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Electron microscopy was used to study the peculiarities of the development of nervous elements in the sympathetic caudal mesenteric ganglion (CMG) in the cat from the moment of birth until the end of the second month of life. The discordance in the rate of maturation of both neurons and their endings was observed. In newborn kittens, mature neurons, glial cells and synapses were observed together with many immature ones. In 14-day-old animals, the proportion of immature neurons decreased, while destruction of neurons was observed more frequently in this age. In CMG of the animals of all the age groups, axodendritic synapses were found most frequently and axosomatic synapses were observed more rarely. Finally, the ultrastructure of CMG in kittens become comparable to that of adult animals at the age of 60 days.

Electrical activity of the cervical sympathetic trunk was studied in newborn, 10-, 20-, 30-day-old, two- and six-month-old rats and cats using the spectral analysis. The amplitude of discharges increased from the period of birth until the first moth of life in rats and until 20 days in cats. Frequencies synchronous with cardiac and respiration those were revealed in all animals. Heart-related frequencies were predominant in rats older than 20 days. Other frequencies were lower. In kittens, we did not observe any age-dependent changes of the spectrum of sympathetic nerve discharge. Discharges with high frequencies were observed in cats from the moment of birth.

Localization and the morphometric characteristics of NADPH-diaphorase--(NADPH-d)-positive neurons were studied in the superior cervical ganglion (SCG), stellate ganglion (SG) and the celiac ganglia (CG) in newborn, 10-, 20-, 30-, 60 and 180-day-old rats, mice and cats. No NADPH-d-positive neurons were found in rats and mice of all the age groups studied. In cats, the largest proportion of NADPH-d-positive neurons was found in the SG, the smaller one--in the SCG, while only the individual neurons we detected in the CG, irrespective of the animal age. In the SG, the proportion of NADPH-d-positive neurons increased during the first 20 days of life and then decreased after 30 days till the end of the second month. The content of NADPH-d-positive neurons in the CG and SCG d-remained unchanged during the development. There were no significant differences in the cross-sectional area between the neurons located in the different ganglia of animals from the same age group. It is concluded that the age development of NADPH-d-positive neurons in different sympathetic ganglia occured heterochronously was finished by the end of the second month of life.

Method based on retrograde axonal transport of horseradish peroxidase was used to study the efferent innervation of the cervical trachea in neonatal, 10-, 20-, 30-day-old and two-month-old kittens. In all the animals, labeled neurons were localized in the cranial cervical, middle cervical and cervicothoracic (stellate) sympathetic ganglia both on the right and on the left sides. Neurons were also localized at the level of medulla oblongata, in the dorsal and ambiguus nuclei of the vagus nerve. Labeled neurons were also found in the ventral horns of C(I-)C(V) spinal segments in the animals before 30 days of life. The number of sympathetic neurons, innervating the trachea, cells increased from the moment of birth, reaching a maximum by the age of 10 and 20 days and then declined up to the second month of life. The total number of parasympathetic neurons decreased gradually in the early development.

Electrical activity of the stellate ganglion was studied in newborn, 10-, 20-, 30-day-old, two- and six-month-old kittens using the spectral analysis. The development of sympathetic activity patterns was different during ontogenesis. The amplitude of discharges increased from the period of birth until the second month of kittens' life. In newborn and 10-day-old kittens, synchronous discharges of postganglionic fibers were represented by slow and low frequency impulses with frequencies of breathing and heart rate. ppears in 20-day-old kittens. The formation of the sympathetic discharge patterns ends at the second month of animals life.

Localization of the spinal cord preganglionic neurons projecting to the stellate ganglion, was studied in kittens from the moment of birth till six month of life, using the method based on retrograde axonal transport of horseradish peroxidase. The number of preganglionic neurons and spinal cord segments connected with the stellate ganglion, increased from the moment of birth till 10th postnatal day, decreasing afterwards. The proportion of preganglionic neurons in different nuclei of the spinal cord changed during the development and became comparable to that in adult animals by 6th month. The proportion of neurons in the nucleus intermediolateralis thoracolumbalis pars principalis was found to increase, while the number of neurons in the nucleus intermediolateralis thoracolumbalis pars funicularis and in the spinal cord ventral horns was decreased.

The enzyme horseradish peroxidase was administered into trachea, esophagus, heart, sternocleidomastoid muscle, and biceps of newborn, 10-, 20-day old kittens, and adult cats. The labeled neurons were located on the topical basis of the stellate ganglion. In newborn kittens, the largest cells take part in the heart innervation. In animals of other ages, the largest cells take part in innervation of the sternocleidomastoid muscle. The findings suggest that, in postnatal ontogenesis, neuronal organisation of the stellate ganglion is changing parallel to an enhancement of the neurons' size and ganglion section area.

In new-born, 10-, and 20-day-old kittens and in adult cats, the stellate ganglia branches contained both continuous and synaptically interrupted fibres. In the course of postnatal ontogenesis, the average conduction velocity of excitation and average amplitude of the responses increased. In new-born and 10-day old kittens, these are C-fibres. Apart from the latter, A delta and B fibres appeared in 20-day old kittens. In adult cats, two subgroups of all types of the fibres appeared. Since the 10-day age, synaptically interrupted responses have been recorded in anastomoses and inferior cardiac nerve following stimulation of cranial and caudal branches of the subclavian loop, the responses being conducted in both directions in adult cats.

By direct and indirect morphometry the cell density maximal diameter and area of section of neurocytes in the zones of the emergence of the basic nerves and in the centre of the stellate ganglion were determined in kittens of various ages and adult cat. There is an increase of the maximal diameter, average area of section of neurons (16.98 +/- 0.07 mm and 132.2 +/- 0.9 mm2 in newborn, 21.7 +/- 0.72 mm and 31.4 +/- 2.6 mm2 in 10-days, 6.69 +/- 0.5 mm and 355 +/- 2.4 mm2 in 20-days kitten, 4.86 +/- 0.6 mm and 634 +/- 36 mm2 in adult cat and reduction of cell density of ganglionic neurons in postnatal ontogenesis. In newborn kitten, kittens of 10- and 20-days of age and adult cat larger neurons were located in the cranial part of the ganglion. In 10 and 20 days kittens and adult cats an asymmetry between right and left stellate ganglia in the maximal diameter and average area of section of neurons was revealed. In adult cat the asymmetry in the cell density was also found between both ganglia.

Retrograde transport of horse radish peroxidase revealed the sources of forming of the initial part of the vertebral nerve in cat. The enzyme was applied on the central region of the nerve near its outlet in ganglion stellatum. Most nerve fibers the vertebral nerve contains are the processes of neurons in ganglion stellatum. Bodies of the labeled neurons in the ganglion are located in the area, attached to the site of the vertebral nerve outlet. It also contains certain number of the afferent fibers of the II-VII thoracic segments spinal ganglia. Axons of motor neurons, the bodies of which are located in ventral cornua of the spinal cord II thoracic segments may also be present. Thus, the cat vertebral nerve is mixed in the site of its forming.