Activation of brown adipose tissue thermogenesis by chemical stimulation of the hypothalamic supraoptic nucleus

Glutamate microinjection (1 M, 250 nl) into the hypothalamic supraoptic nucleus (SON) stimulated heat production in brown adipose tissue (BAT) and caused a rapid and sustained increase in interscapular BAT and core temperatures in urethane-anaesthetized rats. This effect was blocked by intraperitoneal pretreatment with a sympathetic ganglionic blocker, chlorisondamine chloride (2.5 mg/kg), or a ß-adrenergic receptor blocker, propranolol (2.5 mg/kg), but not by prior hypophysectomy or intracerebroventricular pretreatment with specific receptor blockers to vasopressin (d(CH₂)5[Tyr(Me)²]AVP, 5 μg) or oxytocin (d(CH₂5[Tyr(Me)²,Thr⁴,Tyr-NH₂⁹]OVT, 5 μg). The results demonstrate that stimulation of SON cells with glutamate elicits a non-vasopressinergic/non-oxytocinergic neural signal that can bring about a sympathetically-mediated increase in BAT thermogenesis. Heat production in BAT is an important mechanism of thermal protection during cold stimulation, and there is evidence that osmotic stimulation can influence thermoregulation. SON neurons play a major role in osmoregulation via release of the peptide hormones vasopressin and oxytocin. The present results suggest the possibility that apart from releasing peptide hormones for osmoregulation, SON neurons might be involved in mediating the effect of osmotic stimulation on thermoregulatory responses involved in thermal adaptation.     

Ultrastructural distribution of synaptophysin and synaptic vesicle recycling at the frog neuromuscular junction

Synaptic vesicle recycling after intense acetylcholine (ACh) release was studied at the frog neuromuscular junction (NMJ) using the synaptic vesicle transmembrane protein synaptophysin as immunocytochemical marker of the synaptic vesicle membrane during the process of exo-endocytosis. ACh release in cutaneous pectoris nerve-muscle preparations was stimulated by three different means: K⁺, Cd²⁺ in Ca²⁺-free medium, and electrical stimulation in the presence of 4-aminopyridine (4-AP). Cd²⁺ stimulation produced synaptic vesicle depletion and nerve terminal swelling. Electrical stimulation in the presence of 4-AP produced a reduction in the number of synaptic vesicles, deep axolemmal infoldings, coated pits, and coated vesicles. K⁺ stimulation did not produce any observable ultrastructural changes. Synaptophysin was labeled using silver-intensified immunogold in dissociated muscle fibers. Unstimulated and K⁺-stimulated preparations showed synaptophysin immunolabeling associated only with synaptic vesicles. In contrast, in Cd²⁺-stimulated preparations, synaptophysin appeared along the axolemma, mainly at the active zones, and after electrical stimulation it appeared in both axolemmal infoldings and the remaining synaptic vesicles. The results show that when synaptic vesicle recycling is inhibited by Cd²⁺ in Ca²⁺-free medium, or when 4-AP is present during electrical stimulation, synaptic vesicle fusion is accompanied by translocation and incorporation of synaptic vesicle membrane proteins into the axolemma. However, during the latter condition, synaptic vesicles are recycled through coated vesicles arising from the axolemmal infoldings. Conversely, during physiological-like stimulation of ACh release by K⁺ the synaptic vesicles are rapidly recycled at the active zones, by a double and rapid process of exo-endocytosis, without collapse into the axolemma. © 1996 Wiley-Liss, Inc.     

Tetanic stimulation increases the frequency of miniature end-plate potentials at the frog neuromuscular junction in Mn-, CO-, and Ni-saline solutions

