Spontaneous unit activity in the rabbit limbic cortex

Spontaneous unit activity in different parts of the limbic cortex, recorded extracellularly in waking rabbits during chronic experiments, was analyzed. Attention was paid particularly to unit activity in theta- and delta-rhythms. Theta-modulation was found in a small proportion (5–12%) of neurons in all parts except the lateral entorhinal cortex. Delta-activity was found in all structures tested but its characteristics varied. In the subiculum (45% of neurons) it consists of short, high-frequency discharges with long pauses, in the entorhinal cortex (22%) opposite characteristics were found (long loosely packed bursts with short intervals between them). Activating influences raised the frequency and increased the resistance of the theta component and desynchronized the delta volleys in the subiculum and most other structures; in the entorhinal cortex under these circumstances the density of the volleys of spikes was increased but without any change in their frequency or regularity. The spectral composition of unit activity in the presubiculum was mixed. The nature of rhythmic modulation of unit activity in areas of the limbic cortex is discussed.Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 16, No. 6, pp. 753–760, November–December, 1984.     

Effect of electric stimulation of cortical portions of the limbic system on the activity of neurons of the anterior thalamic nuclei in the rabbit

Effects of electrical stimulation of the subiculum (SB) and posterior limbic cortex (PLC) were studied extracellularly in the anteroventral (AV) and anterodorsal (AD) limbic thalamic nuclei of awake chronic rabbits. Stimulation of SB and PLC evoked in some AV neurones discharges of 1-2 spikes. Gradual potentiation and low frequency of following (up to 10-15 Hz) were characteristic of these responses. Activity of the majority of AV cells was suppressed by stimulation with appearance of inactivation bursts, "neuronal spindles" and modulation on delta-frequencies. Spike responses were evoked by SB and (rarely) by PLC stimulation only in a certain class of AD neurones which tentatively are regarded as relay cells. The neurones with high-frequency, low-amplitude discharges (putative inhibitory interneurones) reacted to stimulation of PLC and to a lesser extent of SB by prolonged series of spikes (150 ms--2s). Stimulation of PLC exerted prolonged influence upon neuronal responses to sensory stimuli.     

Effect of sectioning the mammillothalamic tract on neurons of limbic nuclei of the thalamus

Neuronal activity of n. AV (n = 75) and n. AD (n = 55) of the thalamus was recorded extracellularly in unanaesthetized chronic rabbits after complete transection of the mammillo -thalamic tract (MTT). Elimination of this powerful afferent system produced a surprisingly small effect upon spontaneous and evoked neuronal activity. All types of responses were preserved in both nuclei, though some increase of multimodal diffuse tonic responses and decrease of more specialized phasic and complex on-effects occurred in n. AV. In both nuclei short-latency responses (less than 14 ms) to auditory stimuli disappeared. The number of units with dynamic transformations of responses during repeated stimuli application (gradual emergence and shaping of responses, as well as their habituation) decreased 2-3-fold in both nuclei. The impulse activity travelling in MTT seems to be not critical for limbic nuclei sensory reactivity but significant for plasticity of the responses.     

Single unit responses of the reticular and ventral anterior nuclei of the thalamus to electrical stimulation of the centrum medianum

In acute experiments on cats anesthetized with thiopental (30–40 mg/kg, intraperitoneally) and immobilized with D-tubocurarine (1 mg/kg) responses of 145 neurons of the reticular and 158 neurons of the ventral anterior nuclei of the thalamus to electrical stimulation of the centrum medianum were investigated. An antidromic action potential appeared after a latent period of 0.3–2.0 msec in 4.1% of cells of the reticular nucleus and 4.4% of neurons of the ventral anterior nucleus tested in response to stimulation. The conduction velocity of antidromic excitation along axons of these neurons was 1.7–7.6 m/sec. Neurons responding with an antidromic action potential to stimulation both of the centrum medianum and of other formations were discovered, electrophysiological evidence of the ramification of such an axon. Altogether 53.8% of neurons of the reticular nucleus and 46.9% of neurons of the ventral anterior nucleus responded to stimulation of the centrum medianum by orthodromic excitation. Among neurons excited orthodromically two groups of cells were distinguished: The first group generated a discharge consisting of 6–12 action potentials with a frequency of 130–640 Hz (the duration of discharge did not exceed 60 msec), whereas the second responded with a single action potential. Inhibitory responses were observed in only 0.7% of neurons of the reticular nucleus and 4.4% of the ventral anterior nucleus tested. Afferent influences from the relay nuclei of the thalamus, lateral posterior nucleus, and motor cortex were shown to converge on neurons responding to stimulation of the centrum medianum.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 1, pp. 36–45, January–February, 1980.     

