 signaling: Deletion of the IL-1 receptor type I (IL-1rKO) and transgenic over-expression of the IL-1 receptor antagonist (IL-1raTG). Neuropathy was induced by cutting the L5 spinal nerve on one side, following which mechanical and thermal pain sensitivity was measured. Wild-type (WT) mice and the parent strains developed significant allodynia and hyperalgesia in the hind-paw ipsilateral to the injury compared with the contralateral hind-paw. The mutant strains, however, did not display decreased pain threshold in either hind-paw. Pain behavior was also assessed by cutting the sciatic and saphenous nerves and measuring autotomy scores. WT mice developed progressive autotomy, beginning at 7 days post-injury, whereas the mutant strains displayed delayed onset of autotomy and markedly reduced severity of the autotomy score. Electrophysiological assessment revealed that in WT mice a significant proportion of the dorsal root axons exhibited spontaneous ectopic activity at 1, 3, and 7 days following spinal nerve injury, whereas in IL-1rKO and IL-1raTG mice only a minimal number of axons exhibited such activity. Taken together, these results suggest that IL-1 signaling plays an important role in neuropathic pain and in the altered neuronal activity that underlies its development.

Regional Temperature Changes in the Brain during Somatosensory Stimulation

Time-dependent variations in the brain temperature (Tt) are likely to be caused by fluctuations of cerebral blood flow (CBF) and cerebral metabolic rate of oxidative consumption (CMRO2) both of which are seemingly coupled to alterations in neuronal activity. We combined magnetic resonance, optical imaging, temperature sensing, and electrophysiologic methods in alpha-chloralose anesthetized rats to obtain multimodal measurements during forepaw stimulation. Localized changes in neuronal activity were colocalized with regional increases in Tt (by approximately 0.2%), CBF (by approximately 95%), and CMRO2 (by approximately 73%). The time-to-peak for Tt (42+/-11 secs) was significantly longer than those for CBF and CMRO2 (5+/-2 and 18+/-4 secs, respectively) with a 2-min stimulation. Net heat in the region of interest (ROI) was modeled as being dependent on the sum of heats attributed to changes in CMRO2 (Qm) and CBF (Qf) as well as conductive heat loss from the ROI to neighboring regions (Qc) and to the environment (Qe). Although tissue cooling because of Qf and Qc can occur and are enhanced during activation, the net increase in Tt corresponded to a large rise in Qm, whereas effects of Qe can be ignored. The results show that Tt increases slowly (by approximately 0.1 degrees C) during physiologic stimulation in alpha-chloralose anesthetized rats. Because the potential cooling effect of CBF depends on the temperature of blood entering the brain, Tt is mainly affected by CMRO2 during functional challenges. Implications of these findings for functional studies in awake humans and temperature regulation are discussed.

Diurnal and estradiol-dependent changes in gonadotropin-releasing hormone neuron firing activity

A robust gonadotropin-releasing hormone (GnRH) surge is a prerequisite signal for the luteinizing hormone (LH) surge that triggers ovulation. In rodents, the GnRH surge is initiated by elevated estradiol and a diurnal switch in estrogen action from negative to positive feedback. The ability of constant estradiol treatment to induce daily LH surges was tested in adult mice that were ovariectomized (OVX) or OVX and treated with estradiol implants (OVX+E). LH in OVX mice showed no time-of-day difference. In contrast, OVX+E mice showed a large LH surge (8- to 124-fold relative to the a.m.) in p.m. samples on d 2-5 post-OVX+E. Targeted extracellular recordings were used to examine changes in firing activity of GnRH neurons in brain slices. There was no time-of-day difference in cells from OVX mice. In contrast, OVX+E cells recorded in the p.m. showed an increased mean firing rate and instantaneous firing frequency, which could increase GnRH release, and decreased duration of quiescence between bouts of firing, possibly reflecting increased pulse frequency, compared with cells recorded in the a.m. In the a.m., OVX+E cells showed changes in GnRH neuron firing reflecting negative feedback compared with OVX cells, whereas in the p.m., OVX+E cells exhibited changes suggesting positive feedback. These data indicate that differences in pattern and level of individual GnRH neuron firing may reflect the switch in estradiol action and underlie GnRH surge generation. The persistence of altered GnRH neuron activity in slices indicates that this approach can be used to study the neurobiological mechanisms of surge generation.

