Effects of anticonvulsant drugs on substantia nigra pars reticulata neurons

Enhancement of gamma-aminobutyric acid transmission within the substantia nigra has been shown to prevent the motor manifestations of chemically induced and kindled seizures. These findings raise the possibility that the substantia nigra might constitute a site of anticonvulsant drug action if these drugs share an ability to suppress propagation of seizure activity from the nigra to motor effector sites. The current studies monitored effects of a diverse group of anticonvulsant drugs on the extracellular, single unit activity of nondopaminergic neurons of the substantia nigra pars reticulata in awake, paralyzed and locally anesthetized male rats. Intravenous phenytoin (1.25-160 mg/kg) and carbamazepine (1.25-40 mg/kg) did not alter neuronal firing at any dose. Conversely, both diazepam (31.25-8,000 micrograms/kg) and clonazepam (2-500 micrograms/kg) partially inhibited firing (to 46 +/- 11% and 59 +/- 6% of base-line rates, respectively), although clonazepam was approximately 16 times more potent in eliciting equivalent degrees of inhibition. Valproic acid (5-640 mg/kg) and phenobarbital (1.25-80 mg/kg) also slowed firing to 65 to 70% of base-line rates, but did so only at the highest doses administered. However, the anesthetic barbiturate pentobarbital (0.3125-80 mg/kg) completely suppressed firing by the highest dose tested. Of those drugs used exclusively for treatment of absence seizures, trimethadione (12.5-800 mg/kg) caused dose-related inhibitions to 37.6 +/- 9.8% of base-line, whereas ethosuximide (12.5-800 mg/kg) markedly stimulated firing, nearly doubling firing rates after the 200 mg/kg dose.(ABSTRACT TRUNCATED AT 250 WORDS)     

Neurotoxic effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in the substantia nigra and the locus coeruleus in BALB/c mice.

The purpose of the present study was to determine whether 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), administered systemically or as a local infusion, has a direct neurotoxic action upon dopamine (DA) neurons in the substantia nigra (SN) and norepinephrine (NE) neurons in the locus coeruleus (LC) in BALB/c mice. Results indicated that both acute and repeated MPTP infusions (2 micrograms/0.3 microliter per side) significantly impaired locomotor activity, decreased stereotyped behavior and caused a disturbed pattern of locomotion in mice. The biochemical changes parallel the behavioral changes. Repeated MPTP infusions to the SN decreased DA levels markedly in the SN and the striatum; chronic MPTP infusions to the LC reduced NE levels markedly in the LC and the hippocampus. Furthermore, repeated MPTP injections for 7 days (30 mg/kg, one injection per day) have resulted in a long-lasting effect on both the nigral-striatal and the coeruleus-hippocampal systems. DA levels in the SN and the striatum were decreased at 1, 3, 7 and 28 days after the last MPTP injection. Similarly, NE levels in the LC and the hippocampus were also reduced markedly at the same time intervals examined. Behaviorally, repeated MPTP treatment also produced long-lasting motor deficits in mice at all time intervals studied. Moreover, the LC appeared to be more sensitive than the SN to the neurotoxic effects of MPTP. Immunohistochemical results have similarly revealed that repeated MPTP treatment markedly decreased tyrosine hydroxylase-positive cells and fibers in the SN and the LC. It also markedly decreased DA-beta-hydroxylase-positive cells and fibers in the LC.(ABSTRACT TRUNCATED AT 250 WORDS)     

Poststimulation catecholamine synthesis and tyrosine hydroxylase activation in central noradrenergic neurons. I. In vivo stimulation of the locus coeruleus

