Dorsal hippocampus cholinergic and nitrergic neurotransmission modulates the cardiac baroreflex function in rats

Area of Science:

• Neuroscience
• Cardiovascular Physiology
• Neurotransmission

Background:

• The hippocampus, a limbic structure, plays a role in cardiovascular regulation, receiving significant cholinergic input.
• Acetylcholine activation of hippocampal muscarinic receptors may trigger nitric oxide (NO) synthesis, a key neuromodulator of cardiovascular responses.

Purpose of the Study:

• To investigate the role of cholinergic and nitrergic neurotransmission in the dorsal hippocampus (DH) in modulating baroreflex and chemoreflex functions.
• To determine if nitric oxide synthesis in the DH is involved in acetylcholine-mediated cardiovascular responses.

Main Methods:

• Utilized vasoactive drugs (phenylephrine, sodium nitroprusside) and potassium cyanide infusion in awake animals to elicit baroreflex and chemoreflex responses.
• Administered bilateral injections into the DH of acetylcholinesterase inhibitor (neostigmine), muscarinic receptor antagonists (atropine, pirenzepine), and inhibitors of nitric oxide synthesis/signaling (N-propyl, carboxy-PTIO, ODQ).

Main Results:

• Neostigmine reduced baroreflex responses, while atropine and pirenzepine increased them.
• Inhibitors of nitric oxide synthesis and signaling (N-propyl, carboxy-PTIO, ODQ) increased baroreflex responses.
• A neuronal nitric oxide synthase inhibitor abolished the neostigmine-induced reduction in baroreflex responses, and hippocampal cholinergic neurotransmission did not affect chemoreflex function.

Conclusions:

• Cholinergic and nitrergic pathways in the dorsal hippocampus significantly modulate baroreflex control.
• Neuronal nitric oxide synthase (nNOS)-derived nitric oxide in the DH is essential for acetylcholine-evoked baroreflex responses.
• Hippocampal cholinergic neurotransmission does not influence chemoreflex function.