Behavioural parameters in aged rats are related to LTP and gene expression of ChAT and NMDA-NR2 subunits in the striatum.

Striatal parameters were assessed for their relevance to age-related behavioural decline. Forty aged rats (28-30 months) were tested in the water maze and open field. Of these, seven superior and seven inferior learners were compared with each other in terms of levels of in vitro short- and long-term potentiation (STP and LTP), and gene expression of choline acetyltransferase (ChAT) as well as of the NMDA-NR2A-C subunits assessed by quantitative RT-PCR. Results revealed that the superior as compared with the inferior learners had higher levels of ChAT mRNA in the striatum. For the superior group, ChAT mRNA was correlated with escape on to the cued platform in the water maze, whereas level of LTP was predictive of place learning in the water maze and rearing activity in the open field. For the inferior group, expression of NR2A and NR2B was positively correlated with place learning and probe trial performance in the water maze. The results show that individual differences in various behaviours of aged rats were accounted for by variability in striatal parameters, i.e. LTP, ChAT and NMDA-NR2 subunit mRNA. Notably, the correlations found were heterogeneous amid the groups, e.g. variability in place learning was explained by variability in levels of LTP in the superior learners, but in levels of NR2A-B mRNA in the inferior group.

[Probable location of synaptic inputs, evoking generation of long-term IPSP in pyramidal neurons: model studies]. / Veroiatnaia lokalizatsiia sinapticheskikh vkhodov, vyzyvaiushchikh generatsiiu dlitel'nykh TPSP v piramidnykh neironakh: model'nye issledovaniia.

A region of possible location of potassium-conducting synapses responsible for generation of "slow", or "long-term" IPSPs has been determined in computer experiments with the use of neuroscience-oriented software program CRONA on the basis of data of measurement of reversal potential of such IPSPs under natural experiments. Such geometrical parameters as dimensions of neuronal dendritic branches and intracellular potassium concentration have been studied for their effect on determination of the above-mentioned region using the results of natural experimental studies of interaction of long-term IPSPs with polarizing currents. It is shown that synaptic inputs under investigation have non-somatic location and the region of their location on apical dendrites is between 110 and 460 microns from the soma.

[Reaction of neurons of the medial geniculate body to acoustic stimulation]. / Reaktsii neironov media'lnogo kolenchatogo tela na zvukovye razdrazheniia.

Responses of medial geniculate body (MGB) neurons to pure tones and clicks were studied in acute experiments in immobilized cats, preliminary operations being performed under calypsol anaesthesia. MGB units were identified by their reactions to cortical zone AI and brachium of inferior colliculus stimulations. When tonal stimuli were applied relay neurons of pars principalis of MGB usually demonstrated either unimodal tuning curves with narrow frequency band or fragmental ones with several narrow bands. On-response with subsequent inhibition of the background activity or without such an inhibitory period was most frequent type of the reaction (66.6%) of relay MGB neurons to tonal stimulation. The group of relay neurons with the tonic type of reaction (9.1%) was classified for which the duration of tonic response depends on the duration of tonal stimulus. Change of the excitatory reaction to the inhibitory one when the characteristic tone frequency is changed by non-characteristic++ ones is supposed to be a mechanism supplying sharpness of tuning at relay MGB neurons. It is concluded that responses of acoustic cortical neurons to sound stimulation depend to a great extent on the pattern of impulsation that comes from MGB relay units.

[Proposed inhibitory neurons of the auditory cortex in the cat]. / Predpolagaemye tormoziashchie neirony slukhovoi kory koshki.

A complex of properties of inhibitory neurons in the auditory cortex is defined according to the peculiarities of IPSPs recorded in many cortical neurons. 12 units with such properties were found in a group consisting of 54 cells. These low-threshold units were localized predominantly in layers III-IV, had no background activity and responded to afferent volleys by short-latent barbiturate-resistant discharges (1-4 spikes).

[Neuronal interactions in the auditory cortex of the alert cat]. / Mezhneironnye vzaimodeistviia v slukhovoi kore bodrstvuiushchikh koshek.

Background activity of neighbouring neurons was recorded during chronic experiments in auditory cortex of unanesthetized unimmobilized cats. Functional connection between simultaneously observed neurons was estimated by cross-correlation of the spike trains. 20 pairs of neurons were studied. The most frequent type of interaction (50%) was a "shared excitatory input" from specific auditory afferents. Interaction of the "shared inhibitory input" type (5%) and complex patterns of interactions were found. No interaction between cells was observed in 10% of cases. Direct inhibitory influence of a cell on a neighbouring one was not found at all. Probable reasons of absence of direct inhibitory interactions between auditory cortical neurons are discussed. Low level of background activity in inhibitory neurons is regarded to be possible.

[Electrophysiologic study of conduction of afferent impulses through the medial geniculate body]. / Elektrofiziologicheskoe issledovanie provedeniia afferentnykh impul'sov cherez medial'noe kolenchatoe telo.

In experiments carried out on cats immobilzed with d-tubocurarine 280 neurons located in pars principalis of the medial geniculate body and 408 auditory cortical neurons located in AI were studied extra- and intracellularly in response to stimulation of the brachium of the inferior colliculus and geniculocortical fibres. It was shown that the initial stage of the reaction observed in the medial geniculate body neurons response to stimulation of the brachium of the inferior colliculus continue for 13.0 ms. Excitation of 72% of neurons participating in the reaction occurs during the first 3 ms after stimulation. 84% of IPSPs arouse in the same period of time. It is found that some medial geniculate neurons have axons entering the inferior colliculus. Substantial part of fibres in the brachium of the inferior colliculus comes to the auditory cortex without synaptic switching in the medial geniculate body. 76% of medial geniculate neurons from the group excited monosynaptically are thalamocortical relay neurons and the rest are interneurons. 90% of relay neurons in the medial geniculate body are excited monosynaptically. Many medial geniculate neurons respond to stimulation of the brachium of the interior colliculus by EPSP-IPSP sequence or by primary IPSPs. About 20% of primary IPSPs develop monosynaptically. The maximal amount of IPSPs comes into being disynaptically with the participation of inhibitory interneuron located at the input to the medial geniculate body. The inhibition observed in this case is direct afferent one.

[Monosynaptic inhibitory postsynaptic potentials of cerebral cortex neurons]. / O monosinapticheskikh tormoziashchikh postsinapticheskikh potentsialakh neironov kory bol'shikh polusharii

The auditory cortes of cats immobilized with d-tubocurarine was stimulated by monopolar macroelectrodes (tip diameter 100 mu) or micloelectrodes (tip diameter 100--15 mu). In both cases in cortical neurons located closely to the stimulation point IPSPs were recorded with latencies ranging between 0.4--1.2 and 1.4 6.0 ms. It is suggested that IPSPs of the first group are generated in response to direct stimulation of the bodies and axons of the inhibitory cortical neurons (monosynaptically). The amplitude of such IPSPs ranged in different neurons from 3 to 15 mV and their duration was between 4 and 15 ms. Many of them were complicated by later additional inhibitory volleys. 1.5% of all IPSPs generated in response to geniculocortical fibres stimulation had latencies between 0.8--1.3 ms. It is suggested that these IPSPs were also evoked monosynaptically.