Genome-Wide Transcriptional Changes Associated with Enhanced Activity in the Drosophila Nervous System

Neuronal plasticity is an important feature of the developing brain and requires neuronal circuits to reconfigure their functional connectivity depending upon activity patterns. To explore changes in neuronal function that occur downstream of altered activity, we performed an expression analysis in Drosophila mutants with acute or chronic alterations in neuronal activity. We find that seizure induction leads to an overproliferation of synaptic connections, indicating that activity-dependent neuronal rewiring occurs in Drosophila. To analyze transcriptional recoding during altered neuronal activity, we performed genome-wide DNA microarray analysis following multiple seizure induction and recovery paradigms. Approximately 250 genes implicated in cell adhesion, membrane excitability, and cellular signaling are differentially regulated, including the Kek 2 neuronal cell adhesion protein, which, as we demonstrate, functions as a regulator of synaptic growth. These data identify a collection of activity-regulated transcripts that may link changes in neuronal firing patterns to transcription-dependent modulation of brain function, including activity-dependent synaptic rewiring.

(n-3) Polyunsaturated Fatty Acid Deficiency Reduces the Expression of Both Isoforms of the Brain Glucose Transporter GLUT1 in Rats

The altered neuron activity of rats deficient in (n-3) PUFAs may be due in part to a decrease in brain glucose utilization and glucose transport. We measured the glucose transporter protein GLUT1 isoforms at the blood-brain barrier (55-kDa) and in astrocytes (45-kDa) by Western immunoblotting and their mRNA by real time RT-PCR analysis in the cerebral cortex of adult male rats fed diets lacking (n-3) fatty acids (1st generation). The neuron glucose transporter GLUT3 was also assayed. The fatty acids in the phosphatidylcholine (PC), ethanolamine phosphoglycerolipid (EPG), and phosphatidylserine (PS) fractions of isolated microvessels and homogenates of the cerebral cortex were determined. The levels of (n-6) PUFAs [mainly arachidonic acid, 20:4(n-6)] in the phospholipid fractions of microvessels were higher and the levels of (n-3) PUFAs [mainly docosahexaenoic acid, 22:6(n-3)] were lower than in cerebral cortex homogenates. The microvessels and cortex of rats fed the (n-3) PUFA-deficient diet had 50% of the control 22:6(n-3) contents; 22:6(n-3) was replaced by 22:5(n-6). The 55-kDa GLUT1 immunoreactivity in (n-3) PUFA-deficient microvessels was decreased (down 25%, P < 0.01), as was the 45 kDa-GLUT1 in the homogenate (down 30%, P < 0.01). But the amount of immunoreactivity of GLUT3 did not change. The amount of GLUT1 mRNA was not affected by the (n-3) PUFA-deficient diet. These results suggest that the decreased glucose utilization in the cerebral cortex of (n-3) PUFA-deficient rats is due to reduced amounts of the 2 isoforms of GLUT1, indicating post-transcriptional regulation of GLUT1 synthesis.

