Semaphorin 3A is a chemoattractant for cortical apical dendrites

The apical dendrites of pyramidal neurons integrate inputs from various cortical layers and are central to information processing. Here we show that the growth of apical dendrites towards the pial surface is regulated by a diffusible chemoattractant present at high levels near the marginal zone. A major component of this signal is semaphorin 3A (Sema3A), which was previously characterized as a chemorepellant for cortical axons. Soluble guanylate cyclase is asymmetrically localized to the developing apical dendrite, and is required for the chemoattractive effect of Sema3A. Thus the asymmetric localization of soluble guanylate cyclase confers distinct Sema3A responses to axons and dendrites. These observations reveal a mechanism by which a single chemotropic signal can pattern both axons and dendrites during development.

Positron emission tomographic analysis of cerebral structures activated specifically by repetitive noxious heat stimuli

1. To identify the forebrain and brain stem structures that are active during the perception of acute heat pain in humans, we performed H2 15O positron emission tomographic (PET) analyses of cerebral blood flow (CBF) on nine normal volunteers while they received repetitive noxious (50 degrees C) and innocuous (40 degrees C) 5 s heat pulses to the forearm (average resting temperature of 31.8 degrees C). Each subject rated the subjective intensity of each stimulation series according to a magnitude estimation procedure in which 0 = no heat sensation, 7 = barely painful, and 10 = barely tolerable. 2. Three scans were performed at each temperature. Mean CBF images were created for each experimental condition and oriented onto standardized stereotaxic coordinates. Subtraction images were created between conditions for each subject and averaged across subjects. Volumes of interest (VOI) were chosen, based on a priori hypotheses and the results of previously published PET studies. In addition, a separate statistical summation analysis of individual voxels was performed. Statistical thresholds were established with corrections for multiple comparisons. 3. Significant CBF increases to 50 degrees C stimuli were found in the contralateral thalamus, cingulate cortex, S2 and S1 cortex, and insula. The ipsilateral S2 cortex and thalamus, and the medial dorsal midbrain and cerebellar vermis also showed significant CBF increases. All subjects rated the 50 degrees C stimuli as painful (average subjective rating = 8.9 +/- 0.9 SD) and the 40 degrees C stimuli as warm, but not painful (average subjective rating = 2.1 +/- 1.0).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of human cerebral activation pattern during cutaneous warmth, heat pain, and deep cold pain

1. We wished to determine whether there are differences in the spatial pattern and intensity of synaptic activity within the conscious human forebrain when different forms and intensities of innocuous and noxious thermal stimuli are experienced. Accordingly, positron emission tomography (PET) with intravenous injection of H2(15)O was used to detect increases in regional cerebral blood flow (rCBF) in normal humans as they discriminated differences in the intensity of noxious and innocuous thermal stimulation applied to the nondominant (left) arm. After stereotactic registration, subtraction images were formed from each subject by subtracting counts of emissions obtained during lower-intensity stimulation from those obtained during stimulation at higher intensities. A statistical summation analysis (Z score) of individual voxels was performed. In addition, volumes of interest were chosen on the basis of a priori hypotheses and the results of previously published PET studies. In both types of analysis, statistical thresholds were established with corrections for multiple comparisons. 2. Twenty-seven subjects were divided into three groups of nine subjects each for the three phases of this investigation. For studies in which repetitive contact heat stimuli were used, each subject was instructed in magnitude estimation on the basis of a scale for which 0 indicated "no heat sensation," 7 "just barely painful," and 10 "just barely tolerable." For the study of pain elicited by immersion of the hand in cold water, subjects were instructed to use a scale in which 0 represented "no pain" and 10 represented just barely tolerable pain. 3. In the warm-discrimination study, two intensities of innocuous heat (36 and 43 degrees C) were applied with a thermode as repetitive 5-s contacts to the volar forearm for a total of approximately 100 s, 8 stimuli before and 12 during each scan. Each temperature was applied on alternate scans for a total of four scans per subject. Neither stimulus was rated painful. All subjects discriminated the 43 degrees C stimulus (average rating 5.90 +/- 1.43, mean +/- SD) from the 36 degrees C stimulus (1.96 +/- 1.08, mean +/- SD; t = 13.19, P < 0.0001). Significant increases in rCBF to the 43 degrees C stimuli were found in the contralateral ventral posterior thalamus, lenticular nucleus, medial prefrontal cortex (Brodmann's areas 10 and 32), and cerebellar vermis. 4. The procedure for discriminating between noxious and innocuous heat stimuli was identical to that used for warm discrimination except that the stimulation temperatures were 40 and 50 degrees C. All subjects rated the 50 degrees C stimuli as painful (average rating 8.9 +/- 0.9, mean +/- SD) and the 40 degrees C stimuli as warm, but not painful (2.1 +/- 1.0). Significant rCBF increases to 50 degrees C stimuli were found contralaterally in the thalamus, anterior cingulate cortex, premotor cortex, and secondary somatosensory (S2) and posterior insular cortices. Significant activity also appeared within the region of the contralateral anterior insula and lenticular nucleus. The ipsilateral premotor cortex and thalamus, and the medial dorsal midbrain and cerebellar vermis, also showed significant rCBF increases. Cerebral blood flow (CBF) increases just below the threshold for statistical significance were seen in the contralateral sensorimotor cortex [primary motor cortex (M1)/primary somatosensory cortex (S1)]. 5. For discrimination between tonic innocuous cold and tonic cold pain, the left hand was immersed to the wrist, throughout each of six scans, in water kept at an average temperature of either 20.5 +/- 1.15 degrees C (mean +/- SD) or 6.02 +/- 1.18 degrees C (mean +/- SD) on alternate scans. All subjects rated the intensity of the stimuli on a scale in which 0 indicated no pain and 10 represented barely tolerable pain. Subjects rated the 20 degrees C water immersion as painless (average rating 0.18 +/- 0.48, mean +/- SD), but gave ratings indicating i

