Selective depressant action of antidromic impulses on gustatory nerve signals

Obesity in short stem total hip arthroplasty using a minimally invasive supine anterolateral approach-a risk factor for short-term complications?

Purpose

Obesity is associated with increased risk for surgical complications in total hip arthroplasty (THA). The impact of obesity on short-term complication in minimally invasive (MIS) anterolateral approach is not well known. Therefore, this study was conducted to evaluate the early complications within the first 90 days after THA using a MIS anterolateral approach with a short-curved stem stratified by Body Mass Index (BMI).

Patients and methods

A single centre consecutive series of 1052 hips in 982 patients (index surgery 2014–2019) with a short-curved stem and press fit cup implanted using a MIS anterolateral approach in supine position were screened for inclusion. Inclusion criteria were defined as end-stage primary osteoarthritis of the hip. Eventually, 878 implantations in 808 patients were included and stratified by body mass index (BMI). Peri-operative complications, within the first 90 days after surgery, were retrospectively evaluated.

Results

Severely obese patients (BMI ≥ 35 kg/m²) and morbidly obese patients (BMI ≥ 40 kg/m²) demonstrated a significantly increased operation time (p < 0.001) and a higher risk for general surgical complications (p = 0.015) (odds ratio (OR) = 4.365; OR = 4.985), periprosthetic joint infection (PJI) (p = 0.001) (OR = 21.687; OR = 57.653), and revision (OR = 8.793; OR = 20.708).

Conclusion

The risk for early PJI and overall surgical complications in MIS anterolateral approach is significantly increased in severely and morbidly obese patients. This leads to a significantly higher risk for revision surgery after index surgery within the first 90 days. A BMI above 35 kg/m² is the clear threshold for increased risk of PJI in MIS anterolateral THA with a short curved stem. As the surgical complications are comparable to other approaches, MIS anterolateral short stem THA is also feasible with increasing BMI.

Enhancement of Gustatory Neural Responses by Parasympathetic Nerve in the Frog

The autonomic nervous system affects the gustatory responses in animals. Frog glossopharyngeal nerve (GPN) contains the parasympathetic nerve. We checked the effects of electrical stimulation (ES) of the parasympathetic nerves on the gustatory neural responses. The gustatory neural impulses of the GPNs were recorded using bipolar AgCl wires under normal blood circulation and integrated with a time constant of 1 s. Electrical stimuli were applied to the proximal side of the GPN with a pair of AgCl wires. The parasympathetic nerves of the GPN were strongly stimulated for 10 s with 6 V at 30 Hz before taste stimulation. The integrated neural responses to 0.5 M NaCl, 2.5 mM CaCl₂, water, and 1 M sucrose were enhanced to 130-140% of the controls. On the other hand, the responses for 1 mM Q-HCl and 0.3 mM acetic acid were not changed by the preceding applied ES. After hexamethonium (a blocker of nicotinic ACh receptor) was intravenously injected, ES of the parasympathetic nerve did not modulate the responses for all six taste stimuli. The mechanism for enhancement of the gustatory neural responses is discussed.

Inhibitory interactions among rodent taste axons

The left side of the tongue of the Mongolian gerbil, Meriones unguiculatus, was experimentally innervated with both chorda tympani nerves. While this dual innervation did not increase the number or volume of fungiform taste buds on the left side, at least half of the taste buds were dually innervated since they could be neurotrophically maintained by either chorda tympani nerve. Impulse discharges occurred simultaneously in the native (left) and foreign (right) chorda tympani nerves when the taste stimulus was restricted to the left side of the tongue. The marked attenuation of the phasic or tonic portions of some taste responses suggested that dual innervation had enhanced inhibition, especially of foreign chorda tympani responses. This was confirmed when electrical stimulation of the native chorda tympani reduced the peak summated action potential discharges of the foreign chorda tympani to NaCl or sucrose by an average of 52 and 41%, respectively. Inhibition began within seconds and continued with an 11.5-min half-life. The inhibition was unaffected by acutely disconnecting either chorda tympani nerve from the brain. We propose that dual chorda tympani innervation accentuated lateral inhibitory connections that may function normally to reduce spurious sensory signals in taste axons.

Taste as a highly discriminative system: a hamster intrapapillar single unit study with 18 compounds

Seventy-nine single units were recorded with glass micropipettes applied onto taste pores of the anterior portion of the tongue in anesthetized hamsters. The receptive field of each recorded unit was located by iontophoretic stimulation applying either anodal or cathodal current (1-20 microA) to a non-stimulating solution of sodium cyclamate (5 mM). Different kinds of responses to iontophoretic stimulation were described. Eighteen chemical stimuli including sweet and bitter tastants for humans, and amino acids were locally applied to one papilla of the receptive field of 63 of these units. Stimulations were applied in a continuous flow (30 ml/min) in a small chamber. Response criterion was chosen as 2 S.D. above the mean activity recorded during the minute preceding the stimulus arrival. The low amplitude of single unit responses to chemicals is discussed by reference to the recording and stimulating techniques and compared to results of control experiments on whole nerve recordings and psychophysical experiments on human subjects. The importance of a high flow rate during continuous flow stimulation was demonstrated. The possible necessity of mechanical stimulation to facilitate taste responses was outlined. The sensitivity of units to stimuli applied either chemically or iontophoretically was not identical. Contrary to authors expectations, localized sensitivities for a few specific chemicals were disclosed. The response reproducibility to chemical stimulation was 84% (S.D. = 1.6%). chi 2 calculation, correspondence analysis and hierarchical clustering showed small distances between the two profiles representing the same stimulus or the two profiles representing the same unit, but great distances between profiles representing either different stimuli or different units. All stimuli are different from one another. Only 6 pairs of similar units were found among 63 units. Unit clusters could be found only if a few stimuli were considered but they vanished when all 18 stimuli were used in the calculation. The breadth of tuning of units ranged from 0.25 to 0.92 with a mean of 0.68. We show that the peripheral taste system is highly discriminative. Each stimulus evokes a distinct sensory image. At least 8 independent factors are needed to describe the peripheral taste space, setting a lower limit to the number of different peripheral information channels (putative acceptors) involved.

Interaction among different sensory units within a single fungiform papilla in the frog tongue

The possible interaction among different sensory units in the frog tongue was studied using several single papillae dually innervated by the medial and lateral branches of the glossopharyngeal (IXth) nerve. The afferent activity in one branch exposed to NaCl stimulation of the papilla revealed marked inhibition after antidromic electrical stimulation (100 Hz, 30 s, and 3 V) of the other branch. The degree of inhibition depended on the number of sensory responses observed in the electrically stimulated branch as well as the nature of the stimulated sensory units. Statistical analysis suggested that antidromic activation of gustatory units conducting the responses to NaCl and quinine and slowly adapting mechanosensitive units produced a large antidromic inhibition amounting to 19-25%, but that of gustatory units conducting the responses to acetic acid and rapidly adapting mechanosensitive units gave rise to only a slight inhibition. To examine the differential effects of these sensory units in antidromic inhibition, antidromic impulses were evoked by chemical stimulation of the adjacent papilla neuronally connected with the dually innervated papilla under study. Antidromic volleys of impulses elicited by NaCl or quinine stimulation produced a large inhibition of the afferent activity in the other branch, as induced by NaCl stimulation of the dually innervated papilla. Plausible mechanisms of synaptic interaction in peripheral gustatory systems are considered.