The effects of Mn²⁺, Co²⁺, and of Ni²⁺ on quantal acetylcholine (ACh) release have been studied with conventional microelectrode techniques. Increasing the [Co²⁺]₀ or [Ni²⁺]₀ (in the absence of extracellular Ca²⁺) caused an increase in miniature end-plate potential (MEPP) frequency. [Mn²⁺]₀ caused some increase in frequency at low levels, but then there was no rise as the concentration was increased further. In preparations depolarized with 20 mM K⁺, the MEPP frequency was a monotonically increasing function of [Co²⁺]₀ or of [Ni²⁺]₀. In increasing concentrations of [Mn²⁺]₀ there was an increase followed by a levelling off or a depression at higher concentrations. Tetanic stimulation of the motor nerve in solutions containing no added divalent cations or containing MgEGTA produced slight or no increases in MEPP frequency. In Mn²⁺-, Co²⁺- or Ni²⁺- saline solution stimulation of the motor nerve led to substantial increases in MEPP frequencies. The maximum frequency attained in Mn²⁺, Co²⁺, or Ni²⁺ was a power function of : (a) the duration of the tetanus; (b) the frequency of stimulation during the tetanus; or (c) the extracellular concentration of the divalent cation. During stimulation in Mn²⁺-saline solution the MEPP frequency reached a maximum; further stimulation led to a fall in frequency. We conclude that Mn²⁺, Co²⁺, and Ni²⁺ can enter the nerve terminal through a voltage-gated channel. Once within the terminal, they can stimulate quantal release by releasing Ca²⁺ or by causing the liberation of an activator, like H⁺, within the terminal.     

Octopamine is the synaptic transmitter between identified neurons in the buccal feeding network of the pond snail Lymnaea stagnalis

We report the pharmacological properties of synaptic connections from the three octopamine-containing OC interneurons to identified buccal feeding neurons in the pond snail, Lymnaea stagnalis. Intracellular stimulation of an OC interneuron evokes inhibitory postsynaptic potentials in the B3 motoneurons and N2 (d) interneurons, while the synapse between OC and N3 (phasic) interneurons has two components: an initial electrical excitation followed by chemical inhibition. All synaptic responses persist in a saline with elevated calcium and magnesium suggesting that the connections are monosynaptic. Local perfusion of 10⁻⁴ M octopamine produces the same inhibitory membrane responses from these buccal neurons as OC stimulation. These responses also persist in high Mg²⁺/Ca²⁺ saline indicating direct membrane effects. The similarities in reversal potentials for the synaptic hyperpolarization evoked on B3 neurons after OC stimulation (−89.0 mV, S.E.M.=14.1, n=10) and the octopamine response of the B3 neurons (−84.7 mV, S.E.M.=6.6, n=6) indicate that increased K⁺-conductance underlies both responses. Bath application of the octopaminergic drugs phentolamine (10⁻⁶ M), epinastine (10⁻⁶ M) or DCDM (10⁻⁴ M) blocks the inhibitory synapse onto B3 or N2 neurons and the chemical component of the N3 response. They also block the octopamine-evoked inhibition of B3, N2 and N3 neurons. NC-7 (2×10⁻⁵ M) has a hyperpolarizing agonist effect (like octopamine) on these neurons and also blocks their chemical synaptic input from the OC interneurons. These results provide pharmacological evidence that the neurotransmitter between the octopamine-immunopositive OC interneurons and its followers is octopamine. This is the first example of identified octopaminergic synaptic connections within the snail CNS.     

Tetanic stimulation increases the frequency of miniature end-plate potentials at the frog neuromuscular junction in Mn2+-, CO2+-, and Ni2+-saline solutions

The effects of Mn²⁺, Co²⁺, and of Ni²⁺ on quantal acetylcholine (ACh) release have been studied with conventional microelectrode techniques. Increasing the [Co²⁺]₀ or [Ni²⁺]₀ (in the absence of extracellular Ca²⁺) caused an increase in miniature end-plate potential (MEPP) frequency. [Mn²⁺]₀ caused some increase in frequency at low levels, but then there was no rise as the concentration was increased further. In preparations depolarized with 20 mM K⁺, the MEPP frequency was a monotonically increasing function of [Co²⁺]₀ or of [Ni²⁺]₀. In increasing concentrations of [Mn²⁺]₀ there was an increase followed by a levelling off or a depression at higher concentrations. Tetanic stimulation of the motor nerve in solutions containing no added divalent cations or containing MgEGTA produced slight or no increases in MEPP frequency. In Mn²⁺-, Co²⁺- or Ni²⁺- saline solution stimulation of the motor nerve led to substantial increases in MEPP frequencies. The maximum frequency attained in Mn²⁺, Co²⁺, or Ni²⁺ was a power function of : (a) the duration of the tetanus; (b) the frequency of stimulation during the tetanus; or (c) the extracellular concentration of the divalent cation. During stimulation in Mn²⁺-saline solution the MEPP frequency reached a maximum; further stimulation led to a fall in frequency. We conclude that Mn²⁺, Co²⁺, and Ni²⁺ can enter the nerve terminal through a voltage-gated channel. Once within the terminal, they can stimulate quantal release by releasing Ca²⁺ or by causing the liberation of an activator, like H⁺, within the terminal.     

