Dodecafluoropentane Emulsion Extends Window for tPA Therapy in a Rabbit Stroke Model

Dodecafluoropentane emulsion (DDFPe) nanodroplets are exceptional oxygen transporters and can protect ischemic brain in stroke models 24 h without reperfusion. Current stroke therapy usually fails to reach patients because of delays following stroke onset. We tested using DDFPe to extend the time window for tissue plasminogen activator (tPA). Longer treatment windows will allow more patients more complete stroke recovery. We test DDFPe to safely extend the time window for tPA thrombolysis to 9 h after stroke. With IACUC approval, randomized New Zealand white rabbits (3.4-4.7 kg, n = 30) received angiography and 4-mm blood clot in the internal carotid artery for flow-directed middle cerebral artery occlusion. Seven failed and were discarded. Groups were IV tPA (n = 11), DDFPe + tPA (n = 7), and no therapy controls (n = 5). DDFPe (0.3 ml/kg, 2 % emulsion) IV dosing began at 1 h and continued at 90 min intervals for 6 doses in one test group; the other received saline injections. Both got standard IV tPA (0.9 mg/kg) therapy starting 9 h post stroke. At 24 h, neurological assessment scores (NAS, 0-18) were determined. Following brain removal percent stroke volume (%SV) was measured. Outcomes were compared with Kruskal-Wallis analysis. For NAS, DDFPe + tPA was improved overall, p = 0.0015, and vs. tPA alone, p = 0.0052. For %SV, DDFPe + tPA was improved overall, p = 0.0003 and vs. tPA alone, p = 0.0018. NAS controls and tPA alone were not different but %SV was, p = 0.0078. With delayed reperfusion, DDFPe + tPA was more effective than tPA alone in preserving functioning brain after stroke. DDFPe significantly extends the time window for tPA therapy.

Dodecafluoropentane Emulsion (DDFPe) Decreases Stroke Size and Improves Neurological Scores in a Permanent Occlusion Rat Stroke Model

Background:

Dodecafluoropentane emulsion (DDFPe), given IV one hour after stroke, has been shown to greatly reduce the percent stroke volume (%SV) in rabbits. With repeated doses its effect continued for 24 hours.

Purpose:

Test DDFPe as neuroprotective agent in permanent occlusion rat stroke models in Sprague Dawley (SD) and Spontaneously Hypertensive Rats (SHR) measuring both %SV and neurological assessment scores (NAS).

Methods:

The male rats received either saline (control), or one or four doses (1x or 4x) of DDFPe (0.6ml/kg IV) one hour post stroke. Treatment groups were SD (n=26) (control, 1x and 4x; n=12, 7 and 7) and SHR (n=14) (control, 1x and 4x; n=7, 3 and 4). The 4x doses were given at 1.5 hour intervals. At six hours post stroke, the rats received a NAS using standard tests for balance, reflexes, and motor performance. Then rats were euthanized and brains removed for TTC evaluation of %SV.

Results:

For %SV analysis strain differences were not significant therefore strains were combined. DDFPe significantly decreased %SV in 1x and 4xDDFPe groups compared to control groups (2.59±1.81 and 0.98±0.88 vs. 9.24±6.06, p≤0.001 each; p≤0.0001 for the overall test for treatment effect). The 1x versus 4xDDFPe groups were not significantly different (p=0.40). In NAS analysis both strains showed significant improvement with 4xDDFPe therapy vs. controls, (SD: 5.00+2.45 vs. 9.36+3.56, p=0.01; SHR: 7.75+4.43 vs. 12.14+3.08, p=0.05). Differences between the 1x DDFPe group and controls were not significant (SD: 8.43+3.69; SHR: 9. 33+3.51).

Conclusion:

DDFPe treatment provides significant neuroprotection when assessed six hours post stroke.

Progress in dodecafluoropentane emulsion as a neuroprotective agent in a rabbit stroke model

Dodecafluoropentane emulsion (DDFPe) in 250 nm nanodroplets seems to swell modestly to accept and carry large amounts of oxygen in the body at >29 °C. Small particle size allows oxygen delivery even into hypoxic tissue unreachable by erythrocytes. Using permanent cerebral embolic occlusion in rabbits, we assessed DDFPe dose response as a neuroprotectant at 7 and 24 h post-embolization without lysis of arterial obstructions and investigated blood pharmacokinetics. New Zealand White rabbits (N = 56) received cerebral angiography and embolic spheres (diameter = 700-900 μm) occluded middle and/or anterior cerebral arteries. Intravenous DDFPe dosing (2 % w/v emulsion) began at 60 min and repeated every 90 min until sacrifice at 7 or 24 h post-embolization. Seven-hour groups: (1) control (embolized without treatment, N = 6), and DDFPe treatment: (2) 0.1 ml/kg (N = 7), (3) 0.3 ml/kg (N = 9), (4) 0.6 ml/kg (N = 8). Twenty-four-hour groups: (5) control (N = 16), and DDFPe treatment: (6) 0.1 ml/kg (N = 10). Infarcts as percent of total brain volume were determined using vital stains on brain sections. Other alert normal rabbits (N = 8) received IV doses followed by rapid arterial blood sampling and GC-MS analysis. Percent infarct volume means significantly decreased for all DDFPe-treated groups compared with controls, p = <0.004 to <0.03. Blood DDFP (gas) half-life was 1.45 ± 0.17 min with R = 0.958. Mean blood clearance was 78.5 ± 24.9 ml/min/kg (mean ± SE). Intravenous DDFPe decreases ischemic stroke infarct volumes. Blood half-life values are very short. The much longer therapeutic effect, >90 min, suggests multiple compartments. Lowest effective dose and maximum effective therapy duration are not yet defined. Rapid development is warranted.

Modafinil normalized hyperreflexia after spinal transection in adult rats

STUDY DESIGN

Hyperreflexia occurs after spinal cord injury and can be assessed by measuring low frequency-dependent depression of the H-reflex in the anesthetized animal.

OBJECTIVE

To determine the effects of Modafinil (MOD), given orally, following a complete SCI compared with animals receiving MBET and transected untreated animals and examine if changes exist in Connexin 36 (Cx-36) protein levels in the lumbar enlargement of animals for the groups described.

SETTING

Center for Translational Neuroscience, Little Rock, AR, USA.

METHODS

Adult female rats underwent complete transection (Tx) at T10 level. H-reflex testing was performed 30 days following Tx in one group, and after initiation of treatment with MOD in another group, and after MBET training in the third group. The Lumbar enlargement tissue was harvested and western blots were performed after immunoprecipitation techniques to compare Cx-36 protein levels.

RESULTS

Statistically significant decreases in low frequency-dependent depression of the H-reflex were observed in animals that received MOD and those that were treated with MBET compared with the Tx, untreated group. Statistically significant changes in Cx-36 protein levels were not observed in animals treated with MOD compared with Tx, untreated animals.

CONCLUSION

Normalization of the loss of low frequency -dependent depression of the H-reflex was demonstrated in the group receiving MOD and the group receiving MBET compared with the Tx, untreated group. Further work is needed to examine if Cx-36 protein changes occur in specific subregions of the spinal cord.

Smoking during pregnancy: postnatal effects on arousal and attentional brain systems

Prenatal exposure to cigarette smoke is known to produce lasting arousal, attentional and cognitive deficits in humans. The pedunculopontine nucleus (PPN), as the cholinergic arm of the reticular activating system (RAS), is known to modulate arousal, waking and REM sleep. Rapid eye movement (REM) sleep decreases between 10 and 30 days postnatally in the rat, with the greatest decrease occurring at 12-21 days. Pregnant dams were exposed to 150 ml of cigarette smoke for 15 min, three times per day, from day E14 until parturition, and the pups allowed to mature. We analyzed (a) intrinsic membrane properties of PPN neurons in slices from pups aged 12-21 days, and (b) the sleep state-dependent P13 auditory evoked potential, which is generated by PPN outputs, in animals allowed to age to adolescence. We found significant changes in the intrinsic membrane properties of PPN cells in prenatally exposed animals compared to intact ones, rendering these cells more excitable. In addition, we found disturbances in the habituation to repetitive stimulation in adolescent, freely moving animals, suggestive of a deficit in the process of sensory gating. These findings could explain some of the differences seen in individuals whose parents smoked during pregnancy, especially in terms of their hypervigilance and increased propensity for attentional deficits and cognitive/behavioral disorders.

