The Society for Integrative and Comparative Biology, Annual Meeting

Chicago, Illinois January 3-7 2001 Symposium on “Stress: A Comparative Look at Stress

and Adaptation”

Neil GreenbergDepartment of Ecology and Evolutionary Biology

The University of Tennessee, Knoxville

Causes and Consequences

of Stress in lizards

My deep gratitude to:

Colleagues:

Tom Chen, David Crews, Tom Jenssen, Cliff Summers

Graduate Students:

Enrique Font, Jenn Harris

And . . .

Mentors and role-models: Danny Lehrman

Colin Beer

Paul D. MacLean

Stressors and Coping Responses

The organism possesses a remarkable sense of biological priorities

Mechanisms that helped cope with stressors -- fragments of motor patterns and autonomic reflexes -- have been cobbled together by evolution (“bricolage”).

Stressor is a real or perceived challenge to an organism’s ability to meet its real or perceived needs.

Real or perceived NEEDS that must be met:

Physiology ( Homeostasis) (Food comes first, then morals. -Bertolt Brecht)

Safety (security, order, protection)

Sociality ( acceptance, “acceptance”)

Esteem (better reproductive opportunities status, prestige;)

Self-Actualization (reproduction; direct or indirect fitness; “personal fulfillment”)

-apologies to

Maslow

Coping . . .

STRESSORS are internal or external changes which by challenging an organism’s ability to meet its needs evokes a coordinated coping response

. . . constrained by a threshold for detection of the change, for attention based on real or perceived relevance, and capacity to respond at any particular level once the challenge is detected.

COPING RESPONSES:constraints of the system

Input (stress can change the sensitivity of sense organs (e.g., Gandelman 1983); resolve competitive parallel afferent pathways,)

Integration (receptive field modulation; stress can affect arousal, selective attention (e.g., Archer 1973, R.J. Andrew 1972); differential regional sensitivity to hormones or neurotransmitters (e.g., Amy Arnsten 2000); control of microcirculation (e.g., Palmer 1986)

Output (resolve competitive parallel efferent paths to action; energetic reserves and the ability to mobilize them)

COPING RESPONSES: stress sensitive hormones

Sympathoadrenomedullary (SAMS) response (adrenal medullary /chromaffin response to sympathetic activation)

Hypothalamic-pituitary-adrenal (HPA) axis activation (CRF, ACTH, adrenal glucocorticoids)

Opioids (endorphin, enkephalin; affects perception of pain and reproductive axis)

Prolactin (affects reproductive axis)

Angiotensin, Melanotropin?

COPING RESPONSES:problems of interpretation

Bi-phasic (“paradoxical”) responses (responses can be diametrically opposed depending on absolute levels of hormone (e.g., Gandelman 1983) or presence of facilitating hormones (e.g., stress can facilitate classical conditioning [Shors et al. 1992] in males but not in females [Wood & Shors 1998])

Extra-trophic effects (e.g., CRF can enhances effects of novelty, affect learning, (see Koob 1991); ACTH can suppress aggression (see Brain et al 1971); MSH affects motivation, attention (Stratton & Kastin 1973; Kastin et al. 1971)

COPING RESPONSES: hierarchically arrayed

The most ancient (evolutionarily conservative) responses are invoked first (adrenal medullary /chromaffin response to sympathetic activation) (fear –subcortical limbic areas; pleasure --cortical limbic)

As each response’s adaptive scope is exceeded, successive mechanisms deploy (local, neuroendocrine [CRF, ACTH, glucocorticoids], behavior)

Behavior is the final option (invoked when “lower” responses capacity is exceeded or they would be would be too “expensive”)

COPING RESPONSES:not only emergencies !

Elements of the stress response can be invoked whenever there is a mismatch (unmet expectations, cognitive dissonance; (Goldstein 1990))

Stressors can be cumulative (acute, sequential, episodic, or sustained stressors all make demands on the system)

The level of response is related to perceived prospects for success (e.g., learned helplessness; active versus passive coping identified with specific columns within the periaquaductal gray (Paradiso et al. 1999))

COPING RESPONSES:delicately balanced alternatives !

“Fight or flight” (the classic stress alternatives to imminent aggressive threat –not only in animals with a cerebral cortex!)