Double-strand signal sequence breaks in V(D)J recombination are blunt, 5'-phosphorylated, RAG-dependent, and cell cycle regulated

Immunoglobulin and T-cell receptor genes are assembled during lymphocyte development by a novel, highly regulated series of gene rearrangement reactions known as V(D)J recombination. All rearranging loci are flanked by conserved heptamer-nonamer recombination signal sequences. Gene rearrangement results in the imprecise fusion of coding sequences and the precise fusion of signal sequences. DNA molecules with double-stranded breaks near signal sequences have been detected in cells undergoing V(D)J recombination of the TCR delta locus. We have devised a ligation-mediated PCR assay that detects broken-ended molecules in purified genomic DNA. Using this assay we found that DNA breaks occurring precisely at the signal sequence-coding sequence junction are a general feature of V(D)J recombination, appearing in association with each type of rearranging immunoglobulin gene segment. We show that a significant fraction of these broken ends are blunt and 5'-phosphorylated. In addition, detection of these broken-ended signal sequences is dependent on the activity of RAG-1 and RAG-2, and is restricted to the G0/G1 phase of the cell cycle. The pattern of broken-ended molecules detected in cells at various stages of development reflects the activity of the V(D)J recombinase at different loci during B- and T-cell development.

Gender differences in pain perception and patterns of cerebral activation during noxious heat stimulation in humans

The purpose of the present study was to determine whether gender differences exist in the forebrain cerebral activation patterns of the brain during pain perception. Accordingly, positron emission tomography (PET) with intravenous injection of H2(15)O was used to detect increases in regional cerebral blood flow (rCBF) in normal right-handed male and female subjects as they discriminated differences in the intensity of innocuous and noxious heat stimuli applied to the left forearm. Each subject was instructed in magnitude estimation based on a scale for which 0 indicated 'no heat sensation'; 7, 'just barely painful' and 10, 'just barely tolerable'. Thermal stimuli were 40 degrees C or 50 degrees C heat, applied with a thermode as repetitive 5-s contacts to the volar forearm. Both male and female subjects rated the 40 degrees C stimuli as warm but not painful and the 50 degrees C stimuli as painful but females rated the 50 degrees C stimuli as significantly more intense than did the males (P=0.0052). Both genders showed a bilateral activation of premotor cortex in addition to the activation of a number of contralateral structures, including the posterior insula, anterior cingulate cortex and the cerebellar vermis, during heat pain. However, females had significantly greater activation of the contralateral prefrontal cortex when compared to the males by direct image subtraction. Volume of interest comparison (t-statistic) also suggested greater activation of the contralateral insula and thalamus in the females (P < 0.05). These pain-related differences in brain activation may be attributed to gender, perceived pain intensity, or to both factors.

