The Neurotoxicology of attention deficits: Dietary Manganese Exposure as a

Particular Case  

Sabrina E.B. Schuck, Ph.D., Melody Yi, Ph.D. & Francis M. Crinella, Ph.D.

The Child Development CenterUniversity of California, Irvine

Everyone knows what attention is. It is the taking possession in the mind, in clear and vivid form, of one out of what seem several simultaneous object or trains of thought.

William James [The Principles of Psychology, 1890]

ATTENTION HELPS US TO MANAGE CONFLICTING PERCEPTUAL INPUTS

ATTENTION ALLOWS US TO PERSIST IN TASK PERFORMANCE

ATTENTION HELPS US FOCUS ON THE TASK AT HAND

ATTENTION ENABLES US TO PERFORM TASKS THAT REQUIRE PLANNING AND

WORKING MEMORY

ATTENTION ENABLES US TO MAINTAIN VIGILANCE WHEN MONITORING SIGNALS

ATTENTION ENABLES US TO AVOID COSTLY ERRORS

HOWEVER: ATTENTION IS THE MOST FRAGILE OF ALL MENTAL FUNCTIONS

1. ATTENTION CAN BE ADVERSELY AFFECTED BY ANY NUMBER OF INTERNAL AND EXTERNAL INFLUENCES

2. ALL NEURODEVELOPMENTAL AND NEUROPSYCHIATRIC DISORDERS ARE ACCOMPANIED BY ATTENTION DEFICITS

3. ADHD IS BUT ONE OF MANY DIAGNOSABLE CONDITIONS IN WHICH ATTENTION IS AFFECTED

DSM-IV SYMPTOMS OF ADHD

INATTENTION

• CAN’T ATTEND TO DETAILS• CAN’T SUSTAIN ATTENTION• DOESN’T LISTEN• FAILS TO FINISH• CAN’T ORGANIZE TASKS• AVOIDS SCHOOLWORK• LOSES THINGS• EASILY DISTRACTED• FORGETFUL

HYPERACTIVITY/IMPULSIVITY

• FIDGETS• CAN’T STAY SEATED• RUN ABOUT AND CLIMBS• CAN’T PLAY QUIETLY• IS OFTEN ON THE GO• TALKS TOO MUCH• BLURTS OUT ANSWERS• CAN’T WAIT TURN• INTERRUPTS OR INTRUDES

BIOLOGICAL BASIS OF ADHD

I. PSYCHOPHARMACOLOGY

II. MOLECULAR BIOLOGY

III.BRAIN IMAGING

IV.ELECTROPHYSIOLOGY

V. NEUROPSYCHOLOGY

I. PSYCHOPHARMACOLOGY

TREATMENT WITH CNS STIMULANTS

BENZEDRINE (Bradley, 1937)

DEXTROAMPHETAMINES (e.g., Dexedrine, Adderall)

METHYLPHENIDATES (e.g., Ritalin, Concerta)

THE DOPAMINE HYPOTHESIS

Wender P. Minimal brain dysfunction in children. Wiley-Liss, New York (1971).

 

Levy F. The dopamine theory of attention deficit hyperactivity disorder (ADHD). Aust. N. Z. J. Psychiatry 25, 277-83 (1991).

Grady D, Moyzis R, Swanson JM. Molecular genetics and attention in ADHD. Clin. Neurosci. Res. 5, 265-272 (2005).

BIOLOGICAL BASIS OF ADHD II: MOLECULAR BIOLOGY

• DOPAMINE D4 RECEPTOR GENE POLYMORPHISM ASSOCIATED WITH ADHD (Lahoste, Swanson et al., 1996, Molecular Psychiatry)

• ASSOCIATION OF THE DOPAMINE RECEPTOR D4 (DRD4) GENE WITH A REFINED PHENOTYPE OF ADHD (Swanson, Sunohara, Kennedy et al., 1998, Molecular Psychiatry)

• MOLECULAR GENETICS AND ATTENTION IN ADHD (Grady, Moyzis & Swanson, 2005, Clinical Neuroscience Research)

From Grady, Moyzis & Swanson, (2005), Clinical Neuroscience Research, 5, 265-272

From Grady, Moyzis & Swanson (2005), Clinical Neuroscience Research, 5, 265-272.

BIOLOGICAL BASIS OF ADHD III: STRUCTURAL

IMAGING

LONGITUDINAL MAPPING OF CORTICAL THICKNESS AND CLINICAL OUTCOME IN CHILDREN AND ADOLESCENTS WITH ATTENTION-DEFICIT/HYPERACTIVITY DISORDER. Shaw, Lerch, Greenstein et al. (2006), Archives of Genetic Psychiatry, 63, 540-549.

