Richard L. Hauger

Brain and pituitary receptors for corticotropin releasing factor: Localization and differential regulation after adrenalectomy

Specific receptors for corticotropin releasing factor (CRF) were identified in two functionally distinct systems within the brain, the cortex and the limbic system. Autoradiographic mapping of the CRF receptors in the brain revealed high binding density throughout the neocortex and cerebellar cortex, subiculum, lateral septum, olfactory tract, bed nucleus of the stria terminalis, interpeduncular nucleus and superior colliculus. Moderate to low binding was found in the hippocampus, nucleus accumbens, claustrum, nucleus periventricularis thalamus, mammillary bodies, subthalamic nucleus, periaqueductal grey, locus coeruleus and nucleus of the spinal trigeminal tract. As in the anterior pituitary gland, CRF receptors in the brain were shown to be coupled to adenylate cyclase. However, in contrast to the marked decrease in CRF receptors observed after adrenalectomy in the anterior pituitary gland, CRF receptor concentration in the brain and pars intermedia of the pituitary was unchanged. The presence of CRF receptors in areas involved in the control of hypothalamic and autonomic nervous system functions is consistent with the major role of CRF in the integrated response to stress.

Corticotropin-releasing Factor Receptors: Distribution and Regulation in Brain, Pituitary, and Peripheral Tissues

Since the characterization of corticotropin releasing factor (CRF) in 198 1, evidence has accumulated to indicate that the hypothalamic peptide plays an important role in the regulation of ACTH secretion as well as in mediating visceral and behavioral responses to stress.’.’ The initial event in the action of peptide hormones is their binding to a plasma membrane receptor, and labeled ligands were rapidly developed in order to investigate the mode of interaction of C R F with its cellular binding site. Receptors for C R F were first identified in rat pituitary membranes using radioiodinated Tyr-oCRF, and subsequently studied by radioassays in autoradiographic p r o c e d ~ r e s , ~ ~ ~ and cytochernical techniques using biotinylated or fluorescein-conjugated C R F The use of autoradiography facilitated the identification and characterization of C R F receptors in the central and peripheral nervous system, which has contributed to our understanding of the physiological actions of CRF. The most common ligand used for C R F receptor studies is the radiolabeled ovine C R F derivative, Tyr-oCRF, but similar receptor properties have been described using iodinated [NLe”, Tyr3’]oCRFS. Analogues of rat/human C R F have given tracers with reduced biological action and lower binding activity due to peptide damage during the iodination procedure. Since ovine and human C R F bind to the C R F receptor in different species with equal affinities, oCRF can be used for studies in rat and primates. The purpose of this review is to discuss current knowledge of the C R F receptor, including its binding properties, regulation, and distribution in the pituitary, and nervous system.

Characterization of angiotensin II receptors in the anterior pituitary gland

Specific and high affinity binding sites for angiotensin II were demonstrated in the anterior pituitary gland by binding studies with [125I] iodoangiotensin II. The binding properties of the pituitary receptors were similar to those of angiotensin II receptors present in the adrenal gland. The concentration of binding sites in rat anterior pituitary (293 +/- 50 fmoles/mg protein) was less than in the adrenal gland, but was much greater than in smooth muscle. Angiotensin II receptors were identified in the anterior pituitary tissue of mature and immature animals of both sexes, and in species including rat, rabbit and dog. No binding of angiotensin II was detected in posterior pituitary homogenates, or in GH3 pituitary tumor cells. Collagenase-dispersed anterior pituitary cells also contained specific binding sites for angiotensin II, with equilibrium binding constant (Ka) of 3.6 x 10(9) M-1. The presence of specific high-affinity angiotensin II receptor in the anterior pituitary gland provides a mechanism by which angiotensin-like peptides could modulate the process of pituitary hormone secretion.

Chronic corticosterone administration in rats: Behavioral and biochemical evidence of increased central dopaminergic activity

Chronic corticosteroid treatment in humans in frequently complicated by behavioral changes. The present study suggests that chronic steroid administration in rats has distinct neurochemical consequences which are behaviorally relevant. Ten male Sprague-Dawley rats received 7 daily injections of corticosterone, following which they exhibited increased caudate homovanillic acid as well as an attenuated decline in vertical and ambulatory movement (functional measures of dopamine activity) compared to placebo-treated rats. A subgroup of steroid-treated rats which was more behaviorally responsive to corticosterone also showed increased caudate 5-hydroxyindole acetic acid and decreased prefrontal cortex dopamine and serotonin. These results are discussed in relation to the known behavioral side effects of chronic corticosteroid administration in man and the psychiatric manifestations of naturally occurring states of hypercortisolemia.

