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Notes: In order to identify likely sites of action of insulin-like growth factor-I (IGF-I) in rat brain and pituitary gland, we have used the technique of in vitro autoradiography and computerized densitometry to map, characterize and quantify its receptors in coronal and sagittal sections. A discrete and characteristic distribution of IGF-I receptor binding was demonstrated, with specific binding representing 85% of total binding. Displacement and specificity competition curves in the olfactory bulb were typical for authentic IGF-I receptors and computer analysis indicated a single class of binding site with a dissociation constant (Kd) of 13 nM for the choroid plexus and 5.1 nM for the olfactory cortex.IGF-I receptor density was very high in the choroid plexus in ail ventricles, but the binding in other circumventricular organs was variable, with high levels in the median eminence and the sub-fornical organ, and low levels in the organum vasculosum of the lamina terminalis. Highest binding was seen in the glomerular layer of the olfactory bulb and its associated regions the taenia tecta and anteromedial olfactory nucleus. The preoptic and septal regions showed moderate binding, while the hypothalamus, with the exception of the median eminence, showed low IGF-I binding. The pituitary gland showed very high binding density in both anterior and posterior lobes, similar to the median eminence. The thalamus had high IGF-I binding density, while it was low in basal ganglia. In the limbic system the hippocampal CA2, CAS, CA4 layers showed high binding, with little in CA1, while binding was high also in the adjacent amygdala. Binding was low in the mid and hindbrain, with the exception of the geniculate bodies, and the sensory nucleus of the trigeminal nerve. Binding was high in the primary olfactory and endopyriform cortex and in specific superficial layers. Cerebellar binding was also high in the molecular layer. Fibre layers showed no binding.Comparison with insulin receptors revealed common distribution in the choroid plexus, paraventricular nucleus, cerebellum, entorhinal cortex and amygdala, with receptor density three- to five-fold higher for IGF-I than for insulin. In contrast, in the hippocampus, insulin binding was high in the CA1 field, and low in CA2, CA3, CA4 while for IGF-I binding the converse was seen. The arcuate nucleus showed prominent insulin labelling and minimal IGF-I binding, while the median eminence showed low insulin and high IGF-I binding. The hypothalamus was more widely labelled with insulin, while in the thalamus the converse was true. Olfactory bulb laminae were labelled with differing intensity by insulin and IGF-I. In common with insulin receptor distribution was the high density of IGF-I receptors over areas of extensive dendritic arborizations which receive rich synaptic inputs, in the cerebellum, hippocampus and olfactory bulb.We conclude that IGF-I receptors are widespread throughout rat brain and pituitary gland, with concentration in regions concerned with olfaction, autonomie and sensory processing, as well as in regulation of growth hormone release, via feedback at the median eminence and pituitary gland. Many of these regions have in common high rates of metabolic and synthetic activity, which may be mediated by IGF-I and its receptors.

Notes: Immunopositive angiotensin II nerve fibres and terminals are widely distributed throughout the rat brain, including areas of the brain with and without a blood-brain barrier. Ultrastructural examination indicates that in the circumventricular organs (areas which lack a blood-brain barrier), many angiotensin ll-positive nerve terminals are closely aligned with fenestrated blood vessels and do not have synaptic specializations. This appearance is in contrast to that of angiotensin II terminals in regions with a blood-brain barrier where there exists a more typical synaptic configuration. In both cases, angiotensin II is contained within large (100 to 125 nm) vesicles which coexist with smaller, lucent, non-immunoreactive vesicles. These observations suggest a possible duality of function such that angiotensin II in circumventricular organs may be secreted into the circulation, whereas angiotensin II in the remainder of the brain is more likely to be acting as a neurotransmitter or neuromodulator.

Notes: 1. The putative regulatory role of the lamina terminalis in the central control of salivation was investigated in the rat using the viral-tracing technique and Fos-immunohistochemistry.2. Neurons situated in the lamina terminalis, such as the vascular organ of the lamina terminalis (OVLT), median preoptic nucleus (MnPO) and subfornical organ (SFO), were retrogradely labelled after pseudorabies virus injections into the submandibular or sublingual gland.3. Viral tracing combined with glandular denervation showed that lamina terminalis structures sent efferents, in particular, to the parasympathetic side of submandibular gland innervation.4. Saliva lost under heat stress has severe implications for the body fluid economy of rats and a key to the understanding of the central regulation of heat-induced salivation may be the integrative role of the lamina terminalis processing thermoregulatory and osmoregulatory information.