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. 2017 Feb 1;595(3):883-900.
doi: 10.1113/JP272714. Epub 2016 Oct 13.

Supraspinal control of spinal reflex responses to body bending during different behaviours in lampreys

Li-Ju Hsu  1 , Pavel V Zelenin  1 , Grigori N Orlovsky  1 , Tatiana G Deliagina  1
Affiliations

Supraspinal control of spinal reflex responses to body bending during different behaviours in lampreys

Li-Ju Hsu et al. J Physiol. .

Abstract

Key points: Spinal reflexes are substantial components of the motor control system in all vertebrates and centrally driven reflex modifications are essential to many behaviours, but little is known about the neuronal mechanisms underlying these modifications. To study this issue, we took advantage of an in vitro brainstem-spinal cord preparation of the lamprey (a lower vertebrate), in which spinal reflex responses to spinal cord bending (caused by signals from spinal stretch receptor neurons) can be evoked during different types of fictive behaviour. Our results demonstrate that reflexes observed during fast forward swimming are reversed during escape behaviours, with the reflex reversal presumably caused by supraspinal commands transmitted by a population of reticulospinal neurons. NMDA receptors are involved in the formation of these commands, which are addressed primarily to the ipsilateral spinal networks. In the present study the neuronal mechanisms underlying reflex reversal have been characterized for the first time.

Abstract: Spinal reflexes can be modified during different motor behaviours. However, our knowledge about the neuronal mechanisms underlying these modifications in vertebrates is scarce. In the lamprey, a lower vertebrate, body bending causes activation of intraspinal stretch receptor neurons (SRNs) resulting in spinal reflexes: activation of motoneurons (MNs) with bending towards either the contralateral or ipsilateral side (a convex or concave response, respectively). The present study had two main aims: (i) to investigate how these spinal reflexes are modified during different motor behaviours, and (ii) to reveal reticulospinal neurons (RSNs) transmitting commands for the reflex modification. For this purpose in in vitro brainstem-spinal cord preparation, RSNs and reflex responses to bending were recorded during different fictive behaviours evoked by supraspinal commands. We found that during fast forward swimming MNs exhibited convex responses. By contrast, during escape behaviours, MNs exhibited concave responses. We found RSNs that were activated during both stimulation causing reflex reversal without initiation of any specific behaviour, and stimulation causing reflex reversal during escape behaviour. We suggest that these RSNs transmit commands for the reflex modification. Application of the NMDA antagonist (AP-5) to the brainstem significantly decreased the reversed reflex, suggesting involvement of NMDA receptors in the formation of these commands. Longitudinal split of the spinal cord did not abolish the reflex reversal caused by supraspinal commands, suggesting an important role for ipsilateral networks in determining this type of motor response. This is the first study to reveal the neuronal mechanisms underlying supraspinal control of reflex reversal.

Keywords: locomotion; reticulospinal neurons; spinal reflexes.

