Neurotensin Changes Propulsive Activity into a Segmental Motor Pattern in the Rat Colon

Abstract

Background/aims: Neurotensin is a gut-brain peptide with both inhibitory and excitatory actions on the colonic musculature; our objective was to understand the implications of this for motor patterns occurring in the intact colon of the rat.

Methods: The effects of neurotensin with concentrations ranging from 0.1-100 nM were studied in the intact rat colon in vitro, by investigating spatio-temporal maps created from video recordings of colonic motility before and after neurotensin.

Results: Low concentration of neurotensin (0.1-1 nM) inhibited propagating long distance contractions and rhythmic propagating motor complexes; in its place a slow propagating rhythmic segmental motor pattern developed. The neurotensin receptor 1 antagonist SR-48692 prevented the development of the segmental motor pattern. Higher concentrations of neurotensin (10 nM and 100 nM) were capable of restoring long distance contraction activity and inhibiting the segmental activity. The slow propagating segmental contraction showed a rhythmic contraction-- relaxation cycle at the slow wave frequency originating from the interstitial cells of Cajal associated with the myenteric plexus pacemaker. High concentrations given without prior additions of low concentrations did not evoke the segmental motor pattern. These actions occurred when neurotensin was given in the bath solution or intraluminally. The segmental motor pattern evoked by neurotensin was inhibited by the neural conduction blocker lidocaine.

Conclusions: Neurotensin (0.1-1 nM) inhibits the dominant propulsive motor patterns of the colon and a distinct motor pattern of rhythmic slow propagating segmental contractions develops. This motor pattern has the hallmarks of haustral boundary contractions.

Keywords: Absorption; Colonic motility; Neurotensin; Peristalsis; Propulsion.

Figure 1

The development of slow propagating segmental contractions in low concentrations of neurotensin. Experiment 1: (A) The rat colon displayed strong long distance contraction (LDC) activity under control conditions. In all figures, the top shows the most proximal activity. (B) Neurotensin (0.1 nM) added to the bath solution, induces slow propagating segmental contractions (neurotensin is given 5 minutes before start of tracing). (C) Increasing the neurotensin concentration to 0.5 nM, the slow propagating segmental contractions are observed just distal to rhythmic proximal contractions. Experiment 2: (D) The rat colon shows typical LDC and rhythmic propagating motor complex activity before addition of neurotensin at arrow. Neurotensin (0.1 nM), added to the bath, inhibits LDC activity and slow propagating segmental contractions start to develop. In the presence of neurotensin 0.5 nM (E) and 1 nM (F). The activity in 1 nM shows 4 slow propagating segmental contractions starting from the most proximal part of the colon.

Figure 2

The segmental nature of the neurotensin induced contractions. In sequential video images (time between [A] and [B] is 88 seconds and time between [B] and [C] is 14 seconds) the segmental nature of the contractions is seen. The colon is divided into segments. The contractions are also seen to propagate and are seen to periodically relax, given the contractions an on/off/ on/off appearance. See Supplementary Video 1. The activity occurred in the presence of neurotensin (0.5 nM). (D) The spatio-temporal map (same as Fig. 1C) relates to the video images. The video images are moments in time, taken from Supplementary Video 1 whose spatiotemporal map is figure (D). The segmental nature can also be shown in an amplitude profile (E) made at the vertical line.

Figure 3

Bath addition of neurotensin (0.1–1 nM) abolishes long distance contractions (LDCs) and induces slow propagating segmental contractions; neurotensin (10–100 nM) restores LDC activity. Here we show in one experiment the actions of low and high concentrations of neurotensin. (A) Control activity shows prominent rhythmic LDC activity. (B) Neurotensin (0.1nM) was added 10 minutes before recording, the LDC frequency and width decreased, some distal rhythmic propagating motor complexes are present. (C) Neurotensin (0.5 nM) was added, abolishing LDC activity and evoking slow propagating segmental rhythmic waves of contraction. Note the rhythmic changes in amplitude (the on/off pattern of the slow propagating segmental contractions) and the presence of regular proximal contractions. (D) Neurotensin (1 nM) was added, continuing the patterns observed in (C). (E) Neurotensin (10 nM) was added, a transition is seen from the segmental pattern in (C) to the LDC pattern in (F). (F, G) Neurotensin (100 nM) completely restores LDC activity. (F) and (G) are sequential in time.

Figure 4

Intraluminal neurotensin changes long distance contraction (LDC) activity into slow propagating segmental contractions. Experiment 1: (A) Baseline activity shows regular rhythmic LDC activity at 0.6 cpm. (B) Neurotensin (0.1 nM) was added into the lumen 10 minutes before recording. LDCs changed into slow propagating segmental contractions. Strong proximal contractions remained at 0.6 cpm. Experiment 2: (C) Neurotensin (0.1 nM) was added at arrow. LDCs change into slow propagating segmental contractions. Thereafter the concentration was increased to 0.5 nM neurotensin (D).

Figure 5

The neurotensin receptor 1 (NTR1) antagonist SR-48692 inhibits the effect of neurotensin (1 nM). (A) Control activity shows rhythmic long distance contraction (LDC) activity. (B) SR-48692 (0.3 μM) was added 10 minutes before recording, LDC activity is maintained, the rhythmic propagating motor complex activity has become more prominent. (C) Neurotensin (1 nM) did not inhibit LDCs in the presence of SR-48692 and no slow propagating segmental contractions developed.

Figure 6

Spontaneous slow propagating segmental contractions. (A) and (B) show two time periods of a preparation that showed the rare occurrence of spontaneous rhythmic segmental contractions. They occurred in between LDC activity. (C) Video frames showing the segmented colon, as it changes over time; the contractions that create the segments are slowly propagating in anal direction. Time between top and middle image is 24 seconds, between middle and bottom image is 36 seconds. The length of the colon depicted is 14 cm. (D) Amplitude profile at one time point across the colon, at vertical line in (B), showing the segmental nature of the contraction pattern.

Figure 7

Effect of neurotensin in the presence of nerve conduction blockade. Experiment 1: (A) Typical activity in the presence of lidocaine (5.5 μM). Proximal rhythmic contractions are always prominent. (B) After addition of neurotensin (100 nM) the proximal rhythmic contractions increased in frequency and the contractions propagated across the colon. Experiment 2: (C) Activity in the presence of lidocaine (5.5 μM). (D) In the presence of 100 nM neurotensin, strong rhythmic contractile activity occurs in both proximal and distal colon. In the distal colon it is predominantly retrograde.