Alpha-2 adrenergic regulation of pedunculopontine nucleus neurons during development

Rapid eye movement sleep decreases between 10 and 30 days postnatally in the rat. The pedunculopontine nucleus is known to modulate waking and rapid eye movement sleep, and pedunculopontine nucleus neurons are thought to be hyperpolarized by noradrenergic input from the locus coeruleus. The goal of the study was to investigate the possibility that a change in alpha-2 adrenergic inhibition of pedunculopontine nucleus cells during this period could explain at least part of the developmental decrease in rapid eye movement sleep. We, therefore, recorded intracellularly in 12-21 day rat brainstem slices maintained in oxygenated artificial cerebrospinal fluid. Putative cholinergic vs. non-cholinergic pedunculopontine nucleus neurons were identified using nicotinamide adenine dinucleotide phosphate diaphorase histochemistry and intracellular injection of neurobiotin (Texas Red immunocytochemistry). Pedunculopontine nucleus neurons also were identified by intrinsic membrane properties, type I (low threshold spike), type II (A) and type III (A+low threshold spike), as previously described. Clonidine (20 microM) hyperpolarized most cholinergic and non-cholinergic pedunculopontine nucleus cells. This hyperpolarization decreased significantly in amplitude (mean+/-S.E.) from -6.8+/-1.0 mV at 12-13 days, to -3.0+/-0.7 mV at 20-21 days. However, much of these early effects (12-15 days) were indirect such that direct effects (tested following sodium channel blockade with tetrodotoxin (0.3 microM)) resulted in hyperpolarization averaging -3.4+/-0.5 mV, similar to that evident at 16-21 days. Non-cholinergic cells were less hyperpolarized than cholinergic cells at 12-13 days (-1.6+/-0.3 mV), but equally hyperpolarized at 20-21 days (-3.3+/-1.3 mV). In those cells tested, hyperpolarization was blocked by yohimbine, an alpha-2 adrenergic receptor antagonist (1.5 microM). These results suggest that the alpha-2 adrenergic receptor on cholinergic pedunculopontine nucleus neurons activated by clonidine may play only a modest role, if any, in the developmental decrease in rapid eye movement sleep. Clonidine blocked or reduced the hyperpolarization-activated inward cation conductance, so that its effects on the firing rate of a specific population of pedunculopontine nucleus neurons could be significant. In conclusion, the alpha-2 adrenergic input to pedunculopontine nucleus neurons appears to consistently modulate the firing rate of cholinergic and non-cholinergic pedunculopontine nucleus neurons, with important effects on the regulation of sleep-wake states.

Prenatal exposure to cigarette smoke affects the physiology of pedunculopontine nucleus (PPN) neurons in development

Prenatal exposure to cigarette smoke is known to produce lasting arousal, attentional and cognitive deficits in humans. The pedunculopontine nucleus (PPN), as the cholinergic arm of the reticular activating system (RAS), is known to modulate arousal, waking and rapid eye movement (REM) sleep. REM sleep decreases between 10 and 30 days postnatally in the rat, especially at 12-21 days. Pregnant dams were exposed to 350 ml of cigarette smoke for 15 min, 3 times per day, from day E14 until birth, and the pups allowed to mature. Intracellularly recorded PPN neurons in 12-21 day rat brainstem slices were tested for intrinsic membrane properties, including the hyperpolarization-activated cation current Ih, which is known to drive oscillatory activity. Type II (A-current) PPN cells from 12-16 day old offspring of treated animals had a 1/2max Ih amplitude of (mean +/- SE) 4.1 +/- 0.9 mV, while 17-21 day cells had a higher 1/2max Ih of 9.9 +/- 1.1 mV (p < 0.0001). Cells from 12-16 day old control brainstems had a 1/2max Ih of 1.3 +/- 0.1 mV, which was lower (p < 0.05) than in cells from prenatally treated offspring; while 17-21 day old cells from controls had a 1/2max Ih of 3.3 +/- 0.3 mV, which was also lower (p < 0.01) than in cells from prenatally treated offspring. In addition, changes in resting membrane potential [control -65. +/- 0.9 mV (n=32); exposed -55.0 +/- 1.4 mV (n = 27) (p < 0.0001)], and action potential (AP) threshold [control -56.5 +/- 0.7 mV (n = 32), exposed -47.0 +/- 1.4 mV (n = 27) (p < 0.0001)], suggest that prenatal exposure to cigarette smoke induced marked changes in cells in the cholinergic arm of the RAS, rendering them more excitable. Such data could partially explain the differences seen in individuals whose parents smoked during pregnancy, especially in terms of their hypervigilance and increased propensity for attentional deficits and cognitive/behavioral disorders.

Restoration of frequency-dependent depression of the H-reflex by passive exercise in spinal rats

STUDY DESIGN

Hyper-reflexia, measured as a decrease of low frequency-dependent depression of the H-reflex, is known to occur in both humans and animals after spinal cord injury (SCI). Previous studies have shown that passive exercise for 3 months could be used to restore low frequency-dependent depression of the H-reflex after SCI.

OBJECTIVE

To determine the effects of various periods of time on the ability of passive exercise to restore low frequency-dependent depression of the H-reflex.

SETTING

Spinal Cord Injury Mobilization Program of the Center for Translational Neuroscience, the research arm of the Jackson T Stephens Spine and Neuroscience Institute, Little Rock, AR, USA.

METHODS

Adult rats underwent complete spinal cord transection at the T10 level. The hindlimbs were passively exercised in different groups of rats for 1 h/day, 5 days/week for 15, 30, 45, 60, or 90 days, and low frequency-dependent depression of the H-reflex was tested.

RESULTS

Statistically significant low frequency-dependent depression of the H-reflex was evident by 30 days of exercise, although numerical reductions were seen even at 15 days. There was a linear decrease in low frequency-dependent depression of the H-reflex with duration of passive exercise.

CONCLUSIONS

Passive exercise can restore frequency-dependent depression of spinal reflexes in a time-dependent manner if used following complete spinal transection.

Induction of long-lasting depolarization in medioventral medulla neurons by cholinergic input from the pedunculopontine nucleus

Stimulation of the pedunculopontine nucleus (PPN) is known to induce changes in arousal and postural/locomotor states by activation of such descending targets as the caudal pons and the medioventral medulla (MED). Previously, PPN stimulation was reported to induce prolonged responses (PRs) in intracellularly recorded caudal pontine neurons in vitro. The present study used intracellular recordings in semihorizontal slices from rat brain stem (postnatal days 12-21) to determine responses in MED neurons following PPN stimulation. One-half (40/81) of MED neurons showed PRs after PPN stimulation. MED neurons with PRs had shorter duration action potential, longer duration afterhyperpolarization, and higher amplitude afterhyperpolarization than non-PR MED neurons. PR MED neurons were significantly larger (568 +/- 44 microm2) than non-PR MED neurons (387 +/- 32 microm2). The longest mean duration PRs and maximal firing rates during PRs were induced by PPN stimulation at 60 Hz compared with 10, 30, or 90 Hz. The muscarinic cholinergic agonist carbachol induced depolarization in all PR neurons tested, and the muscarinic cholinergic antagonist scopolamine reduced or blocked carbachol- and PPN stimulation-induced PRs in all MED neurons tested. These findings suggest that PPN stimulation-induced PRs may be due to activation of muscarinic receptor-sensitive channels, allowing MED neurons to respond to a transient, frequency-dependent depolarization with long-lasting stable states. PPN stimulation appears to induce PRs in large MED neurons using parameters known best to induce locomotion.

