Neuromediator sensitivity of neurons of the reticular formation and orbital cortex in hungry and satiated rabbits

In conditions of stereotaxic fixation, noradrenaline microionophoresis and stimulation of the lateral hypothalamus acted in the same sense on impulse activity of 35 and 37% of the neurones in the reticular formation of satiated rabbits, in joint action increasing the number of cells with distribution of intervals characteristic of alimentary motivational excitation. Microionophoresis of acetylcholine to the neurones of the orbital cortex in freely behaving rabbits reshaped the impulse activity of 57% of cells in accordance with the pattern of discharge activity characteristic of alimentary motivational excitation. Such excitation, natural as well as artificially evoked, widens polychemical properties of the neurones of the reticular formation and, on the contrary, narrows polychemical properties of the nerve cells of the orbital cortex.     

Dynamics of the reactivity of cortical neurons to repeated electrophoretic application of acetylcholine

Dynamics of reactivity was studied in 50 neurones of the rat sensorimotor cortex to repeated acetylcholine microiontophoresis. By the parameter of response plasticity the neurones are distributed into three groups--unchanging, decreasing and increasing the excitatory component of the reaction. A connection has been established of the type and rate of tonic and evoked activities dynamics with the duration of the excitatory component of neuronal reactions to acetylcholine. The highest probability of these dynamic activity changes manifestation is observed in cholinoceptive neurones with duration of excitatory reaction components to acetylcholine equal to 3.2, 8.1 and 13.5 s.     

The effect of acetylcholine and atropine on the temporal connection in the neuronal populations of the motor cortex]

On alert non-immobilized rabbits the activity of neurones in the sensorimotor cortex was studied at pair combination of brain structures stimulations. During omission of the reinforcing stimulus at the place of its expected presentation a complicated complex develops of neurones impulses reconstructions, consisting in reproduction of responses and activity changes which by their configuration differ from them and usually appear in later terms. Direct acetylcholine application on the cortex promotes manifestation of both types of neurones activity reconstructions. But atropine application depresses mainly the second type of reconstructions. Besides, acetylcholine increases the general duration of the given conditioned effects, but atropine decreases it.     

Integrative properties of the microsystem of cortical neurons during repeated local stimulation

Small groups of neighbouring neurons in neocortex are able to form separate microsystem in model situation of habituation during the local repetitive action of acetylcholine. This new functional unit exhibits a number of main properties which are characteristic of systemic processes of habituation. Only some of the properties don't reproduce in microsystem of cortical neurons. There is no effect of full extinction of responses and no direct relationship between the decrease of speed quantity of responses and stimulus action frequency. The data obtained are considered as significant argument for identification of special intermediate level of integrative processes--microsystem level.     

Cholinergic regulation of the activity of somatosensory cortex neurons during early postnatal ontogeny of the cat

In 11-14 days kittens, about 20% of neurones in the somatosensory cortical zone react to stimulation of subpallidal region which is a source of cholinergic projections to the cerebral cortex. The effect of subpallidal region stimulation is reproduced in case of microiontophoretic acetylcholine application and blocked by atropine what points to its cholinergic nature. Cholinergic stimulation causes inhibition of the background and evoked activities of the cortical neurones while, as it is known, in adult cats, acetylcholine mainly stimulates a reaction of activation. It is postulated that in kittens at the end of the second week of postnatal development, cholinergic innervation of the cortex significantly differs from the definitive one by its quantitative and functional parameters.     

Changes in the cholinosensitivity of sensomotor cortex neurons during conditioned reflex extinction]

Characteristics of neuronal responses of the sensorimotor cortex to ionophoretically administered neuromediators (acetylcholine, L-glutamate) were studied in rabbit in the course of extinction of conditioned defensive reflex. In the majority of neurones the extinction of the conditioned reflex is accompanied by a drop of cholinosensitivity. In a number of neurones the extinction of reflexes either does not change the reaction to acetylcholine, or enhances it. The analysis of these reactions permits to assume the existence of a group of neurones directly involved in the formation, fixation and storage of the temporary connection.     

Effect of the microiontophoretic application of acetylcholine on the formation of conditioned reactions in motor cortex neurons

In alert rabbits the activity of the motor cortex neurones was recorded with simultaneous application of acetylcholine to them in the process of defensive conditioning. Conditioned reorganization, mainly of activation type, were found in 60% of neurones. In most cases conditionally reacting cells were sensitive to acetylcholine. Ionophoretic application of the transmitter promoted the formation of conditioned neuronal responses and increased them in comparison with conditioned reactions evoked in absence of acetylcholine. It is supposed that the influence of acetylcholine on conditioned cellular process is realized due to its action on the state of excitability of the cortical neurones.     

