Studies of internal gelation for the production of microspheres: sonication assisted gelation.

Internal gelation studies are carried out with mixed oxides of uranium and plutonium (MOX) and HMUR (i.e. mixture of hexamethylene tetramine (HMTA) and urea in 1:1 proportion). It is necessary to find surrogate of MOX for the detailed experimental work. Hence, the studies have been carried out with aluminium nitrate and magnesium nitrate. Important parameters of gelation such as temperature and concentration of precursors and the effect of sonication and drying on the gelled particles have been studied using these nitrates and HMUR. It has been found that micromixing (sonication) provides narrow and compact size distribution as compared to macromixing (using magnetic stirrer) and temperature of the precursors does not affect the size distribution of the gelled particles. The effect of drying has been studied using IR (infrared) dryer and oven dryer and it was found that IR drying augments the performance as compared to oven drying. Depending on the solubility of the gel in water and its appearance (as pasty mass which is similar to uranyl nitrate gel) aluminium nitrate is chosen as an appropriate surrogate for MOX. FTIR studies have been carried out for characterization of the gel.

Relearning toward motor recovery in stroke, spinal cord injury, and cerebral palsy: a cognitive neural systems perspective.

In stroke, spinal cord injury, and cerebral palsy there is denervation of target neuron centers, which are self-organizing maps (SOMs) within the neuraxis. Compensatory reinnervation occurs within those SOMs by acquiring synaptic sprouts from whatever neurons in the neighborhood. Such reorganizations are more often maladaptive than beneficial. Motor recovery, if any appears, is incomplete and compromised. Cognitive systems studies indicate that motor paralysis is due to loss of learning <--> recall balance in those compensated SOMs, which had been locked into a stability <--> plasticity dilemma. Treatment/rehabilitation should aim therefore to first restore this learning related balance. The use of botulinum toxin as a neuromotor relearning tool to improve motor recovery is discussed.

Botulinum toxin: from spasticity reliever to a neuromotor re-learning tool.

Botulinum toxin is becoming increasingly popular as the drug of choice for relief of spasticity in a wide range of conditions, from stroke to strabismus to vaginismus. Besides this role as spasticity reliever, several recent clinical reports claim that in stroke, cerebral palsy, spinal cord injury (SCI), and dystonias, BoTx brings about significant improvement in function--attributed to synaptic plasticity of the muscular afferents. The authors' research had shown that BoTx also generates synaptic plasticity in spinal alpha-motoneurons-interneurons. The article describes how BoTx facilitates relearning by Hebbian and Contrastive Hebbian modes and how it can be used as a neuro-relearning tool to enhance and hasten motor recovery in the aforementioned disorders.

Spinal cord injury: reversing the incorrect cortical maps by inductive lability procedure.

Within the brain-stem and on the cerebral cortex there are locomotor control centers arranged in a ladder-form control system. These centers are somatotopic, self-organizing neural network maps capable of simultaneously learning and task execution. In spinal cord injury (SCI) these self-organized maps get erroneously re-organized and maladaptively stabilized. The extent and quality of sensory-motor recovery, if any appears, is affected by and compromised due to incorrect mapping processes. The treatment method based on inductive lability procedure (Krishnan, 2003a, 2003b, 2003c) uses botulinum toxin for the purpose. It recreates competition among synapses in a locomotor training-based corrective re-self-organization of the maps in various steps of the ladder.

Transactivation of erbB2 by short and long isoforms of leptin receptors.

We generated kinase-positive and kinase-negative erbB2 tagged with YFP and the long form of leptin receptor (LEPRb) tagged with CFP. Both were as active as their untagged analogs. Both short and long isoforms of leptin receptor phosphorylated and thereby activated erbB2 upon leptin binding and enhanced MAPK activity. Our results unveil a novel route by which leptin may provoke erbB2's phosphorylation and thus enhance its oncogenic potential independently of HER family ligands or its overexpression. Using FRET technology in living cells, we found no evidence of complex formation between erbB2 and prolactin or leptin receptors, indicating that the transactivation occurs through an indirect interaction.

Relearning of locomotion in injured spinal cord: new directions for rehabilitation programs.

Locomotor activity-based rehabilitation programs seem to bring encouraging recovery to incomplete spinal cord injury paralytics. But in "complete" injuries recovery is long delayed and in small increments. Developmental and computer neural networks studies show that motor relearning requires the participation of redundant numbers of and activity-dependent competition of synapses among spinal interneurons. The present programs do not meet this prerequisite. They focus mainly on the mechanical (retraining) part while the neural (relearning) part plays a rather passive role. Here we suggest how retraining can be integrated with relearning by inductive lability procedures (Krishnan, 2003a, 2003b) with the objective of enhancing and hastening recovery.

