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Injection of muscimol in dorsomedial hypothalamus and stress-induced Fos expression in paraventricular nucleus
S M Morin1, E H Stotz-Potter, J A DiMicco
1Department of Pharmacology and Toxicology and Program in Medical Neurobiology, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA.
Abstract:
Prior microinjection of the GABA(A)-receptor agonist muscimol into the dorsomedial hypothalamus (DMH) in conscious rats attenuates the increases in heart rate, blood pressure, and circulating adrenocorticotrophic hormone seen in air stress. Here, we examined the effect of similar treatment on air stress- or hemorrhage-induced Fos expression in the paraventricular nucleus (PVN). Muscimol (80 pmol/100 nl per side) or saline (100 nl per side) was microinjected bilaterally into the DMH in conscious rats before either air stress, an emotional or neurogenic stressor, or graded hemorrhage, a physiological stressor. Each stressor evoked a characteristic pattern of Fos expression in the parvocellular and magnocellular PVN after saline. Injection of muscimol into the DMH suppressed Fos expression in the PVN associated with air stress but not with hemorrhage. Injection of muscimol at sites anterior to the DMH and closer to the PVN had no effect on Fos expression in the PVN after air stress. Thus activation of neurons in the DMH is necessary for excitation of neurons in the PVN during air stress but not during hemorrhage.
Insights
Microinjection of muscimol into the dorsomedial hypothalamus (DMH) blocks stress-induced Fos expression in the paraventricular nucleus (PVN) during air stress but not hemorrhage.
Area of Science:
- Neuroscience
- Endocrinology
- Stress Physiology
Background:
- The dorsomedial hypothalamus (DMH) plays a role in mediating stress responses.
- The paraventricular nucleus (PVN) is a key hypothalamic nucleus involved in the stress axis.
Purpose of the Study:
- To investigate the role of the DMH in stress-induced Fos expression in the PVN.
- To differentiate the DMH's involvement in emotional/neurogenic versus physiological stressors.
Main Methods:
- Rats were bilaterally microinjected with muscimol (a GABA(A)-receptor agonist) or saline into the DMH.
- Rats were subsequently exposed to either air stress or graded hemorrhage.
- Fos expression in the PVN was analyzed to assess neuronal activation.
Main Results:
- Air stress induced Fos expression in the PVN, which was suppressed by DMH muscimol treatment.
- Hemorrhage-induced Fos expression in the PVN was not affected by DMH muscimol treatment.
- Muscimol injections anterior to the DMH did not alter air stress-induced Fos expression in the PVN.
Conclusions:
- Activation of DMH neurons is essential for PVN neuronal excitation during air stress.
- The DMH is not necessary for PVN activation during hemorrhage.
- These findings highlight differential neural pathways for distinct types of stressors.