The interaction of mediators with protein synthesis processes in the visual cortex neurons in the goal-directed behavior of cats]

The chemical sensitivity was studied of the neurones of cats visual cortex at successive stages of food-procuring instrumental behaviour, formed in conditions of intraventricular administration of the blocker of protein synthesis the cyclohexamide. Animals with cyclohexamide had a low chemical sensitivity of the cortical neurones to microionophoretically applied solutions of acetylcholine and noradrenaline. In comparison with the intact animals, in animals with cyclohexamide the number of neurones reacting with change of the impulse activity at the stages of instrumental behaviour as well as the number of areactive cells, did not depend on the nature of the applied neurotransmitter.     

Morphine excitation in the cerebral cortex.

Microiontophoretic administrations of morphine to cholino-excitable neurones in the cerebral cortex of decerebrate cats evoked a weak excitation which became more prominent upon repeated administrations of the alkaloid. This effect was not antagonized by naloxone. Iontophoresis of methylatropine prevented the excitation induced with acetylcholine and morphine, leaving that caused by glutamate relatively unaltered. Similar applications of morphine to neurones which were not excited by test applications of acetylcholine did not result in excitation but elicited mainly a depression of glutamate-evoked firing. It is suggested that the muscarinic effect of morphine in the cortex may be related to the excitation and convulsions, but not the analgesia, which occurs upon systemic administrations of the narcotic.     

Conditioned feedback and inhibitory reorganization of the receptive fields of the cortical neurons as a basis for the subconscious change in the thresholds of visual recognition and detection

In the paper three groups of facts are compared: significant adaptative and adaptational modification of receptive fields of cat's visual cortex neurones, conditioned selective subsensory change of the threshold of perception (detection and recognition) of a letter by man in relation to two control ones and the role of spatially specialized cortical inhibition in formation and adaptative modifications of receptive fields and detector properties of the visual cortex neurones. Interconnection is discussed of the phenomena described as well as community of their mechanisms.     

Changes in the chemosensitive properties of the central neurons of the snail Helix pomatia and of the mouse as affected by opioid peptides

In experiments on neurones of the isolated ganglia of the snail and surviving hippocampal slices from mice, studies have been made of the effect of Met- and Leu-enkephalins on neuronal sensitivity to acetylcholine and norepinephrine. It was shown that in some cases the enkephalins do not affect bioelectrical activity of the neurones, but changed their responses to acetylcholine and norepinephrine. It is concluded that during investigation of the effect of enkephalins on the nervous cells, alongside with changes in the bioelectrical activity, special attention should be paid to changes in chemoreceptive properties of the neurones.     

Pharmacological and electrophysiological characteristics of neurones in the paramedian reticular nucleus.

1. Neurones in the paramedian reticular nucleus of decerebrate, unanaesthetised cats have been identified by microelectrode recording combined with antidromic activation of their axons in the ipsilateral inferior cerebellar peduncle. Most paramedian reticular neurones were not influenced by somatic stimulation. 2. When applied by iontophoresis from multibarrelled micropipettes acetylcholine and 5-hydroxytryptamine excited all but a few paramedian reticular neurones while l-noradrenaline inhibited almost all the neurones investigated. The excitatory response to acetylcholine could be antagonised by gallamine. 3. The paramedian reticular nucleus appears to be a relatively homogeneous group of neurones, pharmacologically as well as anatomically.     

Several mechanisms of acetylcholine participation in the processes of formation and fixation of temporary connections

Microphoretic application of acetylcholine (ACH) to the neurones of the rabbit sensorimotor cortex elicits changes of spontaneous and evoked activity which do not correlate with one another and which persist up to two minutes after the end of ACH application. Following the formation of a defensive conditioned reflex to sound, the reactions to ACH in units involved in the formation of the temporary connection are intensified as compared with their reactions before conditioning and with reactions of those neurones which did not elaborate a temporary connection. The possible mechanisms of ACH participation in the processes of elaboration and fixation of temporary connections are discussed.     

Effect of cyclic 3',5'-adenosine monophosphate on central neurons

In experiments on unanesthetized non-immobilized rabbits, unit responses in the cortex and thalamus to the cyclic 3',5'-adenosine monophosphate (cAMPh) were studied by means of microionophoresis. It was shown that cAMPh changes the pattern of background unit activity, increasing or decreasing the discharge frequency. cAMPh changes unit responses both to acetylcholine and noradrenaline. These data permit, to assume that cAMPh participates both in adrenergic and in acetylocholinergic mechanisms of excitation processing in brain neurones.     

Neurophysiologic and biochemical aspects of visual system development in the rabbit under conditions of photic deprivation]

Changes in the functional state of the visual cortex were studied by behavioral and electrophysiological cues and the chemism of its neurones at the cellular and subcellular levels in rabbits raised for one to two months in the dark. It has been shown that visual deprivation leads to retarded dynamics of elaboration and consolidation of the conditioned defensive reflex to light and to changes of opposite signs of the visual cortex surface EPs to specific and non-specific stimuli. Typical of the EPs to photic stimuli is a considerable decrease in amplitude and longer latency as compared with normal, and enhanced amplitude and shorter latency to acoustic stimuli. It has been cytochemically established that about half of the pyramidal neurones of the visual cortex layer V of the experimental animals display features of biochemical underdevelopment (of the size of the cytoplasmatic mass, the protein reserve). Under the same conditions activity depression was revealed in cytochromoxydase, Na, P-ATPhase and ACHE, expressed to a different degree in separate subcellular fractions of the visual cortex. The MAO activity selectively augments in the subfraction of cholinergic synaptosomes. It has been assumed that functional and biochemical changes in different groups of the visual cortex neurones due to deprivation are linked with both the properties of the synaptic structures in regard to perception of impulses of different modalities and the peculiarities of their chemism.     

