Cortical cyto- and chemoarchitecture in three small Australian marsupial carnivores: Sminthopsis macroura, Antechinus stuartii and Phascogale calura.

The cyto- and chemoarchitecture of the cerebral cortex has been examined in three small (mouse-sized) polyprotodont marsupial carnivores from Australia (the stripe-faced dunnart, Sminthopsis macroura; the brown antechinus, Antechinus stuartii; and the red-tailed phascogale, Phascogale calura) in order to compare the cortical topography of these marsupials with that of diprotodontids, didelphids and eutherians. All three species studied had similar cortical cytoarchitecture. The isocortical surface was dominated by primary somatosensory (S1) and visual (V1) areas. Putative secondary sensory areas (S2, V2M, V2L) were also identified. The primary somatosensory cortex demonstrated clumps of granule cells in the presumptive mystacial field, whereas the primary visual area showed a distinctive chemical signature of intense calbindin immunoreactivity in layer IV. On the other hand, the primary auditory area was small and indistinct, but flanked by a temporal association area (TeA). A cytoarchitecturally distinct primary motor cortex (M1) with prominent pyramidal neurons in layer V and poor layer IV was identified medially to S1, and at rostral levels a putative secondary motor area was identified medial to M1. Transitional areas between isocortex and allocortical regions showed many cyto- and chemoarchitectural similarities to those reported for eutherian (and in particular rodent) cortex. Medially, two cingulate regions were found at rostral levels, with dysgranular and granular 'retrosplenial' areas identified caudally. Laterally, granular and agranular areas surrounded the rostral rhinal fissure, to be replaced by ectorhinal and perirhinal areas caudally. The findings indicate that the cyto- and chemoarchitectural features which characterize the iso- and allocortex in these small marsupial carnivores are similar to those reported in didelphids and eutherians and our findings suggest the existence of putative dedicated motor areas medial to the S1 field.

In vitro autoradiographic localization of calcitonin and amylin binding sites in monkey brain.

Calcitonin (CT) and amylin are related peptides with potent central actions, including suppression of appetite and gastric acid secretion. Little is known about the distribution and binding characteristics of amylin receptors in species other than rat; therefore, in this study, by using in vitro autoradiography, we have mapped the distribution of 125I-rat amylin binding sites in the monkey brain and compared this distribution to that of binding sites for 125I-salmon CT (125I-sCT). Highest densities of 125I-amylin binding were in the hypothalamus, including the arcuate nucleus and parts of the ventromedial hypothalamic nuclei, and the solitary nucleus. Rostrally, moderate to high density binding was present in parts of the preoptic area, bed nucleus of the stria terminalis, amygdala and accumbens nucleus (Acb). Caudally, binding of amylin was more restricted, with moderate to high density binding present only in dorsal raphe, and area postrema. The primary visual cortex displayed strong and periodic CT binding in layer 4. The subcortical pattern of distribution of amylin and CT receptors in the monkey was similar to that seen previously in the rat, although the relative densities of binding to different brain structures were not always conserved. As with rat, monkey amylin receptors were a subset of the sites labeled with 125I-sCT. Analysis of receptor specificity indicated a greater relative potency of CT peptides in competing for 125I-amylin binding in monkey, when compared to rat, while, there was a decrease in the relative potency of CT gene-related peptides, potentially due to differences the level of receptor activity modifying proteins (RAMPs) in monkey versus rat brain. Amylin receptors in primates are likely to perform a similar role to those in rats; however, the interaction of the receptors with related peptides may differ.

Localization and characterization of angiotensin II receptor binding sites in the human basal ganglia, thalamus, midbrain pons, and cerebellum.

Angiotensin II (Ang II) binding sites were localized in the thalamus, basal ganglia, midbrain, and pons of the human central nervous system by in vitro autoradiography, employing 125I-[Sar1, Ile8]angiotensin II as the radioligand. High-density binding occurs in the substantia nigra pars compacta, the interpeduncular nucleus and two of the raphe nuclei, the raphe magnus, and median raphe nucleus. Moderate densities occur in the caudate nucleus, putamen, bed nucleus of the stria terminalis, rostral linear nucleus, caudal linear nucleus, dorsal and paramedian raphe nuclei, locus coeruleus, and region of the subcoeruleus, oral dorsal paramedian nucleus, and A5/periolivary region. Low levels occur in the region between the subthalamic nucleus and the zona incerta, the mediodorsal thalamic nucleus, the central gray, the lateral and medial parabrachial nuclei, and the molecular layer of the cerebellum. The high density of Ang II receptor binding in the substantia nigra occurs over pigmented, presumably dopaminergic, neurons. The binding in this site, and in the striatum, is not observed in any of the other species we have studied. It displays similar pharmacological characteristics to the Ang II receptor binding site in other regions of the human brain. Overall we demonstrate a discrete pattern of Ang II receptor binding sites in the human brain, which shows a high correlation with the distribution observed in other mammalian species.

