Participation of cholinergic and adrenergic synapses of the medial septal area (MSA) in the natriuretic and kaliuretic responses to intraventricular hypertonic saline (NaCl)

The microinjection of hypertonic sodium chloride into the third ventricle elicits natriuresis and kaliuresis in rats following water loading. These responses were blocked by atropine or phentolamine microinjection into the MSA. The data suggest the interaction between periventricular areas sensible to changes of sodium concentration in the cerebrospinal fluid (CSF) and MSA. Cholinergic and alpha-adrenergic synapses of MSA are involved in this interaction which regulates renal sodium excretion.     

Interaction between cholinergic and osmolar stimulation of the lateral hypothalamic area (LHA) on sodium and potassium excretion

Hypotonic and isotonic solutions into the LHA of unrestrained rats caused no alteration in renal water and electrolyte excretion. Similar results were obtained after injecting hypo, iso and hypertonic glucose solutions. On the other hand, a hypertonic NaCl solution produced an increase in natriuresis and kaliuresis immediately after being injected into the LHA. The carbachol elicited an increase in natriuresis and kaliuresis as well as a decrease in urine output in the first urine samples collected after the injection being injected into the LHA. This response was not modified when the same dose of carbachol was injected associated with NaCl or glucose solutions. The observation of a lack of summation between the effects of carbachol and hypertonic NaCl, as well as the maintenance of the natriuretic and kaliuretic effects in response of the injection of the hypertonic solution even in the presence of blocked cholinergic pathways (atropine), suggests a dissociation between the mechanisms activated by the hypertonic solution and the cholinergic stimulation of the LHA.     

Interaction between the lateral hypothalamic area (LHA) and the medial septal area (MSA) in the control of sodium and potassium excretion in rats

In studies of the role of the hypothalamus in regulating body ionic balances it was found that carbachol injected into the lateral hypothalamic area (LHA) and medial septal area (MSA) elicited an increase in natriuresis and kaliuresis. This efflux reached its peak between 40 and 60 minutes after such injections. A blockage of this response was observed when LHA stimulation by carbachol was performed in animals whose MSA had been blocked previously by atropine or destroyed by electrolytic lesion. Similarly, stimulation of the MSA after pharmacological blockade or destruction of the LHA elicited a response of greatly decreased intensity. On the basis of these results it was concluded that the natriuretic-kaliuretic response elicited by cholinergic stimulation of the LHA depends in part on synapses located in MSA; the response elicited by cholinergic stimulation of the MSA utilized also synapses located in the LHA, unilaterally and bilaterally.     

Masking,De Lange curves and integration time as revealed by the electroretinogram of a tree shrew (Tupaia chinensis)

In order to elucidate the effects of angiotensin II on renal function, angiotensin II (AII; 1 ng/kg per min) and the AII antagonist 1-sar-8-ala-angiotensin II (AIIA; 200 ng/kg per min) were infused into the renal artery of anesthetized dogs (pentobarbital), on either a high (8 mmol/kg per day for seven days) or a low sodium intake (0.5 mmol/kg). In sodium replete dogs AII produced renal vasoconstriction with decreased RBF (–28%;P<0.001), but with less decrease of GFR (–14%;P<0.001), leading to an increase of FF (+19%;P<0.01),andantidiuresis(–39%;P<0.001); the antinatriuresis (–58%;P<0.001) exceeded the antidiuresis (P<0.001). RBF (–10%;P<0.001) was less pronounced (P<0.001) during AII in sodium deplete dogs, GFR remained unchanged, but FF increased to the same extent (+16%;P<0.05); diuresis and urinary electrolyte excretion were however not affected. AIIA did not affect RBF, GFR, FF, nor diuresis in sodium replete dogs suggesting that endogenous AII has no tonic influence on renal function in these conditions. In sodium deplete animals AIIA produced an 11% (P<0.001) increase of RBF, without changes of GFR; FF decreased by 12% (P<0.01), but diuresis, natriuresis and kaliuresis were not affected.     

Nuclear organization of cholinergic,catecholaminergic, serotonergic and orexinergic systems in the brain of the Tasmanian devil (Sarcophilus harrisii)

This study investigated the nuclear organization of four immunohistochemically identifiable neural systems (cholinergic, catecholaminergic, serotonergic and orexinergic) within the brains of three male Tasmanian devils (Sarcophilus harrisii), which had a mean brain mass of 11.6 g. We found that the nuclei generally observed for these systems in other mammalian brains were present in the brain of the Tasmanian devil. Despite this, specific differences in the nuclear organization of the cholinergic, catecholaminergic and serotonergic systems appear to carry a phylogenetic signal. In the cholinergic system, only the dorsal hypothalamic cholinergic nucleus could be observed, while an extra dorsal subdivision of the laterodorsal tegmental nucleus and cholinergic neurons within the gelatinous layer of the caudal spinal trigeminal nucleus were observed. Within the catecholaminergic system the A4 nucleus of the locus coeruleus complex was absent, as was the caudal ventrolateral serotonergic group of the serotonergic system. The organization of the orexinergic system was similar to that seen in many mammals previously studied. Overall, while showing strong similarities to the organization of these systems in other mammals, the specific differences observed in the Tasmanian devil reveal either order specific, or class specific, features of these systems. Further studies will reveal the extent of change in the nuclear organization of these systems in marsupials and how these potential changes may affect functionality.