Adrenergic, cholinergic, and nonadrenergic-noncholinergic intrinsic innervation of the jejunum in horses.

This research investigates the major neurotransmitters that regulate contraction activity in the jejunum (part of the small intestine) of horses. The findings reveal that Acetylcholine and norepinephrine are the essential neurotransmitters controlling smooth muscle contractility in the equine jejunum, with additional nonadrenergic-noncholinergic influences detected.

Methods

• The study used jejunal specimens from 65 horses that showed no gastrointestinal tract lesions.
• These specimens, specifically jejunal smooth muscle strips, were suspended isometrically in muscle baths and oriented in line with the circular or longitudinal muscular layer.
• Researchers triggered neurotransmitter release via electrical field stimulation (EFS) at voltages of 30 and 70, and various frequencies were tested on muscle strips maintained at low or high muscle tones.
• In order to detect residual nonadrenergic-noncholinergic neurotransmission, the response of muscle to EFS in the face of adrenergic and cholinergic blockades was compared against the response in the presence of tetrodotoxin.

Results

• When exposed to Atropine (ATR), the contractile response of muscle strips to EFS diminished under the majority of conditions, although it increased the contractile response of high-tone circular muscle.
• Adrenergic blockades generally accentuated muscle responses to 30 V EFS and in high-tone longitudinal muscle, while decreasing contractile responses in high-tone circular muscle.
• The use of Tetrodotoxin significantly altered the responses to EFS, compared with the adrenergic and cholinergic receptor blockades.

Conclusions

• The research concluded that Acetylcholine and norepinephrine are important neurotransmitters in regulating smooth muscle contractility in the equine jejunum.
• These neurotransmitters, under most conditions, respectively induce contraction and relaxation, but they may induce opposite effects under certain situations.
• The research also discovered the influence of nonadrenergic-noncholinergic excitatory and inhibitory activities.
• Any alterations in the release of Acetylcholine or norepinephrine within the myenteric plexus (a network of neurons in the gastrointestinal tract) of horses could impact gastrointestinal motility.