Influence of volatile induction agents on fMRI and neural activity

Neuroimaging techniques are predominantly based on changes in CBF induced by alterations in neuronal activity and is generally carried out in animals under anesthesia, usually with -chloralose because of its minor effects on cardiovascular, respiratory, and reflex functions1. General anesthetics reduce neuronal activity in various regions of the mammalian CNS2. A considerable number of mechanisms have been suggested to mediate the depressant effects3. However it is still a matter of debate as to which molecular targets are truly relevant in producing the true anesthetic state4. Recent studies reported the relationship between the action of volatile anesthetics occurring on the molecular level and the corresponding effects on neuronal firing5. In this study we have used two volatile anesthetics (isoflurane, halothane) and studied the time-dependent induction effects for functional studies in -chloralose anaesthetized rats. During the animal preparation halothane (0.7%) / isoflurane (0.5%) were used for induction. The same forepaw stimulation protocol (30 s block design; 2 mA; 0.3 ms; 3 Hz) was used for both fMRI and extracellular recordings. All fMRI data (n=10) were obtained on a modified 9.4 T Bruker horizontal-bore spectrometer (Billerica, MA) using a 1 H resonator/surface coil RF probe. The images were aquired with gradient echo EPI sequence (TR/TE=1000/15 ms). Extracellular recordings (n=18) were first filtered to obtain action and field potentials (AP, FP) and then the AP data were binned to obtain spike rates (). The changes in local CBF were measured with a laser-Doppler probe (Oxford Optronix, Oxford, UK). The purpose of this study was to examine the effects of isoflurane and halothane used for induction in a-chloralose anaesthetized rats. The fMRI time courses after 3 hrs (gray) and 5 hrs (black) from isoflurane induction (A) showed generally moderate levels of intra-animal reproducibility, which was lacking with halothane (B). These fMRI responses were supported by similar CBF responses measured with laser-Doppler probes (data not shown). The electrophysiology results after 5 hrs (bottom) showed changes in neuronal activity, but the alterations were far less significant with isoflurane (C) than with halothane (D). These results together suggest that while isoflurane induction may result in a faster hemodynamic response, the changes in neuronal activity are slightly depressed. These results suggest caution for interpreting results from anesthetized rats where volatile agents are used for the induction phase (See Figure 1).

Neuroenergetic basis of regional temperature dynamics in brain

Maintaining near constant brain temperature (Tt) over a wide range of metabolic activity is critical for normal brain function 1. However brain temperature is an often ignored parameter in neuroscience and clinical studies. Time-dependent variations in Tt are likely to be caused by fluctuations of CBF and CMRO2, both of which are seemingly coupled to alterations in neuronal activity. To this end, we combined magnetic resonance, optical imaging, temperature sensing, and electrophysiological methods in -chloralose anesthetized rats to obtain multi-modal measurements during forepaw stimulation. Localized changes in neuronal activity were co-localized with regional increases in Tt (by 0.2%), CBF (by 95%), and CMRO2 (by 73%). The time-to-peak for Tt (4211 s) was significantly longer than those for CBF and CMRO2 (52 and 184 s, respectively). Net heat (Qnet) in the region of interest (ROI) was modeled as being dependent on the sum of heats attributed to changes in CMRO2 (Qm) and CBF (Qf) as well as conductive heat loss from the ROI to neighboring regions (Qc) and to the environment (Qe). Although tissue cooling due to Qf and Qc can occur and are enhanced during activation, the net increase in Tt corresponded to a large rise in Qm, whereas effects of Qe can be ignored. The study shows that Tt increases slowly (by 0.1 C) during physiologic stimulation in -chloralose anesthetized rats. Since the potential cooling effect of CBF depends on the temperature of blood entering the brain, Tt is mainly affected by CMRO2 during functional challenges. While the importance of the uncoupling between changes in CMRO2 and CBF and the temperature of arterial blood for the cooling efficiency of the brain are obvious, our current experimental and theoretical results reveal the significance of the resting CBF and more importantly resting CMRO2 for temperature regulation in the brain. Although the changes in brain temperature recorded for the entire study were spread over a wide range, the stimulation-induced change of 0.1 C in the ROI was significant for the majority of the experiments. The small changes in Tt were reproducibly measured from layer 4 of the rat's somatosensory cortex where the highest neural activity changes (induced by forepaw stimulation) were localized. The current temperature measurements from the brain are in accord with previous functional studies in animals 2, 3. This is the first study which provides a neuroenergetic basis of regional temperature changes in the brain. The results have implications for functional studies and temperature regulation. (See Figure 1).