Changes in synaptic membrane phosphorylation after tetanic stimulation in the dentate area of the rat hippocampal slice

slices of rat brain hippocampus were stimulated electrically in the perforant pathway. After electrical stimulation, known to produce long-lasting post-tetanic potentiation, endogenous phosphorylation of membrane proteins was measured in a crude mitochondrial fraction, prepared from stimulated and unstimulated slices. Tetanic stimulation specifically enhanced the incorporation of [³²P]phosphate into a protein band with apparent molecular weight of 50K. When the same number of pulses were given, but at a much slower rate (1 pulse per 4 sec instead of 15 pulses per sec) no post-tetanic stimulation and concomitantly, no enhanced incorporation of [³²P]phosphate were observed into the 50K band. When the stimulation of the slices was performed in Ca²⁺-free medium, again no potentiation and no enhanced incorporation into the 50K protein band were observed. It is suggested that electrical stimulation enhances the activity of the protein kinase that phosphorylates the 50K protein.     

H-2-Deoxyglucose uptake after electrical stimulation of cardioactive sites in insular cortex and mediodorsal nucleus of the thalamus in rabbits

The uptake of ³H-2-deoxyglucose (³H-2-DG) in selected brain structures was determined subsequent to electrical stimulation of insular cortex (Ins) and the mediodorsal (MD) nucleus of the thalamus in rabbits. Stimulation of Ins elicited parasympathetic-like responding (i.e., bradycardia and depressor responses); whereas MD stimulation produced sympathetic-like responses (bradycardia and pressor responses). Stimulation of Ins also resulted in increased ³H-2-DG activity in ipsilateral MD and the ventromedial/ventroposterior complex as well as the contralateral Ins compared to nonstimulated control subjects. The central nucleus of the amygdala also showed increased activity after Ins stimulation. In 2 animals stimulation of Ins resulted in increased ³H-2-DG activity in the caudate/putamen complex. Stimulation of MD resulted in ipsilateral increases in ³H-2-DG activity in the midline, agranular prefrontal cortex, as well as the ipsilateral Ins, and the caudate nucleus and putamen/globus pallidus complex. Two animals also showed increases in ³H-2-DG activity in ipsilateral substantia nigra. However, no increased activity was observed in the lateral hypothalamus, the parabrachial nuclei, the nucleus tractus solitarius, or the dorsal motor nucleus of the vagus, although it has been shown that efferents from Ins reach these areas. A more significant finding however, was that the reciprocal connections of MD and Ins appear to be activated by stimulation of either structure, even though their relationship to autonomic function appears to be quite different.     

Regulation by calcium of the nitric oxide/cyclic GMP system in cerebellar granule cells and astroglia in culture

Ca²⁺ entry induced by N-methyl-D-aspartate (NMDA) in neurons and by noradrenaline (NA) in astrocytes is known to increase intracellular cyclic GMP (cGMP) levels through stimulation of the Ca²⁺-dependent nitric oxide synthase type I (NOS-I). The possibility that Ca²⁺ entry could also down-regulate intracellular cGMP by activating a Ca²⁺/calmodulin-dependent phosphodiesterase (CaM-PDE) has been investigated here in primary cultures enriched in granule neurons or in astroglia from rat cerebellum. We show that the same agonists that stimulate nitric oxide (NO) formation (NMDA and NA at 100 μM) and the Ca²⁺ ionophore A23187 (10 μM) decrease cGMP generated in response to direct stimulation of soluble guanylyl cyclase (sGC) by NO donors in both cell types. This effect requires extracellular Ca²⁺ and is prevented by the calmodulin inhibitor W7 (100 μM). Membrane depolarization, manipulations of the Na⁺ gradient, and intracellular Ca²⁺ mobilization also decrease NO donor-induced cGMP formation in granule cells. In astroglia Ca²⁺ entry additionally down-regulates cGMP generated by stimulation of the particulate GC by atrial natriuretic peptide (ANF). Decreases in cGMP produced by A23187 were more pronounced in the absence than in the presence of the PDE inhibitor 3-isobutyl-1-methylxanthine (IBMX; 1 mM), indicating that a CaM-PDE was involved. We also show that astroglial cells can accumulate similar amounts of cGMP than neurons in response to NO donors when IBMX is present but much lower levels in its absence. This may result from a lower ratio of sGC to PDE activities in astroglia. J. Neurosci. Res. 49:333–341, 1997. © 1997 Wiley-Liss, Inc.     