The role of intracellular processes in regulating neuronal sensitivity to acetylcholine

Intracellular regulatory mechanisms of neuronal response to acetylcholine were studied on intracellularly perfused isolated neurones of Lymnaea stagnalis using voltage-clamp technique. It was found that at the change of concentration of free intracellular Ca2+ from 0.06 to 0.7 microM the inhibitory effect of intracellularly added serotonin depends on Ca2+, and the modulation of acetylcholine responses by intracellular serotonin is unchanged. The blockers of calmoduline trifluoperazine and W-7 inhibit inward acetylcholine current at both intra- and extracellular introduction. Possible mechanisms mediating the effect of intracellularly added serotonin on the membrane cholinoreceptors of neurones are discussed.     

Reactivity of neurons of the orbito-frontal cortex of the cat during exposure to the scent or sight of food

Reactivity of neurones in orbitofrontal cortex of the cat to the action of light or sound was studied in consecutive stages of alimentary behaviour conditioned by the smell and then the sight of food. Changes were found of the character of neuronal reactions to the light and sound stimuli at the change of smell to the sight of food. A conclusion is drown, that polysensory properties of the neurones of the orbitofrontal cortex provide integral organization of brain sensory function at separate stages of alimentary behaviour.     

Reactions of neurons in the sensory-motor cortex on different amounts of administered acetylcholine

As a result of acetylcholine iontophoresis with different currents 3-fold increase of transmitter compared with the threshold one for reaction has been shown not to result in change of a type of reaction pattern more than in 80.3% of neurones. Such increase of action force is quite enough for the significant lengthening of the reaction excitatory components in the most of investigated neurones. After the following repeated application of smaller quantity of transmitter the number of neurones with growth of frequency of excited impulsive activity recovers as well as the level of firing frequency decrease in the course of repetitive administration of transmitter. The effect of large doses of transmitter results in aftereffect expressed by increasing probability of excitatory component reduction during the repetitive applications of acetylcholine.     

Effect of precursors and cofactors of nucleic acid and protein synthesis on the response of cortical neurons induced by polarization

Injection of K-orotate and folic acid in different proportions and of vitamine B12 produces changes in the S35-methionine inclusion in the proteins of the sensorimotor cortex, basal ganglia, hypothalamus and hippocampus depending on the proportions of the injected agents. In animals with activation of the synthesis in the brain, surface anode polarization increased the mean frequency of spike activity of the neurones in the sensorimotor cortex and reduced the relative number of units, which responded to polarization by inhibition, as compared with the control animals and those in which no activation of protein synthesis was observed. The characteristics of cortical unit responses to surface anode polarization in experimental rats are apparently due to changes in the chemoreactive properties of their membranes, which set in under the influence of changes in the nucleic acid and protein synthesis in these neurones.     

Increased Polyphosphoinositide Responsiveness in the Cerebral Cortex Induced by Cholinergic Denervation

Lesion of the nucleus basalis in the basal forebrain of the rat results in the degeneration of the large cholinergic neurones which innervate the cortex. Parameters of cholinergic function, namely, acetylcholinesterase activity, muscarinic acetylcholine receptor number, and the depolarisation-induced release of acetylcholine, fall in ipsilateral cortex subsequent to lesion. These deficits are likely to reflect the loss of the presynaptic input to the cortex. A reversal in these deficits is seen 1 month after lesion, and a full recovery is seen after 150 days. This is thought to be due to a process of "spared axon sprouting" followed by the reestablishment of synapses. To examine the integrity of the cortical muscarinic receptor response following denervation, an assay of the polyphosphoinositide response was carried out. Cortical tissue slices, prelabelled with [3H]inositol, were incubated for 40 min with carbachol in the presence of Li+; the accumulation of [3H]inositol monophosphate ([3H]IP1) was used as an index of this response. A 92% increase in the carbachol-stimulated production of [3H]IP1 was seen 5 days after lesion compared to normal cortex. Sham-operated animals showed no change in [3H]IP1 accumulation at this time point. Dose-response experiments showed that this increase was due to an increase in the maximal response to carbachol after lesion with no change in EC50 values. Two weeks after lesion, this increased response was much attenuated; tissue slices from denervated cortex showing a strong acetylcholinesterase decrease (36-66%) showed an increase of just 30% above normal.(ABSTRACT TRUNCATED AT 250 WORDS)