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Figures

Figure 1
Figure 1. Experimental design
Brainstem and spinal cord were isolated together with the cranium and the notochord. The preparation was attached to two platforms positioned in the experimental chamber. One of the platforms could be rotated in the horizontal plane, causing right or left bending of the caudal part of the preparation. The chamber was partitioned into two pools by an agar barrier. The rostral pool contained the brainstem; the caudal pool contained the spinal cord. Electrical stimulation of the MLR (MLR stim) or the trigeminal nerve (Trigem stim) was used to evoke FFS or different types of escape behaviour, respectively. During these behaviours, responses of MNs to bending were recorded bilaterally from the VRs at two rostro‐caudal levels (Rost and Caud VRs) by using suction electrodes. In some experiments, RSNs were recorded intracellularly with a microelectrode (ME).
Figure 2
Figure 2. Reflex responses to bending during fast forward swimming
A, an example of MLR‐evoked FFS (a part of the recording delimited by dashed line in B is shown with higher time resolution). Dotted lines between top traces show rostrocaudal phase lags. B–E, responses of caudal (Caud) and rostral (Rost) VRs to bending during FFS caused by MLR stimulation (B and C) and d‐glutamate application to the spinal cord (D and E). Bending was performed in either caudal (∼segment No. 50, Caud bend in B and D) or rostral (∼segment No. 20, Rost bend in C and E) parts of the spinal cord. Three upper traces are VRs recordings and the lower three traces are the same recordings after rectification and smoothing (time constant 0.5 s). The upper bar in B and C indicates the duration of stimulation. R and L are right and left, respectively. Note that since in D (L Rost and L Caud) the amplitude of the recorded spikes varied over a very large range, to see clearly the beginning and the end of the bursts (which were formed by action potentials of small amplitude), as well as small amplitude bursts caused by bending, we used an amplification that clipped the spikes of the largest amplitude. The clipping threshold was set approximately 10 times higher than the amplitude of smallest spikes. Similar clipping was performed in Figs 4 B, 6 and 10 C.
Figure 3
Figure 3. Reflex responses to bending during different types of escape behaviour
A–C, examples of VR responses to bending during SFS (A), BS (B), and contralateral turn (C) caused by stimulation of different sites of the trigeminal nerve. In A, B and C bending was performed at segments No. 50, No. 55 and No. 50, respectively. Rostral and caudal VRs were recorded in segment Nos 20, 25 and 25 and Nos 40, 50 and 40 in A, B and C, respectively. Rostrocaudal phase lags in A and caudorostral phase lags in B are shown by dotted lines between traces. Other designations as in Fig. 2.
Figure 4
Figure 4. Reversal of reflex responses to bending during trigeminal nerve stimulation, which did not evoke any specific behaviour
A and B, an example of reflex reversal in a preparation with intact spinal cord: the left VR responded to right bending before stimulation (A, Control), and to left bending during trigeminal nerve stimulation (B). C, VR responses to bending at different rostrocaudal levels during trigeminal nerve stimulation (N = 16, n (VRs) = 25, where N and n (VRs) are number of preparations and number of recorded VRs, respectively). The bar position indicates the site of recording. Bending at different segments (from No. 20 to No. 70) was performed. Responses in VRs located 5–10 segments rostrally to the bending site were recorded. Horizontal scale indicates the spinal segment number.
Figure 5
Figure 5. Classification of reticulospinal neurons according to their response to stimulation of ipsilateral and contralateral trigeminal nerve, with parameters causing reflex reversal but no specific behaviour
A, an example of a Group 1 neuron activated by stimulation of the ipsilateral (upper panel) and contralateral (lower panel) trigeminal nerve. B, an example of a Group 2 neuron activated by stimulation of the contralateral trigeminal nerve only. C, an example of Group 3 neuron that was not activated by stimulation of either nerve. In A–C, the duration of stimulation is indicated by stimulation artifacts. D, schematic drawing of the brainstem dorsal view with four reticular nuclei: mesencephalic reticular nucleus (MRN), anterior, middle, and posterior rhombencephalic nuclei (ARRN, MRRN and PRRN, respectively). The dashed line separates the rostral and caudal parts of MRRN. E and F, relative number of Group 1, 2 and 3 neurons recorded in different reticular nuclei (E, MRN, n = 6; ARRN, n = 9; MRRN, n = 68; PRRN, n = 16) and in rostral (n = 39) and caudal (n = 29) parts of MRRN (F). G, sites in MRRN, which were stimulated during bending. Sites eliciting the reflex reversal in eight experiments are indicated by red circles. Three sites indicated by blue circles did not evoked reflex reversal in two experiments. The dashed line separates the rostral and caudal parts of MRRN. H and I, electrical stimulation of a site in left MRRN (indicated by a green asterisk in G) caused reversal of the reflex response to bending. Bending caused the convex response before stimulation (H, Control) and the concave response during stimulation (I). Bending was performed at segment No. 45 and the VRs of segment No. 40 were recorded.
Figure 6
Figure 6. Activity of Group 1 neuron during backward swimming
Bending was performed at segment No. 50; rostral and caudal VRs were recorded in segments No. 25 and No. 40, respectively. The dashed line indicates the temporal sequence of activity in the left rostral and caudal VRs. Note that bending during BS causes concave responses in caudal VRs.
Figure 7
Figure 7. Effects of AP‐5 application on reflex reversal
