The raphe magnus/pallidus regulates sweat secretion and skin vasodilation of the cat forepaw pad: A preliminary electrical stimulation study

Cardiovascular dysautonomia and cognitive impairment in Parkinson's disease (Review)

Cognitive impairment is a prevalent non-motor symptom of Parkinson's disease (PD), which can result in significant disability and distress for patients and caregivers. There is a marked variation in the timing, characteristics and rate at which cognitive decline occurs in patients with PD. This decline can vary from normal cognition to mild cognitive impairment and dementia. Cognitive impairment is associated with several pathophysiological mechanisms, including the accumulation of β-amyloid and tau in the brain, oxidative stress and neuroinflammation. Cardiovascular autonomic dysfunctions are commonly observed in patients with PD. These dysfunctions play a role in the progression of cognitive impairment, the incidents of falls and even in mortality. The majority of symptoms of dysautonomia arise from changes in the peripheral autonomic nervous system, including both the sympathetic and parasympathetic nervous systems. Cardiovascular changes, including orthostatic hypotension, supine hypertension and abnormal nocturnal blood pressure (BP), can occur in both the early and advanced stages of PD. These changes tend to increase as the disease advances. The present review aimed to describe the cognitive changes in the setting of cardiovascular dysautonomia and to discuss strategies through which these changes can be modified and managed. It is a multifactorial process usually involving decreased blood flow to the brain, resulting in the development of cerebral ischemic lesions, an increased presence of abnormal white matter signals in the brain, and a potential influence on the process of neurodegeneration in PD. Another possible explanation is this association being independent observations of PD progression. Patients with clinical symptoms of dysautonomia should undergo 24-h ambulatory BP monitoring, as they are frequently subtle and underdiagnosed.

Utility of Autonomic Function Tests to Differentiate Dementia with Lewy Bodies and Parkinson Disease with Dementia from Alzheimer Disease

Objective: We studied autonomic disturbance in patients with dementia with Lewy bodies (DLB), Parkinson disease with dementia (PDD), Alzheimer disease (AD), to determine whether autonomic function tests can be used to distinguish these disorders. Methods: Autonomic function was tested in 56 patients with DLB, 37 patients with PDD, and 59 patients with AD by using the sympathetic skin response, coefficient of variation in R-R interval, the head-up tilt test, serum norepinephrine concentration, and 123I-meta-iodobenzylguanidine cardiac scintigraphy. Symptoms of autonomic dysfunction, such as constipation, urinary symptoms, and orthostatic hypotension, were also noted. Results: The groups did not differ on baseline characteristics other than those associated with Parkinsonism and dementia. All patients with DLB and PDD had some dysautonomia, whereas rates were much lower for patients with AD (19%). Significantly more DLB and PDD patients than AD patients showed abnormalities on autonomic function tests. Conclusions: Autonomic function tests might be quite useful to distinguish DLB and PDD from AD.

The identification and neurochemical characterization of central neurons that target parasympathetic preganglionic neurons involved in the regulation of choroidal blood flow in the rat eye using pseudorabies virus, immunolabeling and conventional pathway tracing methods

