Glucoprivation activates neurons in the perifornical hypothalamus (PeH) and in the rostral ventrolateral medulla (RVLM), which results in the release of adrenaline. The current study aimed to establish 1) whether neuroglucoprivation in the PeH or in the RVLM elicits adrenaline release in vivo and 2) whether direct activation by glucoprivation or orexin release in the RVLM modulates the adrenaline release. Neuroglucoprivation in the PeH or RVLM was elicited by microinjections of 2-deoxy-D-glucose or 5-thio-D-glucose in anesthetized, euglycemic rats. Firstly, inhibition of neurons in the PeH abolished the increase in adrenal sympathetic nerve activity (ASNA) to systemic glucoprivation. Secondly, glucoprivation of neurons in the PeH increased ASNA. Thirdly, in vivo or in vitro glucoprivation did not affect the activity of RVLM adrenal premotor neurons. Finally, blockade of orexin receptors in the RVLM abolished the increase in ASNA to neuroglucoprivation in the PeH. The evoked changes in ASNA were directly correlated to levels of plasma metanephrine but not to normetanephrine. These findings suggest that orexin release modulates the activation of adrenal presympathetic neurons in the RVLM.Glucoprivation is a metabolic challenge capable of eliciting adrenaline release, an important mechanism for the restoration of normal blood glucose levels. Additionally, neuroglucoprivation produced by 2-deoxy-D-glucose (2DG) is used as an experimental tool to study glucoregulatory neurons (1-4). Previous findings suggest that adrenaline release in response to glucoprivation involves activation of neurons in the perifornical hypothalamus (PeH) and rostral ventrolateral medulla (RVLM). Systemic glucoprivation using 2DG excites RVLM sympathetic premotor neurons (5,6) and orexinergic neurons (7) in the PeH (8). Additionally, neurotropic viruses injected into the adrenal gland transsynaptically label neurons in the RVLM (9) and PeH (10). Disinhibition of perifornical neurons produces an increase in endogenous glucose production in the liver, which is mediated by the autonomic nervous system (11). However, it remains unknown whether intrinsic glucose sensitivity or projections from hypothalamic glucose-sensitive neurons (4,12,13) play an important role in the excitation of RVLM adrenal premotor neurons in response to glucoprivation; in particular, whether the responses evoked in RVLM neurons are modulated by orexinergic inputs (14,15).In this study, we hypothesized that PeH neurons respond to neuroglucoprivation and elicit adrenaline release by orexinergic activation of sympathetic premotor neurons in the RVLM. To test this hypothesis, we used a combination of in vivo and in vitro electrophysiological techniques to first examine the role played by neurons in the PeH in driving adrenal sympathetic nerve activity (ASNA). We then demonstrate for the first time that these effects are independent of any intrinsic sensitivity

Genetic tools that permit functional or connectomic analysis of neuronal circuits are rapidly transforming neuroscience. The key to deployment of such tools is selective transfection of target neurons, but to date this has largely been achieved using transgenic animals or viral vectors that transduce subpopulations of cells chosen according to anatomical rather than functional criteria. Here, we combine single‐cell transfection with conventional electrophysiological recording techniques, resulting in three novel protocols that can be used for reliable delivery of conventional dyes or genetic material in vitro and in vivo. We report that techniques based on single cell electroporation yield reproducible transfection in vitro, and offer a simple, rapid and reliable alternative to established dye‐labeling techniques in vivo, but are incompatible with targeted transfection in deep brain structures. In contrast, we show that intracellular electrophoresis of plasmid DNA transfects brainstem neurons recorded up to 9 mm deep in the anesthetized rat. The protocols presented here require minimal, if any, modification to recording hardware, take seconds to deploy, and yield high recovery rates in vitro (dye labeling: 89%, plasmid transfection: 49%) and in vivo (dye labeling: 66%, plasmid transfection: 27%). They offer improved simplicity compared to the juxtacellular labeling technique and for the first time offer genetic manipulation of functionally characterized neurons in previously inaccessible brain regions.

Somatostatin (SST) or agonists of the SST-2 receptor (sst2 ) in the rostral ventrolateral medulla (RVLM) lower sympathetic nerve activity, arterial pressure, and heart rate, or when administered within the Bötzinger region, evoke apneusis. Our aims were to describe the mechanisms responsible for the sympathoinhibitory effects of SST on bulbospinal neurons and to identify likely sources of RVLM SST release. Patch clamp recordings were made from bulbospinal RVLM neurons (n = 31) in brainstem slices prepared from juvenile rat pups. Overall, 58% of neurons responded to SST, displaying an increase in conductance that reversed at -93 mV, indicative of an inwardly rectifying potassium channel (GIRK) mechanism. Blockade of sst2 abolished this effect, but application of tetrodotoxin did not, indicating that the SST effect is independent of presynaptic activity. Fourteen bulbospinal RVLM neurons were recovered for immunohistochemistry; nine were SST-insensitive and did not express sst2a . Three out of five responsive neurons were sst2a -immunoreactive. Neurons that contained preprosomatostatin mRNA and cholera-toxin-B retrogradely transported from the RVLM were detected in: paratrigeminal nucleus, lateral parabrachial nucleus, Kölliker-Fuse nucleus, ventrolateral periaqueductal gray area, central nucleus of the amygdala, sublenticular extended amygdala, interstitial nucleus of the posterior limb of the anterior commissure nucleus, and bed nucleus of the stria terminalis. Thus, those brain regions are putative sources of endogenous SST release that, when activated, may evoke sympathoinhibitory effects via interactions with subsets of sympathetic premotor neurons that express sst2 .

Sympathetic premotor neurons residing within the rostral ventrolateral medulla (RVLM) control the activity of sympathetic nerves and blood pressure. In vivo, the activities of sympathetic nerves and spinally projecting cells in the RVLM display rhythmic bursting that is independent of baroreceptor input. We have previously proposed that such synchronisation could result from functional coupling between spinally projecting neurons. In this study we directly test that hypothesis by examining the prevalence of synaptic connections between pairs of RVLM sympathetic premotor neurons, identified by retrograde transport of tracer microinjected into the spinal cord. We simultaneously recorded membrane voltage and currents in pairs (34 pairs from x neurons) of bulbospinal neurons recorded in whole cell mode in acute brainstem slices prepared from P8 ‐ P20 rats. We injected depolarizing currents to evoke trains of action potentials in the ‘presynaptic’ neuron and used ‘presynaptic’ action potentials to trigger averages of holding current recorded in the ‘post‐synaptic’ neuron. No evidence of monosynaptic connections was observed in any case, despite long and stable recordings from neurons in close proximity to one another. We conclude that direct synaptic connections between bulbospinal neurons are sparse or non‐existent and that direct connections between these cells toes not play a significant functional role.