Quantitative imaging of protein-protein interactions by multiphoton fluorescence lifetime imaging microscopy using a streak camera.

Fluorescence lifetime imaging microscopy (FLIM) using multiphoton excitation techniques is now finding an important place in quantitative imaging of protein-protein interactions and intracellular physiology. Recent developments in multiphoton FLIM methods are reviewed and a novel multiphoton FLIM system using a streak camera is described. An example of a typical application of the system is provided in which the fluorescence resonance energy transfer between a donor-acceptor pair of fluorescent proteins within a cellular specimen is measured.

Spinal cord injury: inductive lability can enhance and hasten recovery.

In spinal cord injury, recovery of function, if any, confirms the presence of survived neural tissue at the injury site. However, recovery several years after the injury remains unexplained. Body weight bearing locomotor exercises seem to bring these new outcomes. Developing locomotor system and computer simulation studies show that motor learning requires the presence of redundant sets of competing synapses within the spinal cord interneurons. The new exercise regimens have not addressed this essential prerequisite; this could perhaps explain the long delays in recovery. We recommend that inclusion of inductive lability procedure (Krishnan, 1983, 1991, 2003) will help hasten and enhance the recovery.

A new extra-vertebral treatment model for incomplete spinal cord injuries.

Advances made in recent times in spinal cord injury repair research will soon take us toward a cure in paraplegics. But what are the prospects for quadriplegics? Certain fundamental issues make treatment approaches to quadriplegia different and difficult. Injury at cervical region poses additional problems for any surgical intervention with life-threatening risks of i) endangering respiratory function, ii) cavitation, cysts, and syringomyelia formation extending cephalad to the injury, and iii) mid-lower cervical injuries, lower motor neuron death, and the resultant degeneration of brachial plexus axons would still leave the upper limbs denervated and paralyzed even as treatment procedures might successfully salvage the lower limbs. With these apparently insurmountable impediments in quadriplegic cord repair, it would be wise to turn to alternative treatment strategies. Conventional treatment models since the days of Ralph Gerard (1940) have all used intra-vertebral procedures. We present here a plausible extra-vertebral repair model suitable for incomplete cord injuries at cervical, thoracic, and lumbar levels. The procedure consists of identifying the extent of viable grey-white matter in the injured area and to utilize it efficiently as a "neural tissue bridge." Next, labile state is induced by using botulinum toxin/colchicine (Krishnan, 1983, 1991; Krishnan et al., 2001 a,b) and Ca+ channel blockers in the motorsensory nerve terminals of polisegmentally innervated skeletal muscles that "bridge" the injured cord segments. This would retrogradely induce a redundant state of intra-spinal growth of nerve terminals and new synaptic connections within those viable neural tissues, as well as promote effective relinking of the injured cord ends and enhance motor-sensory recovery.

Spinal cord injury repair research: a new combination treatment strategy.

The optimism that a cure will soon be found for paraplegia and quadriplegia is strongly founded on the series of discoveries in the last two decades which showed that adult mammalian spinal cord axons can be made to regenerate given appropriate conditions and microenvironment. But then, why no cure yet in sight? Why is the delay? Spinal cord scientists are encountering a newfound obstacle in regeneration research. While axons do regenerate up and down through a graft/transplant placed at the injury site, they fail to regenerate further on once they reach healthy cord tissue beyond the injury zone. Research from our laboratory since the 1980s found that the principal reason for this failure of long distance regeneration is that the neural circuitry these axons have to traverse through are in a well-stabilized state which is unreceptive and refractory to new growth. Successful long distance regeneration is possible only within labilized (destabilized) neural tissues. We have shown simple and reliable methods of inducing labile state in adult spinal cord neural circuitry. This is achieved by inducing polyneuronal spinal motor control in the paralyzed limb muscles. We had predicted (Krishnan, 1991, 1983) two outcomes of inductive lability in paraplegia. One is partial revival of functions in the paralyzed limbs. The second outcome addresses effective relinking of the severed cord ends. Our preliminary results from adult paraplegic frogs convince us that inductive lability in these animals is capable of generating new growth and new connections in the distal isolated cord. Locomotor rhythm and function reappeared in the hind limbs, which enabled these animals to swim and progress on surface for long periods of observation up to 120 days. Based on these results we now recommend that inductive lability should be included as an essential component in the treatment strategy for spinal cord injury repair for effective relinking of the severed cord ends.