Nicotine suppresses the P13 auditory evoked potential by acting on the pedunculopontine nucleus in the rat

We identified a potential novel site of action for nicotine (NIC) since (a) systemic injection of NIC led to a dose-dependent decrease in the amplitude of the sleep state-dependent, vertex-recorded, P13 midlatency auditory evoked potential (generated by the reticular activating system, RAS), (b) localized injections of a nicotinic receptor antagonist into the pedunculopontine nucleus (PPN, the cholinergic arm of the RAS) blocked the effects of systemic NIC on the P13 potential (a measure of level of arousal), and (c) localized injection of a nicotinic receptor agonist into the PPN also led to a decrease in the amplitude of the P13 potential, an effect blocked by PPN injection of a nicotinic receptor antagonist. There were minor changes in the manifestation of the startle response (SR) at the concentrations used; however, NIC did decrease the hippocampal N40 potential, although its effects were not affected by antagonist or agonist injections into the PPN. These results suggest a potential mechanism underlying the anxiolytic effects of NIC-suppression of the cholinergic arm of the RAS.

The P50 midlatency auditory evoked potential in patients with chronic low back pain (CLBP)

OBJECTIVE

Patients with Chronic Low Back Pain (CLBP) show arousal, attentional and cognitive disturbances. The sleep state-dependent P50 midlatency auditory evoked potential was used to determine if patients with CLBP [with and without co-morbid depression (DEP)] show quantitative disturbances in the manifestation of the P50 potential.

METHODS

P50 potential latency, amplitude and habituation to repetitive stimuli at 250, 500 and 1000ms interstimulus intervals (ISIs) was recorded, along with the McGill Pain Questionnaire-Short Form (MPQ-SF). CLBP subjects (n=42) were compared with Controls (n=43), and with subjects with DEP only (n=6). Of the CLBP subjects, 20/42 had clinical depression (CLBP+DEP); 8/20 were taking anti-depressant medication (CLBP+DEP+med), the others were not (CLBP+DEP-med).

RESULTS

There were no differences (ANOVA) in age, sex or P50 potential latency, although there was a trend towards increased latencies in CLBP groups. P50 potential amplitude was lower in CLBP groups, but not in sub-groups, again indicating a trend. P50 potential habituation was decreased in the DEP only subjects at the 250m ISI, and decreased in CLBP+DEP-med subjects at the 500ms ISI. This difference was not present in CLBP+DEP+med subjects. The MPQ-SF revealed that patients with CLBP and CLBP+DEP-med showed lower pain scores than CLBP+DEP+med patients.

CONCLUSIONS

There is decreased habituation of the P50 potential habituation in unmedicated patients with CLBP+DEP compared to Controls.

SIGNIFICANCE

Patients with CLBP+DEP-med may be less able to disregard incoming sensory information, including painful sensations, but anti-depressant medications help correct this deficit. However, their perception of pain may be increased by medication.

The feline fictive startle response and its related potential in the pedunculopontine nucleus

The human P1/P50 midlatency auditory evoked potential and the auditory startle response (SR) have been used for investigating sensory gating and sensorimotor modulation which is impaired in various psychiatric diseases. In the present study, we demonstrated that auditory stimulation was capable of eliciting excitation of flexor and extensor neurograms from the hindlimb nerves in the paralyzed decerebrate cat, a phenomenon which corresponds to a "fictive" startle response (FSR). Previous studies have shown that the SR consists of distinct excitatory components, "early" and "late", separated by an inhibitory phase. However, in the FSR, unlike the SR in the intact preparation, the "late" excitatory phase never occurred. Recordings from the pedunculopontine nucleus (PPN) simultaneously with the FSR revealed the presence of an auditory evoked potential at a 20-25 ms latency, presumably the depth-recorded equivalent of the vertex-recorded wave A, which has been shown to be the feline equivalent of the human P1 potential. The depth-recorded wave A appeared to share neurological substrates with the excitatory phase of the FSR, since both responses were facilitated in a similar manner by increasing stimulus duration. We previously reported that, in the intact rat, the vertex-recorded P13 potential, the putative rodent equivalent of the human P1 potential, is generated, at least in part, by outputs of the PPN, and that the P13 potential shares neurological substrates with the "early" excitatory phase of the SR. Taken together, the results of the present study indicate that, along with the SR and the P13 potential in the intact rat, the FSR and the depth-recorded wave A in the paralyzed cat may be unique animal models for further examining, in the absence of neural structures rostral to the precollicular decerebration, the cellular basis of startle behavior.

Developmental changes in pedunculopontine nucleus (PPN) neurons

The developmental decrease in rapid-eye-movement (REM) sleep in man occurs between birth and after puberty. We hypothesize that if this decrease in REM sleep does not occur, lifelong increases in REM sleep drive may ensue. Such disorders are characterized by hypervigilance and sensory-gating deficits, such as are present in postpubertal onset disorders like schizophrenia, panic attacks (a form of anxiety disorder), and depression. The decrease in REM sleep in the rat occurs between 10 and 30 days of age. We studied changes in size and physiological properties of pedunculopontine nucleus (PPN) cells involved in the control of arousal, i.e., waking and REM sleep. During the largest decrease in REM sleep (12-21 days), cholinergic PPN neurons doubled in cell area, the hypertrophy peaking at 15-16 days, then decreasing in area by 20-21 days. Noncholinergic PPN cells did not change in area during this period. We confirmed the presence of two populations of PPN neurons based on action potential (AP) duration, with the proportion of short-AP-duration cells increasing and long AP duration decreasing between 12 and 21 days. Most cholinergic and noncholinergic cells had short AP durations. Afterhyperpolarization (AHP) duration became segregated into long and short AHP duration after 15 days. Cells with short AP duration also had short AHP duration. The proportion of PPN cells with Ih current increased gradually, peaking at 15 days, then decreased by 21 days. These changes in morphological and physiological properties are discussed in relation to the developmental decrease in REM sleep.

Development of REM sleep drive and clinical implications

Rapid eye movement (REM) sleep in the human declines from approximately 50% of total sleep time ( approximately 8 h) in the newborn to approximately 15% of total sleep time (approximately 1 h) in the adult, and this decrease takes place mainly between birth and the end of puberty. We hypothesize that without this developmental decrease in REM sleep drive, lifelong increases in REM sleep drive may ensue. In the rat, the developmental decrease in REM sleep occurs 10-30 days after birth, declining from >70% of total sleep time in the newborn to the adult level of approximately 15% of sleep time during this period. Rats at 12-21 days of age were anesthetized with ketamine and decapitated, and brain stem slices were cut for intracellular recordings. We found that excitatory responses of pedunculopontine nucleus (PPN) neurons to N-methyl-D-aspartic acid decrease, while responses to kainic acid increase, over this critical period. During this developmental period, inhibitory responses to serotonergic type 1 agonists increase but responses to serotonergic type 2 agonists do not change. The results suggest that as PPN neurons develop, they are increasingly activated by kainic acid and increasingly inhibited by serotonergic type 1 receptors. These processes may be related to the developmental decrease in REM sleep. Developmental disturbances in each of these systems could induce differential increases in REM sleep drive, accounting for the postpubertal onset of a number of different disorders manifesting increases in REM sleep drive. Examination of modulation by PPN projections to ascending and descending targets revealed the presence of common signals modulating ascending arousal-related functions and descending postural/locomotor-related functions.

