Dynorphin(1-8) immunoreactivity in brainstem and hypothalamic nuclei of normotensive and age-matched hypertensive rat strains

Renal responses produced by microinjection of the kappa opioid receptor agonist, U50-488H, into sites within the rat lamina terminalis

Activation of central kappa opioid receptors (KOR) has been demonstrated to produce marked free water diuresis with a concurrent increase in renal sympathetic nerve activity (RSNA). This study investigated the cardiovascular (CV) and renal effects evoked by central activation of KOR in two lamina terminalis sites, the median preoptic area (MPA) and anterolateral division of the bed nuclei of the stria terminalis (BST). Rats anesthetized with urethane alpha-chloralose were instrumented to record mean arterial pressure, heart rate, RSNA, and urine output (V). Rats were infused with isotonic saline (25 μL/min) and urine samples were collected during two 10-min control periods and six consecutive 10-min experimental periods following microinjection of vehicle, U50-448H (U50, KOR agonist) alone or norbinaltorphimine (nor-BNI, KOR antagonist) plus U50. Microinjection of U50 into the BST increased V (peak at 30 min, 84.8 ± 12.9 μL/min) as compared to its respective control, vehicle, or nor-BNI plus U50. This diuretic effect occurred without any significant changes in CV parameters, RSNA, or urinary sodium excretion. In contrast, U50 injection into the MPA significantly increased RSNA (peak at 20 mins: 129 ± 9.9) without increasing the other parameters. This study demonstrated novel sites through which activation of KOR selectively increases V and RSNA. The ability of U50 to increase V without affecting sodium excretion and RSNA raises the possibility that LT neurons could be an important substrate through which drugs targeting KOR could selectively facilitate water excretion in sodium-retaining diseases such as congestive heart failure.

The hypothalamus and hypertension

Most forms of hypertension are associated with a wide variety of functional changes in the hypothalamus. Alterations in the following substances are discussed: catecholamines, acetylcholine, angiotensin II, natriuretic peptides, vasopressin, nitric oxide, serotonin, GABA, ouabain, neuropeptide Y, opioids, bradykinin, thyrotropin-releasing factor, vasoactive intestinal polypeptide, tachykinins, histamine, and corticotropin-releasing factor. Functional changes in these substances occur throughout the hypothalamus but are particularly prominent rostrally; most lead to an increase in sympathetic nervous activity which is responsible for the rise in arterial pressure. A few appear to be depressor compensatory changes. The majority of the hypothalamic changes begin as the pressure rises and are particularly prominent in the young rat; subsequently they tend to fluctuate and overall to diminish with age. It is proposed that, with the possible exception of the Dahl salt-sensitive rat, the hypothalamic changes associated with hypertension are caused by renal and intrathoracic cardiopulmonary afferent stimulation. Renal afferent stimulation occurs as a result of renal ischemia and trauma as in the reduced renal mass rat. It is suggested that afferents from the chest arise, at least in part, from the observed increase in left auricular pressure which, it is submitted, is due to the associated documented impaired ability to excrete sodium. It is proposed, therefore, that the hypothalamic changes in hypertension are a link in an integrated compensatory natriuretic response to the kidney's impaired ability to excrete sodium.

Opioid-like immunoreactive neurons in secretomotor pathways of the guinea-pig ileum

In this study we sought to establish the distribution, projections and neurochemical coding of opioid immunoreactive neurons in secretomotor pathways of the guinea-pig ileum. Non-cholinergic secretomotor neurons in the submucous ganglia have been shown to be immunoreactive for dynorphin A 1-8, dynorphin A 1-17, dynorphin B and alpha neo-endorphin while cholinergic neurons have been shown to be immunoreactive for dynorphin A 1-8 only. Thus all submucous neurons in the guinea-pig ileum are immunoreactive for prodynorphin-derived peptides. Two major populations of opioid immunoreactive fibres projecting to the submucous ganglia have been established. Firstly, neurons immunoreactive for prodynorphin-derived peptides and vasoactive intestinal peptide project anally from the myenteric plexus to the submucous ganglia. Secondly, a substantial proportion of sympathetic postganglionic fibres immunoreactive for tyrosine hydroxylase, and projecting from the coeliac ganglion to submucous ganglia, have been shown to be immunoreactive for prodynorphin-derived peptides. Other smaller populations of opioid-immunoreactive neurons include fibres immunoreactive for substance P, enkephalin and dynorphin A 1-8 which project from the myenteric plexus to the non-ganglionated plexus of the submucosa. These fibres are probably excitatory motor neurons to the muscularis mucosae. The present paper has described several distinct populations of opioid immunoreactive neurons in secretomotor pathways of the guinea-pig ileum. Furthermore we have shown that these enteric or postganglionic sympathetic neurons contain opioid peptides in combination with other neurotransmitter substances. These results should provide a firmer basis on which to plan functional experiments to elucidate the physiological role of opioid peptides in the enteric nervous system.

Strain differences in central nervous system concentrations of cholecystokinin between normotensive Wistar Kyoto (WKY) and spontaneously hypertensive (SH) rats

The regional brain and spinal cord concentrations of cholecystokinin-octapeptide (CCK-8) were measured in age-matched normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SH) rats. The relative order of distribution of CCK-8 in the WKY strain was hippocampus (20.5 +/- 1.3 pmol/g) greater than cortex greater than striatum = hypothalamus greater than midbrain = thalamus greater than spinal cord greater than medulla oblongata/pons (MO/P, 1.6 +/- 0.2 pmol/g) whereas in the SH strain this order was hippocampus (12.9 +/- 0.8 pmol/g) greater than cortex = striatum greater than hypothalamus greater than midbrain greater than thalamus = spinal cord greater than MO/P (1.4 +/- 0.2 pmol/g). The concentrations of CCK-8 in the cerebellum were at the level of assay sensitivity (0.5 pmol/g in both strains). In comparison to the WKY rats, the SH strain had significantly lower levels of CCK-8 in the hippocampus (-37%), cortex (-28%), spinal cord (-23%) and pituitary (-57%). The lowered levels of CCK-8 in the brain of the SH rat may be causally related to, or result from, the cardiovascular, behavioural or morphological abnormalities of this strain.