Early painful diabetic neuropathy is associated with differential changes in tetrodotoxin-sensitive and -resistant sodium channels in dorsal root ganglion neurons in the rat

Diabetic neuropathy is a common form of peripheral neuropathy, yet the mechanisms responsible for pain in this disease are poorly understood. Alterations in the expression and function of voltage-gated tetrodotoxin-resistant (TTX-R) sodium channels have been implicated in animal models of neuropathic pain, including models of diabetic neuropathy. We investigated the expression and function of TTX-sensitive (TTX-S) and TTX-R sodium channels in dorsal root ganglion (DRG) neurons and the responses to thermal hyperalgesia and mechanical allodynia in streptozotocin-treated rats between 4-8 weeks after onset of diabetes. Diabetic rats demonstrated a significant reduction in the threshold for escape from innocuous mechanical pressure (allodynia) and a reduction in the latency to withdrawal from a noxious thermal stimulus (hyperalgesia). Both TTX-S and TTX-R sodium currents increased significantly in small DRG neurons isolated from diabetic rats. The voltage-dependent activation and steady-state inactivation curves for these currents were shifted negatively. TTX-S currents induced by fast or slow voltage ramps increased markedly in neurons from diabetic rats. Immunoblots and immunofluorescence staining demonstrated significant increases in the expression of Na(v)1.3 (TTX-S) and Na(v) 1.7 (TTX-S) and decreases in the expression of Na(v) 1.6 (TTX-S) and Na(v)1.8 (TTX-R) in diabetic rats. The level of serine/threonine phosphorylation of Na(v) 1.6 and In Na(v)1.8 increased in response to diabetes. addition, increased tyrosine phosphorylation of Na(v)1.6 and Na(v)1.7 was observed in DRGs from diabetic rats. These results suggest that both TTX-S and TTX-R sodium channels play important roles and that differential phosphorylation of sodium channels involving both serine/threonine and tyrosine sites contributes to painful diabetic neuropathy.

A unique representation of heat allodynia in the human brain

Skin inflammation causes innocuous heat to become painful. This condition, called heat allodynia, is a common feature of pathological pain states. Here, we show that heat allodynia is functionally and neuroanatomically distinct from normal heat pain. We subtracted positron emission tomography scans obtained during painful heating of normal skin from scans during equally intense but normally innocuous heating of capsaicin-treated skin. This comparison reveals the specific activation of a medial thalamic pathway to the frontal lobe during heat allodynia. The results suggest that different central pathways mediate the intensity and certain qualitative aspects of pain. In making this differentiation, the brain recognizes unique physiological features of different painful conditions, thus permitting adaptive responses to different pain states.

Cerebral processing of acute skin and muscle pain in humans

The human cerebral processing of noxious input from skin and muscle was compared with the use of positron emission tomography with intravenous H2(15)O to detect changes in regional cerebral blood flow (rCBF) as an indicator of neuronal activity. During each of eight scans, 11 normal subjects rated the intensity of stimuli delivered to the nondominant (left) forearm on a scale ranging from 0 to 100 with 70 as pain threshold. Cutaneous pain was produced with a high-energy CO2 laser stimulator. Muscle pain was elicited with high-intensity intramuscular electrical stimulation. The mean ratings of perceived intensity for innocuous and noxious stimulation were 32.6 +/- 4.5 (SE) and 78.4 +/- 1.7 for cutaneous stimulation and 15.4 +/- 4.2 and 73.5 +/- 1.4 for intramuscular stimulation. The pain intensity ratings and the differences between noxious and innocuous ratings were similar for cutaneous and intramuscular stimuli (P > 0.05). After stereotactic registration, statistical pixel-by-pixel summation (Z score) and volumes-of-interest (VOI) analyses of subtraction images were performed. Significant increases in rCBF to both noxious cutaneous and intramuscular stimulation were found in the contralateral secondary somatosensory cortex (SII) and inferior parietal lobule [Brodmann area (BA) 40]. Comparable levels of rCBF increase were found in the contralateral anterior insular cortex, thalamus, and ipsilateral cerebellum. Noxious cutaneous stimulation caused significant activation in the contralateral lateral prefrontal cortex (BA 10/46) and ipsilateral premotor cortex (BA 4/6). Noxious intramuscular stimulation evoked rCBF increases in the contralateral anterior cingulate cortex (BA 24) and subsignificant responses in the contralateral primary sensorimotor cortex (MI/SI) and lenticular nucleus. These activated cerebral structures may represent those recruited early in nociceptive processing because both forms of stimuli were near pain threshold. Correlation analyses showed a negative relationship between changes in rCBF for thalamus and MI/SI for cutaneous stimulation, and positive relationships between thalamus and anterior insula for both stimulus modalities. Direct statistical comparisons between innocuous cutaneous and intramuscular stimulation with the use of Z scores and VOI analyses showed no reliable differences between these two forms of noxious stimulation, indicating a substantial overlap in brain activation pattern. The comparison of noxious cutaneous and intramuscular stimulation indicated more activation in the premotor cortex, SII, and prefrontal cortex with cutaneous stimulation, but these differences did not reach statistical significance. The similar cerebral activation patterns suggest that the perceived differences between acute skin and muscle pain are mediated by differences in the intensity and temporospatial pattern of neuronal activity within similar sets of forebrain structures.