A–C, concave responses to body bending during trigeminal nerve stimulation (A, Control) substantially decreased during bath perfusion of AP‐5 in the brainstem pool (B, AP‐5) and recovered after AP‐5 washout (C, Wash). Bending was performed at segment No. 40 and VRs were recorded in segment No. 35. The bars indicate duration of trigeminal nerve stimulation. D, mean value of A ipsi/A contra ratio (see Methods) before (Control) and during AP‐5 application (N = 5, n (VRs) = 10, n (cycles) = 30, P = 0.0007). Bending was performed at segment Nos 40–45; VRs were recorded in segment Nos 30–35.
Figure 8
Figure 8. Reversal of reflex responses to bending in preparation with longitudinal split of the spinal cord
A and B, an example of reflex reversal in preparation with longitudinal split of the spinal cord: the left VR responded to right bend before stimulation (A, Control), and to left bend during trigeminal nerve stimulation (B). Signals recorded from the left VR were rectified and smoothed with time constant 0.5 s. Bending was performed at segment No. 45 and the VR of segment No. 40 was recorded.
Figure 9
Figure 9. Responses of reticulospinal neurons to bending
A, an example of the left RSN with a concave response to bending (segment No. 50). B and C, responses of a left RSN to bending (No. 50) before (B) and during (C) intracellular injection of a negative current. Note the reverse of hyperpolarization (in C) indicating inhibitory input from SRNs. D, relative number of RSNs with different responses to bending recorded in all reticular nuclei (All), and separately in MRN (n = 4), ARRN (n = 8), MRRN (n = 69), and PRRN (n = 15). Dyn, response to the dynamic part of bending in any direction. E, relative number of RSNs receiving only excitatory inputs (Exc) from SRNs and those receiving inhibitory inputs (Inh) (n = 19).
Figure 10
Figure 10. Responses of Group 1 and Group 2 neurons to bending
A and B, effect of trigeminal nerve stimulation (causing reflex reversal) on response of Group 1 (A) and Group 2 (B) neurons to bending. Bars show relative number of neurons with a particular type of response to bending (A, N = 11, n = 18; B, N = 14, n = 15). Grey part of the bar indicates the relative number of neurons, in which convex response to bending remained during trigeminal nerve stimulation. Black bars indicate the relative number of neurons, in which responses to bending disappeared or remained absent during trigeminal nerve stimulation. C, an example of a Group 1 neuron, which was affected by bending before, but not during reflex reversal caused by trigeminal nerve stimulation. D, an example of a Group 1 neuron, which was activated by left bending before as well as during reflex reversal caused by the trigeminal nerve stimulation. In B and D, the instantaneous frequency (Inst fr) of the recorded RSNs is also shown. Bending was performed at segment No. 55 and VRs were recorded in segment No. 50.
Figure 11
Figure 11. Functional role of the SRN‐mediated spinal reflexes in different motor behaviours and a hypothesis about neuronal mechanisms underlying SRN‐mediated spinal reflex reversal
A and B, functional role of the SRN‐mediated spinal reflexes in different motor behaviours. The upper panels show the schematic body configuration of lamprey during FFS (A) and escape (B). The red line in the lamprey outline indicates SRNs activated by bending. The symbols + and − indicate activation and inhibition of MNs on the corresponding side, respectively. The lower panels show the schematic correlation of body undulation and muscle activity during FFS (A) and escape behaviours (B). During FFS (A), the convex response counteracts the body bend, and contributes to initiation of bending in the opposite direction, thus promoting the generation of undulations. During escape behaviours (B), the concave response increases the undulation amplitude, which is essential for escape behaviours. C and D, changes in a hypothetical circuitry underlying reflex responses to bending during FFS (C) and during escape behaviour (D). The stretched area of the notochord is shown in grey. Activated neurons and muscles are shown in pink, inactivated in white. Red arrows indicate supraspinal influence on spinal interneurons. Abbreviations: MLR, mesencephalic locomotor region, RSN, reticulospinal neuron, SRN, stretch receptor neuron, IN, interneuron, MN, motoneurons. C, stimulation of MLR, which evokes FFS, activates a specific population of RSNs. They inhibit IN2s, and thus bending to the left, which activates right SRNs, results in activation of ipsilateral MNs (convex response). D, stimulation of trigeminal nerves, which evokes escape behaviour, activates Group 1 and Group 2 RSNs. They inhibit IN1s and activate ipsilateral MNs. Therefore bending to the left results in inhibition of right MNs (via IN2s) and bending to the right in their disinhibition (concave response).
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References

    1. Armstrong DM (1986). Supraspinal contributions to the initiation and control of locomotion in the cat. Prog Neurobiol 26, 273–361. - PubMed
    1. Bretzner F & Drew T (2005). Motor cortical modulation of cutaneous reflex responses in the hindlimb of the intact cat. J Neurophysiol 94, 673–687. - PubMed
    1. Brocard F & Dubuc R (2003). Differential contribution of reticulospinal cells to the control of locomotion induced by the mesencephalic locomotor region. J Neurophysiol 90, 1714–1727. - PubMed
    1. Brocard F, Ryczko D, Fénelon K, Hatem R, Gonzales D, Auclair F & Dubuc R (2010). The transformation of a unilateral locomotor command into a symmetrical bilateral activation in the brainstem. J Neurosci 30, 523–533. - PMC - PubMed
    1. Buchanan JT, Brodin L, Dale N & Grillner S (1987). Reticulospinal neurones activate excitatory amino acid receptors. Brain Res 408, 321–325. - PubMed

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