“Flee or freeze” (lizards can apparently calculate prospects for survival based on external threat , internal resources, and environmental possibilities)

“Green or brown” (the Anolis carolinensis dermal chromatophore –the “chromomotor model”)

SURVEY: stress-sensitive behavior

Detection, Arousal and Attention (steroids affect sensory thresholds, EPI intensifies; acute CS enhances salience)

Activity (CRF facilitates in familiar habitat, inhibits in unfamiliar habitat)

Exploration (CRF and ACTH enhances effects of novelty, CS facilitates)

Learning and memory ( EPI, CRF, MSH facilitate acquisition)

Cognition ( catecholamine modulation; taking prefrontal cortex “offline” (Arnsten))

SURVEY: stress-sensitive behavior

Feeding ( CS stimulates or inhibits depending on circulating levels)

Aggression (ACTH suppresses, CS increases or decreases depending on circulating levels)

Social Dominance (CS increases submissiveness)

Reproduction ( ACTH, CS, opiods, and prolactin impair HPG axis)

Dysfunctional behavior (stereotypies, neuroses, psychoses)

The Anolis Model

Small, easily maintained,

displays focal behavioral patterns easily in laboratory

Dermal chromatophore responds only to circulating hormones

Chromomotor model for the stress response

Acute, repetitive, or sustained stressors are integrated in the CNS

Autonomic neurons activate the adrenal medullary response

H-P-A axis integrates the adrenal cortical response

The Anolis body color thus reflects underlying neuroendocrine coping activities

Body color reflects autonomic tone

MSH and aggression

Acute stress depletes MSH

Agonistic winners manifest typical stress response: down (56% (of control values)

Agonistic losers, MSH is slightly up (127% (of control values)

Social Dominants, MSH is slightly up (128% of control values)

Social Subordinates, MSH is significantly up (217% of control values)

PUTATIVE INFLUENCES ON MSH RELEASE

!CRF increases circulating levels (Proulx‑Ferland et al. 1982)

!ACh increases circulating levels (see Hadley & Bagnara 1975)

!SEROTONIN may be MSH‑RF (see Hadley & Bagnara 1975)

!CATECHOLAMINES (EPI, NOREPI, DOPAMINE) may inhibit MSH release from pars intermedia (see Hadley & Bagnara 1975)

!ENDORPHIN reduces MSH binding

!STRESSORS: aggression raises pituitary content (Francis & Peaslee 1974), with increased ACTH)

! BEHAVIOR: activity decreases MSH in goldfish (but not in rats); acute stress (chase or restraint) reduces MSH in anoles; aggression reduces it in winners but increases it in losers; chronic stress (social subordination) increases MSH (Greenberg, Chen, and Vaughan 1986)

PUTATIVE EFFECTS OF MSH RELEASE

! AGGRESSIVENESS is diminished (Patterson et al. 1980)

! "EMOTIONALITY" is decreased (Golus et al. 1979)

! TONIC IMMOBILITY, duration decreased (Stratton & Kastin 1976)

! "MOTIVATION" is increased (Stratton & Kastin 1973)

! ATTENTION is enhanced (Kastin et al. 1971)

! ANXIETY is reduced (Miller et al. 1974)

! ACTH release is increased (Lis et al. 1982)

! AGGRESSION can be evoked (in mice) by release of a pheromone facilitated by MSH synergy with testosterone (Nowell et al. 1980)

! TROPHIC PROPERTIES indicated by stimulation of fetal growth, protein synthesis, wound healing, and liver regeneration (see Swaab and Martin 1981)

Anolis exploratory behavior

Posture and site-changes, tongue-touches and airlicks increase in a new cage IF first mildly stressed (handling)

All exploratory behaviors except air-licking suppressed by more intense stress (evoke eye-spot)

Castration ameliorates the suppressive effect of intense stress

Aggression and Dominance in Anolis

Many lizard species manifest an apparent continuum from strict territoriality to social dominance hierarchies (Chas Carpenter’s experience, Hunsaker & Burrage 1969)

Is there a “dominance threshold”?

Anolis carolinensis males spontaneously establish dominance relationships in laboratory (and in the field, smaller “hidden” males supplant conspicuous dominants removed for testing –Todd Campbell)

Anolis Aggression

Closely matched males compete (resulting in control of limited resources: high perches and females)

Color fluctuations during fights suggest fluctuating (competing?) agonistic tendencies

At fight’s end, winners are typically green and losers brown.

Anolis Dominance

Established after an initial period (mutual testing for strength and stamina?)

Dominants remain green and subordinates become brown and adopt distinctive postures.

Anolis Dominance

Dominants experience an androgen surge around day 1 after the fight

Subordinate androgen is reduced to about 60% in a week

This is about the time dominance is stabilized.

(Greenberg & Crews 1990)

Anolis Dominance

Has a “conditioned avoidance” response been replaced by diminished motivation to compete?

Do behavioral changes secondary to androgen reduction help cope with stress?

Establishment of social dominance hierarchy – Behavioral changes

Color: significantly darker in subordinates

Posture: comparable, subordinates slightly lower

Site selection: significantly lower in subordinates

Will NOT court females

Establishment of social dominance hierarchy – CS changes and effect of castration

I X I, subordinates have elevated CS

I X C, subordinates not significantly higher

C X C, subordinates not significantly higher

Anecdote: some castrates become a “relentless” subordinate, testing the dominant every day. (Intact losers quit after 3 days.) Eventually dominants show repetitive stress syndrome.