Variability of laser-evoked potentials: attention, arousal and lateralized differences

We recorded laser-evoked potentials (LEPs) from 20 normal subjects by stimulating the skin with pulses from an infrared CO2 laser. The conduction velocity of the peripheral afferent fibers mediating the LEPs averaged 14.9 m/sec. The amplitude of the LEP components correlated significantly with perceived stimulus intensity. During repetitive constant intensity stimulation, the peak-to-peak LEP amplitude decreased 38% during a distraction task and 42% during drowsiness and was absent during stage 2 sleep, indicating a modulation of responsiveness to laser stimulation during distraction and decreased states of arousal. Normative data revealed considerable intersubject variability in LEP latencies and amplitudes. Analysis of intrasubject lateralized (side-to-side) differences revealed that the relative peak-to-peak amplitude was less variable than that of the N or P components. For clinical applications using 3 S.D.s to define the normal range, a lateral interpeak amplitude difference greater than 28% would suggest focal or lateralized sensory abnormality in an individual patient. Vigilance and attentiveness to the stimuli should be monitored during the acquisition of LEPs.

Bottom-up assembly of large-area nanowire resonator arrays

Directed-assembly of nanowire-based devices will enable the development of integrated circuits with new functions that extend well beyond mainstream digital logic. For example, nanoelectromechanical resonators are very attractive for chip-based sensor arrays because of their potential for ultrasensitive mass detection. In this letter, we introduce a new bottom-up assembly method to fabricate large-area nanoelectromechanical arrays each having over 2,000 single-nanowire resonators. The nanowires are synthesized and chemically functionalized before they are integrated onto a silicon chip at predetermined locations. Peptide nucleic acid probe molecules attached to the nanowires before assembly maintain their binding selectivity and recognize complementary oligonucleotide targets once the resonator array is assembled. The two types of cantilevered resonators we integrated here using silicon and rhodium nanowires had Q-factors of approximately 4,500 and approximately 1,150, respectively, in vacuum. Taken together, these results show that bottom-up nanowire assembly can offer a practical alternative to top-down fabrication for sensitive chip-based detection.

Nanowire sensors for multiplexed detection of biomolecules

Nanowire-based detection strategies provide promising new routes to bioanalysis that could one day revolutionize the healthcare industry. This review covers recent developments in nanowire sensors for multiplexed detection of biomolecules such as nucleic acids and proteins. We focus on encoded nanowire suspension arrays and semiconductor nanowire-based field-effect transistors. Nanowire assembly and integration with microchip technology is emphasized as a key step toward the ultimate goal of multiplexed detection at the point of care using portable, low power, electronic biosensor chips.