IV. ELECTROPHYSIOLOGYEarly studies of analog EEG:

Satterfield, J.H., & Schell, A.M. (1984). Childhood brain function differences in delinquent and non-delinquent hyperactive boys. Electroencephalography and Clinical Neurophysiology, 57, 199-207.

Finding: Abnormal maturational effects of auditory event- related potential differentiated ADHD from non-ADHD subjects

Recent brain mapping studies:

Pliszka, S.R., Liotti, M., & Woldorff, M.G. (2000). Inhibitory control in children with attention-deficit/hyperactivity disorder. Biological Psychiatry, 48,238-46.

Finding: Event related potentials identify the processing component and timing of an impaired right-frontal response-inhibition mechanism.

V: NEUROPSYCHOLOGICAL EVIDENCE

• ADHD conceptualized as “frontal lobe” disorder (e.g., Douglas, 1980; Chelune et al., 1986)

• ADHD conceptualized as disorder of “executive function” (Pennington et al., 1990; Barkley 1997; Schuck & Crinella, 2000)

Brief Definitions of Executive Function

• Appropriate set maintenance to achieve a future goal (Pennington, Welsh & Grossier, 1990)

• A process that alters the probability of subsequent responses to an event, thereby altering the probability of later consequences (Barkley, 1997).

• A process which enables the brain to function as many machines in one, setting and resetting itself dozens of times in the course of a day, now for one type of operation, now for another (Sperry, 1955)

EXECUTIVE FUNCTIONS CAN BE ADVERSELY AFFECTED BY ANY

NUMBER OF NEUROTOXINS

FOR EXAMPLE:

• PESTICIDES

• LEAD (Pb)

• CNS STIMULANTS

Odds Ratio of Detectable Pesticide in SerumChildren 8-12 Years Old (n = 167)

Oahu vs. Neighbor Islands

3.8

1.7

1.01.4

0

1

2

3

4

5

HeptachlorEpoxide

pp'-DDE Oxychlordane trans-Nonachlor

From Baker, Yang & Crinella, 2004, Neurotoxicology, 25, 700-701

STANDARD SCORES ON NEUROBEHAVIORAL TESTS FOR SUBJECTS BORN ON OAHU (n = 332) vs.

SUBJECTS BORN ELSEWHERE (n = 112)

STUDIES ASSOCIATING HAIR MANGANESE [Mn] LEVELS WITH ADHD

Pihl, R.O. & Parks, M. (1977). Hair element content in learning disabled children. Science, 198, 204-206.

Collip, P.J., Chen, S.Y. & Maitinsky, S. (1983). Manganese in infant formulas and learning disability. Annals of Nutrition and Metabolism, 27, 488-494.

Marlowe, M. & Bliss, L. (1993). Hair element concentrations and young children's behavior at school and home. Journal of Orthomolecular Medicine, 9, 1-12.

Cordova, E.J., Ericson, J., Swanson, J.M., & Crinella, F.M. (1997). Head hair manganese as a biomarker for ADHD. Proceedings of the 15th Annual Conference on Neurotoxicology.

HEAD HAIR Mn LEVEL

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

ADHD CONTROL

PPM

IS MN EXPOSURE AN ETIOLOGIC AGENT IN ADHD?

1. CHILDREN WITH ADHD HAVE HIGH LEVELS OF HEAD HAIR MN

2. MN IS A KNOWN NEUROTOXIN

3. MN TOXICITY AFFECTS BRAIN DOPAMINE SYSTEMS

4. ADHD IS A PRIMARILY DOPAMINERGIC DISORDER

Critical Observations Regarding Mn in infants and children

Manganese in head hair of children with ADHD may be the result of soy-based infant formulas (Collip et al., 1983)

Term infants fed soy formula have significantly higher blood Mn than breast-fed infants (Kirchgessner et al., 1981)

High, positive retention of Mn from formula, but not breast milk in preterm infants (Lonnerdal, 1994)

INFANT DIETARY MN INTAKE

HYPOTHESES

Since Mn is well absorbed from infant diets, and absorbed Mn is retained by the body, it will accumulate in brain, resulting in:

1. Depleted striatal DA

2. Neuromotor delay

3. Executive function deficits

an

Other measurements Hb and Wt

Control (0)50 µg Mn/d250 µg Mn/d500 µg Mn/d

Tissue Mn Assays

d1 d6 d10 d14 d20 d35 d58 d60

Passive Avoidance (60-64)

Digging latencyrunning time (d58)

Passive Avoidance(d35)Righting

(d6) Homing(d10)