The ability of increased neuronal activity to accelerate catecholamine biosynthesis and tyrosine hydroxylase activity in the rat brain was tested. Noradrenergic neurons of the locus coeruleus (LC) were stimulated unilaterally at 20 Hz and the cortex and/or hippocampus from stimulated and contralateral (control) sides of the brain were analyzed and compared. Rats were injected with a dopa decarboxylase inhibitor and the accumulation of endogenously synthesized dopa used as an in vivo index of tyrosine hydroxylase activity. Thirty minutes after termination of 15 min of unilateral LC stimulation, dopa accumulation was 35% greater in the ipsilateral cortex + hippocampus. In untreated rats, at the end of 15 min of LC stimulation, there was an ipsilateral depletion of cortical norepinephrine (NE) which recovered within 30 min. When rats were injected with [3H]tyrosine (i.v.) during this half-hour recovery period, a poststimulation increase in [3H]catecholamine synthesis was observed in both the cortex (63%) and hippocampus (55%). In the cortex, there was more newly synthesized [3H]dopamine than [3H]NE, but LC stimulation preferentially increased the synthesis of [3H]NE. The hippocampus contained negligible amounts of [3H]dopamine and was used in subsequent studies. Tyrosine hydroxylase activity was assayed in vitro in supernatants derived from stimulated and control hippocampi. Ten minutes of LC stimulation (20 Hz) maximally activated hippocampal tyrosine hydroxylase and this activation was maintained for up to 20 min after stimulation was terminated. The results illustrate a stimulation-induced activation of NE biosynthesis and tyrosine hydroxylase activity in central NE neurons in vivo. This activation is maintained in the immediate poststimulation period and is not necessarily due to removal of end product inhibition by NE.     

Inhibitory effects of substantia nigra on impulse transmission from nociceptors.

In precollicularly decerebrated cats immobilized with Flaxedil (2 mg/kg, i.v.), a dopamine mechanism played a role in the inhibition produced by brain stem stimulation of nociceptive activated cells in the spinal cord. Lamina V cell activity evoked by natural stimulation (pinch not touch) to the left hind limb or electrical stimulation (0.1 msec pulses at 1/sec) to the left sural nerve exposed at the popliteal fossa was recorded at levels L₆ and L₇. Brain stimulation consisted of 100 msec trains of either single rectangular pulses or 3 pulses/sec for 1 min. The stimulation was delivered to substantia nigra, periaqueductal gray (PAG) and dorsal raphe nucleus via concentric bipolar electrodes. Descending inhibition of the late burst of lamina V cell discharge elicited by mechanical pinch or sural shock could be demonstrated following individual stimulation of the 3 brain stem sites. Nigral-induced inhibition was abolished by injecting tetrabenazine (40 mg/kg, i.v.) or bulbocapnine (20 mg/kg, i.v.); the inhibition was re-established by L-DOPA (20 mg/kg, i.v.) or apomorphine (20 mg/kg, i.v.) indicating that a dopaminergic link has access to the descending inhibitory action on segmental transmission of “pain” impulses. Both nigral and PAG actions were sensitive to methysergide (1 mg/kg, i.v.), while the serotonergic blockade could be overcome by 5-hydroxytryptamine (70 mg/kg, i.v.). We proposed that nigral and PAG actions were relayed in part through the descending raphe system. Through this relay, they exhibit their antinociceptive effects.     

Effects of drugs on stimulus control of behavior. III. Analysis of effects of pentobarbital and d-amphetamine

Key-peck responses of pigeons on one of two keys were reinforced intermittently under a multiple fixed-interval schedule. In one component of the schedule, a houselight provided general illumination of the experimental chamber, and responses on a red key produced food according to a 5-min fixed-interval schedule. In the alternate component, the houselight was off and responses on an amber key produced food according to the 5-min fixed-interval schedule. Each response randomly (P = .5) alternated the positions of the key colors (right or left) and the two components (houselight on or off) alternated in a mixed sequence. Thus, there were two sources of discriminative control over responding: 1) the presence or absence of the houselight and 2) the key colors. Stimulus control was assessed by comparing the relative frequencies of red-key responses in the presence and absence of the houselight. Pentobarbital decreased stimulus control of responding at intermediate (3.0-10.0 mg/kg) doses that did not appreciably alter average rates of responding. Whereas d-amphetamine decreased stimulus control only at high doses (3.0-5.6 mg/kg) that also substantially decreased response rates. The results of subsequent studies suggested that the two drugs primarily affected stimulus control exerted by the colors of the response keys. Furthermore, the effects on stimulus control produced by the two drugs were modified by a number of environmental conditions, in particular those that alter the degree of stimulus control existing before drug administration.     

