Changes in Sensorimotor Connectivity to dI3 Interneurons in Relation to the Postnatal Maturation of Grasping

Abstract

Primitive reflexes are evident shortly after birth. Many of these reflexes disappear during postnatal development as part of the maturation of motor control. This study investigates the changes of connectivity related to sensory integration by spinal dI3 interneurons during the time in which the palmar grasp reflex gradually disappears in postnatal mice pups. Our results reveal an increase in GAD65/67-labeled terminals to perisomatic Vglut1-labeled sensory inputs contacting cervical and lumbar dI3 interneurons between postnatal day 3 and day 25. In contrast, there were no changes in the number of perisomatic Vglut1-labeled sensory inputs to lumbar and cervical dI3 interneurons other than a decrease between postnatal day 15 and day 25. Changes in postsynaptic GAD65/67-labeled inputs to dI3 interneurons were inconsistent with a role in the sustained loss of the grasp reflex. These results suggest a possible link between the maturation of hand grasp during postnatal development and increased presynaptic inhibition of sensory inputs to dI3 interneurons.

Complexity of modular neuromuscular control increases and variability decreases during human locomotor development

“…Work in animal models shows that the basic neural circuits underlying locomotor-like behavior are laid down in the spinal cord at early stages of development, well before birth 54,55 . However, they are then modified extensively over a prolonged postnatal period by experience, with spontaneous neural activity, sensory feedback, and supraspinal control playing a critical role in shaping progressively the locomotor function 24,40,41,56 . Similarly, developmental studies in humans show that locomotor-like behavior is present prior to and at birth 25,[32][33][34][35][36]42 , but the kinematic and kinetic features typical of mature locomotion are reached only after several years 57 .…”

Methimazole‐induced gestational hypothyroidism affects the offspring development and differently impairs the conditioned fear in male and female adulthood rodents

“…The physical parameter included pinna unfolding, incisor eruption, and eye opening (Sanches et al, 2019). The following behavioral reflexes were also assessed: righting reflex (the pups ware placed in the dorsal decubitus over a flat surface and observed the age that each pup returns from the prone position) (Anjos et al, 2022), negative geotaxis (pups were kept on a 45° inclined plane face‐down and observed the age that each pup was able to rotate at least 135°) (Ruhela et al, 2019), palmar grasp reflex (light pressure with a paper clip was applied until the pup showed a palmar grasp with the forepaw) (Laliberte et al, 2021), auditory startle (body retraction, with a transitory immobility in response to a sound stimulus) (Fragoso et al, 2017), and vibrissae placing (pup held by tail with head facing edge of bench with vibrissae just touching vertical surface and observed the lifting of the head and the extension of the forepaws in a direction of the bench) (Smart & Dobbing, 1971). On PND22, the offspring were weaned and distributed according to theirs sex and litter size and housed in groups of four per cage.…”

Changes in synaptic inputs to dI3 INs and MNs after complete transection in adult mice

“…dI3 INs are a population of spinal neurons residing in laminae V-VII of the spinal cord (Bui et al, 2013). They are characterized by the expression of Isl1 (Bui et al, 2016;Capelli et al, 2017), a LIMhomeodomain transcription factor that is also expressed in various tissues and populations of neurons, including motoneurons and sensory neurons (Pfaff et al, 1996;Liem et al, 1997) dI3 INs form sensorimotor circuits linking sensory afferents and neurons for motor control in the spinal cord (Bui et al, 2013(Bui et al, , 2016Laliberte et al, 2022). Immunohistochemical labeling of VGLUT1 + has shown that dI3 INs are contacted by primary sensory afferents (Alvarez et al, 2004), and electrophysiological experiments have confirmed this observation as dI3 INs received monosynaptic input from proprioceptive and low threshold cutaneous afferents (Bui et al, 2013), many of which are under the control of axoaxonic GABAergic inputs (Laliberte et al, 2022).…”

“…They are characterized by the expression of Isl1 (Bui et al, 2016;Capelli et al, 2017), a LIMhomeodomain transcription factor that is also expressed in various tissues and populations of neurons, including motoneurons and sensory neurons (Pfaff et al, 1996;Liem et al, 1997) dI3 INs form sensorimotor circuits linking sensory afferents and neurons for motor control in the spinal cord (Bui et al, 2013(Bui et al, , 2016Laliberte et al, 2022). Immunohistochemical labeling of VGLUT1 + has shown that dI3 INs are contacted by primary sensory afferents (Alvarez et al, 2004), and electrophysiological experiments have confirmed this observation as dI3 INs received monosynaptic input from proprioceptive and low threshold cutaneous afferents (Bui et al, 2013), many of which are under the control of axoaxonic GABAergic inputs (Laliberte et al, 2022). Furthermore, dI3 INs are glutamatergic and project ipsilaterally within the spinal cord targeting motoneurons and spinal locomotor circuits (Bui et al, 2016).…”