Selective opiate modulation of nociceptive processing in the human brain

Fentanyl, a mu-opioid receptor agonist, produces analgesia while leaving vibrotactile sensation intact. We used positron emission tomography (PET) to study the mechanisms mediating this specific effect in healthy, right-handed human males (ages 18-28 yr). Subjects received either painful cold (n = 11) or painless vibratory (n = 9) stimulation before and after the intravenous injection of fentanyl (1.5 microgram/kg) or placebo (saline). Compared with cool water (29 degrees C), immersion of the hand in ice water (1 degrees C) is painful and produces highly significant increases in regional cerebral blood flow (rCBF) within the contralateral second somatosensory (S2) and insular cortex, bilaterally in the thalamus and cerebellum, and medially in the cerebellar vermis. Responses just below the statistical threshold (3.5 < Z < 4.0) are seen in the contralateral anterior cingulate, ipsilateral insular cortex, and dorsal medial midbrain. The contralateral primary sensory cortex (S1) shows a trend of activation. Except for slight changes in intensity, this pattern is unchanged following a saline placebo injection. Fentanyl reduces the average visual analogue scale ratings of perceived pain intensity (47%) and unpleasantness (50%), reduces pain-related cardioacceleration, and has positive hedonic effects. After fentanyl, but not placebo, all cortical and subcortical responses to noxious cold are greatly reduced. Subtraction analysis [(innocuous water + fentanyl) - (innocuous water + no injection)] shows that fentanyl alone increases rCBF in the anterior cingulate cortex, particularly in the perigenual region. Vibration (compared with mock vibration) evokes highly significant rCBF responses in the contralateral S1 cortex in the baseline (no injection) and placebo conditions; borderline responses (3.5 < Z < 4. 0) are detected also in the contralateral thalamus. Fentanyl has no effect on the perceived intensity or unpleasantness of vibratory stimulation, which continues to activate contralateral S1. Fentanyl alone [(mock vibration + fentanyl) - (mock vibration + no injection)] again produces highly significant activation of the perigenual and mid-anterior cingulate cortex. A specific comparison of volumes of interest, developed from activation peaks in the baseline condition (no injection), shows that fentanyl strongly attenuates both the contralateral thalamic and S1 cortical responses to noxious cold stimulation (P < 0.048 and 0.007, respectively) but fails to affect significantly these responses to vibrotactile stimulation (P > 0.26 and 0.91, respectively). In addition, fentanyl, compared with placebo, produces a unique activation of the mid-anterior cingulate cortex during fentanyl analgesia, suggesting that this region of the cingulate cortex participates actively in mediating opioid analgesia. The results are consistent with a selective, fentanyl-mediated suppression of nociceptive spinothalamic transmission to the forebrain. This effect could be implemented directly at the spinal level, indirectly through cingulate corticofugal pathways, or by a combination of both mechanisms.

Programmed assembly of DNA-coated nanowire devices

Combining biomolecular function with integrated circuit technology could usher in a new era of biologically enabled electronics. A key challenge has been coupling different molecular functions to specific chip locations for communication with the circuit. We used spatially confined electric fields to assemble different populations of DNA-coated nanowires to desired positions with an accuracy that enabled postassembly fabrication of contacts to each individual nanowire, with high yield and without loss of DNA function. This combination of off-chip synthesis and biofunctionalization with high-density, heterogeneous assembly and integration at the individual nanowire level points to new ways of incorporating biological functionality with silicon electronics.

Temporal and spatial dynamics of human forebrain activity during heat pain: analysis by positron emission tomography

To learn about the sequence of brain activation patterns during heat pain, we acquired positron emission tomographic (PET) brain scans at different times during repetitive heat stimulation (40 or 50 degrees C; 5-s contact) of each subject's left forearm. Early scans began at the onset of 60 s of stimulation; late scans began after 40 s of stimulation, which continued throughout the 60-s scan period (total stimulus duration 100 s). Each subject (14 normal, right-handed subjects; 10 male, 4 female; ages 18-42) used a visual analog scale to rate the perceived stimulus intensity (0 = no heat, 7 = pain threshold, 10 = barely tolerable pain) after each scan. The 40 degrees C stimulation received an average intensity rating of 2.19 +/- 1.22 (mean +/- SD) and the 50 degrees C an average rating of 8.93 +/- 1.33. During the scan sessions, subjects did not report a difference between early and late scans. To examine the effect of the duration of stimulation specifically, 8 of these subjects rated the perceived intensity of each of 20 sequential 5-s duration contact heat stimuli (40 or 50 degrees C; 100 s of stimulation). We used a graphical method to detect changes in perceived unpleasantness. There was no difference in perceived intensity or unpleasantness during the 40 degrees C stimulation. However, during 50 degrees C stimulation, perceived unpleasantness increased and subjects perceived the last five, but not the second five, stimuli as more intense than the first five stimuli. These psychophysical changes could be mediated by brain structures with increasing activity from early to late PET scans or that are active only during late scans. These structures include the contralateral M1/S1 cortex, bilateral S2 and mid-insular cortex, contralateral VP thalamus, medial ipsilateral thalamus, and the vermis and paravermis of the cerebellum. Structures that are equally active throughout stimulation (contralateral mid-anterior cingulate and premotor cortex) are less likely to mediate these psychophysical changes. Some cortical, but not subcortical, structures showed significant or borderline activation only during the early scans (ipsilateral premotor cortex, contralateral perigenual anterior cingulate, lateral prefrontal, and anterior insular cortex); they may mediate pain-related attentive or anticipatory functions. Overall, the results reveal that 1) the pattern of brain activation and the perception of heat pain both change during repetitive noxious heat stimulation, 2) cortical activity can be detected before subcortical responses appear, and 3) timing the stimulation with respect to the scan period can, together with psychophysical measurements, identify brain structures that are likely to participate in the perception of pain.

