Use of a simplified method of optical recording to identify foci of maximal neuron activity in the somatosensory cortex of white rats.

Eight mongrel white male rats were studied under urethane anesthesia, and neuron activity evoked by mechanical and/or electrical stimulation of the contralateral whiskers was recorded in the primary somatosensory cortex. Recordings were made using a digital USB chamber attached to the printer port of a Pentium 200MMX computer running standard programs. Optical images were obtained in the barrel-field zone using a differential signal, i.e., the difference signal for cortex images in control and experimental animals. The results obtained here showed that subtraction of averaged sequences of frames yielded images consisting of spots reflecting the probable position of activated groups of neurons. The most effective stimulation consisted of natural low-frequency stimulation of the whiskers. The method can be used for preliminary mapping of cortical zones, as it provides for rapid and reproducible testing of the activity of neuron ensembles over large areas of the cortex.

[Application of the simplified method of optic recording for mapping focuses of the neuronal activity in the somatosensory cortex of the white rats]. / Primenenie uproshchennogo metoda opticheskoi registratsii dlia opredeleniia fokusov maksimal'noi aktivnosti neironov somatosensornoi kory belykh krys.

In rats, a differential signal was used for evoking an optical image in the barrel-field zone which represented a difference between cortical images during the control and the stimulation periods. After a subtraction of averaged sequences of frames, an image of spots reflecting a probable location of activated groups of neurones was obtained. Natural low frequency stimulation of vibrissae is supposed to be the most effective. The method of intrinsic optical activity imaging can be applied for preliminary mapping of cortical zones.

Functional mapping of the motor cortex of the white mouse by a microstimulation method.

Studies on 33 anesthetized white mice were used to determine the motor representation of facial muscles and limb muscles by an intracortical microstimulation method. Microstimulation produced predominantly ipsilateral movement responses of facial muscles and contralateral responses in fore- and hindlimb muscles. Low-threshold stimulation in the left and right hemispheres showed a clear asymmetry of the motor representation of the facial muscles. Movement responses of the hindlimbs were obtained on microstimulation of the frontal regions of the neocortex, demonstrating the existence of multiple motor representations of muscles in the neocortex.

Use of artificial ion channels for quasi-intracellular recording of cerebral cortex neuron activity.

Action potentials and synaptic potentials were recorded in vivo from cortical neurons in baby rats aged 20-25 days using a new method based on the ionophore nystatin. Nystatin solution was used to fill a standard glass extracellular microelectrode, and became inserted into membranes. Spikes which were initially recorded as extracellular spikes showed increases in amplitude and were transformed into unipolar quasi-intracellular spikes at 0.5-5.0 min after formation of the high-conductance contact. This method allows stable recording of neuronal activity from cells for at least 1 h, and provides a good signal-to-noise ratio. The electrode does not puncture the neuron membrane, with the result that experiments do not require any isolation from vibration. Thus, the results obtained demonstrate that the method is highly efficient for recording the in vivo activity of small nerve cells.

[Functional mapping of the motor cortex in the white mouse by microstimulation]. / Funktsional'noe kartirovanie motornoi kory beloi myshi metodom mikrostimuliatsii.

Motor representations of the face muscles and muscles of limbs were determined by means of intracortical microstimulation (ICMS) in 33 anaesthetized white mice. ICMS evoked mostly ipsilateral motor responses of facial muscles and contralateral motor responses of forelimb and hindlimb. Clear asymmetry of the face muscles's motor representation was found using low-threshold stimulation in left and right hemispheres. Hindlimb's motor responses to ICMS in rostral areas of frontal neocortex were observed and it indicates the presence of multiple motor representations in the mouse neocortex.

[The use of artificial ion channels for the quasi-intracellular recording of the activity of cerebral cortex neurons]. / Ispol'zovanie iskusstvennykh kanalov dlia kvazivnutrikletochnoi registratsii aktivnosti neironov kory golovnogo mozga.

Both the action and synaptic potentials were recorded in cortical neurons in vivo in the rat pups. A new recording technique needed no special vibroisolation and provided a stable recording with a satisfactory signal/noise ratio.