Effects of pedunculopontine nucleus (PPN) stimulation on caudal pontine reticular formation (PnC) neurons in vitro

Stimulation of the pedunculopontine nucleus (PPN) is known to induce changes in arousal and postural/locomotor states. Previously, PPN stimulation was reported to induce prolonged responses (PRs) in extracellularly recorded PnC neurons in the decerebrate cat. The present study used intracellular recordings in semihorizontal slices from rat brain stem (postnatal days 12-21) to determine responses in PnC neurons following PPN stimulation. Two-thirds (65%) of PnC neurons showed PRs after PPN stimulation. PnC neurons with PRs had higher amplitude afterhyperpolarizations (AHP) than non-PR (NPR) neurons. Both PR and NPR neurons were of mixed cell types characterized by "A" and/or "LTS," or neither of these types of currents. PnC cells showed decreased AHP duration with age, due mostly to decreased AHP duration in NPR cells. The longest mean duration PRs were induced by stimulation at 60 and 90 Hz compared with 10 or 30 Hz. Maximal firing rates in PnC cells during PRs were induced by PPN stimulation at 60 Hz compared with 10, 30, or 90 Hz. BaCl2 superfusion blocked PPN stimulation-induced PRs, suggesting that PRs may be mediated by blockade of potassium channels, in keeping with increased input resistance observed during PRs. Depolarizing pulses failed to elicit, and hyperpolarizing pulses failed to reset, PPN stimulation-induced PRs, suggesting that PRs may not be plateau potentials. Pharmacological testing revealed that nifedipine superfusion failed to block PPN stimulation-induced PRs; i.e., PRs may not be calcium channel-dependent. The muscarinic cholinergic agonist carbachol induced depolarization in most PR neurons tested, and the muscarinic cholinergic antagonist scopolamine reduced or blocked PPN stimulation-induced PRs in some PnC neurons, suggesting that some PRs may be due to muscarinic receptor activation. The nonspecific ionotropic glutamate receptor antagonist kynurenic acid failed to block PPN stimulation-induced PRs, as did the metabotropic glutamate receptor antagonist (R, S)-alphamethyl-4-carboxyphenylglycine, suggesting that PRs may not be mediated by glutamate receptors. These findings suggest that PPN stimulation-induced PRs may be due to increased excitability following closing of muscarinic receptor-sensitive potassium channels, allowing PnC neurons to respond to a transient, frequency-dependent depolarization with long-lasting stable states. PPN stimulation appears to induce PRs using parameters known best to induce locomotion. This mechanism may be related to switching from one state to another (e.g., locomotion vs. standing or sitting, waking vs. non-REM sleep or REM sleep).

Effect of age on sensory gating of the sleep state-dependent P1/P50 midlatency auditory evoked potential

The P1/P50 midlatency auditory evoked potential is a sleep state-dependent waveform present during waking and rapid eye movement (REM) sleep and absent during slow-wave sleep. The P50 potential was studied in normal male and female subjects of various ages including post-pubertal adolescents (12-19 yrs), young adults (24-39 yrs), middle-aged adults (40-55 yrs) and older adults (55-78 yrs). There were no statistically significant differences in the mean peak amplitude or mean peak latency of the P50 potential between males and females or between age groups. Using a paired stimulus paradigm, the degree of sensory gating of the P50 potential was tested at three different interstimulus intervals (ISIs), 250, 500 and 1000 msec. There were no statistically significant differences in the sensory gating of the P50 potential between males and females. However, there was a significant decrease in sensory gating of the P50 potential in the adolescent group compared to each of the other age groups at the 250 msec ISI, but not at the 500 or 1000 msec ISI. These results suggest the presence of decreased sensory gating in normal adolescents compared to normal, older age groups.

Disinhibition of the sleep state-dependent p1 potential in Parkinson's disease-improvement after pallidotomy

We previously reported that the P1 or P50 midlatency evoked potential underwent decreased habituation or disinhibition in patients with Parkinson's Disease. This sleep state-dependent response appears to be generated by cholinergic elements of the reticular activating system. We attempted to determine if the decreased habituation or disinhibition of the P1 potential would be altered by bilateral pallidotomy. Twenty-three patients who met inclusion criteria for surgery underwent pre- and post-operative evaluation using a Modified United Parkinson's Disease Rating Scale (UPDRS) and P1 potential recordings. Decreased habituation of the P1 potential was determined using a paired stimulus paradigm in which click stimuli were presented at 250, 500 and 1000 msec interstimulus intervals (ISI). Pre-operatively, patients showed disinhibition of the P1 potential at the 250 msec ISI (60 37% vs. 21 20%) and 500 msec ISI (78 47% vs. 43 31%) compared to age-matched control subjects. Post-operatively, the same patients showed a significant improvement in habituation of the P1 potential at the same ISIs (250 msec 37 21%; 500 msec 43 32%). UPDRS scores for these patients pre-operatively were 59 18 and 24 11 post-operatively, resulting in a significant reduction in symptom severity. We conclude that bilateral pallidotomy resulted in a significant improvement in symptom ratings and reduced the disinhibition of the P1 midlatency evoked response.

Pedunculopontine stimulation induces prolonged activation of pontine reticular neurons

Extracellular and intracellular recordings were carried out from neurons in the region of the pontine reticular formation at the transition between the nucleus reticularis pontis oralis and caudalis, and in the pontis caudalis. Responses were studied after stimulation of the mesopontine cholinergic pedunculopontine nucleus in precollicular-postmammillary transected, paralyzed preparations. Recordings of neurographic activity in hindlimb flexor and extensor nerves served to detect changes in fictive locomotion and muscle tone induced by pedunculopontine nucleus stimulation or occurring spontaneously. Short duration trains of pedunculopontine nucleus stimulation induced long lasting responses, on average over 12s in duration, in one-third of pontine reticular neurons. These prolonged responses were stimulation frequency-dependent such that the longest durations were induced by stimulation at 20-60Hz. In some cells, stimulation at lower (10Hz) or higher (100Hz) frequencies induced responses of shorter duration or were absent, while in others, higher frequencies prolonged the excitatory effects of pedunculopontine nucleus stimulation. We conclude that these stimulation frequency-dependent effects may be related to the modulation of postural muscle tone and locomotion by the pedunculopontine nucleus.

Cholinergic modulation of the sleep state-dependent P13 midlatency auditory evoked potential in the rat

Injections into the pedunculopontine nucleus (PPN) of the cholinergic receptor agonist, carbachol (CAR), were found to reduce the amplitude of the vertex-recorded, sleep state-dependent P13 midlatency evoked potential in a dose- and time-dependent manner. This effect was blocked or reduced by pretreatment with the muscarinic receptor antagonist, scopolamine, injected into the PPN.

Locus coeruleus involvement in the effects of immobilization stress on the p13 midlatency auditory evoked potential in the rat

1. Adult male rats were prepared for recording midlatency auditory evoked responses from the vertex (Vx, P13 potential) and auditory cortex (ACx, P7 potential). 2. The P13 potential is the rodent equivalent of the human P1 or P50 potential, which exhibits decreased sensory gating in posttraumatic stress disorder. 3. Immobilization (IMB) stress for 60 min led to a significant decrease in P13 potential amplitude and sensory gating of the potential for the first 30-40 min of IMB. 4. The effects of IMB on the P13 potential were reduced by pre-treatment with the alpha-2 adrenergic receptor blocker yohimbine (YOH). 5. Injections of corticotropin releasing factor (CRF) into the locus coeruleus (LC), but not injections dorsal or ventral to the LC, induced a dose-dependent decrease in P13 potential amplitude and sensory gating. 6. The effects of CRF were blocked by cotreatment with the CRF receptor antagonist alpha-helical CRF (alpha-h CRF). 7. The effects of IMB on the P13 potential were mimicked by injections of the alpha-2 adrenergic receptor agonist dexmedetomidine (DEX) into the pedunculopontine nucleus (PPN). 8. The effects of DEX injections into PPN were reduced by pre-treatment with the alpha-2 adrenergic receptor blocker YOH. 9. The effects of IMB on P13 potential amplitude and sensory gating may be mediated in part via CRF activation of LC, which sends inhibitory alpha-2 adrenergic projections to PPN, a major source of the P13 potential.