Recovery of locomotor function in adult paraplegic frogs by inductive lability in the distal isolated spinal cord neural networks.

We postulated (Krishnan, 1991) that in a spinal cord transected adult paraplegic mammal locomotor functions can be revived if polyneuronal innervation is reinduced in the paralyzed hind limb muscles. This procedure destabilizes the neural networks and induces new synaptic growth in the distal isolated cord. In this pilot project we tested the hypothesis in cord-transected adult paraplegic frogs. Polyneuronal innervation was reinduced by crushing the sciatic nerve in the right upper thigh. Left limb sciatic nerve was not crushed and served as control. Another group of adult frogs had only cord transection without nerve crush. Five to seven weeks postnerve crush, full powered flexion-extension movements in the hip and knee joints appeared in the right hind limb and were used for swimming and surface progression. Movements gradually declined over the next weeks, which in some animals was seen preserved even beyond 120 days. Paraplegic frogs without nerve crush did not show any recovery of locomotor function. Interestingly, the uncrushed contralateral limb also produced transient, weak locomotor-like movements. This lasted for 4 to 6 days and waned out completely thereafter. These results validate our hypothesis on methods to generate new synaptic sprouts and reconnections to redrive the locomotor system. We had recommended earlier that destabilization procedure should be included as an essential component in treatment strategies for spinal cord injury repair for effective relinking of the severed cord ends.

Induction of plasticity in the isolated spinal cord in paraplegia.

In adult life a severe injury of the spinal cord results in total loss of locomotor functions of the hind limbs, i.e., paraplegia. However, after similar injury in neonatal life most hind limb functions are retained unaffected into adult life. Can such survival of locomotor function be produced in an adult paraplegic? Observations based on our previous studies suggest that sparing of function in the neonate is due to: 1) incomplete development of descending cord tracts 2) the presence of polyneuronal control of limb muscles by spinal motoneurons and 3) active growth of synaptic connections occurring in the cord while limbs are polyneuronally innervated. Such growth and remodelling ceases once mononeuronal (= adult) control of limb muscles is established. We suggest that recreation of conditions similar to neonatal life would be able to revive lost locomotor functions in the adult paraplegic. Experimental animal models are outlined here which may form a basis for future research.

A theory on the lability and stability of spinal motoneuron soma size and induction of synaptogenesis in the adult spinal cord.

There exists a dynamic relationship between the soma size of a motoneuron and its motor unit size. Adult motoneuron soma size can be experimentally increased if the neuron is allowed to innervate more muscle fibers than it normally innervates. In postnatal mammals a transition from polyneuronal to mononeuronal innervation of limb muscle fibers occurs which is temporally related to a plastic change in the perikaryal size. This lability of postnatal motoneuron size is temporally related to growth of synaptic connections on the motoneuron. In adult mammal, regenerating motor axons polyneuronally innervate the muscle fibers for a transient period. This hypothesis proposes that a plastic change in soma size occurs in these adult motoneurons. This short-lived labile state may revive the embryonic properties and evoke growth of synaptic boutons. Experimentally induced labile state in motoneuron pools and spinal ganglion neurons in the adult mammal should offer a basis for the study of mechanisms of synaptogenesis in the spinal cord.

Size plasticity of intact motoneurons as reaction to partial denervation of muscle.

It is known that partial denervation of muscle leads to the enlargement of the intact motor units by collateral sprouting of the intramuscular axons. After partially denervating the hind limb muscles in the frog, its effect on the intact motoneuron cell size was investigated. It was found that motoneurons increase in size when their motor unit territory expanded. This increase indicates size plasticity and the dynamic nature of motoneuron size. It is proposed that there are two distinct, but interacting states relating to motoneuron size (the stable in equilibrium labile states). The implications of size plasticity of motoneuron on synaptogenesis/synaptic reorganization on its membrane surface is discussed.

Corticospinal tract interaction in locomotor development and motor units formation: an hypothesis.

In rat and kitten postnatal development the Corticospinal Tract (CST) growth has a temporal relationship with the development of mature locomotion and the elimination of polyneuronal innervation, and the formation of motorunits in the hindlimb muscles. This temporal correlation suggests a possible interaction of the CST with spinal motoneurons in the formation of functional groups of motorunits. Further, evidence is also given that spinal motoneuron size is plastic in the polyneuronal period; this indicates that motoneurons adapt themselves to their motorunits in postnatal life. This hypothesis suggests a causal interaction among these three neuronal events; the relevance of this interaction to the maturation of locomotor function is discussed.