[The electrophysiological characteristics of long-term homo- and heterotopic cortical transplants in the rat motor cortex]. / Elektrofiziologicheskie kharakteristiki dolgovremennykh gomo- i geterotopicheskikh korkovykh transplantatov v motornoi kore krysy.

Microelectrode experiments were performed on the transplants (TPs) in the motor cortex, MI, of adult rats 2 to 6 mo and 8 to 11 mo after grafting TPs taken from one of hemispheres of newborn rat. Within TPs, latencies of neuronal responses evoked by means of electrocutaneous stimulation of forelimbs, hindlegs and vibrissal pads were ranged, from 13 to 30 ms, 17 to 38 ms and 10 to 15 ms, respectively. The values are similar with those in intact MI in both experimental and normal rats. A trend to widening receptive fields was observed in many neurons recorded in long-surviving TPs. In some units, a predominance of ipsilateral somesthetic inputs over contralateral ones was demonstrated which is more usual phenomenon for immature neurons in MI during early normal development. It indicates on the deficiency of maturation's mechanisms for synaptic inputs into the TPs. No motor responses were induced by low-threshold microstimulation in TPs and only on the depths lower than 2000 microns motor responses were obtained in a few cases, presumably due to the activation of white matter axons.

The recovery of locomotion following partial extirpation of the motor cortex and transplantation of cortical tissue in the white rat.

The changes in the parameters of locomotion in three groups of white rats at ages from 5 to 16 weeks were investigated in this study: 1) following unilateral extirpation of an area of cerebral cortex in the zone of the motor representation of the hind limb at the age of 5 weeks; 2) following homotypical transplantation of cortical tissue from newborn rats to the zone of decortication at the same age; 3) intact animals of the same litters (control). An age-related increase in the step length took place in the rats of all groups. By contrast with the intact rats, in which the increase in the values of the step length and width took place smoothly over the course of the entire period, a lag in the locomotion parameters investigated was observed in the operated animals. After two to five weeks the features of recovery were already observed in the grafted rats, while a tendency toward an alteration in the character of the gait was detected after 9 to 11 weeks: their step length exceeded that of both the operated and intact rats. Histological control confirmed the taking of all grafts without signs of rejection or necrotic changes. The possible mechanisms of participation of endogenous and exogenous factors in the elimination of the hemiparetic sequelae are discussed.

[Changes in evoked cortico-motor responses in the rat during aging and after partial decortication]. / Izmeneniia vyzvannykh kortiko-motornykh reaktsii u krys s vozrastnom i posle chastichnoi dekortikatsii.

Some changes of the organization of cortical motor representations, which were revealed by means of the intracortical microstimulation (ICMS) in aged rats after unilateral partial decortication, were true consequences of the decortication, but had no significant relationship to the aging. Distributions of latent periods of contralateral hind-leg EMG-responses to the ICMS had no significant shifts both during aging and after the surgery. Values of short-latency responses of ipsilateral proximal and axial muscles to the ICMS were in late time periods, from 8 to 16 months after surgery, significantly lower than ones of contralateral homonymous muscles. It is supposed, that ipsi- and bilateral short-latency responses to the ICMS in proximal and axial muscles of operated rats during late time periods are relayed through some pathways from the brain stem to the spinal cord.

[Restoration of locomotion after partial extirpation of the motor cortex and transplantation of cortical tissue in the white rat]. / Vosstanovlenie lokomotsii posle chastichnoi ékstirpatsii motornoi kory i transplantatsii korkovoi tkani u beloi krysy.

Changes of the locomotion parameters were studied in three groups of rats of 5 to 16 weeks of age: 1) after unilateral removal of a part of the hindleg motor representation in 5-week animals; 2) after homotopic transplantation of neonatal cortical tissue into the ablation site; 3) in intact rats. In operated rats, a delay in the usual increase of the step length occurred. Clear signs of the restoration of locomotor parameters were found in rats with transplants within 2 to 5 weeks after the grafting. A significant trend towards increasing step length occurred within 9 to 11 weeks after the transplantation. Possible mechanisms of participation of both endogenous and exogenous factors in the restoration after the effects of partial decortication, are discussed.

