Motor-sensory and visual behavior after hemispherectomy in newborn and mature rats

Abstract

Immature mammals are widely believed to compensate functionally for nervous system alterations better than adults with comparable disorders. Embryos restitute huge losses, but plasticity, remodeling, or use of alternate mechanisms said to underly compensation in injured infants are not understood. Toward understanding these, the effects of ablating or altering parts of the nervous system in infant and mature rats are being studied. In these experiments one lateral half of the forebrain and diencephalon was largely removed at birth or maturity and the consequences to nervous system structure and motor-sensory and visual behavior were observed. Similarities between animals operated on as adults or infants were loss of tactile placing opposite the ablation, ability to discriminate visual patterns, and gauge variable jumping distances visually. Some subjects performed the visual tasks using the eye opposite the hemispherectomy alone, which was exclusively supplied with uncrossed retinogeniculate fibers. Differences were: loss of tactile placing after operation in infants was delayed until the seventeenth day; stride was impaired in animals operated on as adults but was spared in infant subjects ; with appropriate ablations, Fink-Heimer-Nauta stains showed that after hemispherectomy, infants, but not adults, developed a small, uncrossed corticospinal tract. The stride component in locomotion seemed dependent on the corticospinal tract system, and was partially dissociated from the placing reaction essential for locomotion on rough terrain. The possibility was considered that the small remodeled corticospinal tract spared the stride component.

Formation of Descending Pathways Mediating Cortical Command to Forelimb Motoneurons in Neonatally Hemidecorticated Rats

“…Previous anatomical studies showed that corticospinal neurons in the undamaged SMC of hemidecorticated rats send bilateral axonal projections to the spinal gray matter (Barth and Stanfield 1990;Castro 1975;Hicks and D'Amato 1970;Leong 1976;Ono et al 1990Ono et al , 1991Ono et al , 1994Ono et al , 1995Rouiller et al 1991;Takahashi et al 2009). To examine whether these corticospinal axons exert synaptic effects on both sides of the spinal gray matter, we analyzed the effect of pyramidal stimulation on extracellular field potentials in the cervical spinal cord ( Fig.…”

“…Pyramidal neurons project aberrant collateral fibers that cross the midline to the superior colliculus, the red nucleus, and the pontine nuclei on the side contralateral to their normal targets in addition to their normal projections (Kartje-Tillotson et al 1986;Leong 1976;Leong and Lund 1973;Nah and Leong 1976a,b;Naus et al 1985;Takahashi et al 2009;Wenk et al 1999). In addition, the corticospinal tract projects aberrant fibers to the ipsilateral gray matter in the spinal cord after crossing the midline at the pyramidal decussation (Barth and Stanfield 1990;Castro 1975;Hicks and D'Amato 1970;Kuang and Kalil 1990;Leong 1976;Ono et al 1990Ono et al , 1991Ono et al , 1994Ono et al , 1995Rouiller et al 1991;Takahashi et al 2009). The aberrant collaterals possessed bouton-like swellings along their course that may function as presynaptic terminals.…”

A comparison of the role of the motor cortex in recovery from cerebellar damage in young and adult rats

“…Often operations in infants produce less debilitating or less persistent deficits than similar lesions in adults (Kennard, 1938 and1942;Tucker, Kling and Scharlock, 1968;Goldman, Rosvold and Mishkin, 1970;Hicks and D'Amato, 1970;Schneider, 1970;and many others). However, in at least one case (Hicks, D'Amato, Klein, Austin and French, 1969), neonatally1Research supported by grant GB 35315X from NSF, and grants MH 19793-02 and MH 11095-07 from NIMH.…”

Functional magnetic resonance studies of the reorganization of the human hand sensorimotor area after unilateral brain injury in the perinatal period.

“…In this model, it has been shown that the remaining hemisphere develops a new, uncrossed corticospinal tract to the ipsilateral spinal cord in addition to the usual crossed one (7). Huttenlocher et al (8,9) have succeeded in making separate cortical maps of the neurons forming the aberrant (uncrossed) and normal (crossed) tracts.…”