Loss of NeuN immunoreactivity in rat spinal cord neurons during aging.

A morphologic study of the impact of aging on neuron marker expression was performed in different segments of the rat spinal cord. Spinal cord specimens from young (5 months), middle-aged (12 months) and senile (32 months) female rats were assessed. We found a complete loss of neuron-specific nuclear protein (NeuN) immunoreactivity in cervical, thoracic and lumbar segments of the senile animals whereas neuron-specific enolase (NSE) immunoreactivity was comparable in young and senile rats. These findings in otherwise morphologically well preserved spinal cord neurons are of interest and reveal that NeuN may not be a reliable marker to identify neurons in the spinal cord of aging rats.

Morphometry of cervical segments grey matter in the male rat spinal cord.

The cervical portion of the spinal cord is an area frequently affected by alterations of medical and veterinary importance. Since there is scarce quantitative anatomical data on this region, we undertook a morphometric study of the grey matter of all segments of the rat cervical spinal cord of male rats in order to generate reference patterns to be used in future experimental studies. Using image analysis software, the total spinal cord length and grey and white matter area of each segment was recorded. The morphometric characteristics of the neurones populating the laminae of the grey matter of the cervical segments was also recorded. Neurones were classified into small, medium and large sizes for each lamina and statistically compared. The present data fill an anatomical information gap by providing quantitative data about the normal anatomical features of the rat cervical cord. The anatomical data found could be used to better understand the physiological relevance of that region in the rat.

Impact of very old age on hypothalamic dopaminergic neurons in the female rat: a morphometric study.

Dopaminergic neurons of the A(12) (tuberoinfundibular dopaminergic system) and A(14) (periventricular dopaminergic system) hypothalamic areas exert a tonic inhibitory control of prolactin secretion. Tuberoinfundibular dopaminergic system neuron function is known to decline during aging in rats, but little is known about the impact of extreme age on neuron number and morphology in the two systems. We morphometrically assessed the neurons of the tuberoinfundibular dopaminergic system and the periventricular dopaminergic system in female rats 6 (young, Y), 24 (old, O), and 30-32 (senescent, S) months old. Serial coronal sections of fixed hypothalami were immunohistochemically labeled for tyrosine hydroxylase, and immunoreactive perikarya from the A(12) and A(14) areas were quantitatively characterized and compared among the three age groups. Radioimmunoassay was used to measure serum prolactin. The number of A(12) tyrosine hydroxylase-immunoreactive perikarya showed a steady decline with age, whereas the number of A(14) tyrosine hydroxylase-immunoreactive perikarya remained stable from young to old age but showed a sharp drop in the senescent rats. In the old rats, tyrosine hydroxylase-immunoreactive neuronal area (A(12) = 135.37 and A(14) = 158.79 microm(2)) was significantly higher than that of young (A(12) = 72.56 and A(14) = 99.7 microm(2)) and senescent animals (A(12) = 95.5 and A(14) = 106.5 microm(2)). Densitometric assessment of median eminence tyrosine hydroxylase immunoreactivity revealed a steady age-related reduction of tyrosine hydroxylase content in the median eminence. Serum prolactin levels increased steadily with age. We conclude that, in the female rat, aging brings about a progressive loss of both tuberoinfundibular dopaminergic system and periventricular dopaminergic system neurons, which becomes more conspicuous at extreme ages.