Prelimbic prefrontal cortex mediates respiratory responses to mild and potent prolonged, but not brief, stressors

Prefrontal Cortex Metabolome Is Modified by Opioids, Anesthesia, and Sleep

Obtundation of wakefulness caused by opioids and loss of wakefulness caused by anesthetics and sleep significantly alter concentrations of molecules comprising the prefrontal cortex (PFC) metabolome. Quantifying state-selective changes in the PFC metabolome is essential for advancing functional metabolomics. Diverse functions of the PFC suggest the PFC metabolome as a potential therapeutic entry point for countermeasures to state-selective autonomic dysfunction.

Hippocampal modulation of cardiorespiratory function

Changes in cardiorespiratory control accompany the expression of complex emotions, indicative of limbic brain inputs onto bulbar autonomic pathways. Previous studies have focussed on the role of the prefrontal cortex in autonomic regulation. However, the role of the hippocampus, also important in limbic processing, has not been addressed in detail. Anaesthetised, instrumented rats were used to map the location of hippocampal sites capable of evoking changes in cardiorespiratory control showing that stimulation of discrete regions within the CA1 fields of both the dorsal and ventral hippocampus potently alter breathing and cardiovascular activity. Additionally, tracing of the neuroanatomical tracts and pharmacological inactivation studies were used to demonstrate a role of the basomedial amygdala in hippocampal evoked responses. Collectively, these data support the existence of a hippocampal-amygdala neural circuit capable of modulating bulbar cardiorespiratory control networks and may suggest a role for this circuit in the top-down regulation of breathing and autonomic outflow necessary for the expression of complex emotions.

Differential role of hypothalamic orexin/hypocretin neurons in reward seeking motivated by cocaine versus palatable food

Hypothalamic orexin/hypocretin (Orx/Hcrt) neurons are thought to mediate both food-reinforced behaviors and behavior motivated by drugs of abuse. However, the relative role of the Orx/Hcrt system in behavior motivated by food versus drugs of abuse remains unclear. This investigation addressed this question by contrasting hypothalamic Orx/Hcrt neuronal activation associated with reinstatement of reward seeking induced by stimuli conditioned to cocaine (COC) versus highly palatable food reward, sweetened condensed milk (SCM). Orx/Hcrt neuronal activation in the lateral hypothalamus, dorsomedial hypothalamus and perifornical area, determined by dual c-fos/orx immunocytochemistry, was quantified in rat brains, following reinstatement of reward seeking induced by a discriminative stimulus (S⁺ ) conditioned to COC or SCM. The COC S⁺ and SCM S⁺ initially produced the same magnitude of reward seeking. However, over four subsequent tests, behavior induced by the SCM S⁺ decreased to extinction levels, whereas reinstatement induced by the COC S⁺ perseverated at undiminished levels. Following both the first and fourth tests, the percentage of Orx/Hcrt cells expressing Fos was significantly increased in all hypothalamic subregions in rats tested with the COC S⁺ but not rats tested with the SCM S⁺ . These findings point toward a role for the Orx/Hcrt system in perseverating, compulsive-like COC seeking but not behavior motivated by palatable food. Moreover, analysis of the Orx/Hcrt recruitment patterns suggests that failure of Orx/Hcrt neurons in the lateral hypothalamus to respond to inhibitory inputs from Orx/Hcrt neurons in the dorsomedial hypothalamus/perifornical area may contribute to the perseverating nature of COC seeking.

Integrity of the dorsolateral periaqueductal grey is essential for the fight-or-flight response, but not the respiratory component of a defense reaction

Periaqueductal grey is believed to be one of the key structures of the central respiratory stress network. Previous studies established that stimulation of the periaqueductal grey, especially its dorsolateral division (dlPAG), evokes tachypnea as well as increases in other autonomic parameters and motor activity. We investigated the effects of blockade of the dlPAG with GABAA agonist muscimol on respiration during stress and presentation of brief alerting stimuli in conscious unrestrained rats. We found that integrity of the dlPAG is not essential for stress-induced increase in basal/resting respiratory rate or for generation of respiratory responses to brief alerting stimuli. However, blockade of the dlPAG reduced the amount of motor activity and concomitant high-frequency respiratory activity during restraint and the first 5min of novelty stress. We conclude that the integrity of the dlPAG is not essential for generation of respiratory component of the defense reaction, but it mediates expression of the fight-or-flight response including its respiratory component.

Blockade of the dorsomedial hypothalamus and the perifornical area inhibits respiratory responses to arousing and stressful stimuli

The dorsomedial hypothalamus (DMH) and the perifornical area (DMH/PeF) is one of the key regions of central autonomic processing. Previous studies have established that this region contains neurons that may be involved in respiratory processing; however, this has never been tested in conscious animals. The aim of our study was to investigate the involvement of the DMH/PeF area in mediating respiratory responses to stressors of various intensities and duration. Adult male Wistar rats ( n = 8) received microinjections of GABAA agonist muscimol or saline into the DMH/PeF bilaterally and were subjected to a respiratory recording using whole body plethysmography. Presentation of acoustic stimuli (500-ms white noise) evoked transient responses in respiratory rate, proportional to the stimulus intensity, ranging from +44 ± 27 to +329 ± 31 cycles/min (cpm). Blockade of the DMH/PeF almost completely abolished respiratory rate and tidal volume responses to the 40- to 70-dB stimuli and also significantly attenuated responses to the 80- to 90-dB stimuli. Also, it significantly attenuated respiratory rate during the acclimatization period (novel environment stress). The light stimulus (30-s 2,000 lux) as well as 15-min restraint stress significantly elevated respiratory rate from 95 ± 4.0 to 236 ± 29 cpm and from 117 ± 5.2 to 189 ± 13 cpm, respectively; this response was abolished after the DMH/PeF blockade. We conclude that integrity of the DMH/PeF area is essential for generation of respiratory responses to both stressful and alerting stimuli.