The choroidal blood vessels of the eye provide the main vascular support to the outer retina. These blood vessels are under parasympathetic vasodilatory control via input from the pterygopalatine ganglion (PPG), which in turn receives its preganglionic input from the superior salivatory nucleus (SSN) of the hindbrain. The present study characterized the central neurons projecting to the SSN neurons innervating choroidal PPG neurons, using pathway tracing and immunolabeling. In the initial set of studies, minute injections of the Bartha strain of the retrograde transneuronal tracer pseudorabies virus (PRV) were made into choroid in rats in which the superior cervical ganglia had been excised (to prevent labeling of sympathetic circuitry). Diverse neuronal populations beyond the choroidal part of ipsilateral SSN showed transneuronal labeling, which notably included the parvocellular part of the paraventricular nucleus of the hypothalamus (PVN), the periaqueductal gray, the raphe magnus (RaM), the B3 region of the pons, A5, the nucleus of the solitary tract (NTS), the rostral ventrolateral medulla (RVLM), and the intermediate reticular nucleus of the medulla. The PRV+ neurons were located in the parts of these cell groups that are responsive to systemic blood pressure signals and involved in systemic blood pressure regulation by the sympathetic nervous system. In a second set of studies using PRV labeling, conventional pathway tracing, and immunolabeling, we found that PVN neurons projecting to SSN tended to be oxytocinergic and glutamatergic, RaM neurons projecting to SSN were serotonergic, and NTS neurons projecting to SSN were glutamatergic. Our results suggest that blood pressure and volume signals that drive sympathetic constriction of the systemic vasculature may also drive parasympathetic vasodilation of the choroidal vasculature, and may thereby contribute to choroidal baroregulation during low blood pressure.

Location of cat brain stem neurons that drive sweating

The brain stem premotor pathways controlling most noncardiovascular sympathetic outflows are unknown. Here, we mapped the brain stem neurons that drive sweating, by microinjecting excitant amino acid (L-glutamate or D,L-homocysteate: 0.4-3 nmol) into 420 sites over the pons and medulla of eight chloralose-anesthetized cats (70 mg/kg iv). Sweating was recorded by the electrodermal potential at the ipsilateral forepaw pad. Responses were classified as immediate (<5 s latency) or delayed (>10 s latency). Immediate responses were obtained from 16 sites (1-3 per animal) and were accompanied by no change in blood pressure. Those sites were clustered between the facial nucleus and the pyramidal tract in the rostral ventromedial medulla (RVMM). Microinjections into 33 surrounding sites caused delayed electrodermal responses of lesser amplitude, while the remaining 371 sites evoked none. To retrogradely label bulbospinal neurons that may mediate electrodermal responses, fluorescent latex microspheres were injected into the region of the intermediolateral cell column in the fourth thoracic segment in an earlier preparatory procedure on six of the animals. A cluster of retrogradely labeled neurons was identified between the facial nucleus and the pyramidal tract. Neurons in this discrete region of the RVMM, thus, drive sweating in the cat's paw and may do so via direct spinal projections.

Measurements of sweat response and skin vasomotor reflex for assessment of autonomic dysfunction in patients with diabetes

AIMS

Some physical or arousal stimuli induce a rise in sweat secretion (sympathetic sweat response or SSwR) and a reduction in skin blood flow (skin vasomotor reflex or SkVR) to the palm. We recorded SSwRs and SkVRs in diabetic patients and assessed the usefulness of these parameters for evaluating autonomic dysfunction in diabetes.

METHODS

We studied 42 diabetic patients (58+/-12 years) and 42 normal control subjects (59+/-11 years). Focal sweat secretion and skin blood flow were measured on the palm by a sudorometer and a Doppler flowmeter, respectively. SSwRs and SkVRs to deep inspiration, mental arithmetic, and isotonic exercise were recorded. SSwR amplitude was measured from baseline to peak, and SkVR amplitude (reduction rate) was calculated as: (blood flow reduction/basal blood flow)x100%. We also conducted head-up tilt tests and R-R interval variation tests (coefficient of variation of R-R intervals or CV(R-R)).

RESULTS

The SSwR or SkVR amplitudes in the diabetic group were significantly lower than those in the control group for any stimulus. CV(R-R) in the diabetic group was significantly less than that in the control group. The diabetic group showed a significantly greater reduction in systolic blood pressure during head-up tilt compared with the control group. In the diabetic group, there were significant correlations in SSwR or SkVR amplitudes versus blood pressure falls during the head-up tilt test, and CV(R-R) values.

CONCLUSION

We believe that SSwR and SkVR are useful indexes for the evaluation of autonomic involvement in diabetic patients.