IMMEDIATE PHYSIOLOGICAL CONSEQUENCES OF LOSING

CATECHOLAMINE SURGES (body color, nuchal crest erection, Greenberg et al. 1984)

NE LOWER RELATIVE TO WINNER (Summers & Greenberg 1994)

CORTICOSTERONE INCREASED (Greenberg et al. 1984)

MSH INCREASED (relative to winners, Greenberg, Chen, and Vaughan 1986)

SEROTONIN ACTIVITY INCREASED IN THE MIDBRAIN, HIND BRAIN (Summers & Greenberg 1995), HIPPOCAMPUS, AND NUCLEUS ACCUMBENS (Summers et al. 1998)

LONG-TERM PHYSIOLOGICAL CONSEQUENCES OF LOSING

ANDROGEN REDUCED (Greenberg & Crews 1990)

CORTICOSTERONE ELEVATED (Greenberg et al. 1984)

MSH INCREASED (relative to dominants, Greenberg, Chen, and Vaughan 1986)

DOPAMINE ACTIVITY DIMINISHED, ADRENERGIC ACTIVITY ENHANCED IN THE MID AND HIND BRAIN (but back to control values by one month) (Summers & Greenberg 1995)

EFFECTS of CORTICOSTERONE

CS-implanted A sagrei: reduced approach and aggression (Tokarz 1987)

CS-implanted Uta: reduced aggression even if implanted with testosterone (DeNardo & Licht 1993)

CS-implanted A carolinensis: initial agonistic responses vigorous but rapidly manifest submissiveness when adversary answers display (Greenberg unpubl pilot study)

LIFE AS A SUBORDINATE

Many dominant/subordinate pairs stabilize and can maintain long-term relationship

Subordinates do not typically succumb to “diseases of adaptation”

Contribution from trophic MSH effects?

Contribution from androgen reduction?

EFFECTS of CASTRATION

Could androgen reduction be stress-adaptive?

Castrated A. carolinensis in fights, latency & duration of EPI-dependent eyespot extended (Summers & Greenberg 1984)

Castrated A. carolinensis subordinates: -body color not significantly darker, circulating CS not significantly higher than dominants or isolates (Greenberg et al. 1984)

In A. carolinensis, acute stress impairment of exploratory responses in a novel habitat much less severe in castrates (except for airlicking, Greenberg 1993)

EFFECTS of ANDROGEN IMPLANTS

Prospective adversaries both had testosterone implants

Social dominance realtionship established but subordinate androgen levels could not be reduced

Anticipated continuing stressful exchanges never occurred, the subordinate had enhanced attention to the dominant and was effectively a “super-subordinate.”

Unlike typical subordinates, an androgen-implanted subordinate would court females whenever the dominant was out of sight.

STRESS and the EVOLUTION of BEHAVIOR

“In animals, almost invariably, a change in behavior is the crucial factor initiating evolutionary innovation” (Ernst Mayr 1988).

Behavior creates new selective pressures (Mark Baldwin via Deacon 1998)

STRESS and the EVOLUTION of BEHAVIOR

The “Ritualization” of signals a model:

fragments of motor patterns or autonomoic reflexes become temporally or spatially associated as an ensemble (Morris 1956, Hinde and Tinbergen 1958)

The “Central Adaptation Syndrome” (Huether 1996).

Controllable stressors lead to a “go and specialize” strategy (e.g., earlier recognition and avoidance, improved fighting strategies, refined submission behavior)

Uncontrollable stressors lead to a “wait and reorganize” strategy (e.g., CS reorganization of neural circuits; tuning of learning, motivation, and emotional states)

STRESS and the EVOLUTION of BEHAVIOR

Stress-sensitive intersections of motivation, affect, and cognition are candidates for evolutionary change.

Valence of affect : positive, cortical-limbic areas; negative, subcortical-limbic areas (Paradiso et al. 1999)

note: male anoles with subcortical lesions act like castrates- they attend stimuli but are not motivated to respond aggressively (“social agnosia,” recalling autistic failure to recognize signals)

Active versus passive coping parallel autonomic strategies correlated with activity in discrete columns of periaquaductal gray (Bandler et al. 2000)

ENVOI, POSTLUDE

Renewed respect for the role of MELANOTROPIN (its trophic role)

Effectiveness of nonspecific stress and sex steroids in arousal and attention (Exploration study)

An appreciation for close ethological description and temporal resolution (CS & androgen implant studies)

A sensitivity to comparative approach (possibilities inherent in the taxon)

A need for field and laboratory mutual respect and reciprocity (overcoming the narrowness of disciplinary depth)

An understanding of differential effects in the brain (opposite effects in different structures)

Awareness of the potential for the multiple input, integration, and output options and pathways for evolutionary bricolage (the cobbling together of whatever evolutionary raw material is