Application of electrophysiological method to study interactions between ibogaine and cocaine

The psychoactive indole alkaloid, ibogaine (IBO), has been investigated for over a decade concerning its reported anti-addictive properties for opioids as well as psychomotor stimulants. The mechanism for the anti-addictive action of IBO is still unclear. IBO interactions with opioid, NMDA, nicotinic, adrenergic, and serotonergic receptor sites have been suggested. The involvement of the dopaminergic system in IBO action is well documented. Increased or decreased levels of dopamine (DA) in specific brain regions following IBO pretreatment have been seen concomitantly with increased or decreased motor activity after subsequent amphetamine or cocaine administration. In this report, in vivo electrophysiological measures were monitored in awake adult male rats in order to investigate alterations of the electrocorticogram (ECoG) resulting from interactions between IBO and cocaine (COC). Rats were implanted bilaterally with bipolar ECoG electrodes. They were either injected with saline, COC alone (20 mg/kg, i.p.) or IBO (50 mg/kg, i.p.) and COC 1 hr later. The concentrations of DA, 5-HT, and their metabolites DOPAC, HVA, and 5-HIAA were assessed in the caudate nucleus in separate groups of saline-, COC-, and IBO/COC-treated rats. An alpha1 power increase was observed within 10 min after COC injection, which lasted for less than 20 min. A desynchronization over alpha2 and both beta power bands was observed throughout the recording. In IBO/COC-treated rats, a significant increase in delta, theta, and alpha1 power occurred within 20 min after COC injection (p <0.05). This effect lasted for up to an hour. DA levels significantly increased after COC only and decreased after IBO administration. A further decrease in levels of DA was observed in IBO/COC-treated rats. DA turnover increased significantly after IBO alone but was not observed after IBO/COC treatment. The alterations in ECoG and neurotransmitter levels suggest a decreased response to COC following IBO pretreatment.

Reduced sensory gating of the P1 potential in rape victims and combat veterans with posttraumatic stress disorder

The P1 midlatency auditory evoked potential was studied in female rape victims with Posttraumatic Stress Disorder (PTSD) and compared to an age-matched female control group; and in male combat veterans with PTSD and compared to three groups of age-matched male control subjects. Sensory gating of the P1 potential was determined using a paired click stimulus paradigm in which the stimuli were presented at 250, 500 and 1000 msec interstimulus intervals (ISI). Results showed that sensory gating of the P1 potential was significantly decreased at the 250 msec ISI, and that there was a numerical, but not a statistically significant, decrease in sensory gating at the other intervals tested in both male and female PTSD subjects compared to all control groups. Since the P1 potential may be generated, at least in part, by the reticular activating system, dysregulation of sensory processing by elements of this system may be present in PTSD.

Serotonergic modulation of the P13 midlatency auditory evoked potential in the rat

The vertex-recorded, sleep state-dependent P13 midlatency auditory evoked potential in the rat may be generated, in part, by pedunculopontine nucleus (PPN) projections. Injections into the PPN of the 5-HT(1A) serotonin receptor agonist, 8-hydroxy-2-di-n-propylaminotetralin hydrobromide (DPAT), were found to reduce the amplitude of the P13 potential in a dose- and time-dependent manner. The suppressive effect of DPAT was blocked or reduced by pretreatment with the 5-HT(1A) serotonin receptor antagonist, Pindobind. These results show that the P13 potential can be modulated by known inhibitory serotonergic inputs to the PPN.

Neurochemical modulation of the P13 midlatency auditory evoked potential in the rat

Previous studies have shown that the vertex-recorded P13 auditory evoked potential in the rat appears to be the rodent equivalent of the human P1 (or P50) potential. This sleep state-dependent potential appears to be generated, at least in part, by cholinergic pedunculopontine nucleus projections. The present studies used localized microinjections of neuroactive compounds into the region of the pedunculopontine nucleus in order to modulate the vertex-recorded P13 potential. Both the GABAergic agonist, muscimol, and the noradrenergic alpha2 receptor agonist, clonidine, were found to reduce the amplitude of the P13 potential in a dose-dependent manner. The suppressive effect of clonidine on P13 potential amplitude was blocked by pretreatment with the noradrenergic alpha2 receptor antagonist, yohimbine. In addition, habituation of the P13 potential, measured using a paired stimulus paradigm, was increased by micro-injection of a dose of muscimol or clonidine which did not change the amplitude of the P13 potential induced by the first stimulus of a pair. In contrast, microinjection of yohimbine decreased habituation of the P13 potential. These results show that the vertex-recorded P13 potential and its habituation can be modulated by activation of known inhibitory synapses, both GABAergic and noradrenergic, at the level of the pedunculopontine nucleus. This provides further evidence that the P13 potential is generated, at least in part, by pedunculopontine nucleus outputs.

Effects of fetal spinal cord tissue transplants and cycling exercise on the soleus muscle in spinalized rats

Studies were carried out to determine if an intraspinal transplant (Trpl) of fetal spinal cord tissue or hind limb exercise (Ex) affected the changes in myosin heavy chain (MyHC) composition or myofiber size that occur following a complete transection (Tx) of the lower thoracic spinal cord of the adult rat. In one group of animals, transplants were made acutely, whereas in a second group, daily cycling exercise was initiated 5 days after injury, with animals in both groups being sacrificed 90 days after injury. The soleus muscle is normally composed of myofibers expressing either type I (90%) or type IIa (10%) MyHC. Following a spinal transection, expression of type I MyHC isoform decreased (18% of myofibers), type IIa MyHC expression increased (65% of myofibers), and the majority of myofibers (80%) expressed type IIx MyHC. Most myofibers coexpressed multiple MyHC isoforms. Compared with Tx only, with Ex or with Trpl, there was a decrease in the number of myofibers expressing type I or IIa isoforms but little change in expression of IIx MyHC. Myofibers expressing the IIb isoform appeared in several transplant recipients but not after exercise. Transection resulted in atrophy of type I myofibers to approximately 50% of normal size, whereas myofibers were significantly larger after exercise (74% of control) and in Trpl recipients (77% of control). Type IIa myofibers also were significantly larger in Trpl recipients compared with the Tx only group. Overall, the mean myofiber size was significantly greater after exercise and in Trpl recipients compared with myofibers in Tx only animals. Thus, although neither strategy shifted the MyHC profile towards the control, both interventions influenced the extent of atrophy observed after spinalization. These data suggest that palliative strategies can be developed to modulate some of the changes in hind limb muscles that occur following a spinal cord injury.

Sensory gating of the P13 midlatency auditory evoked potential and the startle response in the rat

The human P1/P50 midlatency auditory evoked potential and the startle response (SR) have been used as measures of sensory and sensorimotor gating, respectively. In the present study, both prepulse and paired stimulus paradigms were used in order to investigate the relationship between sensory gating mechanisms of the P13 potential, the putative rodent equivalent of the P1 potential, and those of the SR. In addition, these were compared to the properties of the N40 potential, another measure of sensory gating. Simultaneous recordings from the vertex (P13 potential and N40 potential) and neck musculature (SR) showed that (1) in a prepulse paradigm, increasing the intensity of the prepulse or decreasing the interstimulus interval resulted in increased inhibition of the P13 potential, N40 potential (to a lesser degree) and the SR (to a greater degree), (2) when using a low signal-to-noise ratio between the prepulse intensity and the background level, prepulse inhibition of the SR was reduced or absent while that of the P13 potential was present, (3) the amplitude of the 'prepulse evoked' P13 potential was significantly correlated with prepulse inhibition of the P13 potential, the N40 potential and the SR, (4) in a paired identical stimulus paradigm, decreasing the interstimulus interval resulted in increased habituation of the P13 potential, N40 potential (to a lesser degree) and the SR, and (5) increasing the intensity of the paired stimulation resulted in increased habituation of the P13 potential and the N40 potential (to a lesser degree), but not of the SR. These results demonstrate the presence of prepulse inhibition of the P13 potential, the N40 potential and the SR in a parallel manner, but show certain specific differences in their responses to parametric changes.