Spontaneous unit activity of locus coeruleus neurons after destruction of some nuclei of the medulla oblongata

Bilateral lesions of the nuclei prepositus hypoglossi produced a more than twofold decrease in the mean frequency discharges in the neurons of the nucleus coeruleus. The number of neurons with burst activity and the number of polymodal neurons substantially increased. Lesion of the nucleus tractus solitarius resulted in an increase in the number of neurons with regular activity and certain decrease in the mean discharge frequency of coeruleus neurons. The results confirm the suggestion about a substantial role of the nucleus prepositus hypoglossi in relaying afferent effects to the activity of locus coeruleus neurons.     

Responses of neurons of the anterodorsal nucleus of the thalamus and comparative analysis of 3 limbic nuclei

Comparison of the three limbic thalamic nucleic shows that in spite of some common features of organization and connections, these nuclei presumably play different functional roles. N. AV may be regarded as an important "on-line" functional link of the limbic circuit. N. AD, possibly serves as input from the specific auditory structures to the limbic system. N. AM may participate in regulation of the general level of activity together with unspecific thalamic nuclei.     

Characteristics of background unit activity in the nucleus reticularis of the human thalamus

Background firing activity was examined in 240 neurons belonging to the thalamic nucleus reticularis (Rt) in the unanesthetized human brain by extracellular microelectrode recording techniques during stereotaxic surgery for dyskinesia. The cellular organization of Rt was shown to be nonuniform, and distinguished by the presence of three types of neuron: one with arrhythmic single discharge (A-type, 40%), another with rhythmic (2–5 Hz) generation of short high-frequency (of up to 500/sec) burster discharges (B-type, 49%) and a third with aperiodic protracted high-frequency (of up to 500/sec) bursting discharges separated by "silent" intervals of a constant duration of 80–150 msec (i.e., C-type, 11%). Differences between the background activity pattern of these cell types during loss of consciousness under anesthesia are described. Tonic regulation of neuronal type was not pronounced but a tendency was noticed in the cells towards a consistent rise in firing rate, rhythmic frequency and variability, etc. in both A and B units, especially in the latter. Findings pointing to the absence of a direct relationship between rhythmic activity in the Rt and parkinsonian tremor were confirmed. Background activity in B-type cells was found to increase and then stabilize with a rise in the degree of tremor. The nature of regular bursting activity patterns in B and C neurons is discussed in the light of our findings.Institute of Chemical Physics, Academy of Sciences of the USSR, Moscow. Institute of Neurosurgery, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 19, No. 4, pp. 456–466, July–August, 1987.     

Effect of repeated daily electrical stimulation on seizure activity in the rabbit limbic system

The order of appearance, the functional relations, and changes in the epileptiform effects of electrical stimulation of the limbic system (septum, amygdala, hippocampus) were studied. During repeated electrical stimulation regular changes took place in the seizure activity: the duration, frequency, and amplitude of the after-discharges were increased, their polarity was changed, seizures and unsynchronized high-amplitude activity appeared, and the after-discharges were reactivated. The most common variants of the seizure patterns are described. Close correlation was found between the greatest intensity of the after-discharges and the appearance of seizures. Besides a critical number of after-discharges, their parameters and their degree of irradiation also play an important role in the onset of the seizures. It is postulated that the limbic structures may play the role of an organized epileptogenic focus. Facts indicating that the seizure activity in response to direct electrical stimulation of the limbic structures may have a reflex mechanism are presented.     

A quantitative comparison of the hominoid thalamus: II. Limbic nuclei anterior principalis and lateralis dorsalis

Structures in the limbic system are commonly thought to be similar in form and function in all mammalian brains. In the study reported here, two thalamic limbic nuclei, N. anterior principles and N. lateralis dorsalis, were compared among a group of extant of extant hominoids. The nuclear volumes, neuronal densities, number of neurons per nucleus, and volumes of neuronal perikarya were measured. Humans have much larger nuclei but the nuclei constitute a similar proportion of the whole thalamus as found in the other hominoids. Whereas the human limbic nuclei were observed to have a decrease in the densities of nerve cells compared with those of the other hominoids, this difference is less than that found in most other thalamic nuclei. Consequently the estimated number of neurons is much higher for humans. The total number of neurons best separates the human limbic nuclei from those of the other hominoids. This preliminary study suggests that during hominid evolution neurons were preferentially added to the limbic nuclei of the thalamus.     

Spontaneous fluctuations in the activity of rabbit skeletal muscle NAD-kinase]

Spontaneous fluctuations in the time of the activity of the 280-300-fold purified NAD-kinase preparation from rabbit skeletal muscle following its dilution are described. Defrosted but undiluted enzyme preparation failed to exhibit any fluctuations in its activity.     

