Interneuronal Activity in Reflex Pathways from Group II Muscle Afferents Is Monitored by Dorsal Spinocerebellar Tract Neurons in the Cat

Abstract

The main aim of the study was to investigate whether group II muscle afferents contribute to the inhibition of dorsal spinocerebellar tract (DSCT) neurons and thereby modulate information provided by these neurons in the cat. In intracellular recordings, we found disynaptic IPSPs from group II afferents in the majority of DSCT neurons, most often in parallel with IPSPs evoked from group I afferents. In an attempt to identify interneurons that mediate these IPSPs, the second aim of the study, laminas IV-VII in midlumbar segments were searched for interneurons antidromically activated by stimuli applied within Clarke's column. Such interneurons were found in regions in which focal field potentials were evoked by group I and II afferents, or ventral to them, and most were coexcited by these afferents. The input to these interneurons and their location indicate that they belonged to the previously identified population of premotor interneurons in disynaptic pathways between group I and II afferents and hindlimb motoneurons. The study leads thus to the conclusion that inhibitory actions of group II afferents on DSCT neurons are collateral to actions on motoneurons and that DSCT neurons monitor inhibitory actions of group II afferents on motoneurons as closely as they monitor actions of group I afferents. The results also indicate that interneurons mediating disynaptic reflex actions from tendon organ (group Ib) afferents and those mediating disynaptic actions from secondary muscle spindle (group II) afferents to motoneurons may be parts and parcel of the same interneuronal population rather than constitute distinct interneuronal populations.

Rhythmic activity of feline dorsal and ventral spinocerebellar tract neurons during fictive motor actions

“…No disynaptic inhibitory input from reciprocal Ia inhib- itory interneurons was found in DSCT cells (Hongo et al 1983a;Lindstrom and Takata 1977), but "Ib" inhibitory interneurons (Hongo et al 1983a;1983b), as well as group Ib/II inhibitory interneurons (Jankowska and Puczynska 2008), contact DSCT cells. The Ib inhibitory interneurons are known to be silenced (or inhibited) during fictive locomotion (McCrea et al 1995) and fictive scratch (Perreault et al 1999), while the Ia inhibitory (Geertsen et al 2011) and subpopulations of the Ib/II inhibitory interneurons (Shefchyk et al 1990;Stecina 2006) are rhythmically active during both fictive locomotion and scratch.…”

Inhibitory inputs to four types of spinocerebellar tract neurons in the cat spinal cord

“…Postsynaptic and presynaptic inhibitory actions on various populations of spinocerebellar neurons may also vary as much as the excitatory ones, both in origin and degree (Lundberg and Weight, 1971;Burke et al, 1971a;Edgley and Jankowska, 1988;Jankowska and Puczynska, 2008;Jankowska et al, 2010;Krutki et al, 2011). The aim of the present study was therefore to extend our previous investigation of excitatory input to four types of spinocerebellar tract neurons based on immunohistochemical analysis of nerve terminals in contact with labelled neurons (Shakya- by making a similar analysis of inhibitory input to these neurons.…”

“…Inhibitory terminals on ccDSCT and dhDSCT neurons should likewise originate from spinal neurons but from a smaller range of interneuron populations including intermediate zone inhibitory premotor interneurons in pathways from group Ib and II afferents but not Ia inhibitory interneurons and Renshaw cells (Hongo et al, 1983;Jankowska and Puczynska, 2008). Another source of inhibitory input to these neurons might be dorsal horn interneurons relaying information from group II afferents which are shown to have terminal projections in laminae IV, V and VI of the dorsal horn (Bannatyne et al, 2006(Bannatyne et al, , 2009.…”

Collateral Actions of Premotor Interneurons on Ventral Spinocerebellar Tract Neurons in the Cat

“…4). The gastrocnemius and soleus and posterior biceps and semitendinosus motor nuclei were selected for the purposes of this study as representative extensor and flexor motor nuclei and because disynaptic IPSPs and excitatory postsynaptic potentials (EPSPs) from group I and group II afferents are evoked in high proportions of motoneurons in these nuclei (Eccles and Lundberg 1959;Eccles et al 1957b), in parallel with disynaptic PSPs in VSCT and dorsal spinocerebellar tract neurons (Hongo et al 1983a;Jankowska and Puczynska 2008;Lindström and Schomburg 1974;Lundberg and Weight 1970). The stimulators used were designed by E. Eide, D. Magnusson, and N. Pihlgren (University of Gothenburg; Eide 1973).They allow the use of square constant voltage or constant current pulses via inbuilt isolation units and setting the constant voltage stimuli in multiples of threshold for activation of nerve fibers via 15 output channels.…”