Hearing Rehabilitation Using the BAHA Bone-Anchored Hearing Aid: Results in 40 Patients

OBJECTIVE

This study evaluates the U.S. experience with the first 40 patients who have undergone audiologic rehabilitation using the BAHA bone-anchored hearing aid.

STUDY DESIGN

This study is a multicenter, nonblinded, retrospective case series.

SETTING

Twelve tertiary referral medical centers in the United States.

PATIENTS

Eligibility for BAHA implantation included patients with a hearing loss and an inability to tolerate a conventional hearing aid, with bone-conduction pure tone average levels at 60 dB or less at 0.5, 1, 2, and 4 kHz.

INTERVENTION

Patients who met audiologic and clinical criteria were implanted with the Bone-Anchored Hearing Aid (BAHA, Entific Corp., Gothenburg, Sweden).

MAIN OUTCOME MEASURES

Preoperative air- and bone-conduction thresholds and air-bone gap; postoperative BAHA-aided thresholds; hearing improvement as a result of implantation; implantation complications; and patient satisfaction.

RESULTS

The most common indications for implantation included chronic otitis media or draining ears (18 patients) and external auditory canal stenosis or aural atresia (7 patients). Overall, each patient had an average improvement of 32+/-19 dB with the use of the BAHA. Closure of the air-bone gap to within 10 dB of the preoperative bone-conduction thresholds (postoperative BAHA-aided threshold vs. preoperative bone-conduction threshold) occurred in 32 patients (80%), whereas closure to within 5 dB occurred in 24 patients (60%). Twelve patients (30%) demonstrated 'overclosure' of the preoperative bone-conduction threshold of the better hearing ear. Complications were limited to local infection and inflammation at the implant site in three patients, and failure to osseointegrate in one patient. Patient response to the implant was uniformly satisfactory. Only one patient reported dissatisfaction with the device.

CONCLUSIONS

The BAHA bone-anchored hearing aid provides a reliable and predictable adjunct for auditory rehabilitation in appropriately selected patients, offering a means of dramatically improving hearing thresholds in patients with conductive or mixed hearing loss who are otherwise unable to benefit from traditional hearing aids.

Sequential specification of neurons and glia by developmentally regulated extracellular factors

Cortical progenitor cells give rise to neurons during embryonic development and to glia after birth. While lineage studies indicate that multipotent progenitor cells are capable of generating both neurons and glia, the role of extracellular signals in regulating the sequential differentiation of these cells is poorly understood. To investigate how factors in the developing cortex might influence cell fate, we developed a cortical slice overlay assay in which cortical progenitor cells are cultured over cortical slices from different developmental stages. We find that embryonic cortical progenitors cultured over embryonic cortical slices differentiate into neurons and those cultured over postnatal cortical slices differentiate into glia, suggesting that the fate of embryonic progenitors can be influenced by developmentally regulated signals. In contrast, postnatal progenitor cells differentiate into glial cells when cultured over either embryonic or postnatal cortical slices. Clonal analysis indicates that the postnatal cortex produces a diffusible factor that induces progenitor cells to adopt glial fates at the expense of neuronal fates. The effects of the postnatal cortical signals on glial cell differentiation are mimicked by FGF2 and CNTF, which induce glial fate specification and terminal glial differentiation respectively. These observations indicate that cell fate specification and terminal differentiation can be independently regulated and suggest that the sequential generation of neurons and glia in the cortex is regulated by a developmental increase in gliogenic signals.