Midlatency auditory-evoked potentials in the rat: effects of interventions that modulate arousal

The vertex-recorded P13 midlatency auditory-evoked potential in the rat shows the same characteristics as the P1 potential in the human, namely, sleep-state dependence, rapid habituation and blockade by the cholinergic antagonist scopolamine. The P13 potential appears to be generated, at least in part, by projections of the pedunculopontine nucleus, the cholinergic arm of the reticular activating system. On the other hand, the auditory cortex-recorded P7 potential appears to be of primary cortical origin. Simultaneous recordings from the vertex and the auditory cortex showed that (1) the P13 potential was suppressed by administration of the anesthetics ketamine, pentobarbital or halothane in a dose-dependent manner, but the P7 potential was not; (2) the P13 potential was suppressed by intragastric injections of ethanol in a dose-dependent manner, but the P7 potential was not; (3) the amplitude of the P13 potential was negatively correlated with blood ethanol levels; (4) both the P13 and P7 potentials were still present following injections of the neuromuscular blocker pancuronium bromide; and (5) both the P13 and P7 potentials were decreased by diffuse brain injury induced by a weight-drop device in a weight-dependent manner. These findings suggest that the P13 potential is more sensitive than the P7 potential to changes in arousal and that the P13 and P7 potentials are not of myogenic but of neural origin.

Combat veterans with posttraumatic stress disorder exhibit decreased habituation of the P1 midlatency auditory evoked potential

The current study used a paired stimulus paradigm to investigate the P1 midlatency auditory evoked potential in Vietnam combat veterans with posttraumatic stress disorder (PTSD) and three comparison groups: alcohol dependents, combat-exposed normals, and combat-unexposed normals. Compared to each comparison group, PTSD subjects exhibited significantly diminished habituation of the P1 potential. P1 potential habituation within the PTSD group, correlated significantly with intensity of PTSD reexperiencing symptoms, such as trauma-related nightmares and flashbacks. These findings are discussed as consistent with a sensory gating defect at the brainstem level in PTSD, and are further discussed in the context of other psychophysiological measures in PTSD and of P1 potential findings in psychiatric disorders other than PTSD.

Decreased habituation of midlatency auditory evoked responses in Parkinson's disease

The P1 midlatency auditory evoked potential was studied in patients with Parkinson's disease and compared to that in age-matched controls. Habituation of the potential was determined by using a two-click stimulus paradigm in which the stimuli were presented at 250-, 500-, and 1,000-ms interstimulus intervals. Results showed that habituation of the P1 potential had a statistically significant decrease at the 250-ms and 500-ms interstimulus intervals in patients with Parkinson's disease compared to normal controls. The degree of decreased habituation was found to increase with severity of the disease such that stage 5 patients showed greater decreases in habituation compared to stage 4, as did stage 4 compared to stage 3. These findings may be explained by the presence of a dysregulation of sensory processing, possibly by elements of the reticular activating system, including the pedunculopontine nucleus, in Parkinson's disease.

Developmental changes in serotonergic receptor-mediated modulation of embryonic chick motoneurons in vitro

Intracellular recordings were obtained from antidromically identified motoneurons in an embryonic chick spinal cord slice preparation at two developmental stages (embryonic days 12 and 18, E12 and E18) which bracket a critical period in spinal cord growth. The resting membrane potential of chick motoneurons did not change significantly between E12 and E18, but there was a significant decrease in neuronal input resistance. A small inward rectification was present in cells of both ages, although a lower proportion of E12 motoneurons exhibited inward rectification compared to E18 motoneurons. Injection of depolarizing current pulses revealed that most E12 motoneurons exhibited spike adaptation, while the majority of E18 motoneurons showed high frequency tonic firing. Bath application of serotonin (5-HT) and its agonists 5-carboxamido-tryptamine (5-CT, a 5-HT1 agonist) and alpha-methyl 5-HT (a 5-HT2 agonist) produced hyperpolarizing responses accompanied by decreased input resistance in all E12 motoneurons studied. The same three agonists produced depolarizing responses and increased input resistance in all E18 motoneurons studied. The effects of serotonergic agonists on motoneuronal excitability were tested using depolarizing current pulses. In most cases, serotonergic agonists caused a decrease in firing frequency during the hyperpolarizing response in E12 neurons. At E18, bath application of 5-HT, 5-CT or alpha-methyl 5-HT produced an increase in firing frequency in all motoneurons during the depolarizing response. Our results indicate that both 5-HT1 and 5-HT2 receptor subtypes contribute to modulation of chick motoneuron excitability and appear to reverse the polarity of their effects on membrane potential after a critical period in development of the spinal cord.

Lesioning of the inferior olive using a ventral surgical approach. Characterization of temporal and spatial astrocytic responses at the lesion site and in cerebellum

Activated astrocytes, intrinsic components of both local and remote (axonal target regions) central nervous system injury responses, are now recognized as active metabolic and regulatory mediators in many neurological disorders. To further define these responses, we devised a new ventral surgical approach to unilaterally lesion the inferior olivary nuclear complex, which has a single predominant remote target, the cerebellum. Activated astrocyte number, volume, and density, as well as the total volume of brainstem involved in the astrocytic response, all peaked at postlesion day (pld) 4, returning toward, but not to, unoperated control values at pld 24 (p < 0.05). In contrast, the peak astrocyte response in the cerebellum was delayed, being greatest at pld 6 (p < 0.05 compared to control or pld 2). These responses were associated with increases in overexpression of S100 beta, an astrocyte-derived neurite growth factor, and with an increase in cerebellar steady-state levels of a neuronal injury response protein, the beta-amyloid precursor protein (beta-APP). This is similar to correlated increases in these two proteins that are found in epilepsy and Alzheimer disease. Our studies defining remote astrocytic and neuronal responses may be important for understanding glial-neuronal mechanisms underlying the spread of neuropathological changes in conditions such as Alzheimer disease.

Developmental changes in the effects of serotonin and N-methyl-D-aspartate on intrinsic membrane properties of embryonic chick motoneurons

A spinal cord slice preparation was developed in order to study developmental changes in intrinsic membrane properties and in responses to N-methyl-D-aspartate and serotonin in embryonic chick motoneurons. Transverse spinal cord slices were obtained from chick embryos over a series of developmental stages (embryonic days 12-18). Intracellular recordings were obtained from 87 antidromically identified motoneurons. During the stages examined, the average resting membrane potential did not vary significantly, the voltage threshold of current-evoked action potentials became significantly more negative, there was a non-significant trend towards a decrease in the recorded input resistance, but there were no significant changes observed in the membrane time constant. There were significant developmental changes in the waveform of the current-evoked action potentials. The average amplitude of the action potentials increased over the stages studied, while the action potential duration measured at half-amplitude decreased. All of the motoneurons examined were maximally depolarized by bath application of 50 microM N-methyl-D-aspartate. The depolarization persisted in the presence of tetrodotoxin but was blocked by 100 microM 2-amino-5-phosphonopentanoic acid and, therefore, was at least partially due to a direct action of N-methyl-D-aspartate on motoneuronal receptors. The average amplitude of the N-methyl-D-aspartate-induced depolarizations decreased significantly over the stages examined. In contrast, bath application of 50 microM serotonin produced either depolarizing or hyperpolarizing responses depending on the developmental age of the motoneuron. Serotonin induced a depolarization in about 50% of the motoneurons at embryonic day 12, 69% of the motoneurons at embryonic day 15 and 100% of the motoneurons recorded from at embryonic day 18. These findings reveal important developmental changes in intrinsic membrane responses and action potential properties of chick motoneurons recorded from a slice preparation. We have also documented changes in the motoneuronal responses to serotonin, a neurotransmitter used by a major descending projection, and N-methyl-D-aspartate, which activates glutamate receptors known to contribute to synaptic activity in segmental circuits.

