Interruption Of Neural Connections Research Articles

In vitro bronchial hyperresponsiveness after lung transplantation in the rat.

In this study, we examined the effect of unilateral lung transplantation on in vitro responses of bronchial smooth muscle to electrical field stimulation (EFS) and exogenous acetylcholine (ACh). In syngeneic Lewis rats, we compared the contractile responses of the left hilar transplanted bronchus with that of the nontransplanted right bronchus and the left and right bronchi from control and sham-operated animals. Atropine-sensitive bronchial contraction to EFS was greater on left transplanted than on right nontransplanted bronchi at all frequencies and voltages used. In control and sham-operated animals, contractile responses to EFS were identical on left and right sides and similar to the responses of the right nontransplanted bronchus of the lung transplant recipient. Concentration-response curves to exogenous ACh were similar on transplanted and all control bronchi. Intramural cholinergic nerve cell bodies reactive for acetylcholinesterase were present in the transplanted bronchus. We conclude that EFS-induced cholinergic contraction of rat bronchial smooth muscle is enhanced after lung transplantation. Enhancement is not a result of medication, inflammation, or rejection, absent from our syngeneic transplant, or of upregulation of muscarinic post-junctional receptors because the response to exogenous ACh was normal. Hence, an increased release of ACh from cholinergic nerve terminals may occur, due either to hyperexcitability of postganglionic parasympathetic nerves or to loss of inhibitory mechanism resulting from interruption of neural connections with the central nervous system.

Data on protein synthesis of deafferented hypothalamic arcuate neurons.

Protein synthesizing activity of the rat hypothalamic arcuate nucleus following partial or total deafferentation of the medial basal hypothalamus was studied by light and electron microscopic autoradiography when administering tritiated leucine into the lateral ventricle. There were significantly more grains over the arcuate nucleus 21 days after disconnection of this hypothalamic region than over the intact nucleus. Isolation of a temporal cortical region induced similar changes in the isolated area, although this effect was not so pronounced as in the arcuate region. Data suggest that the protein synthesizing activity of arcuate neurons increases significantly after interruption of neural connections of the medial basal hypothalamus. It is assumed that the effect is primarily due to transneuronal alteration and/or interruption of inhibitory afferents.

Absence of a circadian rhythm in persisting corticosterone fluctuations following surgical isolation of the medial basal hypothalamus.

To determine whether the circadian rhythm in pituitary-adrenal function is abolished after interruption of neural connections of the medial basal hypothalamus (MBH), corticosterone patterns were examined in individual adult female rats following surgical isolation of the MBH (MBHI rats). Non-stress plasma corticosterone levels were assessed fluorometrically in blood samples obtained from a tail vein of each rat at 4-h intervals for 44 h, 7-8 weeks after surgery. The highest corticosterone levels for most intact and sham-operated controls were obtained in samples collected at the period of light-dark transition. Individual MBHI rats demonstrated steroid excursions of normal amplitude that were not linked with time of day; these patterns appeared asynchronous and devoid of a 24-h cycle. The data indicate that major excursions in plasma corticosterone levels persist following surgical interruption of connections of the MBH, but circadian rhythmicity is abolished.