Human brain derived neurotrophic factor (BDNF) genes, splicing patterns, and assessments of associations with substance abuse and Parkinson's Disease

Potential roles for variants in the human BDNF gene in human brain disorders are supported by findings that include: (a) influences that this trophic factor can exert on important neurons, brain regions, and neurotransmitter systems, (b) changes in BDNF expression that follow altered neuronal activity and drug treatments, and (c) linkages or associations between genetic markers in or near BDNF and human traits and disorders that include depression, schizophrenia, addictions, and Parkinson's disease. We now report assembly of more than 70 kb of BDNF genomic sequence, delineation of 7 noncoding and 1 coding human BDNF exons, elucidation of BDNF transcripts that are initiated at several alternative promoters, identification of BDNF mRNA splicing patterns, elucidation of novel sequences that could contribute to activity-dependent BDNF mRNA transcription, targeting and/or translation, elucidation of tissue-specific and brain-region-specific use of the alternative human BDNF promoters and splicing patterns, identification of single nucleotide polymorphism (SNP), and simple sequence length polymorphism (SSLP) BDNF genomic variants and identification of patterns of restricted haplotype diversity at the BDNF locus. We also identified type 2 BDNF-locus transcripts that are coded by a novel gene that is overlapped with type 1 BDNF gene and transcribed in reverse orientation with several alternative splicing isoforms. Association studies of BDNF variants reveal no associations with Parkinson's disease. Comparisons between substance abusers and controls reveal modest associations. These findings increase interest in this diverse human gene.

Neuronal activity in the basal ganglia and thalamus in patients with dystonia

Objective: To explore the role of abnormal neuronal activity in the basal ganglia and thalamus in the generation of dystonia. Methods: Microelectrode recording was performed in the globus pallidus internus (GPi), ventral thalamic nuclear group ventral oral posterior/ventral intermediate, Vop/Vim) and subthalamic nucleus (STN) in patients with primary dystonia ( n=11) or secondary dystonia ( n=9) during surgery. Electromyogram (EMG) was simultaneously recorded in selected muscle groups. Single unit analysis and cross-correlations were carried out. Results: Three hundred and sixty-seven neurons were obtained from 29 trajectories (GPi: 13; Vop/Vim: 12; STN: 4), 87% exhibited altered neuronal activity including grouped discharges in GPi ( n=79) and STN ( n=37), long-lasting neuronal activity ( n=70) and rapid neuronal discharge ( n=86) in Vop/Vim. There were neurons in Vop, GPi and STN firing at the same frequency as EMG during dystonia (mean: 0.39 Hz, range 0.12–0.84 Hz). Significant correlations between neuronal activity and EMG at the frequency of dystonia were obtained (GPi: r 2=0.7 ( n=31), Vop/Vim: r 2=0.64 ( n=18) and STN: r 2=0.86 ( n=17)). Conclusions: Consistent with previous findings of abnormalities observed in Vop/VIM and GPi in relation to dystonia, the present data further show that the altered activity in GPi, specifically in dorsal subregions of GPi, Vop/Vim and STN is likely to be directly involved in the production of dystonic movement. Dystonia-related neuronal activity observed in motor thalamus and basal ganglia nuclei of GPi and STN indicates a critical role of their interactions affecting both indirect and direct pathways in the development of either generalized or focal dystonia. Significance: These data support a central role of the basal ganglia in producing dystonic movements.

Synaptic plasticity and AMPA receptor trafficking.

Alterations in neuronal activity can elicit long-lasting changes in the strength of synaptic transmission at excitatory synapses and, as a consequence, may underlie many forms of experience-dependent plasticity, including learning and memory. The best-characterized forms of such synaptic plasticity are the long-term depression (LTD) and long-term potentiation (LTP) observed at excitatory synapses in the CA1 region of the hippocampus. It is now well accepted that the trafficking of AMPA receptors to and away from the synaptic plasma membrane plays an essential role in both LTP and LTD, respectively. Here we review current models of AMPA receptor trafficking and how this trafficking may be regulated at the molecular level in order to produce the observed changes in synaptic strength. We also review recent work from our lab suggesting that synaptic plasticity in the mesolimbic dopamine system may contribute importantly to the neural adaptations elicited by drugs of abuse.

