NO-Dependent mechanisms of amygdalofugal modulation of hypothalamic autonomic neurons.

Neurophysiological and histochemical experiments on rats were performed to study the effects of the central nucleus of the amygdala on the activity of cells in various areas of the hypothalamus. Electrical stimulation of the medial part of the nucleus evoked marked excitatory reactions in neurons in the medial part of the paraventricular nucleus of the hypothalamus and the rostral part of the lateral hypothalamic area. Intravenous administration of N(G)-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg) led to increases in evoked neuron responses. A series of histochemical studies following activation of the central nucleus demonstrated increases in the quantity and optical densities of NADP diaphorase (NADP-d)-positive neurons in the parvocellular zone of the paraventricular nucleus of the hypothalamus and the medial part of the lateral hypothalamic area. The activity of nitroergic cells in the ventrolateral part of the lateral hypothalamic area was suppressed in these conditions. These mechanisms may underlie the amygdalofugal modulation of the autonomic functions of the hypothalamus.

[NO-dependent mechanisms of the amygdalofugal modulation of the hypothalamus vegetative neurons].

In neurophysiological and histochemical experiments on rats, amygdalo-fugal modulation of cells within NO-producing areas of the hypothalamus was studied. Electrical stimulation of the medial area of the central nucleus caused obvious excitatory neuronal reactions within the medial part of the paraventricular nucleus and rostral portion of the lateral hypothalamic area. The observed amygdala-induced neuronal responses were enhanced after i.v. N-nitro-1-arginine methyl ester (L-NAME, 10 mg/kg). The nistochemical study revealed that the central nucleus stimulation caused an increase in number and optical density of the NADPH-d-positive cells within the parvicellular zone of the paraventricular nucleus and in the medial part of the lateral hypothalamic area. The NO-producing cells within the ventrolateral part of the lateral hypothalamic area were inhibited. The described phenomenon may underlie the amygdalo-fugae modulation of autonomic outflow.

Changes in the synapses in the parietal cortex of senescent rats.

Quantitative parameters characterizing the density of the synapses, the pre- and postsynaptic elements, and the synaptic contact zones (SCZ) in the parietal cortex of young adult (3-month-old) and aged rats (24 months) were investigated using an automated computer system. A big loss of axospinous, but not of axodendritic synapses, was observed in the aged rats. The parameters for the synaptic vesicles and SCZ were changed also only in the axospinous synapses. The changes in the quantitative parameters are accompanied by changes in the structure of synapses. The structural changes may be considered as being degenerative and regenerative.

Prenatal development of the myenteric plexus in cat stomach.

The prenatal development of the myenteric (Auerbach) plexus in cat stomach has been studied light- and electronmicroscopically. Neuroblasts and axon bundles of the myenteric plexus are found in the gastric wall of the smallest embryos studied (10-15 mm) even before its layers are formed. The plexus elements are not separated from the mesenchyme with a basal membrane. In the larger embryos (40-55 mm) the myenteric plexus is already between two muscle layers. The ganglia are shaped and contain more neuroblasts. A small part of the nerve cells are advanced in their maturation--primary and secondary dendrites are emanated and they are slightly AChE-positive. The maturation of the nerve perikarya is intense during prenatal life. In 95-115 mm long embryos the differentiation of a considerable part of the nerve cells is advanced and it is possible to distinguish some ultrastructural types of myenteric neurones. The number of AChE-positive neuroblasts is increased and there are more dendritic profiles in the neuropile.

Postnatal development of the myenteric plexus in cat stomach.

The postnatal development of the myenteric plexus in cat stomach has been studied at birth, on the 14th, 30th, 45th and 180th postnatal days, using light- and electronmicroscopic methods. In newborn kittens the main network of the Auerbach plexus is well formed, but the myenteric ganglia are composed of nerve cells with different maturity and a scarce neuropile. During the first two postnatal weeks the dimensions of the ganglia increase owing to the increase of the nerve bodies and the rising number of glials cells and intercellular fibres. This is accompanied by a potentiation of the AChE-activity, mainly in the nerve cell bodies and to a lesser extent in the neuropile. Impregnation reveals different in calibre and form nerve fibres and terminals. Different ultrastructural types of neurones are identified on the 14th day. Later development is expressed in the formation of large compact ganglia and thick connecting strands. The number of AChE-positive fibres in the neuropile increases. Owing to the increase in the cell organelles and their more advanced maturity, it is possible to define the ultrastructural type of an ever increasing number of neurones.

Evoked potentials and rhythmic afterpotentials in relation to pre-stimulus EEG activity during quiet waking state.

The relationship between the frequency-characterized EEG activity preceding the stimulus presentation and the amplitude-characterized evoked potentials (EPs) and rhythmic afterreactions (RARs) was investigated. The experiments were performed on the somatosensory cortex of cats during quiet waking state. It was found that upon one and the same parameters of stimulation the amplitude of the EPs and the RARs depended significantly on the frequency of the spontaneous EEG activity recorded one second before the stimulus. A decrease of the frequency of the on-going EEG favoured the appearance of the high-amplitude early and late components of the evoked potentials and of the rhythmic afterpotentials. Conversely, the probability of appearance of low-amplitude EPs increased and that of RARs decreased when the frequency of the on-going EEG increased.

Behavioural reactions and changes in the spontaneous and evoked EEG-activity upon microinjection of noradrenaline and isoprenaline in cat nucleus raphe dorsalis.

Experiments are carried out on five cats with bipolar electrodes chronically implanted in various brain structures. The electrode intended to be introduced into raphe dorsalis is placed in a "guiding" isolated cannule. The spontaneous EEG-activity, the evoked potentials of photo- and electrostimulation as well as the behavioural reactions are studied for each animal before and after administration of noradrenaline (NA), isoprenaline (ISO) respectively, into nucleus raphe dorsalis (RD). The evoked potential are tape-recorded and averaged on Nicolet--1072 computer. Administration of NA in cat RD is followed by manifestations characterized by vegetative and motor symptoms and accompanied by EEG-changes. Desynchronization develops immediately after the injection of both NA and ISO in RD. The restoration of the amplitude-frequency characteristics of the EEG-activity take place in RD at the latest. Considerable changes are also observed in the evoked potentials recorded from the different structures. The EEG-changes observed after injection of NA, respectively ISO, in RD suggest functional connections between RD and the other brain structures studied. Both the EEG-changes and the observed behavioural reactions are probably largely based on the inhibition of the cerebral serotonin tonus by the catecholamines NA and ISO injected into RD and the resulting disruption of the balance between the adrenergic and serotoninergic cerebral systems.

Interaction of visual evoked potentials in groups of stimuli with different interstimulus intervals in cats. I. Experimental design. Dispersion analysis.

Quantitative estimation of excitability is performed at present in a pair of stimuli by studying the so-called recovery cycles. Random mixing of the interstimulus intervals and their appropriate grouping (grouped pairs) can provide new information about the course of excitability in time. An experimental setup is described in which by planning of the experiment (BIB-design) the interstimulus intervals are randomized and all components of the evoked potentials (EP) are placed under equal conditions with respect to the influence of the preceding intervals. The effects of the interstimulus intervals simultaneously on different components of visual evoked potentials in cats are estimated by means of dispersion analysis. The results show the existence of a significant effect only on definite amplitudes of the EP (predominantly with great latencies). The interactions of the effects of definite interstimulus intervals are determined, which permits the assumption of an interaction among different components of EP.