[Trigeminal motor nuclei in the mouse: effects of microstimulation and sources of afferent projections]. / Troinichnoe motornoe iadro myshi: effekty mikrostimuliatsii i istochniki afferentnykh proektsii.

Motor responses of low jaw to the microstimulation of the motor nucleus of the trigeminal nerve (MNTN) of albino mice have been recorded. They had the latency ranged of 2.5 to 13.5 ms. After microinjections of horseradish peroxidase into the MNTN, retrogradely labeled neurons were revealed ipsilaterally in both sensory and mesencephalic trigeminal nuclei, in the medullary reticular formation, etc.

[Facial motor responses to microstimulation of the superior colliculi in the white mouse]. / Litsevye dvigatel'nye otvety na mikrostimuliatsiiu verkhnikh kholmov u beloi myshi.

Facial motor responses to microstimulation of different zones of the superior colliculi have been investigated in the albino mice craniotomized under thiopental anaesthesia. Local responses of the mystacial vibrissae, upper lip and eyelids were initiated by microstimulation of the rostral parts of the inner layers of the colliculus superior (high-frequency volleys of 5-7 pulses with a current limit of 35 microA). Sequential changes in the pattern of facial responses were observed within microelectrode traces indicating vertical orientation of facial motor representations in the superior colliculus. Some differences in the localization and pattern of facial responses in the right and left superior colliculi were revealed: 1) vibrissae and lip representations in the right superior colliculus occupy more extensive zone (vertical distribution from 300 to 2,300 microns) as compared to those in the left one (700-2,000 microns); 2) microstimulations of the right superior colliculus produce both uni- and bilateral vibrissal motor responses, whereas stimulation of the left superior colliculus evokes only unilateral responses. The duration of the latent period of the vibrissal and lip motor responses to stimulation of the right superior colliculus varied from 10 to 26 ms (16.1 +/- 2.4 ms; n = 199), to stimulation of the left one-from 10 to 18 ms (mean 14.9 +/- 1.8 ms; n = 55). It is suggested that polysynaptic motor responses to microstimulation of the superior colliculi are realized via the reticular and other premotor nuclei of the brain stem which have direct inputs from the superior colliculus and direct projections to the facial motor nucleus.

[Changes in the parameters of locomotion following partial extirpation of the motor cortex in white rats]. / Izmeneniia parametrov lokomotsii posle chastichnoi ékstirpatsii motornoi kory u belykh krys.

Quantitative locomotion changes have been studied in the norm and in different periods after local ablation of motor projection of hind paw in the right hemisphere of 5-16 weeks white rats. The length and width of step gradually increase with the age, and coefficients of gait asymmetry reflecting individual characteristics, are relatively stable in intact animals. Local decortication is accompanied by significant shifts of all locomotion parameters clearly expressed in the first days after ablation. The most sensitive characteristic of gait anomaly is the standard deviation of half-step. In 5 weeks after ablation a lag is observed of operated rats behind the control ones in all parameters. Load application contributes to revealing of locomotion parameters shifts from the norm in later periods after decortication. In 9 and 11 weeks after surgery, the signs of supercompensation are observed in a number of parameters.

[Restructuring of the topical organization of the rat motor cortex after damage to the opposite hemisphere]. / Perestroika topicheskoi organizatsii motornoi kory krysy posle povrezhdeniia v protivopolozhnom polusharii.

Topical organization of the motor cortex was compared in outbred rats by the method of intracortical microstimulation in the norm and in different periods after unilateral partial decortication of the motor projection (MP) of the hind-leg. Stable state of the MPs of the fore- and hind-limbs was in the norm, and within their bounds there was an individual variability of MP zones of separate joints. After the operation, the reconstruction of the motor cortex organization in the opposite hemisphered appeared in later periods, in 5-7 months. Expansion was observed of the boundaries of the excitable area in caudal direction and reduction of the part of responses of the limbs distal muscles as compared to proximal ones and of the body muscles. 8-16 months after the operation, the reactions of axial muscles, including the ipsi- and bilateral ones, became more expressed.