Projections from the vestibular nuclei to the hypothalamic paraventricular nucleus: morphological evidence for the existence of a vestibular stress pathway in the rat brain

Abstract

Although it has been reported by several laboratories that vestibular stress activates the hypothalamo-pituitary-adrenocortical axis (HPA), the existence of neuronal connections between vestibular and hypothalamic paraventricular neurons has not yet been demonstrated. By the use of a virus-based retrograde trans-synaptic tracing technique in the rat, here we demonstrate vestibular projections to the paraventricular nucleus (PVN). Pseudorabies virus (Bartha strain, type BDR62) was injected into the PVN, and the progression of the infection along synaptically connected neurons was followed in the pons and the medulla, 3 and 4 days post-inoculation. Virus-infected neurons were revealed mainly in the medial vestibular nucleus. Labeled cells were scattered in the spinal, and very rarely in the superior nuclei, but none of them in the lateral vestibular nucleus. Injections of cholera toxin B subunit, a monosynaptic retrograde tracer into the PVN failed to label any cells in the vestibular nuclei. These results provide anatomical evidence for the existence of a vestibulo-paraventricular polysynaptic pathway and support the view that the HPA axis is modulated by vestibular stress.

Reduction of long-term potentiation at Schaffer collateral-CA1 synapses in the rat hippocampus at the acute stage of vestibular compensation

“…Expression of glutamate ionotropic receptor NMDA type subunit 2A was altered in the ipsilateral CA1 at 10 hours post-UVD in guinea pigs [31]. An anatomical study has documented that vestibular axonal projections reach to major structures responsible for autonomic functions such as hypothalamus, locus coeruleus, and solitary nucleus [32]. Experimental evidence linking unilateral vestibular deafferentation to the long-lasting activation of the hypothalamic–pituitary–adrenal (HPA) axis has also been shown [33].…”

Interactions between Stress and Vestibular Compensation – A Review

“…Electrical and caloric stimulation of the vestibular pathways results in a response in PVN neurons in the guinea pig (Azzena et al, 1993; Liu et al, 1997) and an increase in plasma AVP levels in the rat (Horii et al, 2001). Retrograde viral tracing in the rat brain has demonstrated the presence of a direct vestibulo-paraventricular projection (Markia et al, 2008) and similarly a paraventricular–vestibular pathway has also been described (Horowitz et al, 2005). Further neural pathways linking the vestibular system and hypothalamus have been suggested in models of the neuroanatomical linkage of balance and anxiety (Balaban and Thayer, 2001) and are supported by recent behavioral experiments in genetically modified mice with either abnormal vestibular systems or altered levels of anxiety-like behavior (Kalueff et al, 2008; Avni et al, 2009).…”

Rebalancing the commissural system: Mechanisms of vestibular compensation

“…In addition, both unilateral and bilateral vestibular deafferentation have profound effects on neurons in the hippocampus and re-lated cortical areas (review [55]), in line with the important dynamic contribution of vestibular signals to spatial cognition and navigation. Direct pathways from the brainstem vestibular nuclei to the hypothalamus and other forebrain areas also exist [45,72]. Consequently "vestibular compensation", the overall functional and behavioural recovery that follows damage to the vestibular system, is a rather broad term that may implicate adaptive changes in neuronal and synaptic function in many brain areas.…”