Fos immunoreactivity in hypocretin-synthesizing and hypocretin-1 receptor-expressing neurons: effects of diurnal and nocturnal spontaneous waking, stress and hypocretin-1 administration

Hypocretin/orexin modulates sleep–wake state via actions across multiple terminal fields. Within waking, hypocretin may also participate in high-arousal processes, including those associated with stress. The current studies examined the extent to which alterations in neuronal activity, as measured by Fos immunoreactivity, occur within both hypocretin-synthesizing and hypocretin-1 receptor-expressing neurons across varying behavioral state/environmental conditions associated with varying levels of waking and arousal. Double-label immunohistochemistry was used to visualize Fos and either prepro-hypocretin in the lateral hypothalamus or hypocretin-1 receptors in the locus coeruleus and select basal forebrain regions involved in the regulation of behavioral state/arousal. Animals were tested under the following conditions: 1) diurnal sleeping; 2) diurnal spontaneous waking; 3) nocturnal spontaneous waking; and 4) high-arousal waking (diurnal novelty–stress). Additionally, the effects of hypocretin-1 administration (0.07 and 0.7 nmol) on levels of Fos were examined within these two neuronal populations. Time spent awake, scored for the 90-min preceding perfusion, was largely comparable in diurnal spontaneous waking, nocturnal spontaneous waking and high-arousal waking. Nocturnal spontaneous waking and high-arousal waking, but not diurnal spontaneous waking, were associated with increased levels of Fos within hypocretin-synthesizing neurons, relative to diurnal sleeping. Within hypocretin-1 receptor-expressing neurons, only high-arousal waking was associated with increased levels of Fos. Hypocretin-1 administration dose-dependently increased levels of Fos within hypocretin-1 receptor-expressing neurons to levels comparable to, or exceeding, levels observed in high-arousal waking. Combined, these observations support the hypothesis that hypocretin neuronal activity varies across the circadian cycle. Additionally, these data suggest that waking per se may not be associated with increased hypocretin neurotransmission. In contrast, high-arousal states, including stress, appear to be associated with substantially higher rates of hypocretin neurotransmission. Finally, these studies provide further evidence indicating coordinated actions of hypocretin across a variety of arousal-related basal forebrain and brainstem regions in the behavioral state modulatory actions of this peptide system.

Cognitive effects of nicotine in humans: an fMRI study

To elucidate the neural correlates of cognitive effects of nicotine, we examined behavioral performance and blood oxygenation level-dependent regional brain activity, using functional magnetic resonance imaging, during a parametric “n-back” task in healthy nonsmoking males after the administration of nicotine (12 μg/kg body weight) or saline. Nicotine, compared to placebo, improved accuracy ( P = 0.008) in all active conditions (2%–11%), and had a load-specific effect on latency ( P = 0.004; 43.78% decrease at the highest memory load). Within a network of parietal and frontal areas activated by the task ( P < 0.05, corrected at the voxel level), nicotine produced an increased response ( P < 0.05; uncorrected within the regions of interest) in the anterior cingulate, superior frontal cortex, and superior parietal cortex. It also produced an increased response in the midbrain tectum in all active conditions and in the parahippocampal gyrus, cerebellum, and medial occipital lobe during rest ( P = 0.05; uncorrected). The present observations point to altered neuronal activity in a distributed neural network associated with on-line task monitoring and attention and arousal systems as underlying nicotine-related enhancement of attention and working memory in human subjects.

Neurotransmitter and imaging studies in anorexia nervosa: new targets for treatment.

