All animal experiments described below were approved by the Committee for Medical Ethics and the use of Experimental Animals at the University of Antwerp (file number 2012-42).
1. Tissue Preparation of Jejunal and Colonic Afferent Nerves
Figure 1: Schematic Overview of the Purpose-built Recording Chamber and Suction Electrode. Detailed overview of the technical setup with the suction electrode and the recording chamber in place. Please click here to view a larger version of this figure.
Figure 2: Representative Tracing of the In Vitro Recording of Jejunal Afferent Nerve Activity. Typical recording of jejunal multi-unit afferent nerve activity (imp.sec-1) (upper panel) at baseline and in response to 2 ramp distensions up until 60 mmHg (lower panel), and the subsequent identification (wavemark analysis) of different single-units in the nerve signal (third panel). Please click here to view a larger version of this figure.
Figure 3: Neuroanatomy of the Colon. A) Sensory information from the colon is conveyed via the lumbar colonic nerves (LCN) towards the central nervous system, with the LCN running in close proximity to the inferior mesenteric artery (IMA). A portion of the fibers from this lumbar colonic nerve will course along the intermesenteric nerve (IMN) to form the lumbar splanchnic nerves (LSN). The inferior mesenteric ganglion (IMG) is located at the origin of the IMA from the abdominal aorta. Recording distally of the IMG is mandatory should researchers wish to study viscerofugal afferent nerve activity. B) A schematic overview of the experimental set-up. Afferent recording of the LCN is performed in an organ both by means of a suction electrode connected to the data acquisition system. Ramp distension can be performed upon closure of the outlet port while continuing the inflow of Krebs solution. Please click here to view a larger version of this figure.
2. Data Acquisition
3. Analysis5,20
Figure 4: Schematic Representation of the Different Afferent Fiber Units Based on Their Mechanosensitive Profile. Units are classified based upon the percentage (LT%) of their firing rate at 20 mmHg distension pressure compared to the maximum firing response during distension. Low threshold fibers (upper left panel) predominantly display an increased nerve activity at low distension pressures, resulting in an LT% of over 55%. High threshold units (upper right panel) on the contrary only display an increase in firing rate at noxious pressures (%LT < 15). Wide dynamic range fibers (lower left panel) display a gradual increase in nerve activity during the entire distension (%LT ranging between 15 and 55), whereas mechanically insensitive fibers (lower right panel) do not respond to increasing distension pressures. LT%: (afferent firing at 20 mmHg / maximal afferent firing) Please click here to view a larger version of this figure.
Jejunal afferent nerve activity was measured at baseline and in response to ramp distension in 9 eight-week old male OF-1 mice. Animals were housed in groups in standardized conditions (6 animals per cage, 20 – 22 °C, humidity 40 – 50%, 12 hr light-dark cycle) with unlimited access to tap water and regular chow. Jejunal segments of mice displayed irregular spontaneous afferent nerve discharge at baseline at an intraluminal pressure of 0 mmHg (mean spontaneous activity 11.47 ± 3.31 imp/sec).
The jejunal afferent nerve activity increased upon performing ramp distensions up until 60 mmHg. Typically, the increase in afferent nerve activity following the rise in intraluminal pressure is characterized by a biphasic response (Figure 5), consisting of an initial rapid increase in firing activity up until the intraluminal pressure reaches 20 mmHg, which can mainly be attributed to the increased firing rate of low threshold fibers. This is then followed by a plateau phase, after which a second increase in firing activity can be observed from 40 mmHg onwards, representing the activation of predominantly high threshold fibers.
Based upon their waveforms, single-units can be discriminated in each multi-unit recording and classified in one of the aforementioned four categories. In 9 mice, we discriminated 40 different units (4.44 ± 1.01 units/jejunal afferent nerve), with the LT units being the most prevalent ones, followed by WDR and HT fibers (Figure 6). The firing activity of the different units in response to ramp distension can be observed in Figure 7.
Figure 5: Mesenteric Afferent Nerve Discharge (imp.sec–1) in Wild-type Mice during Ramp Distension. Mesenteric multi-unit afferent nerve discharge (imp/sec-1) in wild-type mice during ramp distension for the whole nerve. Values represent mean afferent discharge ± s.e.m., n = 9 mice. imp.sec-1: impulses per second. Please click here to view a larger version of this figure.