Reproducibility of sonographic measurement of the substantia nigra

The aim of this study was to evaluate inter-reader, intra-investigator and inter-investigator reproducibility and correlations in the assessment of substantia nigra (SN) echogenicity and area measurement by a physician-sonographer (PS), a sonographic laboratory assistant (SLA) and a physician without sonographic experience (PN). A total of 22 patients with extrapyramidal symptoms were examined using transcranial sonography (TCS). SN images were encoded and evaluated by the three readers. A second TCS examination was performed after 7+/-2 d. A second investigator performed TCS examination 1 mo later. Spearman rank correlation and Pearson's correlation coefficient were used when assessing the agreement between readers. All three readers identified the same 15 patients with SN echogenicity III or more. Inter-reader SN echogenicity and area measurement correlations were r=0.55 to 0.82 and r=0.31 to 0.74 between PS and SLA and r=0.55 to 0.77 and 0.49 to 0.62 between PS and PN, respectively (p<0.05 in all cases). Intra-reader echogenicity and area measurement correlations (r=0.85 to 0.96 and r=0.51 to 0.69) were statistically significant only for PS (p<0.001). All intra- and inter-investigator correlations of SN area measurement (r=0.69 to 0.88 and r=0.5 to 0.61) and SN echogenicity (r=0.64 to 0.92 and r=0.51 to 0.69) were statistically significant (p<0.05). Semiquantitative evaluation of SN echogenicity and area using TCS is highly dependent on the experience of the sonographer. Only an experienced sonographer was able to produce very reproducible results with statistically significant correlations; SLA and PN intra-reader correlations were poor.     

Iron accumulation in the substantia nigra in rats visualized by ultrasound.

In recent studies, we have found a marked increase in substantia nigra (SN) echogenicity in patients with Parkinson's disease (PD) using transcranial ultrasound. Because a substantial body of evidence has accumulated indicating a selective elevation of iron in the SN from patients with PD, we set out to test the hypothesis that trace metals like iron could lead to the observed increase of SN echogenicity in PD. Rat brains were scanned after stereotactic injection of iron in different concentrations into the SN and after injecting ferritin, zinc and 6-OHDA alone, and after the addition of desferrioxamine. The amount of iron in the SN was measured spectroscopically. For iron, and partly for 6-OHDA, in different concentrations, a dose-dependent increase of SN echogenicity could be visualized, corresponding to an increase of iron measured by spectroscopy. No increase of echogenicity was visualized after the injection of ferritin and the addition of desferrioxamine to 6-OHDA, though an increase of iron was measured by spectroscopy. Therefore, we conclude that iron not bound to these proteins may lead to an increase of echogenicity of the SN.     

抑颤汤对帕金森病大鼠旋转行为、黑质细胞及神经递质的影响

目的:探讨抑颤汤治疗帕金森病在脑黑质细胞及神经递质方面的作用机制。方法:运用6-羟基多巴诱发法建立帕金森病大鼠模型,通过随机分组,观察抑颤汤对帕金森病大鼠行为特征的影响;采用脑组织液微透析技术,用高效液相色谱法测定各组大鼠脑组织细胞外液中儿茶酚胺类物质含量的变化,并分别用光镜和电镜观察各组大鼠脑黑质细胞的形态学变化。结果:治疗后40min旋转次数抑颤汤组为(61.63±17.93)次,生理盐水组为(340.90±52.97)次,表明抑颤汤能明显改善帕金森病模型大鼠的旋转行为(t=2.762,P<0.01);帕金森病大鼠损毁侧脑组织透析液中3,4-二羟基苯酸(DOPAC)、高香草酸、多巴胺、5-羟色胺水平明显低于未损毁侧(P<0.05或P<0.01),治疗后抑颤汤组含量则明显高于生理盐水对照组(P<0.05或P<0.01),而未损毁侧各递质的含量3组比较差异均没有统计学意义(P>0.05);病理学观察,大鼠受损侧脑黑质神经细胞数量抑颤汤组明显比生理盐水组多,且神经元体积较饱满,结构较清晰,细胞内高尔基氏体、线粒体等接近正常。结论:抑颤汤能减轻帕金森病模型大鼠脑黑质细胞的受损程度,促进其修复,改善黑质纹状体系统的分泌功能,提高脑组织中内源性儿茶酚胺类物质的含量,从而改善帕金森病大鼠的旋转行为。     