Anorexia and Bulimia Nervosa are disorders of unknown etiology that invariably begin during adolescence and near in time to puberty in young women. These disorders are associated with aberrant eating behaviors, body image distortions, impulse and mood disturbances, as well as characteristic temperament and personality traits. It is well known that malnutrition produces changes in neuroendocrine function. More recently, disturbances in neuronal systems have been found to play a role in the modulation of feeding, mood, and impulse control. These neuronal systems include neuropeptides (CRH, opioids, neuropeptide-Y (NPY) and peptide YY (PYY), vasopressin and oxytocin, CCK, and leptin) and monoamines (serotonin, dopamine, norepinephrine). Disturbances of most of these neuronal systems have been found when people are ill with an eating disorder, but it was not certain whether they were a cause or consequence of symptoms. In order to address these questions, a growing number of studies have investigated whether neuromodulatory disturbances persist after recovery. Studies from several centers tend to show altered serotonin activity persists after prolonged normalization of weight, nutrition, and menstrual function, as do anxiety, obsessionality, and perfectionism. While there are fewer data, there may be persistent alterations of dopamine or some neuropeptides in some subjects in a recovered state. The inaccessibility of the central nervous system has made it difficult to understand brain and behavior. In the past decade, new tools, such as brain imaging, have offered the possibility of better characterization of complex neuronal function and behavior. Such studies have tended to consistently find that alterations of brain regions, such as the temporal lobe, occur in people who are ill with anorexia nervosa and appear to persist after some degree of weight gain and recovery. New imaging technology, that marries Positron Emission Tomography (PET) imaging with selective neurotransmitter radioligands, confirms that altered serotonin neuronal pathway activity persists after recovery from an eating disorder and supports the possibility that these psychobiological alterations might contribute to traits, such as increased anxiety or extremes of impulse control, that, in turn, may contribute to a vulnerability to the development of an eating disorder. In summary, studies of pathophysiology are starting to nominate new candidates for treatment leading to the possibility of finding effective treatments for this often chronic or fatal disorder.

Workshop Y: Neuro-Endocrino-Immunology: Y.1–Y.14

Experimental evidence has revealed the role of mitochondria in various aspects of neuronal physiology. Mitochondrial failure results in alterations that underlie the pathogeneses of many neurodegenerative disorders, such as Parkinson’s disease, Alzheimer’s disease, Huntington’s disease (HD) and amyotrophic lateral sclerosis. The mitochondrial toxin 3-nitropropionic acid (3-NP) has been used to model failure; for example, systemic administration of 3-NP imitates the striatal degeneration that is exhibited in the postmortem tissue of patients afflicted with HD. We have demonstrated that low, sub-chronic doses of 3-NP are sufficient to initiate the damage to striatal neurons that is associated with changes in neurotrophin expression levels. However, the mechanisms underlying the alterations in neuronal activity and neurotransmission due to 3-NP-induced mitochondrial dysfunction remain to be elucidated. In this paper, we focus on how corticostriatal transmission and its modulation by neurotrophins are altered in vivo after 5 days of mitochondrial inhibition with 3-NP.Recordings of population spikes and a paired pulse (PP) stimulation protocol were used to document changes in corticostriatal synapses in 3-NP-treated brain slices. The corticostriatal synapses were modulated by neurotrophins but displayed differential amplitude increases in the presence of brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), or neurotrophin-4/5 (NT-4/5) under control conditions. Neurotrophin-mediated synaptic modulation was decreased in slices from 3-NP-treated mice. The protein and mRNA levels of neurotrophins and their receptors were also modified in the 3-NP-treated tissue. Neuronal structural evaluation demonstrated that synaptic length and density were reduced in the 3-NP-treated mice, which partially explained the changes in the amplitudes of the synaptic field responses. Our results demonstrate that corticostriatal synapses are differentially modulated by neurotrophins and that this modulation is altered by mitochondrial failure. Mitochondrial dysfunction also affects neurotransmitter release in corticostriatal synapses, neurotrophin availability, dendritic arborization and the lengths of the striatal medium spiny neurons (MSNs).