Botulinum Toxin A reduces neurogenic flare but has almost no effect on pain and hyperalgesia in human skin

Botulinum toxin A (BoNT/A) has been used therapeutically to treat muscular hypercontractions and sudomotor hyperactivity. There is increasing evidence that BoNT/A might also have analgesic properties, in particular in headache. In the present investigation we tested the often cited hypothesis that BoNT/A-induced analgesia can be attributed to inhibition of neuropeptide release from nociceptive nerve fibers. In 15 healthy volunteers BoNT/A (5, 10, 20 mouse units BOTOX) or saline (contralateral side) was injected intracutaneously on the volar forearm. On day zero, the day of injection, no further tests were performed. We repeatedly elicited pain, mechanical hyperalgesia and neurogenic flare by transcutaneous electrical stimulation simultaneously on the BoNT/A and saline treated side on day 1, 2, 3, 7 and 14 after injection. Before each session, sweating and local anhidrosis was assessed by iodine starch staining. BoNT/A suppressed sweating as early as from the second day after injection (p < 0.001). The size of electrically induced flare was smaller on the BoNT/A treated arm (BoNT/A side: 21.46 cm² ± 3.58, saline side 24.80 ± 3.46, p < 0.005) and BoNT/A reduced electrically-induced pain by about 10 % (p < 0.001). However, hyperalgesia to pin-prick and allodynia after electrical stimulation were unchanged. In conclusion our results indicate that peripheral neuropeptide release is attenuated by BoNT/A. In contrast, the analgesic effect of BoNT/A was very limited. Therefore we assume that other than neuropeptide mechanisms must be important for BoNT/A induced pain relief in clinical pain syndromes. Received: 24 April 2002, Received in revised form: 5 September 2002, Accepted: 13 September 2002 Correspondence to PD Dr. Frank Birklein     

Medial amygdaloid suppression of predatory attack behavior in the cat: I. Role of a substance P pathway from the medial amygdala to the medial hypothalamus

The medial amygdala is known to powerfully suppress predatory attack behavior in the cat, but the mechanisms underlying such modulation remain unknown. The present study tested the hypothesis that medial amygdaloid suppression of predatory attack is mediated, in part, by a pathway from the medial amygdala to the medial hypothalamus which utilizes substance P as a neurotransmitter. Stimulating electrodes were implanted into the medial amygdala and cannula electrodes were implanted into both the medial and lateral hypothalamus. Predatory attack behavior was elicited by electrical stimulation of the lateral hypothalamus. In the first phase of the study, paired trials compared attack latencies of single stimulation of the lateral hypothalamus with those following dual stimulation of the lateral hypothalamus and medial amygdala. Attack latencies were significantly elevated following dual stimulation of the medial amygdala and lateral hypothalamus. In the second phase of the study, dose and time dependent decreases in response suppression were noted following the infusion of the substance P (NK₁) receptor antagonist, CP96,345 (in doses of 0.05, 0.5 and 2.5 nmol) into the medial hypothalamus. In third phase of the study, the effects of microinjections of the substance P receptor agonist, [Sar⁹,Met(O₂)¹¹]-substance P (in doses of 0.5, 1.0 and 2.0 nmol), directly into the medial hypothalamus upon lateral hypothalamically elicited predatory attack behavior were determined. Microinfusion of this drug elevated attack response latencies in a dose- and time-dependent manner. In addition, pretreatment with CP96,345 into the medial hypothalamus blocked the suppressive effects of subsequent delivery of [Sar⁹,Met(O₂)¹¹]-substance P into the same medial hypothalamic site. Other parts of the study demonstrated the presence of: (1) high densities of substance P receptors in the ventromedial hypothalamus, and (2) neurons that are positively labeled for substance P that project from the medial amygdala to the ventromedial hypothalamus as demonstrated by retrograde labeling with Fluoro-Gold. These findings provide support for the hypothesis that medial amygdaloid suppression of lateral hypothalamically elicited predatory attack behavior includes a substance P pathway from the medial amygdala to the medial hypothalamus. The findings further suggest that stimulation of the medial amygdala activates substance P receptors in the medial hypothalamus, thus triggering an inhibitory mechanism from the medial to the lateral hypothalamus, resulting in suppression of predatory attack behavior.     

