Fabrication and Implantation of Miniature Dual-element Strain Gages for Measuring <em>In Vivo</em> Gastrointestinal Contractions in Rodents.

Abstract

Gastrointestinal dysfunction remains a major cause of morbidity and mortality. Indeed, gastrointestinal (GI) motility in health and disease remains an area of productive research with over 1,400 published animal studies in just the last 5 years. Numerous techniques have been developed for quantifying smooth muscle activity of the stomach, small intestine, and colon. In vitro and ex vivo techniques offer powerful tools for mechanistic studies of GI function, but outside the context of the integrated systems inherent to an intact organism. Typically, measuring in vivo smooth muscle contractions of the stomach has involved an anesthetized preparation coupled with the introduction of a surgically placed pressure sensor, a static pressure load such as a mildly inflated balloon or by distending the stomach with fluid under barostatically-controlled feedback. Yet many of these approaches present unique disadvantages regarding both the interpretation of results as well as applicability for in vivo use in conscious experimental animal models. The use of dual element strain gages that have been affixed to the serosal surface of the GI tract has offered numerous experimental advantages, which may continue to outweigh the disadvantages. Since these gages are not commercially available, this video presentation provides a detailed, step-by-step guide to the fabrication of the current design of these gages. The strain gage described in this protocol is a design for recording gastric motility in rats. This design has been modified for recording smooth muscle activity along the entire GI tract and requires only subtle variation in the overall fabrication. Representative data from the entire GI tract are included as well as discussion of analysis methods, data interpretation and presentation.

Gastric vagal motoneuron function is maintained following experimental spinal cord injury

“…Rats were then intubated with a tracheal tube to maintain an open airway and a laparotomy was performed. The stomach was isolated and a 6 × 8 mm encapsulated sub‐miniature strain gage of our own fabrication was aligned with the circular smooth muscle fibers and sutured to the ventral surface of the gastric corpus . The strain gage leads remained exteriorized before closure of the abdominal incision.…”

“…After 1 h of stabilization, 10 min of baseline motility was recorded before any experimental manipulation. The effects of TRH, (0, 3, or 10 pmoles/60 nL) microinjected in the left DVC (at coordinates from calamus scriptorius: +0.1 to 0.3 mm rostrocaudal, 0.1–0.3 mm mediolateral and −0.3 to 0.5 mm dorso‐ventral) adjacent to the AP, were observed as recorded peaks that increased in frequency, height, and/or rose above baseline …”

Diminished gastric prokinetic response to ghrelin in a rat model of spinal cord injury

“…Rats were then intubated with a tracheal tube (PE‐240, Becton Dickinson, Franklin Lakes, NJ) to maintain an open airway and permit the clearance of respiratory secretions, a femoral venous catheter (PE‐50, Becton Dickinson) was inserted for the intravenous delivery of drugs, and a laparotomy was performed. The stomach was partially exteriorized and a 6 × 8‐mm encapsulated sub‐miniature strain gage of our own fabrication was aligned with the circular smooth muscle fibers and sutured to the ventral surface of the gastric corpus . The strain gage leads were exteriorized before closure of the abdominal incision.…”

“…Motility was recorded for the 10‐min period immediately preceding infusion, and 10‐min immediately following the termination of ghrelin infusion. Gastric motility was analyzed using the motility index originally reported by Ormsbee and Bass and described by our laboratory . Briefly, the formula for motility index (whereby N equals the total number of peaks in a particular milligram range) is as follows: …”

“…The stomach was partially exteriorized and a 6 × 8-mm encapsulated sub-miniature strain gage of our own fabrication was aligned with the circular smooth muscle fibers and sutured to the ventral surface of the gastric corpus. 37 The strain gage leads were exteriorized before closure of the abdominal incision.…”