Midlatency auditory evoked potentials and the startle response in the rat

The P13 midlatency auditory evoked potential in the rat is (i) sleep state dependent, (ii) undergoes rapid habituation and (iii) is blocked by the cholinergic antagonist scopolamine. As such, the P13 potential in the rat shows the same characteristics as the P1 (or P50) potential in the human. These potentials are thought to be mediated, at least in part, by the cholinergic arm of the reticular activating system. Previous studies have linked the reticular activating system with the startle response. The present study was undertaken to explore this relationship by simultaneously recording the P13 potential and the electromyographically recorded startle response using stimuli designed to elicit each response. Simultaneous recordings from the vertex and neck musculature following auditory click stimuli showed that: (i) the mean threshold of the P13 potential was 69.3 +/- 1.9 dB, while that for the startle response was 87.9 +/- 6.4 dB; (ii) the P13 potential was present during waking and paradoxical sleep, but absent during slow-wave sleep, while the startle response was present reliably only during waking; (iii) both responses habituated in response to paired stimuli, but the startle response was more habituated than the P13 potential; and (iv) both responses were facilitated by trains of stimuli in a similar manner. Recordings carried out from the auditory cortex verified that the primary cortical response had properties different from the P13 potential; i.e. it was present during all sleep-wake states, had a lower threshold and did not habituate rapidly. Finally, different patterns of startle responses were detected in the neck muscles. In every case, the P13 potential occurred during the middle, inhibitory phase of the startle response. These results suggest that the P13 potential and the startle response share response features, but the P13 potential appears to be more sensitive to auditory stimulation and to sleep-wake states. The startle response may be modulating descending systems by priming the spinal cord to respond in a "fight vs flight" fashion. On the other hand, the P13 response may be modulating ascending systems by triggering thalamocortical activity and resetting descending systems to allow novel motor strategies.

Effects of exercise and fetal spinal cord implants on the H-reflex in chronically spinalized adult rats

This study investigated the modulation of hindlimb reflex excitability after transection of the spinal cord in adult rats. After transection, the H-reflex exhibited decreased depression at high stimulation frequencies compared to intact animals. Groups of animals which received a spinal cord transection followed by either an exercise regimen for the hindlimbs or a fetal spinal cord implant, showed high stimulation frequency depression similar to controls. This suggests that each of these palliative strategies helped to "normalize' the excitability of specific spinal reflexes.

Synaptic evoked potentials from regenerating dorsal root axons within fetal spinal cord tissue transplants

Previously injured dorsal roots were electrically stimulated to determine if regenerating sensory axons can form physiologically active synaptic contacts with neurons within fetal spinal cord tissue transplants. Dorsal rootlets, sectioned at their spinal cord entry zone, were apposed to intraspinal transplants of fetal spinal cord tissue grafted along each side of a nerve growth factor treated nitrocellulose implant. Two to six months later, the rootlets were transected between the spinal cord and their respective ganglia and electrically stimulated. Evoked potentials were recorded from the dorsal surface of the transplant, but were absent from adjacent ipsilateral and contralateral spinal cord regions. A glass micropipette was advanced through the transplant and used to record intramedullary field potentials evoked by dorsal root stimulation. Maximal negative potentials occurred 400-700 micron below the dorsal surface of the transplant, shifting to positive potentials deeper into the transplant. Additionally, both spontaneous and electrically evoked single neuronal action potentials were observed along the microelectrode track. Evoked potentials were abolished following transaction of the rootlets between the stimulation site and the transplant. Immunocytochemical evidence of the production of fos protein following electrical stimulation of the regenerated dorsal rootlets was demonstrated within transplant neurons and some ventrally located host neurons, providing an anatomical correlate to the electrophysiological recordings of synaptic activation. These results provide evidence of the structural and functional integration of regenerated sensory axons with both transplant and host neurons.

In vivo and in vitro evidence supporting a role for the inflammatory cytokine interleukin-1 as a driving force in Alzheimer pathogenesis

Interleukin-1 (IL-1), an inflammatory cytokine overexpressed in the neuritic plaques of Alzheimer's disease, activates astrocytes and enhances production and processing of beta-amyloid precursor protein (beta-APP). Activated astrocytes, overexpressing S100 beta, are a prominent feature of these neuritic plaques, and the neurite growth-promoting properties of S100 beta have been implicated in the formation of dystrophic neurites overexpressing beta-APP in neuritic plaques. These facts collectively suggest that elevated levels of the inflammatory cytokine IL-1 drive S100 beta and beta-APP overexpression and dystrophic neurite formation in Alzheimer's disease. To more directly assess this driver potential for IL-1, we analyzed IL-1 induction of S100 beta expression in vivo and in vitro, and of beta-APP expression in vivo. Synthetic IL-1 beta was injected into the right cerebral hemispheres of 13 rats. Nine additional rats were injected with phosphate-buffered saline, and seven rats served as uninjected controls. The number of astrocytes expressing detectable levels of S100 beta in tissue sections from IL-1-injected brains was 1.5 fold that of either control group (p < 0.01), while tissue S100 beta levels were approximately threefold that of controls (p < 0.05). The tissue levels of two beta-APP isoforms (approximately 130 and 135 kDa) were also significantly elevated in IL-1-injected brains (p < 0.05). C6 glioma cells, treated in vitro for 24 h with either IL-1 beta or IL-1 alpha, showed significant increases in both S100 beta and S100 beta mRNA levels. These results provide evidence that IL-1 upregulates both S100 beta and beta-APP expression, in vivo and vitro, and support the idea that overexpression of IL-1 in Alzheimer's disease drives astrocytic overexpression of S100 beta, favoring the growth of dystrophic neurites necessary for evolution of diffuse amyloid deposits into neuritic beta-amyloid plaques.

The pedunculopontine nucleus--auditory input, arousal and pathophysiology

This review describes the role of the pedunculopontine nucleus (PPN) in various functions, including sleep-wake mechanisms, arousal, locomotion and in several pathological conditions. Special emphasis is placed on the auditory input to the PPN and the possible role of this nucleus in the manifestation of the P1 middle latency auditory evoked response. The importance of these considerations is evident because the PPN is part of the cholinergic arm of the reticular activating system. As such, the auditory input to this region may modulate the level of arousal of the CNS and, consequently, abnormalities in the processing of this input can be expected to have serious consequences on the level of excitability of the CNS. The involvement of the PPN in such disorders as schizophrenia, anxiety disorder and narcolepsy is discussed.

Mesopontine neurons in schizophrenia

Findings reported here show that there is a significant increase in the number of neurons in the pedunculopontine nucleus in most schizophrenic patients compared to age-matched controls. Nicotinamide adenine dinucleotide phosphate diaphorase histochemistry was used to label putative cholinergic neurons in the pedunculopontine nucleus and laterodorsal tegmental nucleus, while noradrenergic locus coeruleus neurons were labeled immunocytochemically using an antibody to tryosine hydroxylase. Cell counts of these neuronal groups were carried out using a Biographics image analysis system. We found significantly increased cell numbers in the pedunculopontine nucleus of schizophrenic patients compared to controls. The number of laterodorsal tegmental nucleus neurons was increased but this was not statistically significant. However, the total cell counts for pedunculopontine and laterodorsal tegmental nuclei were significantly higher in schizophrenic subjects. The number of locus coeruleus noradrenergic neurons was similar in both groups. These results implicate the brainstem reticular formation as a pathophysiological site in at least some patients with schizophrenia. In addition, these findings suggest a developmental etiology for the disease and account for some, but not all, of the symptoms of schizophrenia, including sensory gating abnormalities, sleep-wake disturbances and, perhaps, hallucinations. Overdriving of thalamic and substantia nigra function by cholinergic afferents from the midbrain may account for some of the symptoms seen in schizophrenia. These findings suggest that, at least in some schizophrenic patients, there is an increased number of neurons in the cholinergic arm of the reticular activating system. This may explain some of the symptoms of schizophrenia and points to a prenatal disturbance as one of the possible causes of the disease.

