Electrical and mechanical activity recorded from rabbit urinary bladder in response to nerve stimulation

Area of Science:

• Neuroscience
• Physiology
• Pharmacology

Background:

• The rabbit bladder smooth muscle membrane exhibits spontaneous action potentials.
• Understanding the neurotransmitters involved in bladder function is crucial for treating urinary disorders.

Purpose of the Study:

• To investigate the electrical responses of the rabbit bladder smooth muscle to intramuscular nerve stimulation.
• To identify the neurotransmitters responsible for excitatory and inhibitory signaling in the bladder.

Main Methods:

• Micro-electrode recordings and double sucrose-gap techniques were employed.
• Pharmacological agents including acetylcholine, ATP, noradrenaline, tetrodotoxin, neostigmine, atropine, guanethidine, and apamine were used to probe receptor activation and neurotransmitter function.

Main Results:

• Nerve stimulation elicited excitatory junction potentials (e.j.p.s) with superimposed spikes and a late depolarization, all abolished by tetrodotoxin.
• The late depolarization was identified as muscarinic receptor-mediated, while e.j.p.s were not adrenergic, tryptaminergic, histaminergic, or purinergic.
• Adenosine triphosphate (ATP) transiently increased action potential frequency but did not act as a non-cholinergic excitatory transmitter, and apamine/tetraethylammonium (TEA) indicated hyperpolarization due to increased potassium conductance.

Conclusions:

• The rabbit bladder receives input from both cholinergic and noncholinergic excitatory neurons.
• Adenosine triphosphate (ATP) is unlikely to be the primary non-cholinergic excitatory neurotransmitter in the rabbit bladder.
• Hyperpolarization appears to be mediated by increased potassium conductance, though its precise origin (neurotransmitter-mediated inhibition or spike afterhyperpolarization) remains unclear.