Defining the difference: What Makes Biologics Unique

Biologics differ from chemically derived drugs in ways that affect their cost, production, administration, and clinical efficacy. Here's a look at the most important differences and their implications.

Medial frontal cortex lesions selectively attenuate the hot plate response: possible nocifensive apraxia in the rat

Lesions in the cingulate cortex have attenuated pain-related behavior in humans. We wished to evaluate an animal model of this effect by studying the effects of bilateral lesions within the medial frontal cortex, including rat cingulate cortex, on performance in 3 behavioral tests: the formalin, hot-plate, and tail-flick tests. Average hot-plate latencies, but not formalin test scores or tail-flick latencies, were significantly increased by an average of 82% in rats with medial frontal cortex lesions, as compared to sham-operated control rats. Motor function, as tested by righting and foot lifting responses and clinical observation, was not impaired. No effects were seen on hot-plate latencies, tail-flick latencies, and formalin pain scores in sham-operated rats. These results suggest that the medial frontal cortex of the rat mediates certain types of supraspinally organized responses to noxious heat pain. Lesions that include the medial frontal and anterior cingulate cortex appear to disrupt the integration of increasing heat nociceptive input with motor responses that are necessary to execute quickly the escape behavior in the hot-plate test.

Ventral posterior thalamic neurons differentially responsive to noxious stimulation of the awake monkey

Of 76 cutaneously activated neurons recorded from the ventral posterior thalamus of awake, behaving monkeys, nine were weakly excited by innocuous skin stimulation and responded maximally only when noxious mechanical cutaneous stimuli were delivered within small, contralateral receptive fields. These results show that neurons capable of encoding the spatial and temporal features of noxious stimuli are located in the ventral posterior thalamus of the awake primate.

Lawson Criterion for Ignition Exceeded in an Inertial Fusion Experiment

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion.

Cocaine: evidence for supraspinal, dopamine-mediated, non-opiate analgesia

Cocaine (25 mg/kg i.p.) produces analgesia in the rat within 5 min and for a duration of 90 min as determined by the formalin test or for 30 min as determined by the hot plate test. Cocaine analgesia is unaffected by doses of naloxone that are sufficient to attenuate morphine analgesia in both tests. Chlorpromazine (3 mg/kg i.p.), SCH 23390 (100 micrograms/kg i.p.; a D1 dopamine receptor antagonist), and eticlopride (75 micrograms/kg i.p.; a D2 dopamine receptor antagonist) each attenuate cocaine analgesia in both tests at doses that alone do not affect performance in either test. Measurements of blood pressure and heart rate indicate that cocaine analgesia is not due to the activation of baroreceptor reflex afferents. We conclude that cocaine is a supraspinally acting, dopamine-mediated, non-opiate analgesic in the rat.

Long-term changes in behavior and regional cerebral blood flow associated with painful peripheral mononeuropathy in the rat

We identified long-term (up to 12 weeks), bilateral changes in spontaneous and evoked pain behavior and baseline forebrain activity following a chronic constriction injury (CCI) of the sciatic nerve. The long-term changes in basal forebrain activation following CCI were region-specific and can be divided into forebrain structures that showed either: (1) no change, (2) an increase, or (3) a decrease in activity with regard to the short-term (2 weeks) changes we previously reported. All the rats showed spontaneous pain behaviors that persisted throughout the 12-week observation period, resembling the pattern of change found in four limbic system structures: the anterior dorsal thalamus, habenular complex, and the cingulate and retrosplenial cortices. In contrast, heat hyperalgesia was delayed in onset until 4 weeks following CCI, but then persisted, showing a nearly constant level of increased responsiveness. The forebrain activation that resembles this behavioral pattern of change is found in somatosensory cortex, and in the hypothalamic paraventricular nucleus and the basolateral amygdala. Finally, mechanical allodynia, which was maximal during the first 2 weeks following nerve injury and gradually recovered by the seventh post-operative week uniquely matches the time course of changes in ventrolateral and ventroposterolateral thalamic activity. Our results indicate that peripheral nerve damage results in persistent changes in behavior and resting forebrain systems that modulate pain perception. The persistent abnormalities in the somatosensory cortex and thalamus suggest that the sensory thalamocortical axis is functionally deranged in certain chronic pain states.

