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SUMMARY1. The reflex responses of y-motoneurones to discharges of muscle receptors innervated by Group III axons have been examined in hind-limb muscles of decerebrated and spinal cats.2. Electrical stimulation of the gastrocnemius medialis nerve at a strength sufficient to excite Group III axons caused excitation of gastrocnemius lateralis or soleus y-motoneurones. The excitation was more prominent in the spinal animal.3. Excitation of either silent or tonically firing y-motoneurones was a secure, driven type of response consisting ofone or two spikes occurring at fairly fixed latency in response to a single stimulus. Eighteen out of thirty-nine y-motoneurones studied showed such excitation.4. Subtracting peripheral conduction times of the y-motoneurone impulse and the earliest component of the Group III volley from the latency of reflex excitation gave a range of central delays of 1-8-4-8 msec (mean 3 0 msec).5. Inhibitory Group III effects were also seen but were less pronounced than the excitation.6. The origin of the receptors connected to the Group III axons whose discharge causes driven excitation of y-motoneurones was investigated.7. Isometric twitch contractions of a muscle caused pronounced facilitation or excitation of homonymous and heteronymous y-motoneurones. Excitation occurred close to the peak or during relaxation of the twitch with a range in latency of 30-110 msec. The muscles studied were triceps surae, flexor digitorum and hallucis longus.8. Pressure or light taps applied to the gastrocnemius medialis muscle caused an increase in discharge frequency in twenty out of twenty-eight y-motoneurones of the same muscle (four were inhibited). The response to a steady stimulus adapted but could outlast it by many seconds. Pressure was more effective when applied to the proximal or distal parts of the muscle.9. Fifteen out of thirty-eight gastrocnemius medialis receptors having Group III axons (conduction velocities 5-27 m/sec) were found to discharge one, or occasionally two, spikes to twitch contractions of the parent muscle at latencies of 30-80 msec.10 11. We conclude that discharges in Group III axons from receptors which respond to non-noxious, low threshold mechanical stimuli cause a tightly coupled excitation of y-motoneurones. The likely contribution of this reflex to the control of movement is discussed.

In view of conflicting reports of skeletal muscle and skin blood flow participation in baroreceptor-mediated reflexes, we studied the effects of graded lower body negative pressure (LBNP) on cutaneous and muscular components of forearm blood flow (FBF) in seven male subjects at 28 degrees C. FBF was measured by venous occlusion plethysmography and cutaneous flow by laser-Doppler velocimetry, the difference being the muscular flow. Mean FBF decreased by 39 and 56% from control at LBNP of 20 and 50 Torr, respectively. Skin flow decreased linearly with graded LBNP contributing 32% of the decrease of total blood flow at 20 Torr and then 50% of total decrease of blood flow at 50 Torr. Conversely, the decrease in muscle flow represented 68% of the total decrease at LBNP of 20 Torr and then 50% of the total decrease at LBNP of 50 Torr. We concluded that both skin and muscle circulations participate in sustained peripheral vasoconstriction during LBNP, with muscle flow achieving near maximum vasoconstriction by 20 Torr and skin showing a graded vasoconstriction to decreases in LBNP.

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The stimulus-response characteristics of cardiopulmonary baroreflex control of forearm vascular resistance (FVR) were studied in five unfit [UF, maximal O2 consumption (VO2 max) = 38.5 ml X min-1 X kg-1] and six fit (F, VO2 max = 57.0 ml X min-1 X kg-1) subjects. We assessed the relationship between reflex stimulus, i.e., changes in central venous pressure (CVP) and response, i.e., FVR, during selective unloading of the cardiopulmonary mechanoreceptors with lower body negative pressure (0 to -20 mmHg). The linear relationship between FVR and CVP, the gain of this baroreflex, was significantly diminished in the F subjects, -2.42 +/- 0.57 U/mmHg, compared with the UF, -5.15 +/- 0.58 U/mmHg. Both groups, F and UF, had similar resting values for CVP and FVR; thus the diminished gain in F subjects was not simply an artifact resulting from a shift of the set point along the baroreflex stimulus-response curve. We also found a linear relationship between baroreflex gain and total blood volume (r = 0.59, P less than 0.05). We conclude that the gain of this vascular reflex is attenuated in trained individuals and is related to cardiovascular adaptations, such as an increased blood volume, associated with exercise training.

In the past few years internet addiction (IA) and internet gaming disorder (IGD) have become very frequent, leading to many personality and psychiatric disorders including low self-esteem, impulsivity, poor sleep quality, mood disorder, and suicide. IA has been included in Appendix III of the Diagnostic and Statistical Manual for Mental Disorders (DSM-5) as IGD. In addition, IA leads to many neuroanatomical and neurochemical alterations including cortical thinning of various components of the brain and altered dopaminergic reward circuitry. Due to widespread neuropsychiatric and neurobiological implications of IA, multiple therapeutic approaches are needed. Integrative therapy in the form of yoga and mindfulness has proven to be effective in many addiction disorders including IA.

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