Figure 6: Single Unit Distribution of 40 Units Identified in Jejunal Afferent Nerves from 9 Wild-type Mice. HT: high threshold fiber, LT: low threshold fiber, MIA: mechanically insensitive fiber, WDR: wide dynamic range fiber. Please click here to view a larger version of this figure.
Figure 7: Pressure-response Curves for the Different Types of Subunits in Wild-type Mice. The single-unit afferent nerve discharge (imp.sec-1) from the four different units that can be identified, in wild-type mice during ramp distensions. A low threshold fiber (LT, upper left figure) is characterized by an initial rapid increase in firing activity during distensions, whilst the high threshold fibers (HT, lower left figure) only display increased firing during noxious intraluminal pressures. Wide dynamic range fibers (WDR, upper right figure) show a steady increase in firing activity during the entire distension, and mechano-insensitive afferent fibers (MIA, lower right figure) do not respond to increasing intraluminal pressures. Values represent mean afferent discharge ± s.e.m. imp.sec-1: impulses per second. Please click here to view a larger version of this figure.
sodium chloride (NaCl) | VWR Chemicals | 27,810,295 | compound Krebs solution |
potassium chloride (KCl) | Acros organics | 196770010 | compound Krebs solution |
sodium dihydrogen phosphate (NaH2PO4) | VWR Chemicals | 1,063,461,000 | compound Krebs solution |
sodium bicarbonate (NaHCO3) | Merck | 1,063,291,000 | compound Krebs solution |
magnesium sulfate (MgSO4) | Merck | 1,058,861,000 | compound Krebs solution |
calcium chloride (CaCl2) | Merck | 23,811,000 | compound Krebs solution |
D-glucose | VWR Chemicals | 1011175P | compound Krebs solution |
Distilled water | compound Krebs solution | ||
PVC tubing | Scientific Laboratory Supplies | The intestinal segment should be mounted over PVC tubing | |
Silicone tubing | Scientific Laboratory Supplies | The rest of the tubing, ideally silicone-based – more easily dislodging of debris in the tubing | |
Silk thread | Pearsall Limited | 10B15S220 | Attachment of the segment over the PVC tubing |
Syringe driver | Harvard Apparatus | 55-2222 | Intraluminal infusion of Krebs |
Binocular – including 10x magnification in oculair | Zeiss STEMI 2000 | Optimal visualization for the dissection of the afferent nerve | |
Homeothermic Blanket Control Unit | Harvard Apparatus | 507214 | Heating of the organ chamber |
Custom made organ bath with Sylgard covered bottom | |||
Spike2 software | Recording and analysis of the data | ||
Insect pins, 500 pieces, stainless steel, diameter 0.2 mm | Austerlitz insect pins minutiens | Dissection of the afferent nerve | |
Tweezer Dumont #5 inox 11cm | World Precision Instrument | 500341 | Dissection of the afferent nerve |
Scissors, spring, 14 cm | World Precision Instrument | 15905 | Dissection of the afferent nerve |
DB digitimer | NL 108T2/10 | pressure transducer | |
Micromanipulator | Narishige | M-3333 | 3D manipulation of the suction electrode |
Micromanipulator | X-4 rotating block | 3D manipulation of the suction electrode | |
Micromanipulator | GJ-8 magnetic stand | 3D manipulation of the suction electrode | |
LightSource | Euromex Microscopes Holland EK-1 | Optimal visualization for the dissection of the afferent nerve | |
CED 1401 Recording Apparatus | Recording of afferent nerve activity | ||
Humbug 50/60Hz Noise Eliminator | Quest Scientific Instruments | Elimination of background noise | |
Infusion Pump | Gibson Minipuls 2 | Infusion of the organ chamber in which the segment is mounted | |
Microelectrode Holder Half Cells 1.5 mm | World Precision Instrument | MEH2SW | Suction electrode for isolation of the afferent fiber |
Borosilicate Glass Capillaries, 300 pc; 1.5/0.84 OD/ID | World Precision Instrument | 1B150-4 | Capillary for the isolation of the afferent nerve |
Afferent nerves not only convey information concerning normal physiology, but also signal disturbed homeostasis and pathophysiological processes of the different organ systems from the periphery towards the central nervous system. As such, the increased activity or 'sensitization' of mesenteric afferent nerves has been allocated an important role in the pathophysiology of visceral hypersensitivity and abdominal pain syndromes.
