Effects of spontaneous and forced running on activation

of hypothalamic corticotropin-releasing

hormone neurons in rats

Introduction

Stressors such as immobilization, restraint, foot shock, & communication box activate CRH-containing neurons in the PVN

Acute physical stress – treadmill running – induces strong CRH mRNA expression in the PVN

Introduction

Physical exercise = stressor Physical exercise triggers the HPA

axis starting with the CRH neurons CRH neurons project to brain areas

involved in mood/affect

HPA axis

Introduction

Forced physical exercise (running/swimming) produces negative adaptations to stress responses with activation of CRH neurons

Therefore, physical exercise could alter psychological effects

Introduction

Spontaneous physical exercise could be beneficial to all aspects of health, so…

Effects of CRH neuron activation by physical exercise should differ between spontaneous & forced

Purpose of the Study

Compare hypothalamic CRH neuronal activation during spontaneous wheel runners (SWR) & forced wheel runners (FWR) with double-staining for c-Fos and CRH in the PVN

Materials & Methods

Twenty adult male Wistar rats Individual housed cages attached to

voluntarily accessible running wheels unlocked in all cages for habituation 1 week before testing

12h light/dark cycle Ad libitum access to food and H2O

Figure 1

M & M

FWR distance = SWR distance 1 hr spontaneous or forced wheel

running in the dark cycle FWR were “softly” prodded when

they stopped running Control rats were left in locked

wheels for 1 hr without wheel running or prodded 25-30 times

M & M

30 mins after running, rats were put to sleep by injection and perfused by heparin, other stuff, and PBS

Brains frozen, cut on coronal plane, and collected in PBS + Na+ azide

Antibodies were used to visualize c-Fos & CRH

Figure 2

M & M

Anti-CRH antibody reacts only with CRH peptide

c-Fos localized to cell nuclei and appeared as a dark gray-black stain

CRH localized to cell cytoplasm and appeared as light-brown staining

M & M

Quantitative analysis performed on all PVN coronal sections

c-Fos & CRH counted on PVN sections

c-Fos counted in the LC sections

Figure 3

Results

Double Fos/CRH-positive cells ↑FWR, ↓SWR & controls

Increase of FWR was extremely significant Prodding alone did not increase

c-Fos/CRH cells significantly Both FWR & SWR enhanced Fos

expression in the LC compared to controls

Figure 4

Discussion

Forced physical exercise = strong stressor

Previously, forced swimming strongly induces CRH mRNA in PVN

Forced Swim Stress

↑CRH hnRNA after 10 min swim stress and then returned to baseline

AVP hnRNA in PVN (colocalization w/CRH) remained relatively the same @ 10min

Significantly ↑AVP 2h after stress Pre-Tx w/dexamethasone → no

CRH/AVP increase after stress

Figure 1

Figure 2

Discussion

Synergistic effects of FWR + prodding likely comprised the significant rise in Fos/CRH-positive neurons

Previously, several negative adaptations were revealed during treadmill running (equivalent to FWR)

Discussion

Chronic HPA axis stimulation produces negative physiological adaptations such as depression and anxiety

Spontaneous exercise training could improve stress response

SWR = mild stressor

Discussion

FWR & SWR enhanced Fos in LC which conflicts with CRH neuronal effects in the PVN

Both FWR & SWR ↑NE levels Acute stress ↑effects on LC & PVN

neurons → ↑Fos This study showed CRH activation

might depend on exercise type

Discussion

Acute exercise effects on CRH activation definitely depends on modality rather than intensity

Bye-Bye!