Neurotransmitter diversity in pre‐synaptic terminals located in the parvicellular neuroendocrine paraventricular nucleus of the rat and mouse hypothalamus

Abstract

Virtually all rodent neuroendocrine corticotropin-releasing-hormone (CRH) neurons are in the dorsal medial parvicellular (mpd) part of the paraventricular nucleus of the hypothalamus (PVH). They form the final common pathway for adrenocortical stress responses. Their activity is controlled by sets of GABA-, glutamate-, and catecholamine-containing inputs arranged in an interactive pre-motor network. Defining the nature and arrangement of these inputs can help clarify how stressor type and intensity information is conveyed to neuroendocrine neurons. Here we use immunohistochemistry with high-resolution 3-dimensional image analyses to examine the arrangement of single- and co-occurring GABA, glutamate, and catecholamine markers in synaptophysin-defined pre-synaptic terminals in the PVHmpd of unstressed rats and Crh-IRES-Cre;Ai14 transgenic mice: respectively, vesicular glutamate transporter 2 (VGluT2), vesicular GABA transporter (VGAT), dopamine β-hydroxylase (DBH), and phenylethanolamine n-methyltransferase (PNMT). Just over half of all PVHmpd pre-synaptic terminals contain VGAT, with slightly less containing VGluT2. The vast majority of terminal appositions with mouse CRH neurons occur non-somatically. However, there are significantly more somatic VGAT than VGluT2 appositions. In the rat PVHmpd, about five times as many pre-synaptic terminals contain PNMT than DBH only. However, because epinephrine release has never been detected in the PVH, PNMT terminals may functionally be noradrenergic not adrenergic. PNMT and VGluT2 co-occur in some pre-synaptic terminals indicating the potential for co-transmission of glutamate and norepinephrine. Collectively, these results provide a structural basis for how GABA/glutamate/catecholamine interactions enable adrenocortical responses to fast-onset interosensory stimuli, and more broadly, how combinations of PVH neurotransmitters and neuromodulators interact dynamically to control adrenocortical activity.

Connect-seq to superimpose molecular on anatomical neural circuit maps

“…Our results suggest that CRHNs can be activated by numerous glutamatergic presynaptic neurons, but that many other upstream neurons may suppress CRHN activity via GABA transmission. Previous studies indicate that upstream GABAergic neurons can provide tonic inhibition to CRHNs, the release of which can lead to CRHN activation by disinhibition (11,25). In addition, some upstream GABAergic neurons might be involved in stimulus-induced suppression of CRHN responses, as previously reported for certain odors (26,27).…”

“…Glutamate and GABA were expressed in 24.8% and 36.8% of the neurons, respectively, while the other neurotransmitters were expressed in far fewer neurons (1.7% for acetylcholine and 17.1% for glycine). CRHNs have ligand-gated channels for both glutamate (20) and GABA (21,22) and receive direct synaptic input from both neurotransmitters (11,23,24). Our results suggest that CRHNs can be activated by numerous glutamatergic presynaptic neurons, but that many other upstream neurons may suppress CRHN activity via GABA transmission.…”

“…Surges in blood stress hormones occur in response to a variety of external and internal dangers or "stressors," including predator odors, tissue injury, inflammation, and emotional and psychological stress (7,8). Studies using classical neuroanatomical and neurophysiological approaches have provided a large body of information on PVN inputs that may affect CRHNs and the effects of classical neurotransmitters on CRHN activity and function (7,(9)(10)(11)(12). However, the exact identities of upstream neurons that control CRHN functions and the mechanisms by which they do so have not been defined.…”

Glutamate Cotransmission in Cholinergic, GABAergic and Monoamine Systems: Contrasts and Commonalities

“…The situation appears to be drastically different in adrenergic neurons as, for example, most terminals of adrenergic C1 neurons in the dorsal motor nucleus of the vagus, visualized after conditional expression of ChR2, appear to be TH-immunoreactive and to also be VGLUT2-immunopositive (DePuy et al, 2013). Intriguingly, adrenergic projections in the paraventricular nucleus of the hypothalamus of both rats and mice appear to be more heterogeneous in their expression of VGLUT2, with only approximately 20% of terminals labeled with the adrenaline biosynthetic enzyme phenylethanolamine N-methyltransferase (PNMT) also positive for VGLUT2 (Johnson et al, 2018). Similarly, only a subset of DA beta-hydroxylase-positive terminals in the intermediolateral cell column of the spinal cord were found to be VGLUT2-postive (Nakamura et al, 2004).…”

Neuromodulation of maternal circuits by oxytocin

“…Importantly, oxytocin neurons receive various inputs (Brown et al, 2013; Johnson et al, 2018) which may be activated in different contexts and, thus, promote or inhibit the stereotyped bursting activity. Burst generation and the milk ejection reflex are occluded by low frequency activation of the lateral and medial septum (Boudaba and Poulain, 1991; Lebrun et al, 1983; Lebrun and Poulain, 1982) which play a role in maternal aggression important for offspring protection (Lonstein and Gammie, 2002).…”