Substance P increases hypothalamic blood flow via an indirect adrenergic-cholinergic interaction

Area of Science:

• Neuroscience
• Physiology
• Pharmacology

Background:

• Hypothalamic blood flow (HBF) regulation is crucial for brain function.
• The role of Substance P in modulating cerebral blood flow, particularly in the hypothalamus, requires further elucidation.

Purpose of the Study:

• To investigate the effects of Substance P on hypothalamic blood flow in conscious rabbits.
• To identify the neurochemical pathways involved in Substance P-induced HBF changes.

Main Methods:

• Hypothalamic blood flow (HBF) was measured using the 133xenon washout technique in conscious rabbits.
• Pharmacological interventions included cholinoceptor blockade (atropine, mecamylamine), chemical sympathectomy (6-hydroxydopamine), adrenoceptor blockade (propranolol, phenoxybenzamine), and INP manipulation (destruction, barbiturate/bicarbonate blockade).

Main Results:

• Substance P (50 or 500 ng) significantly increased HBF, while a lower dose (5 ng) had no effect.
• Cholinoceptor blockade and chemical sympathectomy abolished the vasodilator effect of Substance P.
• Blockade or destruction of the intracerebral noradrenergic pathway (INP) also prevented Substance P's vasodilator action.

Conclusions:

• Substance P may increase HBF through the release of endogenous acetylcholine.
• Acetylcholine appears to stimulate the intracerebral noradrenergic pathway (INP), mediating the vasodilator effect.
• These findings highlight a novel mechanism for Substance P in regulating hypothalamic perfusion.