Neurotensin-dopamine interactions in the substantia nigra of the rat brain

Single or multiple doses of the potent dopamine releaser, methamphetamine (METH), increases the content of neurotensin (NT)-like immunoreactivity (NTLI) in the substantia nigra of the rat brain by 2- to 3-fold. Concurrent blockade of D-1 receptors with METH treatment completely antagonized the increase in nigral NTLI content induced by this drug. These results suggest that activation of D-1 receptors by endogenous dopamine results in an increase in the level of NTLI in the substantia nigra. The present study was performed to characterize further the mechanisms underlying dopaminergic regulation of nigral NT systems. Prior selective destruction of the nigrostriatal dopamine pathway completely prevented the increase in nigral NTLI content induced by treatment with METH, which suggests that the effects of METH on nigral NT systems are mediated by the nigrostriatal dopamine projections. However, unlike METH, treatment of rats with the direct-acting, D-1-selective agonist, SKF 38393, did not alter nigral NTLI content but when combined with stimulation of D-2 receptors, a significant increase in the level of NTLI occurred. Surprisingly, activation of only D-2 receptors caused a significant decrease in nigral NTLI content. These data suggest that although activation of D-2 receptors alone has an effect opposite to that of the D-1 subtype, in combination with D-1 stimulation they facilitate the effect of D-1 receptors on nigral NT systems. In addition to the effects of direct or indirect stimulation of dopamine activity on nigral NT levels, basally released dopamine also appeared to regulate the level of NTLI in the substantia nigra. Thus, interruption of tonic dopamine activity by reserpine-induced depletion of dopamine significantly reduced the level of NTLI in the substantia nigra. The role of D-1 receptors in this tonic dopaminergic regulation of nigral NT systems was evident when concurrent activation of D-1, but not D-2, receptors with reserpine treatment prevented or reversed the decrease in NTLI content caused by dopamine depletion. Additional evidence for the D-1-mediated tonic regulation of NT systems in the substantia nigra was that blockade of D-1 receptors with SCH 23390 decreased the nigral NTLI content but blockade of D-2 receptors with sulpiride had no effect.     

银杏叶提取物及银杏总内酯对帕金森病大鼠黑质神经元损伤的保护作用

目的:观察银杏叶提取物及银杏总内酯预防和治疗帕金森病模型大鼠黑质细胞损伤的作用。方法:实验于2004-07在锦州医学院动物实验室完成。选用健康成年SD雄性大鼠80只。①预防性用药实验:选取40只大鼠,随机分为5组,每组8只:银杏叶提取物预防组,按100mg/kg剂量灌胃银杏叶提取物溶液(含黄酮24%,银杏内酯6%,由北京第四制药厂提供,生产批号0310469,5mL/支),银杏总内酯高剂量预防组,按12mg/kg剂量给予银杏总内酯溶液(首都医科大学药物研究所提供,生产批号2003196,2mg/支),银杏总内酯低剂量预防组,按6mg/kg剂量给予银杏总内酯溶液,对照组和模型组灌胃等体积生理盐水。给药1次/d,连续14d,最末次给药1h后,模型组和用药组通过6-羟基多巴脑立体定向注射术建立帕金森病大鼠模型。②治疗性用药实验:于另40只大鼠中选用8只为对照组(灌胃等体积生理盐水)。将其余32只造成帕金森病模型,均造模成功。随机分为4组,每组8只:银杏叶提取物治疗组(按100mg/kg剂量灌胃银杏叶提取物溶液),银杏总内酯高剂量治疗组(按12mg/kg剂量给予银杏总内酯溶液),银杏总内酯低剂量治疗组(按6mg/kg剂量给予银杏总内酯溶液),模型组(灌胃等体积生理盐水)。给药1次/d,连续14d。③预防性给药组于造模后,治疗性给药组于给药14d后将各组大鼠断头取脑,分离双侧纹状体,采用高压液相色谱仪紫外检测器测定多巴胺浓度;严格按购于南京建成生物研究所的试剂盒说明对右侧黑质超氧化物歧化酶、丙二醛含量进行检测。④计量资料差异比较采用t检验。结果:大鼠80只均进入结果分析。①多巴胺含量:银杏叶提取物预防组和银杏总内酯高、低剂量预防组和对照组大鼠患侧纹状体明显高于模型组(P<0.05～0.01);各组健侧纹状体差异不明显(P>0.05);银杏总内酯高剂量治疗组帕金森大鼠患侧纹状体明显高于模型组(P<0.05),对照组大鼠患侧纹状体明显高于模型组(P<0.01);各组健侧纹状体差异不明显(P>0.05)。②右侧黑质丙二醛含量:各用药预防组和各用药治疗组及对照组明显低于模型组(P<0.05)。③右侧黑质超氧化物歧化酶活力:各用药预防组和各用药治疗组及对照组明显高于模型组(P<0.05)。结论:银杏叶提取物及银杏总内酯可以预防和对抗6-羟基多巴造成的黑质多巴胺能神经元损伤。     