Concentrations of Mn in brain of rats killed at day 14, 21 and 35

Brain

0

1

2

3

4

d14 d21 d35

0250500

Striatal Dopamine in Animals Killed at d35

0

10

20

30

0 50 250 500

Mn dose (ug/day)

DA

(n

g/1

0 m

g w

et

tiss

ue)

*Significant difference between control and low Mn exposure

**

PASSIVE AVOIDANCE TEST

Results of Passive Avoidance Test at d32

control 50 ug 250 ug 500 ug0.0

2.5

5.0

7.5

Mn (ug/day)

No

. o

f F

oo

tsh

ock

s

Results of Burrowing Detour Test d55

Digging Latency

Control 50 250 5000

100

200

300

400

500

Mn (g/day)

Tim

e (

sec)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 50 250 500

TREATMENT LEVEL (ug/l)

DA

LE

VE

L (n

g/m

g)STRIATAL DOPAMINE LEVELS AT d65

NONHUMAN PRIMATE MODELS

ADVANTAGES OVER RODENT MODEL– Maturity of brain development at birth– Prolonged period of postnatal brain

development– Complexity of behavioral repertoire– Assessments similar to humans

Study Design

• Subjects: Male newborn rhesus monkeys

• Treatment: Exclusively formula fed freom 0-4 months of age

• Groups (n = 8): Cow’s milk based infant formula, 0.03 µg

Mn /ml Soy based infant formula, 0.3 µg Mn/ml Soy + Mn; soy based infant formula with

added manganese, 1 µg Mn/ml

Behavior testing schedule APOMORPHINE DRUG CHALLENGE

NON-MATCH TO SAMPLE

POSITION REVERSAL

DIURNAL ACTIVITY

MOTOR MATURATION

IMPULSIVITY TESTS:

CPT

FORMULA FEEDING

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Gross Motor Maturation

02468

10 12 14 16 18 20

0

5

10

15

20

25

30

0

2

4

6

8

10

0

2

4

6

8

10

12

14

02468

10 12 14 16 18 20

0

1

2

3

4

5

Walk

Climb

Manual

1 2 3 4 5 6 7 8 9 10 11 12

Session

Soy + Mn

Soy

Control

Amount of activity

0

20

40

60

80

100

120

Num

ber

of c

ount

s/ 2

min

0

2

4

6

8

10

12

14

4 months 8 months

SLEEP

WAKE

Soy + Mn

Soy

Cow’s milk

*.01

WGTA

Sliding test board

One-way mirror Door on pulley

Delayed nonmatch to sample

0

.02

.04

.06

.08

.1

.12

Per

cent

Balks-no sample choice made

.

.

.

.

.

Soy + Mn

Soy

Cow’s milk

Test board 1

Test board 2

Position reversals

0

1

2

3

4

5

6

7

8

Sess

ions

Test board

sessions to criterion for learning

6Soy + Mn

Soy

Cow’s milk

*.05

Test board

MOTORIMPULSIVITYTEST

Food reward

Sliding opaque cover

Impulsivity-response inhibition

0

2.5

5

7.5

10

12.5

15

17.5

20

22.5

25

num

ber

of

tria

ls

*.04

*.03

0 1-6 7 balk interval

average number of trials (of 40) on which the monkey responded at each interval

Soy + Mn

Soy

Cow’s milk

CANTABFixed interval;dopamine challenge

Continuous performance test

Dopamine drug challenge

-150

-125

-100

-75

-50

-25

0

25

50

75

100

Cha

nge

in r

espo

nse

rate

fro

m v

ehic

le in

ject

ion

0.1 mg/kg

0.2 mg/kg .0.3 mg/kg

-------apomorphine-----

*.01

*.02haloperidol haloperidol+

apomorphine

amphetamine

apomorphine, dopamine agonist, response ratehaloperidol, dopamine antagonist, response rate

Fixed interval responding

Soy + Mn

Soy

Cow’s milk

Social Interaction Study

• Method-videotape of dyadic interaction

• Familiar same group, unfamiliar same group, unfamiliar opposite group

• Social buffering

• Used previously to compare field cage with nursery reared males

0

5

10

15

20

25

30

35

40

num

ber

of o

ccur

renc

es

Chase play Rough play cling

Soy+Mn

Soy

control

dyadic interactions during round robin socialization (16 sessions)

