Functional neuroanatomy and plasticity of the hypothalamic circuits

regulating autonomic responses to stress

Krisztina J. KovácsLaboratory of Molecular Neuroendocrinology

Institute of Experimental MedicineBudapest, Hungary

ACUTE STRESS

Heart rate

Blood pressure

Muscle tension

Respiratory rate

Plasma glucose

Gastrointestinal actvity

HPASympato-medullar activitySympato-adrenal

Metabolic X syndrome

Mood swingsAnxietyDepressionConfusion / forgetfulnessBurnout

Eating disordersSleeping disordersSocial withdrawal / aggressionDrug abuse

CHRONIC or UNRESOLVED

Selye explains STRESS – induced activation of HPA axis

Nature, July 4, 1936.A Syndrome produced by Diverse Nocuous Agents

“…. a typical response appears, the symptoms of which are independent of the nature of the damaging agent…and represent rather a response to damage as such”

H. Selye

PARAVENTRICULAR NUCLEUS

Magnocellular part Parvocellular part

Hypophyseotropic Autonom projection

•Medial parvocellular dorsal•Periventricular

•Medial parvocellular ventral•Dorsal parvocellular•Lateral parvocellular

BATBAT

HEARTHEART

SKINSKIN SUDOMOTORSUDOMOTOR

ADRENAL ADRENAL MEDULLAMEDULLA

VASCULAR VASCULAR TONETONE

AVPAVPOXYOXYCRHCRH

CRH & AVPCRH & AVP

AVP & OXYAVP & OXY

PVNPVN Brain stem & spinal cordBrain stem & spinal cord

HPA AXIS ACTIVATION

OSMOREGULATIONOSMOREGULATIONCARDIOVASCULAR REGULATIONCARDIOVASCULAR REGULATION

Afferent connections of the hypothalamic PVN

“Blood borne”

Acustic

Nociceptive

Visceral

SomatosensoryVisual

Corticosterone

Challenge-induced Activation of PVN Neurons

c-Fos-ir 90 min after stress* Kovács et al, 2005

MAGNOCELLULAR

PARVOCELLULAR

CRHVASOPRESSIN

Dynorphin

Angiotensin II

Enkephalin

Dopamine

Galanin

VIP/PHI

OXYTOCIN

CRH

CCK

Enkephalin

TRH Enkephalin

CCK

Angiotensin II

Neurotensin

Galanin

VIP/PHI

Vasopressin

Colocalization of neuropeptides in the hypothalamic PVN

?

Oxytocin

CRH

Vasopressin

Somatostatin

Dynorphin

Enkephaline

Functional plasticity in the PVN - adrenalectomy

Control

Adrenalectomy

ADX + DEX/PVN

Vasopressin potentiates CRH action at the corticotropes

Rivier et al, 1984

ETHER STRESS-INDUCED VASOPRESSIN TRANSCRIPTION IN THE PARAVENTRICULAR NUCLEUS

Autonomic projection neurons in the PVN

Approx. 1500 neurons in 3 different parvocellular subdivisions:(dorsal-, ventral aspect of medial parvocellular- and lateral-)

Neurochemical specificity of these neurons is less known:(Oxytocin, vasopressin, corticotropin-releasing hormone, somatostatin, dynorphin, enkephalin, dopamine…..)

Efferent connections: to medullar and spinal preganglionic cells for both divisions (sympathetic and parasympathetic) of the ANS-spinal cord (intermediolateral cell column) - predominantly OXYdorsal vagal complex - predominantly AVP

Express ER-beta, MC4R, IRS-2 etc

Physiological evidences for mediation of sympatoexcitation...

FUNCTIONAL PLASTICITY OF HYPOTHALAMICAUTONOMIC-RELATED NEURONS

Laugero et al, Endocrinology, 2001

+ sucrose

+ / - sucrose

1. wk 2. wk 3.wk 4.wk 5. wk

Record body weight, fluid and foodconsumption

Blood samplingperfusion

ADX / SHAM

adaptation

Adult male Wistar rats1M sucrose, 0.5% NaCl, water

6. wk

CRH mRNA in situAVP mRNA in situ

Sucrose ingestion results in neuronal activation in neuroendocrine and autonomic-related neurons

Hypothalamus coordinates autonomic responses in part through AVP, released in NTS.

AVP inhibits afferent synaptic transmission in the NTS:1. By decreasing glutamate release probability (V1a receptor)2. By inducing synaptic failures and increased conduction times

How to study complex autonomic circuits ?

Trans synaptic tracing using pseudorabies virus

(PRV)

PRV: pseudorabies virus, Bartha strain

“self-amplifying transsynaptic tracer”.

Trans-synaptic spread)

Virus-infected neurons in the PVN following inoculation into the kidney

Virus-infected neurons in the dorsal parvocellular subdivision

PRV-ir neurons after virus inoculation into a peripheral target

1. Spinal cord, intermediolateral cell column

2. Rostral ventrolateral medulla

3. A5 noradrenergic cell group

4. Hypothalamus, PVN

5. Insular cortex

Comparison of autonomic innervation of WAT and BATDouble-virus infection

WAT BAT

PRV injections

Ba-Dup-Lac (red)- iWAT Ba-Dup-Green- BAT

Outline of the brain circuit that provides sympathetic innervation of different target tissues

Target organ

Five cell groups in the brain appear to regulate

the entire sympathetic outflow:

the paraventricular hypothalamic nucleus (PVH),

A5 noradrenergic cell group,

caudal raphe region,

rostral ventrolateral medulla,

and ventromedial medulla.

CORTEX

LIMBIC CORTEX

PVN

Medial parvo

Magno Auton.related

BNST Amygdala

A5

Parabrachial

PREGANGLIONIC NEURONS

IML DVC

PITUITARY

AP PP

ADRENAL

CORTEX MEDULLA

ACTHVP, OXY

CRH, VP

AUTONOMICENDOCRINE BEHAVIORAL

OXY, VP, CRHDYN, ENK