Receptor-mediated actions of corticotropin-releasing factor in pituitary gland and nervous system.

High-affinity corticotropin-releasing factor (CRF) receptors which mediate the actions of the hypothalamic peptide on adrenocorticotropic hormone (ACTH) release have been identified in the rat anterior pituitary gland. Occupancy of the pituitary receptor by CRF agonists stimulates ACTH release via activation of adenylate cyclase and cyclic adenosine monophosphate dependent protein kinase. In the regulation of ACTH secretion, the effects of CRF on the corticotroph are integrated with the stimulatory actions of cyclic adenosine monophosphate-independent stimuli such as angiotensin II, vasopressin and norepinephrine, and the inhibitory effects of glucocorticoids and somatostatin. In contrast to the major importance of the inhibitory effect of glucocorticoid feedback on ACTH secretion, somatostatin has relatively little effect on CRF-stimulated ACTH release in the normal rat corticotroph. Following adrenalectomy, the progressive elevation of plasma ACTH levels is accompanied by a concomitant decrease in pituitary CRF receptors. The postadrenalectomy loss of CRF receptors, which is prevented by dexamethasone treatment, is caused by a combination of occupancy and processing of the pituitary sites during increased secretion of the hypothalamic peptide. Recently, specific receptors for CRF have been localized in the rat and monkey brain and adrenal medulla, where they are also coupled to adenylate cyclase. Brain CRF receptors are most abundant in the cerebral and cerebellar cortices and in structures related to the limbic system and control of the autonomic nervous system. The actions of CRF on the central and peripheral nervous systems, as well as on the pituitary gland, emphasize the role of CRF as a key hormone in the integrated response to stress.

Characteristics of [3H](+)-amphetamine binding sites in the rat central nervous system

Recent studies in our laboratory have demonstrated the presence of specific binding sites for [3H] (+)-amphetamine in crude membrane preparations derived from rat brain. In this report we have further characterized the specific binding of [3H] (+)-amphetamine in various subcellular fractions of rat brain and demonstrate a greater than five-fold enrichment in the crude synaptosomal (P2) fraction compared to a crude membrane preparation. Specific [3H] (+)-amphetamine binding in crude synaptosomal membranes is saturable and stereospecific with an apparent dissociation constant, Kd, of 2.8 +/- 0.5 microM and an estimated maximum number of binding sites, Bmax, of 60.4 +/- 8.4 pmoles/mg protein derived by Scatchard or Klotz analysis of binding data using filtration assays. Centrifugation assays yield a similar Kd though the apparent Bmax is higher. In addition specific [3H] (+)-amphetamine binding is: rapidly reversible, temperature sensitive, labile to preincubation in Tris buffer, inhibited by sodium ions and unevenly distributed in various brain regions. Specific [3H] (+)-amphetamine binding sites are found almost exclusively in the rat central nervous system (the brainstem, hypothalamus, and striatum exhibiting relatively high levels of binding), whereas peripheral tissues such as liver, kidney and heart have very low to undetectable levels of specific binding.

Regulation of the Stress Response by Corticotropin-Releasing Factor Receptors

Late in the 19th century, William James, the American philosopher and psychologist, and the Danish scientist Carl Lang, independently concluded that human emotion is the perception of material changes in bodily states generated by the impact of external stimuli. James believed that one could not think of fear unless “... feelings of quickened heart-beats [or] of shallow-breathing, ... of trembling lips [or] of weakened limbs, ... of goose-flesh [or] of visceral stirring, were present.” This idea that cognition can be influenced by “hot” emotional experiences can be traced from Aristotle to Descartes to James to Walter Cannon. From this general concept, the theory evolved that physiological systems mediate emotion. In a classic paper published in the American Journal of Insanity in 1913, Harvey Cushing expanded the concept of the interdependence of bodily and emotional states by suggesting that a “primary derangement of the nervous system” generates “glandular hyperplasias” and, reciprocally, that a “primary secretory derangement” of the pituitary gland causes “psychic disturbances.” Cushing’s ground-breaking hypotheses constituted an important cornerstone of contemporary psychoneuroendocrine research.

CRF-2 Corticotropin-Releasing Factor Receptor

The CRF2 receptor is a member of the B1 subfamily of 7-transmembrane (TM) receptors. Like the …