Immunotoxin Lesion of Hypothalamically Projecting Norepinephrine and Epinephrine Neurons Differentially Affects Circadian and Stressor-Stimulated Corticosterone Secretion

Abstract

Hindbrain norepinephrine (NE) and epinephrine (E) neurons play a pivotal role in the central distribution of sensory signals derived from the internal environment. Their projections influence the various secretory patterns of the hypothalamo-pituitary-adrenal axis and are essential for feeding and adrenal medullary responses to glucoprivation. NE and E terminals in the paraventricular nucleus of the hypothalamus (PVH) and associated hindbrain cell bodies can be virtually eliminated by PVH microinjection of a retrogradely transported conjugate of saporin (SAP, a ribosomal toxin) and a monoclonal antibody against dopamine beta-hydroxylase (dbetah), i.e. dbetah mouse monoclonal antibody conjugated to SAP (DSAP). To examine the effects of selective elimination of NE/E afferents on hypothalamo-pituitary-adrenal activation, we injected DSAP into the PVH and measured corticosterone secretion under basal circadian conditions and in response to two distinct challenges: glucoprivation and forced swim. DSAP lesions profoundly impaired glucoprivation-induced corticosterone secretion and induction of CRH heteronuclear RNA and Fos mRNA in the PVH, without impairing basal CRH mRNA expression, circadian corticosterone release, or the corticosterone response to swim stress. Thus, NE/E projections influence corticosterone secretion only in certain circumstances. They are required for the response to glucoprivation, but are dispensable for circadian activation and for the response to swim stress.

Catecholaminergic Control of Mitogen-Activated Protein Kinase Signaling in Paraventricular Neuroendocrine NeuronsIn VivoandIn Vitro: A Proposed Role during Glycemic Challenges

“…Because these responses also occur after intravenous 2-DG and insulin (Ritter et al, 2003;Khan and Watts, 2004;Gorton et al, 2006;Rapp et al, 2006), our data show that NE is sufficient for recapitulating neuroendocrine responses to these glycemic challenges. Moreover, because hindbrain CA afferents are necessary for these responses (Ritter et al, 2001(Ritter et al, , 2003Rapp et al, 2006), NE appears both sufficient and necessary for CRH neuroendocrine neurons to respond to glycemic challenges. Supporting this, local PVH or systemically delivered 2-DG trigger NE release in the PVH vicinity (McCaleb and Myers, 1982;Peinado and Myers, 1987;Nagatani et al, 1996).…”

“…Establishing these linkages requires, in part, identifying afferents signaling the PVH during glycemic challenge and the neurotransmitter(s) involved in such signaling. Ritter et al (2001) identified an essential afferent pathway by showing that selectively destroying PVH afferents originating from hindbrain CA cell groups impaired the feeding and PVH responses to 2-DG or insulin challenges (elevated CRH hnRNA, Fos mRNA, and circulating corticosterone) but not those occurring basally or from forced-swim challenge (Ritter et al, 2003). These lesions also impair PVH phospho-ERK1/2 responses to insulin (Rapp et al, 2006).…”

“…For example, Ritter et al, (2003) reported that hindbrain catecholaminergic (CA) neurons, which richly innervate the PVH, are absolutely required for full neuroendocrine responses to glycemic challenges. Specifically, selective CA deafferentation markedly reduced corticosterone release triggered by insulin/2-DG (but not that triggered by basal circadian mechanisms or forced-swim challenge) and prevented 2-DG from elevating PVH Crh expression.…”

Noradrenergic Innervation of the Dorsal Medial Prefrontal Cortex Modulates Hypothalamo-Pituitary-Adrenal Responses to Acute Emotional Stress

“…Previous studies endorse anti-DBH-saporin as a tool for achieving focal aminergic denervation by ablating the neurons that project to targeted terminal fields (Ritter et al, 2003;Schiltz and Sawchenko, 2007). The approach exploits the fact that DBH on the inner surface of synaptic vesicles is exposed to the extracellular space during transmitter release, providing a target for antiserum to bind the enzyme, and toxin to be internalized, in the normal course of vesicle recycling (Wrenn et al, 1996).…”

“…This was achieved by comparing the effects of selectively lesioning noradrenergic inputs to the mPFCd on indices of acute stress-induced PVH activation (Fos protein, CRF mRNA) and pituitary-adrenal hormonal output. Lesions were performed by the focal administration of an axonally transported immunotoxin, anti-dopamine-␤-hydroxylase-saporin (anti-DBH-saporin), which targets specifically noradrenergic terminals and the neurons that give rise to them (Wrenn et al, 1996;Ritter et al, 2001Ritter et al, , 2003. Ancillary analyses were also performed to assess the impact of noradrenergic denervation of mPFCd on stress-induced activational responses in both the mPFC and LC.…”