Topical capsaicin selectively attenuates heat pain and A delta fiber-mediated laser-evoked potentials

Cutaneous stimulation with CO2 laser pulses activates A delta of nociceptive afferents and evokes late cerebral potentials (LEPs), the amplitude of which correlates parametrically with the perceived magnitude estimation of laser pulses. Capsaicin is known to desensitize the nociceptive terminals of C fibers. In this double-blind, vehicle-controlled experiment, we tested the hypothesis that topical capsaicin would inactivate A delta afferents and lead to an attenuation of the LEPs. Subjects applied capsaicin cream to the dorsum of one hand and vehicle cream to the other 3 times daily for a period of 5 weeks. At weekly intervals before starting, during administration and after discontinuation of capsaicin, LEPs were recorded and psychophysical thresholds and magnitude estimation for several sensory modalities were determined. The results of this study showed that topical capsaicin significantly and reversibly decreased the magnitude estimation of suprathreshold heat pain, laser pulses and amplitude of the LEPs. There was no statistically significant difference in light touch, deep pain and mechanical pain detection thresholds between the capsaicin- and vehicle-treated hands. It indicated that topical capsaicin caused a definite functional and reversible inactivation of A delta nociceptive afferent transmission. The decline in the magnitude estimation of laser pulses concomitantly with the attenuation of LEP amplitudes supports the hypothesis that some A delta afferents mediate noxious heat in humans. These findings demonstrate the usefulness of LEP in the physiological evaluation of nociceptive pathways and its potential usefulness in objectively documenting the effect of pharmacological treatment on pain perception.

Bilateral behavioral and regional cerebral blood flow changes during painful peripheral mononeuropathy in the rat

A unilateral chronic constriction injury (CCI) of the sciatic nerve produced bilateral effects in both pain related behaviors and in the pattern of forebrain activation. All CCI animals exhibited spontaneous pain-related behaviors as well as bilateral hyperalgesia and allodynia after CCI. Further, we identified changes in baseline (unstimulated) forebrain activation patterns 2 weeks following CCI by measuring regional cerebral blood flow (rCBF). Compared to controls, CCI consistently produced detectable, well-localized and typically bilateral increases in rCBF within multiple forebrain structures in unstimulated animals. For example, the hindlimb region of somatosensory cortex was significantly activated (22%) as well as multiple thalamc nuclei, including the ventral medial (8%), ventral posterior lateral (10%) and the posterior (9%) nuclear groups. In addition, several forebrain regions considered to be part of the limbic system showed pain-induced changes in rCBF, including the anterior dorsal nucleus of the thalamus (23%), cingulate cortex (18%), retrosplenial cortex (30%), habenular complex (53%), interpeduncular nucleus (45%) and the paraventricular nucleus of the hypothalamus (30%). Our results suggest that bilateral somatosensory and limbic forebrain structures participate in the neural mechanisms of prolonged persistent pain produced by a unilateral injury.

Cutaneous pain and detection thresholds to short CO2 laser pulses in humans: evidence on afferent mechanisms and the influence of varying stimulus conditions

Pain and detection thresholds to short CO2 laser pulses were studied in healthy human subjects. Pain thresholds were significantly higher than detection thresholds in both hairy and glabrous skin; in the glabrous skin both thresholds were higher in the hairy skin. The range from detection threshold to pain threshold was larger in the glabrous skin. The minimal energy per surface area needed to produce any sensation (detection) or pain sensation decreased with increasing stimulus surface, and this spatial summation effect was to equal magnitude in the hairy and the glabrous skin. With decreasing stimulus pulse duration (from 45 to 15 msec) the detection and pain thresholds were elevated: this effect was stronger on pain thresholds. With increasing adapting skin temperature, less energy was needed to produce any sensation (detection) or pain sensation. The effect of adapting skin temperature was equal on pain and detection thresholds. The conduction velocity of fibers mediating laser evoked first sensations was in the thin fiber range (less than 10 msec), according to a reaction time study. The results suggest that short CO2 laser pulses produce both non-pain and pain sensations, but that both these sensations are based on the activation of the same primary afferent fiber population of slowly conducting nociceptive fibers. Central summation of primary afferent impulses is needed to elicit a liminal non-painful sensation, and an increased number of impulses in the same fibers produces pain.