Angiotensin receptor binding in human hypothalamus: autoradiographic localization.

Binding of 125I-[Sar1,Ile8]angiotensin II in the human hypothalamus was mapped by in vitro autoradiography carried out on frozen sections of hypothalamus from two human brains. Regions showing the greatest specific binding of this radioligand were the organum vasculosum of the lamina terminalis, median preoptic nucleus, subfornical organ, median eminence, arcuate nucleus and paraventricular nucleus. These regions may be sites of angiotensin II receptors involved in the regulation of blood pressure, fluid balance and pituitary hormone secretion.

Angiotensin converting enzyme in rat brain visualized by quantitative in vitro autoradiography.

Angiotensin converting enzyme was localized in rat brain by quantitative in vitro autoradiography using an [125I]labelled converting enzyme inhibitor called "351A". This radioligand was found to bind with high affinity and specificity to angiotensin converting enzyme. Very high levels of converting enzyme were observed in the ventricular choroid plexus, ependyma of all ventricles and large and medium blood vessels, subfornical organ, and organum vasculosum of the lamina terminalis. High levels of converting enzyme were found in the basal ganglia including caudate putamen, nucleus accumbens, globus pallidus, entopenduncular nucleus and substantia nigra pars reticulata. The neurosecretory nuclei, paraventricular nucleus and supraoptic nucleus, as well as the median eminence and posterior pituitary displayed high levels of the enzyme. In the amygdala, basolateral, lateral, basomedial, medial and anterior cortical nuclei showed moderate converting enzyme activity. The medial habenula and molecular layer of the dentate gyrus showed high levels of activity. In the cerebellum, dense labelling was observed in the Purkinje cell layer. Moderate levels of converting enzyme occurred in the gelatinosus subnucleus of the caudal part of the nucleus of the spinal tract of the trigeminal. There was a close correspondence between the distribution of angiotensin converting enzyme and angiotensin II in the neurosecretory nuclei (paraventricular and supraoptic nuclei) and median eminence and this suggests a role of angiotensin converting enzyme in the production of angiotensin II in this system. There was also a good correspondence between the distribution of angiotensin converting enzyme and angiotensin II in the subfornical organ, median preoptic nucleus, and organum vasculosum of the lamina terminalis, structures abutting the anterior wall of the third ventricle which are implicated in fluid and electrolyte homeostasis. A striking discrepancy occurs in the basal ganglia which is reported to contain very little angiotensin II or angiotensin II receptors but is very rich in angiotensin converting enzyme. It is concluded that the enzyme may act to convert circulating angiotensin I to angiotensin II in circumventricular organs; generate intraneuronal angiotensin II in pathways such as the hypothalamic-hypophyseal tract; and process neuropeptides other than angiotensin II in regions such as basal ganglia.

Central and peripheral contributions to hypothalamic epinephrine.

Hypothalamic epinephrine concentrations were examined following adrenal demedullation or after surgical hemisection of ascending projections to the hypothalamus. Following surgical transection epinephrine in the ipsilateral hypothalamus was depleted by approximately 60%. Adrenal demedullation had no effect on hypothalamic epinephrine concentrations. It was concluded that hypothalamic epinephrine was central in origin.

alpha-Adrenergic modulation of hypothalamic self-stimulation: effects of phenoxybenzamine, yohimbine, dexamphetamine and their interactions with clonidine.

The alpha-adrenoceptor agonist clonidine (12.5--50.0 microgram/kg) produced a dose-dependent increase in the latency to initiate lateral hypothalamic stimulation. The insurmountable postsynaptic alpha-adrenoceptor antagonist phenoxybenzamine (0.2-0.8 mg/kg) had no effect on self-stimulation by itself, but potentiated the inhibitory effects of clonidine. The fact that the concurrent escape behavior to the intracranial stimulation was unchanged by either clonidine or the phenoxybenzamine-clonidine combination suggests that the inhibition is specific to the rewarding component of hypothalamic stimulation. Yohimbine (0.5--2.0 mg/kg) produced a dose-dependent increase in both response latencies. This lack of behavioral specificity may reflect yohimbine's wide range of pharmacological activity, Dexamphetamine (0.25--0.50 mg/kg) reversed clonidine's inhibition of self-stimulation reward in a specific and dose-dependent fashion. This reversal could be blocked by previous inhibition of catecholamine synthesis with alpha-methyl-p-tyrosine. These data support the concept that the alpha-adrenoceptors play a critical role in the modulation of hypothalamic self-stimulation reward. They further suggest that the inhibitory effects of clonidine on self-stimulation reward represent an agonist effect on presynaptic alpha-adrenoceptors.