Trends in the prevalence and mortality of cognitive impairment in the United States: Is there evidence of a compression of cognitive morbidity?

BackgroundRecent medical, demographic, and social trends might have had an important impact on the cognitive health of older adults. To assess the impact of these multiple trends, we compared the prevalence and 2-year mortality of cognitive impairment (CI) consistent with dementia in the United States in 1993 to 1995 and 2002 to 2004.MethodsWe used data from the Health and Retirement Study (HRS), a nationally representative population-based longitudinal survey of U.S. adults. Individuals aged 70 years or older from the 1993 (N = 7,406) and 2002 (N = 7,104) waves of the HRS were included. CI was determined by using a 35-point cognitive scale for self-respondents and assessments of memory and judgment for respondents represented by a proxy. Mortality was ascertained with HRS data verified by the National Death Index.ResultsIn 1993, 12.2% of those aged 70 or older had CI compared with 8.7% in 2002 (P < .001). CI was associated with a significantly higher risk of 2-year mortality in both years. The risk of death for those with moderate/severe CI was greater in 2002 compared with 1993 (unadjusted hazard ratio, 4.12 in 2002 vs 3.36 in 1993; P = .08; age- and sex-adjusted hazard ratio, 3.11 in 2002 vs 2.53 in 1993; P = .09). Education was protective against CI, but among those with CI, more education was associated with higher 2-year mortality.ConclusionsThese findings support the hypothesis of a compression of cognitive morbidity between 1993 and 2004, with fewer older Americans reaching a threshold of significant CI and a more rapid decline to death among those who did. Societal investment in building and maintaining cognitive reserve through formal education in childhood and continued cognitive stimulation during work and leisure in adulthood might help limit the burden of dementia among the growing number of older adults worldwide.     

Feedback Stimulation of Somatodendritic Serotonin Release: A 5-HT3 Receptor-Mediated Effect in the Raphe Nuclei of the Rat

Slices from rat midbrain containing the raphe nuclei and from hippocampus were prepared, loaded with [³H]5-HT and superfused and the resting and the electrically stimulated [³H]5-HT release was measured. The 5-HT₃ receptor agonist 2-methyl-5-HT (1 to 10 μmol/l) increased the resting tritium outflow in superfused raphe nuclei slices, EC₅₀ 5.3 μmol/l. The 2-methyl-5-HT-induced increase of tritium outflow was an external Ca²⁺-independent process and was not altered by reserpine pretreatment but it was reversed by addition of the 5-HT uptake inhibitor fluoxetine (1 μmol/l). The 5-HT₃ receptor antagonists ondansetron and GYKI-46 903 (1 μmol/l) did not antagonize the stimulatory effect of 2-methyl-5-HT on resting tritium outflow. 2-Methyl-5-HT in lower concentration increased the electrically induced tritium overflow from raphe nuclei slices (EC₅₀ 0.56 μmol/l) and also from hippocampal slices preloaded with [³H]5-HT. These effects were reversed by 1 μmol/l of ondansetron and GYKI-46903. The 5-HT₃ receptor antagonists (1 μmol/l) were without effects on depolarization-evoked [³H]5-HT release at 2 Hz stimulation, when 10 Hz stimulation was used, ondansetron and GYKI-46 903 reduced the tritium overflow from raphe nuclei slices. These data indicate that 5-HT₃ receptors positively alter depolarization-induced somatodendritic 5-HT release in the raphe nuclei. They also show that 2-methyl-5-HT is able to evoke 5-HT release not only from vesicles but also from cytoplasmic stores via a transporter-dependent exchange process.     