Low-dose methylphenidate actions on tonic and phasic locus coeruleus discharge

Methylphenidate (MPH) and other psychostimulants are highly effective in the treatment of attention deficit hyperactivity disorder (ADHD). Evidence indicates the therapeutic actions of stimulants in ADHD probably involve the locus coeruleus (LC)-norepinephrine system. LC neurons display different firing modes (tonic and phasic), each associated with distinct behavioral and cognitive processes. To date, the impact of low, clinically relevant doses of psychostimulants on LC discharge is unknown. The present study examined the effects of low-dose MPH on LC tonic and phasic discharge in the halothane-anesthetized rat. In these studies, MPH produced a dose-dependent suppression of tonic and phasic discharge that was relatively modest at the lower doses. Nonetheless, these lower doses of MPH suppressed the signal-to-noise ratio of excitatory phasic discharge and increased the signal-to-noise ratio of the inhibitory component of the phasic response. Largely comparable effects were observed with oral and intraperitoneal administration of MPH. Combined, these observations indicate relatively modest suppression of LC neuronal discharge activity by low-dose MPH and that evoked discharge may be more sensitive than tonic activity to the lowest doses of MPH. It is posited that the behavioral-calming and cognition-enhancing effects of low-dose psychostimulants probably involve modest alterations in LC discharge combined with increased catecholamine efflux within select forebrain regions (i.e., the prefrontal cortex).     

银杏叶提取物及银杏总内酯对帕金森病大鼠黑质神经元损伤的保护作用

目的：观察银杏叶提取物及银杏总内酯预防和治疗帕金森病模型大鼠黑质细胞损伤的作用。 方法：实验于2004—07在锦州医学院动物实验室完成。选用健康成年SD雄性大鼠80只。①预防性用药实验：选取40只大鼠，随机分为5组，每组8只：银杏叶提取物预防组，按100mg／kg剂量灌胃银杏叶提取物溶液（含黄酮24％，银杏内酯6％，由北京第四制药厂提供，生产批号0310469，5mL／支），银杏总内酯高剂量预防组，按12mg／kg剂量给予银杏总内酯溶液（首都医科大学药物研究所提供，生产批号2003196，2mg／支），银杏总内酯低剂量预防组，按6mg／kg剂量给予银杏总内酯溶液，对照组和模型组灌胃等体积生理盐水。给药1次／d，连续14d，最末次给药1h后，模型组和用药组通过6-羟基多巴脑立体定向注射术建立帕金森病大鼠模型。②治疗性用药实验：于另40只大鼠中选用8只为对照组（灌胃等体积生理盐水）。将其余32只造成帕金森病模型，均造模成功。随机分为4组，每组8只：银杏叶提取物治疗组（按100mg／kg剂量灌胃银杏叶提取物溶液），银杏总内酯高剂量治疗组（按12mg／kg剂量给予银杏总内酯溶液），银杏总内酯低剂量治疗组（按6mg／kg剂量给予银杏总内酯溶液），模型组（灌胃等体积生理盐水）。给药1次／d，连续14d。③预防性给药组于造模后，治疗性给药组于给药14d后将各组大鼠断头取脑，分离双侧纹状体，采用高压液相色谱仪紫外检测器测定多巴胺浓度；严格按购于南京建成生物研究所的试剂盒说明对右侧黑质超氧化物歧化酶、丙二醛含量进行检测。④计量资料差异比较采用t检验。 结果：大鼠80只均进入结果分析。①多巴胺含量：银杏叶提取物预防组和银杏总内酯高、低剂量预防组和对照组大鼠患侧纹状体明显高于模型组（P〈0．05～0．01）；各组健侧纹状体差异不明显（P〉0．05）；银杏总内酯高剂量治疗组帕金森大鼠患侧纹状体明显高于模型组（P〈0．05），对照组大鼠患侧纹状体明显高于模型组（P〈0．01）；各组健侧纹状体差异不明显（P〉0．05）。②右侧黑质丙二醛含量：各用药预防组和各用药治疗组及对照组明显低于模型组（P〈0．05）。③右侧黑质超氧化物歧化酶活力：各用药预防组和各用药治疗组及对照组明显高于模型组（P〈0．05）。 结论：银杏叶提取物及银杏总内酯可以预防和对抗6-羟基多巴造成的黑质多巴胺能神经元损伤。     

Effects of N-n-propylnorapomorphine enantiomers on single unit activity of substantia nigra pars compacta and ventral tegmental area dopamine neurons