*.003

*.01

*.003

*.003

.06

*.03

Age and formula effects onCSF catecholamine metabolites

0

20

40

60

80

100

120

140

160

Cel

l Mea

n

hi mn

low mn

control

0

50

100

150

200

250

300

350

400

450

500

Cel

l Mea

n

5HIAA HVA

3 10 12 3 10 12

Months of age

Relationship between CSF catecholamine metabolites and impulsivity

51015202530354045

10 20 30 40 50 60 70 80 90 100

R2 = 0.156

5HIAA- 10 months of age

51015202530354045

Ear

ly re

spon

ses

150 200 250 300 350 400 450 500 550

R2 = 0.19

HVA- 10 months of age

THE “TOOTH FAIRY” STUDY

• Participants: 27 children (11 boys) from the NICHD Study of Early Child Care and Youth Development

• Procedures:•

– Shed molars collected from 400 children (ages 11-13); 27 teeth randomly selected

– Measures of children’s behavioral disinhibition collected from ages 3 to 9 years.

– IMS analyses of teeth performed by CAMECA IMS 1270

– Concentration of manganese in the molar cusp tip (formed at approximately the 20th gestational week) used as an indication of prenatal Mn absorption

Tooth Enamel Biomarker

• Tooth enamel layers, like tree rings, provide a temporal record of mineral absorption

• Absorbed minerals, as reflected in the tooth enamel record, may be associated with embryogenetic variations

• Depending on corresponding embryological developments in CNS, Mn absorption, as reflected in tooth enamel record, may be associated with specific variation in behavioral outcomes

Human Tooth Enamel

• As tooth develops over rime, incremental growth rings of enamel are deposited

• Oldest enamel is found at the incisal tip

• Mature enamel is a metabolic isolate

• Mn is stable in calcium hydroxyapatite

Analytical Measurements

• ion microprobe mass spectrometer (ims)• 10 - 35 um spot resolution• auger & sputter sample• measurement of Mn concentration• detection <30 ppb• 90% accuracy

Behavior Battery

• Data base of NICHD Early Childhood Study

• Administered Age 3, Grade 1 and Grade 3• Teachers, mothers, and standardize tests

of subjects• 21 behavior measures (disinhibition,

intelligence and depression) over 5 years• Same subjects maintain position

RESULTSMn LEVELS WERE POSITIVELY CORRELATED

WITH:

Increased play with “Forbidden Toy” (36 mo.)

More impulsive errors on CPT (54 mo.)

More impulsive errors on Stroop Test (54 mo.)

Higher ratings on externalizing behavior and attentional problems (teachers and mothers; 1st and 3rd grades)

Higher incidence of disruptive disorders (ADHD, hyperactivity/impulsivity, and inattention (teachers, 1st and 3rd grades)

MULTIPLE REGRESSION ANALYSIS

(Predicting Mn Level With Behavioral Measures)

CPT (54 months)

Stroop (54 months)

CBCL Inattention (1st grade)

DBD3 HYPERACTIVITY (3RD GRADE)

R2 = 0.62; df = 4, 26; P < .001

Adjustment for socioeconomic confounds did not increase significance

• Mother’s education

• Income

• Ethnicity

(F of change = .13, p = .97)

DISCUSSION• A link was demonstrated between prenatal Mn

absorption and measures of behavioral disinhibition in later childhood

• The source of Mn was unknown, but may have been due to maternal gestational anemia, a common occurrence during pregnancy that results in overabsorption of Mn.

CONCLUSIONS• Attention deficits are observed in almost all neuropsychiatric

disorders, including ADHD

• ADHD symptoms may are associated with a number of genetic, epigenetic and environmental influences, including toxic exposures

• Mn serves as an example of a toxic exposure that can produce ADHD-like symptoms in rodents, non-human primates, and humans

• The Mn-ADHD link is likely to be mediated by toxic effects on DRD4 and DAT genes.

CONCLUSIONS (CONT’D)• The Mn-ADHD link is likely to be mediated by toxic effects on DRD4

and DAT genes.

• A DAT1 40bp VNTR 9/10 polymorphism was reliably associated with greater symptoms of ADHD. Barkley, Smith, Fischer & Bradford, (2006), American Journal of Medical Genetics. 141B, 487-498.

• And, there is persistent evidence that DAT can be adversely impacted by Mn. Kern, Stanwood & Smith, (2010), Synapse, 64, 363-378.

CONTRIBUTORS  University of California, Irvine

Aleksandra Chicz-DeMetLouis LeMike ParkerJonathon E. EricsonK. Alison Clarke-StewartVirginia D. AllhusenTony ChanRichard T. Robertson

University of California, DavisBo LonnerdalMari GolubWinyoo ChowanadisaiStacey GermannCasey Hogrefe

University of California, San FranciscoTrinh Tran

City University of New YorkJoey Trampush