Normal dopamine transporter binding in dopa responsive dystonia

We report the clinical manifestations of dopa responsive dystonia (DRD) in 2 patients from the same family. The brain magnetic resonance images (MRI) were normal. The dopamine transporter (DAT) imaging with ^99mTc-TRODAT-1 was performed in the 2 probands, 8 patients with young onset Parkinson disease (YOPD) and 16 normal controls. The ratios of ^99mTc-TRODAT-1 brain SPECT in the striatum were 2.40 ± 0.12 (right) and 2.30 ± 0.17 (left) in these 2 DRD patients as compared with 1.38 ± 0.18 (right), 1.41 ± 0.20 (left) in YOPD patients, and 2.15 ± 0.35 (right), 2.14 ± 0.32 (left) in normal controls respectively. A normal DAT uptake was found in DRD suggesting a normal presynaptic nigrostriatal dopaminergic terminal. We conclude that a normal DAT in parkinsonian patients can differentiate DRD from YOPD. In addition, DAT with ^99mTc-TRODAT-1 is a reliable and convenient tool to study the function of the presynaptic dopaminergic axonal terminals. Received: 18 October 2001 Received in revised form: 1 February 2002 Accepted: 6 February 2002     

Vulnerability to stressor-induced disturbances in self-stimulation from the dorsal and ventral A10 area: Differential effects of intraventricular D-Ala-Met-enkephalinamide, D-Ala, N-Me-Phe, Gly-Ol-enkephalin, and D-Pen, D-Pen- enkephalin administration

D-Ala²-Met⁵-enkephalinamide (DALA) (1.0 μg/μl) was administered intraventricularly to mice responding for electrical stimulation from the dorsal or ventral aspects of the VTA immediately prior to footshock (Experiment 1). Predictably, footshock reduced self-stimulation from the dorsal but not the ventral VTA immediately, 24, and 168 h following the stressor. Intraventricular DALA administration effected a partial attenuation of stressor-induced self-stimulation reductions from the dorsal VTA immediately and 24 h poststressor. Deficits appeared among DALA-Shocked mice responding for brain stimulation from the ventral VTA during comparable test intervals. The long-term depressant influence of footshock on self-stimulation from the dorsal VTA was abolished among DALA-treated mice and DALA-associated reductions in self-stimulation from the ventral A10 region among stressed mice were not evident 1 week later. Administration of D-Ala², N-Me-Phe⁴, Gly-Ol⁵-enkephalin (DAGO) (0.01 μg/μl) or D-Pen², D-Pen⁵-enkephalin (DPDPE) (1.0 μg/μl) intraventricularly prior to footshock effected an immediate and a delayed antagonism, respectively, of the stressor on self-stimulation from the dorsal VTA, which persisted for 1 week. Prophylactic administration of 0.001 μg/μl DAGO or 0.01 μg/μl DPDPE prior to the stressor failed to influence self-stimulation from the ventral VTA (Experiment 2). Administration of 0.01 μg/μl DAGO or 1.0 μg/μl DPDPE among mice responding for brain stimulation from the dorsal VTA following footshock produced a weak therapeutic effect immediately poststressor, but effected protracted amelioration of footshock-induced reductions of self-stimulation from the dorsal VTA (Experiment 3). Taken together, μ, δ, and μ-δ activation influenced self-stimulation differentially from the dorsal and ventral VTA according to the temporal order of opioid peptide challenge relative to stressor imposition. These data are discussed with respect to stressors, motivational alterations, and the putative modulating influence of endogenous enkephalin activity in subareas of the VTA.     