Prompted by conflicting reports of both agonist and antagonist properties of the S-(+)-enantiomer of the potent dopamine agonist R-(-)-N-n-propylnorapomorphine (NPA), we carried out extracellular, single unit recording studies to compare the effects of both enantiomers on substantia nigra and ventral tegmental area (VTA) dopamine neurons in male rats anesthetized with chloral hydrate. Like the classic dopamine agonist apomorphine, R-(-)-NPA inhibited cell firing in both populations. Mean cumulative doses to inhibit firing by 50% (ID50) were 0.53 micrograms/kg for nigral and 0.50 micrograms/kg for VTA dopamine cells, respectively, reflecting a potency for R-(-)-NPA 10-fold greater than that of apomorphine for inhibition of nigral dopamine cells (ID50 5.3 micrograms/kg). Inhibitions elicited by R-(-)-NPA could be fully reversed by i.v. haloperidol (0.2 mg/kg) but not by S-(+)-NPA in doses up to 0.9 mg/kg. Interestingly, S-(+)-NPA also exhibited agonist activity in both cell groups but with a much lower potency than R-(-)-NPA. In addition, VTA dopamine cells displayed a significantly greater sensitivity to the drug: ID50 values of 149 micrograms/kg vs. 514 micrograms/kg for VTA and substantia nigra neurons, respectively (P less than .01). Prior administration of haloperidol (0.1 mg/kg) consistently and fully prevented the inhibitory effects of S-(+)-NPA on all cells tested, although subsequent administration of haloperidol (up to 1.6 mg/kg) did not reverse completely S-(+)-NPA-induced inhibitions in all cases.(ABSTRACT TRUNCATED AT 250 WORDS)     

Microiontophoretic studies on noradrenergic inhibition from locus coeruleus of spinal trigeminal nucleus neurons.

Microiontophoretic studies using cats anesthetized with alpha-chloralose and local anaesthetic were undertaken in an attempt to determine whether or not norepinephrine (NE) derived from the locus coeruleus (LC) acts on neurons of the spinal trigeminal nucleus (STN) as an inhibitory transmitter. Both conditioning stimulation of the LC and iontophoretic application of NE inhibited orthodromic spike generation by interior alveolar nerve stimulation in 9 out of 14 STN relay neurons, without affecting antidromic spikes elicited by stimulation of the contralateral medial lemniscus. Glutamate-induced spike firing of the STN relay neurons, however, remained unaltered with iontophoretic application of NE up to 200 nA. The LC conditioning stimulation inhibited orthodromic spikes in 22 out of 25 type-B interneurons in the STN, while iontophoretic NE application seldom had an effect on orthodromic spikes and spontaneous firing of the interneurons. Only 5 out of the 25 interneurons exhibited an inhibition of orthodromic spike generation and spontaneous firing with iontophoretic NE. These neurons fired spikes upon orthodromic stimulation with a relatively short latency, compared with the spike latency of neurons unaffected by iontophoretic NE. The present results strongly suggest that NE released from the terminals of the LC neurons inhibits transmission of STN relay neurons, probably by acting on primary afferent terminals to produce presynaptic inhibition.     

In vivo mapping of the human locus coeruleus

The locus coeruleus (LC) is a brainstem structure that has widespread cortical and sub-cortical projections to modulate states of attention. Our understanding of the LC's role in both normal attention and clinical populations affected by disrupted attention would be advanced by having in vivo functional and structural markers of the human LC. Evidence for LC activation can be difficult to interpret because of uncertainty about whether brainstem activity can be accurately localized to the LC. High resolution T1-turbo spin echo (T1-TSE) magnetic resonance imaging (MRI) (in-plane resolution of 0.4 mm × 0.4 mm) was used in this study to characterize the location and distribution probability of the LC across 44 adults ranging in age from 19 to 79 years. Utilizing a study-specific brainstem template, the individual brainstems were aligned into standard space, while preserving variations in LC signal intensity. Elevated T1-TSE signal was observed in the rostral pons that was strongly correlated with the position and concentration of LC cells previously reported in a study of post-mortem brains (r = 0.90). The elevated T1-TSE signal was used to produce a probabilistic map of the LC in standard Montreal Neurological Institute (MNI) coordinate space. This map can be used to test hypotheses about the LC in human structural and functional imaging studies. Such efforts will contribute to our understanding of attention systems in normal and clinical populations.