Contrasting interactions of the locus coeruleus as compared to the ventral noradrenergic bundle with CNS and pituitary pools of vasopressin, dynorphin and related opioid peptides in the rat

Abstract

The present study examines the influences of selective destruction of the locus coeruleus (LC) or of the ventral noradrenergic bundle (VB) upon discrete CNS and pituitary pools of vasopressin, dynorphin and related opioid peptides in the rat. The selectivity of the lesions was indicated by the fact that destruction of the LC strongly depressed levels of noradrenaline in the cortex in contrast to the hypothalamus, whereas destruction of the VB decreased noradrenaline in hypothalamus but not cortex. Rats sustaining VB lesions displayed a parallel depletion neurointermediate, but not anterior, lobe levels of immunoreactive- (irdynorphin 1–17 (DYN), ir-DYN 1–8, ir-α-neo-endorphin (ir-α-NE) and ir-vasopressin (ir-VP) whereas those of ir-Met-enkephalin (ir-ME) were unaffected. In the hypothalamus, the content of ir-DYN and ir-VP tended to rise and that of ir-DYN 1–8 and ir-α-NE was significally elevated, whereas that of ir-ME was not altered. LC destruction failed, in contrast, to modify levels of ir-VP, ir-DYN, ir-DYN 1–8, ir-α-NE or ir-ME in any of the above structure. It was found to, however, result in depression in levels of ir-DYN and ir-α-NE, but not of ir-ME or ir-VP, in both the hippocampus and striatum whereas VB lesions were, in this respect, ineffective. Further, in the spinal cord, LC lesions resulted in a significant elevation in levels of ir-DYN and ir-α-NE in comparison to those of ir-DYN 1–8, ir-VP and ir-ME. Neither type of lesion significantly altered the content of any opioid peptide examined in thalamus, cortex, septum or midbrain. These data indicate that: (1) the LC as compared to the VB interact differently with discrete pools of ir-DYN, ir-DYN 1–8, ir-α-NE and ir-VP in brain, pituitary and spinal cord; (2) it is the VB rather than the LC which modulates the activity of magnocellular neurones projecting to the neural lobe of the pituitary; (3) ir-DYN, ir-DYN 1–8 and ir-α-NE are, in all tissues, regulated independently of ir-ME; (4) levels of ir-DYN, ir-DYN 1–8 and ir-α-NE are co-regulated with those of ir-VP in the hypothalamus-neural obbe axis but not in extrahypothalamic brain tissues for the spinal cord; and (5) DYN, DYN 1–8 and α-NE might, in certain cases, be modulated differentially of one another, possibly reflecting alterations in precursor processing.