Spontaneous and receptor-controlled soluble guanylyl cyclase activity in anterior pituitary cells

Nitric oxide (NO)-dependent soluble guanylyl cyclase (sGC) is operative in mammalian cells, but its presence and the role in cGMP production in pituitary cells have been incompletely characterized. Here we show that sGC is expressed in pituitary tissue and dispersed cells, enriched lactotrophs and somatotrophs, and GH(3) immortalized cells, and that this enzyme is exclusively responsible for cGMP production in unstimulated cells. Basal sGC activity was partially dependent on voltage-gated calcium influx, and both calcium-sensitive NO synthases (NOS), neuronal and endothelial, were expressed in pituitary tissue and mixed cells, enriched lactotrophs and somatotrophs, and GH(3) cells. Calcium-independent inducible NOS was transiently expressed in cultured lactotrophs and somatotrophs after the dispersion of cells, but not in GH(3) cells and pituitary tissue. This enzyme participated in the control of basal sGC activity in cultured pituitary cells. The overexpression of inducible NOS by lipopolysaccharide + interferon-gamma further increased NO and cGMP levels, and the majority of de novo produced cGMP was rapidly released. Addition of an NO donor to perifused pituitary cells also led to a rapid cGMP release. Calcium-mobilizing agonists TRH and GnRH slightly increased basal cGMP production, but only when added in high concentrations. In contrast, adenylyl cyclase agonists GHRH and CRF induced a robust increase in cGMP production, with EC(50)s in the physiological concentration range. As in cells overexpressing inducible NOS, the stimulatory action of GHRH and CRF was preserved in cells bathed in calcium-deficient medium, but was not associated with a measurable increase in NO production. These results indicate that sGC is present in secretory anterior pituitary cells and is regulated in an NO-dependent manner through constitutively expressed neuronal and endothelial NOS and transiently expressed inducible NOS, as well as independently of NO by adenylyl cyclase coupled-receptors.     

Spontaneous activity of the isolated rabbit superior cervical sympathetic ganglion

Investigation of spontaneous activity (mean amplitude of spikes 200–300 µV, frequency from 0.07 to 2.9 Hz) in the rabbit superior cervical sympathetic ganglion by the sucrose gap method showed that this activity was completely blocked by D-tubocurarine and hexamethonium; its frequency was increased in hypertonic solution, by an increase in the external potassium concentration, and by the addition of theophylline and ethanol. These observations suggest that the activity observed is due to spontaneous liberation of acetylcholine mediator from preganglionic nerve endings. However, addition of tetrodotoxin and an increase in the external calcium concentration to 10 mM block spontaneous activity in the ganglion. This suggests that the observed spontaneous activity consists of action potentials.     

Spontaneous and evoked unit activity in the visual cortex in mutant mice

Spontaneous and evoked unit activity was investigated in the visual cortex of mice with the "ocular retardation" (or/or) mutation, in which the action of the gene is manifested phenotypically by defective development of the optic nerve, with the consequent total blindness of the animals. Control experiments were carried out on inbred C57Br mice. A raised level of spontaneous activity was found in the neurons of the mutant animals and also differences in the distribution of the cells on the basis of the types of their spontaneous activity: A regular type of activity was found 2.5 times more often in the "or/or" mice than in the control group, whereas the proportion of cells with a volley type of discharge was 2.7 times smaller. In addition, visual cortical neurons of the "or/or" mice were more able to respond to acoustic stimulation, when 78% of the responses were tonic in character. Of the unit responses to electrical stimulation of the skin 70% also were tonic, and most were responses of excitation. In 42% of visual cortical neurons of the mutants convergence of heteromodal afferent influences was observed. The functional features described are evidently phenotypical manifestations of the action of the mutant gene on cortical neurons.P. K. Anokhin Institute of Normal Physiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 8, No. 6, pp. 568–574, November–December, 1976.     

Monoamine oxidase activity in rabbit brain nuclei in experimental acute emotional stress

Activity of monoamine oxidase in the neurons of catecholamine-synthesizing nuclei of hypothalamic and brainstem of rabbits with different resistance of cardiovascular functions to emotional stress was studied by the Glenner et al. method. An acute experimental emotional stress was induced by non-periodic electric stimulation of the hypothalamic ventromedial nucleus and the skin in immobilized adult chinchilla rabbits. It was found that monoamine oxidase activity in the neurons of groups A5, A6, A7 and A14 under acute experimental emotional stress increased in rabbits "resistant"to stress and remained unchanged in rabbits "predisposed" to stress. The activity of monoamine oxidase in the neurons of group A12 remained unchanged in the rabbits "resistant"to stress and decreased in the rabbit "predisposed" to stress.