Mesenteric afferent nerve activity can be measured in vitro in an isolated intestinal segment that is mounted in a purpose-built organ bath and from which the splanchnic nerve is isolated, allowing researchers to directly assess nerve activity adjacent to the gastrointestinal segment. Activity can be recorded at baseline in standardized conditions, during distension of the segment or following the addition of pharmacological compounds delivered intraluminally or serosally. This technique allows the researcher to easily study the effect of drugs targeting the peripheral nervous system in control specimens; besides, it provides crucial information on how neuronal activity is altered during disease. It should be noted however that measuring afferent neuronal firing activity only constitutes one relay station in the complex neuronal signaling cascade, and researchers should bear in mind not to overlook neuronal activity at other levels (e.g., dorsal root ganglia, spinal cord or central nervous system) in order to fully elucidate the complex neuronal physiology in health and disease.
Commonly used applications include the study of neuronal activity in response to the administration of lipopolysaccharide, and the study of afferent nerve activity in animal models of irritable bowel syndrome. In a more translational approach, the isolated mouse intestinal segment can be exposed to colonic supernatants from IBS patients. Furthermore, a modification of this technique has been recently shown to be applicable in human colonic specimens.
Afferent nerves not only convey information concerning normal physiology, but also signal disturbed homeostasis and pathophysiological processes of the different organ systems from the periphery towards the central nervous system. As such, the increased activity or 'sensitization' of mesenteric afferent nerves has been allocated an important role in the pathophysiology of visceral hypersensitivity and abdominal pain syndromes.
Mesenteric afferent nerve activity can be measured in vitro in an isolated intestinal segment that is mounted in a purpose-built organ bath and from which the splanchnic nerve is isolated, allowing researchers to directly assess nerve activity adjacent to the gastrointestinal segment. Activity can be recorded at baseline in standardized conditions, during distension of the segment or following the addition of pharmacological compounds delivered intraluminally or serosally. This technique allows the researcher to easily study the effect of drugs targeting the peripheral nervous system in control specimens; besides, it provides crucial information on how neuronal activity is altered during disease. It should be noted however that measuring afferent neuronal firing activity only constitutes one relay station in the complex neuronal signaling cascade, and researchers should bear in mind not to overlook neuronal activity at other levels (e.g., dorsal root ganglia, spinal cord or central nervous system) in order to fully elucidate the complex neuronal physiology in health and disease.
Commonly used applications include the study of neuronal activity in response to the administration of lipopolysaccharide, and the study of afferent nerve activity in animal models of irritable bowel syndrome. In a more translational approach, the isolated mouse intestinal segment can be exposed to colonic supernatants from IBS patients. Furthermore, a modification of this technique has been recently shown to be applicable in human colonic specimens.
Afferent nerves not only convey information concerning normal physiology, but also signal disturbed homeostasis and pathophysiological processes of the different organ systems from the periphery towards the central nervous system. As such, the increased activity or 'sensitization' of mesenteric afferent nerves has been allocated an important role in the pathophysiology of visceral hypersensitivity and abdominal pain syndromes.
Mesenteric afferent nerve activity can be measured in vitro in an isolated intestinal segment that is mounted in a purpose-built organ bath and from which the splanchnic nerve is isolated, allowing researchers to directly assess nerve activity adjacent to the gastrointestinal segment. Activity can be recorded at baseline in standardized conditions, during distension of the segment or following the addition of pharmacological compounds delivered intraluminally or serosally. This technique allows the researcher to easily study the effect of drugs targeting the peripheral nervous system in control specimens; besides, it provides crucial information on how neuronal activity is altered during disease. It should be noted however that measuring afferent neuronal firing activity only constitutes one relay station in the complex neuronal signaling cascade, and researchers should bear in mind not to overlook neuronal activity at other levels (e.g., dorsal root ganglia, spinal cord or central nervous system) in order to fully elucidate the complex neuronal physiology in health and disease.
Commonly used applications include the study of neuronal activity in response to the administration of lipopolysaccharide, and the study of afferent nerve activity in animal models of irritable bowel syndrome. In a more translational approach, the isolated mouse intestinal segment can be exposed to colonic supernatants from IBS patients. Furthermore, a modification of this technique has been recently shown to be applicable in human colonic specimens.