Variability in Response to Transcranial Direct Current Stimulation of the Motor Cortex

BackgroundResponses to a number of different plasticity-inducing brain stimulation protocols are highly variable. However there is little data available on the variability of response to transcranial direct current stimulation (TDCS).ObjectiveWe tested the effects of TDCS over the motor cortex on corticospinal excitability. We also examined whether an individual's response could be predicted from measurements of onset latency of motor evoked potential (MEP) following stimulation with different orientations of monophasic transcranial magnetic stimulation (TMS).MethodsFifty-three healthy subjects participated in a crossover-design. Baseline latency measurements with different coil orientations and MEPs were recorded from the first dorsal interosseous muscle prior to the application of 10 min of 2 mA TDCS (0.057 mA/cm²). Thirty MEPs were measured every 5 min for up to half an hour after the intervention to assess after-effects on corticospinal excitability.ResultsAnodal TDCS at 2 mA facilitated MEPs whereas there was no significant effect of 2 mA cathodal TDCS. A two-step cluster analysis suggested that approximately 50% individuals had only a minor, or no response to TDCS whereas the remainder had a facilitatory effect to both forms of stimulation. There was a significant correlation between the latency difference of MEPs (anterior–posterior stimulation minus latero-medial stimulation) and the response to anodal, but not cathodal TDCS.ConclusionsThe large variability in response to these TDCS protocols is in line with similar studies using other forms of non-invasive brain stimulation. The effects highlight the need to develop more robust protocols, and understand the individual factors that determine responsiveness.     

A pharmacokinetic analysis of the vagal release of 5-hydroxytryptamine in the cat

Summary The kinetics of 5-hydroxytryptamine (5-HT) release into the portal system after efferent electrical vagal stimulation were studied in anin vivo model. Blood samples were drawn from cats before, during and after vagal nerve stimulation, and portal plasma levels of 5-HT were measured. Portal plasma concentration of 5-HT rose during stimulation. After termination of stimulation, the plasma levels returned to steady state values and were used to calculate half-life and elimination rate constant. When pharmacokinetic principles were applied, the plasma half-life (T1/2) was determined to be 1.32 min and the elimination rate constant (k_E), 0.5246 min^–1. Pharmacokinetic principles also were applied to data from earlierin vitro studies using exogenously administered 5-HT, and a half-life of 1.03 min and a k_E of 0.67 min^–1 were calculated. Therefore, it appears that exogenously administered 5-HT and neurogenically released endogenous 5-HT are metabolized at a similar rate, both having a short half-life.     

Analysis of brainstem A1 and A2 noradrenergic inputs to the preoptic area using microdialysis in the rat

Noradrenergic inputs to the preoptic area (POA) are involved in regulating a variety of homeostatic functions. However, the accurate measurement of endogenous noradrenaline (NA) release in the POA has been difficult to achieve and consequently little has been done to characterise the different noradrenergic pathways. By combining the technique of intracranial microdialysis with tissue pre-loading of [³H]NA we have developed a sensitive index of NA release in the POA [8]. Using this method we have now examined and compared the effects of electrical stimulation of the brainstem A1 and A2 cell groups on NA release in the POA. Anaesthetized proestrus rats were implanted with microdialysis probes either unilaterally or bilaterally in the POA and stimulating electrodes positioned in either the A1 or A2 regions. Electrical stimulation (10 Hz, 10s on/off for 20 min) of the A1 region resulted in repeatable, calcium-dependent increases in radioactivity outflow from the ipsilateral POA(P < 0.01). A1-evoked release was twice as large as that observed after equivalent 10 Hz electrical stimulation of the A2 region(P < 0.05). In experiments using bilateral POA microdialysis and A1 stimulation, a significant increase in release from the contralateral POA, amounting to approximately 80% of that observed in the ipsilateral POA, was observed. Experiments involving the blockade of A1-stimulated release in the ipsilateral POA by perfusion with a calcium-free medium demonstrated that increases in radioactivity measured in the contralateral POA were not originating from the ipsilateral POA. These results provide a functional evaluation of the A1 and A2 noradrenergic inputs to the POA and provide evidence that (i) electrical activation of the A2 cell group increases NA release in the POA, although stimulated release is less than that resulting from equivalent A1 stimulation, and that (ii) stimulation of the A1 group alters NA release bilaterally in the POA.     

