Pressor response to l-cysteine injected into the cisterna magna of conscious rats involves recruitment of hypothalamic vasopressinergic neurons

The sulfur-containing non-essential amino acid l-cysteine injected into the cisterna magna of adult conscious rats produces an increase in blood pressure. The present study examined if the pressor response to l-cysteine is stereospecific and involves recruitment of hypothalamic vasopressinergic neurons and medullary noradrenergic A1 neurons. Intracisternally injected d-cysteine produced no cardiovascular changes, while l-cysteine produced hypertension and tachycardia in freely moving rats, indicating the stereospecific hemodynamic actions of l-cysteine via the brain. The double labeling immunohistochemistry combined with c-Fos detection as a marker of neuronal activation revealed significantly higher numbers of c-Fos-positive vasopressinergic neurons both in the supraoptic and paraventricular nuclei and tyrosine hydroxylase containing medullary A1 neurons, of l-cysteine-injected rats than those injected with d-cysteine as iso-osmotic control. The results indicate that the cardiovascular responses to intracisternal injection of l-cysteine in the conscious rat are stereospecific and include recruitment of hypothalamic vasopressinergic neurons both in the supraoptic and paraventricular nuclei, as well as of medullary A1 neurons. The findings may suggest a potential function of l-cysteine as an extracellular signal such as neuromodulators in central regulation of blood pressure.     

Morphological changes in the central canal of the cat after kaolin injection into the cisterna magna

40 adult cats were made hydrocephalic by intracisternal injection of 200 mg Kaolin. 34 survived between 24 hours to 4 months. In 19 cases a ventriculostomy was carried out, whereby in 13 animals a contrast filling of the central canal occurred. The contrast medium injected into the ventricles entered the external CSF-space in the lumbo-sacral junction of the filum terminale. Light- and electron-microscopic studies showed adaptive structural changes of the central canal epithelium in the early stages. In later stages massive destructions of ependyma and spinal cord parenchyma were found.