Ontogeny of medullary raphe nuclei in the rabbit brain stem: a Golgi study

Novel axonal projection from the caudal end of the ventrolateral medulla to the intermediolateral cell column

We used an optical imaging technique to investigate whether axons of neurons in the caudal end of the ventrolateral medulla (CeVLM), as well as axons of neurons in the rostral ventrolateral medulla (RVLM), project to neurons in the intermediolateral cell column (IML) of the spinal cord. Brain stem-spinal cord preparations from neonatal normotensive Wistar-Kyoto and spontaneously hypertensive rats were stained with a voltage-sensitive dye, and responses to electrical stimulation of the IML at the Th2level were detected as changes in fluorescence intensity with an optical imaging apparatus (MiCAM-01). The results were as follows: 1) depolarizing responses to IML stimulation during low-Ca high-Mg superfusion were detected on the ventral surface of the medulla at the level of the CeVLM, as well as at the level of the RVLM, 2) depolarizing responses were also detected on cross sections at the level of the CeVLM, and they had a latency of 24.0 ± 5.5 (SD) ms, 3) antidromic action potentials in response to IML stimulation were demonstrated in the CeVLM neurons where optical images were detected, and 4) glutamate application to the CeVLM increased the frequency of excitatory postsynaptic potentials (EPSPs) and induced depolarization of the IML neurons. The optical imaging findings suggested a novel axonal and functional projection from neurons in the CeVLM to the IML. The increase in EPSPs of the IML neurons in response to glutamate application suggests that the CeVLM participates in the regulation of sympathetic nerve activity and blood pressure and may correspond to the caudal pressor area.

Ventral tegmental area of the rabbit brain: a developmental Golgi study

The ventral tegmental area (VTA) of the rabbit mesencephalon was examined with Golgi-Cox impregnation at neonatal (days 3-21 of age) and young adult (6-12 months of age) stages of development. Neurons in the dorsal midline were small, with sparsely-branched, vertically-oriented dendrites. Neurons in the ventral midline were medium-sized, oval cells with sparse, vertically-oriented dendrites, and multipolar cells with more abundant diffusely-oriented dendrites. Neurons in the medial zone of the VTA, between the midline and the exiting III nerve fibers, were oval in shape, medium in size, and possessed vertical dendritic arborizations of greater size and extent of branching than those in the dorsal midline. Lateral neurons, found among III nerve fibers, were medium-sized and possessed dendritic trees that were specifically oriented in a vertical or horizontal plane, or were diffusely-branched with more abundant arborizations than their specifically oriented counterpart. Very small neurons with short, single branches were scattered among all regions of the VTA. The major cell types showed a similar pattern of dendritic maturation. At 3-9 days of age, the dendrites were generally short, spiny and poorly branched. From days 9-21, the branches increased in number and length, spines were lost, and these neurons rapidly approached adult size and form. The neurons of VTA appear isodendritic in form, and developed in a pattern consistent with other areas of reticular formation, suggesting that VTA may be part of the reticular core of the brain stem.(ABSTRACT TRUNCATED AT 250 WORDS)

Ontogeny of biogenic amines in respiratory nuclei of the rabbit brainstem

The concentrations of the biogenic amines, norepinephrine, dopamine and serotonin, were determined in 5 respiratory-related brainstem regions by use of a micropunch technique and a sensitive enzymatic isotopic assay. Samples were taken from rabbits at different ages (term fetuses, 3, 7, 14, 21 days and 2-year-old adults). All brain regions contained norepinephrine, dopamine, and serotonin in measurable amounts, but the distribution was not uniform. Norepinephrine and dopamine remained relatively low (less than 5 ng/mg) in the fetus and during the first weeks of life. Norepinephrine achieved its highest levels in the nucleus tractus solitarius and the locus coeruleus of adult animals. Dopamine concentrations did not change significantly in any nuclear groups over the ages tested. Compared with the newborn values, high concentrations of serotonin were seen in all brainstem nuclei in the term fetus. Adult serotonin levels were not achieved during the neonatal period. These data demonstrate pre- and postnatal changes in neurotransmitter levels in brainstem nuclei which regulate respiratory control. The susceptibility of the newborn to abnormalities in respiratory control may be related to low serotonin levels observed during the postnatal period.