Two persons with multiple disabilities use a mouth-drying response to reduce the effects of their drooling

These two studies involved a boy and a man with multiple disabilities, who were taught to use a mouth-drying response to reduce the effects of their drooling. Both studies relied on microswitch technology to monitor the drying response and follow it with positive stimulation (i.e., during intervention). In Study I, the boy performed the drying response via a special napkin. The microswitch technology consisted of touch/pressure sensors and a radio transmitter hidden inside the napkin. Drying responses led the boy to 8 s of preferred stimulation. In Study II, the man performed the drying response via a handkerchief. The microswitch technology consisted of an optic sensor and a radio transmitter at the man's chest. Drying responses led the man to 8–10 s of preferred stimulation. The stimulation time/conditions were subsequently modified to promote a reduction in the man's response frequency. The experimental design involved an ABAB sequence (Study I) or an ABABB¹B² sequence (Study II), with the second B or the B¹B² combination spreading over periods of about 3 months. The results indicated vast increases in drying responses and decreases in chin wetness during the intervention phases. The frequencies of the drying response remained consistent for the boy and stabilized at a lower level (i.e., in line with the manipulation of the stimulation conditions) for the man. Implications of the findings and limitations of the studies are discussed.     

Individualized tDCS modeling predicts functional connectivity changes within the working memory network in older adults

BackgroundWorking memory decline has been associated with normal aging. The frontal brain structure responsible for this decline is primarily located in the prefrontal cortex (PFC). Our previous neuroimaging study demonstrated a significant change in functional connectivity between the left dorsolateral PFC (DLPFC) and left ventrolateral PFC (VLPFC) when applying 2 mA tDCS in MRI scanner during an N-Back task. These regions were part of the working memory network. The present study is the first study that utilizes individualized finite element models derived from older adults’ MRI to predict significant changes of functional connectivity observed from an acute tDCS application.MethodsIndividualized head models from 15 healthy older adults (mean age = 71.3 years) were constructed to create current density maps. Each head model was segmented into 11 tissue types: white matter, gray matter, CSF, muscle, blood vessels, fat, eyes, air, skin, cancellous, and cortical bone. Electrodes were segmented from T1-weighted images and added to the models. Computed median and maximum current density values in the left DLPFC and left VLPFC regions of interest (ROIs) were correlated with beta values as functional connectivity metrics measured in different timepoint (baseline, during stimulation) and stimulation condition (active and sham).Main resultsPositive significant correlations (R² = 0.523 for max J, R² = 0.367 for median J, p < 0.05) were found between the beta values and computed current densities in the left DLPFC ROIs for active stimulation, but no significant correlation was found during sham stimulation. We found no significant correlation between connectivity and current densities computed in the left VLPFC for both active and sham stimulation.ConclusionsThe amount of current within the left DLPFC ROIs was found positively correlated with changes in functional connectivity between left DLPFC and left VLPFC during active 2 mA stimulation. Future work may include expansion of number of participants to further test the accuracy of tDCS models used to predict tDCS-induced functional connectivity changes within the working memory network.     

Lactate accumulation following concussive brain injury: the role of ionic fluxes induced by excitatory amino acids

During the first few minutes following traumatic brain injury, cells are exposed to an indiscriminate release of glutamate from nerve terminals resulting in a massive ionic flux (e.g., K⁺ efflux) via stimulation of excitatory amino acid (EAA)-coupled ion channels. The present study was undertaken to elucidate the causal relationship between these ionic shifts and lactate accumulation in the injured brain, by examining the effects of ouabain (an inhibitor of Na⁺/K⁺-ATPase), Ba²⁺ (an inhibitor of non-energy-dependent glial K⁺ uptake) and kynurenic acid (KYN; a broad-spectrum EAA antagonist) on lactate accumulation. Two microdialysis probes were placed bilaterally in the rat parietal cortex. One was perfused with a test drug (1.0 mM ouabain, 2.0 mM Ba²⁺ or 10 mM KYN) and the other with Ringer's solution (control) for 30 min prior to injury. Following a 2.2–2.7 atm fluid-percussion injury, lactate levels in the dialysate increased (up to 116.6% above baseline) for the first 16 min and returned to baseline levels within 20 min after injury. This lactate accumulation was attenuated by preinjury administration of ouabain and KYN and was prolonged by Ba²⁺ administration. These findings indicate that lactate accumulation following concussive brain injury is a result of increased glycolysis which supports ion-pumping mechanisms, thereby, restoring the ionic balance which was disrupted by stimulation of EAA-coupled ion channels.