A middle-latency auditory-evoked potential in the rat

Previous studies have established the presence of a middle-latency auditory-evoked potential that is characterized by a) sleep-state dependence, b) low following frequency (i.e., rapid habituation to repetitive stimulation), and c) blockade by the cholinergic antagonist, scopolamine. A vertex-recorded evoked potential having these characteristics was described in humans at a 50-80 ms latency (termed the P1 or.P50 potential) and in the cat at a 20-25 ms latency (termed wave A). These studies were undertaken to determine if a click stimulus-evoked potential having the same characteristics was present in the intact rat. Vertex and auditory cortex recordings in intact rats studied in a sound-attenuating chamber and exposed to free-field click stimuli showed a) the presence of a vertex recorded potential at a 11-15 ms latency, termed P13, and of an auditory cortex recorded potential at a 7-11 ms latency, termed Pa; b) the P13 was present during waking and paradoxical sleep but absent in slow-wave sleep, while Pa was present in all sleep-wake states; c) the P13 habituated markedly at stimulation rates above 1 Hz while Pa did not; and d) the P13 was blocked by low doses of scopolamine while Pa was not. These studies demonstrate the presence of a P1-like potential in the rat at a 13 +/- 2 ms latency.

Auditory input to the pedunculopontine nucleus: II. Unit responses

The pedunculopontine nucleus (PPN) has been implicated in sleep-wake control, arousal responses, and motor functions. The PPN also has been implicated in the generation of the P1 middle-latency auditory-evoked potential. The present study was undertaken to determine the nature of the responsiveness of single neurons in and around the PPN following auditory stimulation. Somatosensory responsiveness also was tested in some cells. These results demonstrate a) the presence of a significant proportion of PPN neurons that respond to auditory click stimuli; b) two populations of neurons showing either low threshold/short latency/low habituation or high threshold/longer latency/high habituation; c) the responses of longer latency neurons precede the onset and peak of depth- and vertex-recorded middle-latency auditory-evoked potentials; d) thresholds of longer latency neurons similar to the threshold for wave A in the intact cat, the P13 potential in the intact rat, or the startle reflex; and e) convergent somatosensory and auditory responses at a similar latency in a number of PPN neurons. These findings suggest that neurons in and around the PPN may participate in auditory and somatosensory information processing related to arousal, and may contribute to the manifestation of the P1 auditory middle-latency evoked potential.

Auditory input to the pedunculopontine nucleus: I. Evoked potentials

The pedunculopontine nucleus (PPN) has been implicated in sleep-wake control, arousal responses, and motor functions. The PPN also has been implicated in the generation of the P1 middle-latency auditory-evoked potential. The present study was undertaken to determine the topographical distribution, threshold, and response properties of depth-recorded potentials following auditory click stimulation. Experiments were conducted in both decerebrate cat and rat, with a view towards determining the presence of P1-like middle-latency auditory-evoked potentials in the midbrain of both species. These results demonstrate a) the presence in and around the PPN of a P1-like potential in the decerebrate rat similar to that described in the accompanying article as the P13 in the intact rat; b) the presence in and around the PPN of a P1-like potential in the decerebrate cat similar to that previously described by others as wave A in the intact cat; c) although thresholds for these potentials were similar to those of intact preparations, following frequencies were higher in the decerebrate preparations, i.e., responsiveness to repetitive stimulation was higher; and d) depth-recorded somatosensory-evoked potentials also were studied in the cat and found to show an evoked potential at a similar latency as middle-latency auditory depth-recorded potentials. These findings suggest that click stimulus-evoked, depth-recorded potentials are present in and around the PPN in the decerebrate rat and cat, i.e., in the absence of cortex, at a similar latency as in intact preparations.

Electrical activation and inhibition of respiration in vitro

The present studies employed the neonatal rat rib-attached brain stem-spinal cord preparation to examine the effects of electrical stimulation of the medulla and the pons on respiratory-like activity. The investigation focused on determining whether electrical stimulation of the medulla can be used to modulate respiratory-like activity, whether electrical stimulation of the pons can inhibit respiratory-like activity, and how the preparation responds when both the medulla and the pons are stimulated simultaneously. The results suggest that: (1) stimulation of the ventromedial part of the medulla entrains the onset and the frequency of respiratory-like electromyographic (EMG) bursting most effectively and drives the respiratory rate as high as 0.4 Hz; (2) both ventromedial and ventrolateral pontine stimulation inhibited respiratory-like EMG bursting, but only ventrolateral pontine stimulation was followed by post-stimulation inhibition; (3) when the medulla and the pons were stimulated simultaneously, pontine stimulation-induced inhibition outweighed medullary stimulation-induced activation and resulted in a temporary cessation of respiratory-like EMG bursting.

The P1: insights into attention and arousal

The authors provide evidence that four mesencephalic nuclei, two of which are cholinergic and two of which are catecholaminergic, serve as oscillators capable of modulating a number of interrelated rhythmic functions. These include sleep-wake cycles, locomotion, blood pressure, respiratory rate, heart rate, mastication, micturition, and saccadic eye movements. The P1 auditory evoked potential is generated by ascending cholinergic projections from one of these nuclei, the pedunculopontine nucleus, and thus serves as a clinical tool to monitor the integrity of this system.

Respiration in vitro: I. Spontaneous activity

The present report describes respiratory-like activity recorded from intercostal muscles in the neonatal rat in vitro brain stem-spinal cord, rib-attached preparation. In this preparation from 1- to 4-day-old rats, spontaneous rhythmic and synchronized upward movements of the rib cage coincided with the recorded muscle activity. Spontaneous respiratory-like activity showed a frequency in the range of 0.05-0.2 Hz, with single-, double-, and mixed-burst patterns. Spontaneous activity declined over time, but increased in frequency as temperature increased. Multilevel recordings showed a cephalocaudal order of bursting of intercostal muscles. Brain stem transections at the prepontine level did not affect spontaneous frequency, whereas premedullary transections resulted in an increase in spontaneous respiratory frequency. High spinal transections eliminated spontaneous respiratory-like activity. These results suggest that there is a well-organized pontomedullary pattern generator for respiratory-like activity in this preparation, which can be modulated by temperature. The characteristics of these electromyographic (EMG) recordings allow comparison with previous in vitro studies of respiratory-like activity using nerve activity and in vivo studies using EMG activity. These results provide basic information on the spontaneous activity of this preparation as a prelude to the study of the effects of electrical stimulation of the spinal cord to induce respiratory-like activity, as described in the companion article.

Spinal cord stimulation-induced locomotion in the adult cat

Epidural and subdural stimulation of the dorsal surface of the spinal cord was found to elicit locomotion in the decerebrate cat in the active and fictive locomotion preparations. Stimulation of the cervical enlargement induced stepping in all four limbs, while stimulation of the lumbosacral enlargement induced hindlimb stepping. Lumbosacral enlargement stimulation induced hindlimb locomotion starting four hours following an acute midthoracic spinal cord transection. The preservation of the overall locomotor pattern and relationships between muscle groups, and of coordination between hindlimbs following transection, suggests that lumbar enlargement stimulation may be activating an intrinsically organized system. These findings suggest a method which may be applied clinically for the induction of limb alternation following epidural stimulation of the spinal cord.

Respiration in vitro: II. Electrical stimulation

The present report describes electrical-stimulation-induced activity recorded from intercostal muscles in the neonatal rat rib-attached, in vitro brain stem-spinal cord preparation. The muscle bursts induced by electrical stimulation included a short-latency twitch contraction and a long-latency modulated contraction similar to that observed during spontaneous respiratory-like activity. Multilevel recordings showed a cephalocaudal order of recruitment of intercostal muscles similar to that observed during spontaneous activity. The optimal parameters of stimulation were 2-msec pulses delivered at 0.1-0.2 Hz. Trains of pulses also were effective. These movements could be induced following stimulation of various sites within each segment of the spinal cord, with the lowest threshold sites located in the ventrolateral funiculus and intermediate gray. Stimulation of every cervical segment was effective in inducing respiratory-like activity, with the lowest-threshold segments being C1, C2, and C5. These results suggest that low-frequency, long-duration pulses applied directly to the spinal cord can induce respiratory-like activity similar to that observed during spontaneous activity in the neonatal rat, rib-attached in vitro brain stem-spinal cord preparation. The ability to elicit a coordinated respiratory pattern even after a high spinal transection suggests that such stimulation may be effective in inducing respiratory-like activity in the absence of descending brain stem connections.