Spinothalamic and spinohypothalamic tract neurons in the cervical enlargement of rats. I. Locations of antidromically identified axons in the thalamus and hypothalamus

Abstract

1. Seventy-seven neurons in the cervical enlargement of rats anesthetized with urethan were initially antidromically activated using currents < or = 30 microA from the contralateral posterior thalamus. A goal of these experiments was to determine the course of physiologically characterized spinal axons within the diencephalon. Therefore, in 38 cases, additional antidromic mapping was done throughout the mediolateral extent of the diencephalon at multiple anterior-posterior planes. 2. Electrolytic lesions marking the recording sites were recovered for 71 neurons. Thirty-one were located in the superficial dorsal horn (SDH); 39 were in nucleus proprius or the lateral reticulated area of the deep dorsal horn (DDH), and one was in the ventral horn. 3. Eight of 38 (21%) neurons that were tested for more anterior projections could only be antidromically activated with currents < or = 30 microA from sites in the contralateral posterior thalamus. Such neurons are referred to as spinothalamic tract (STT) neurons. Lesions marking the lowest threshold points for antidromic activation were located in or near the posterior thalamic group (Po). At more anterior levels, considerably higher currents were required for antidromic activation or it was not possible to activate the neurons with currents up to 500 microA. Four of these neurons were physiologically characterized and each responded preferentially to noxious mechanical stimuli (wide dynamic range, WDR). Each of the three neurons that were tested responded to noxious heat stimuli. These findings confirm anatomic studies that have shown that a number of STT axons terminate in Po and suggest that such axons that originate in the cervical enlargement carry nociceptive input from the upper extremity. 4. In 15 cases, electrode penetrations were made systematically throughout much of the contralateral ventrobasal complex (VbC). In 17 cases, penetrations were made throughout the intralaminar nuclei contralaterally, including the central lateral nucleus (CL). Surprisingly, only one of the examined axons was antidromically activated with low currents from CL and one from VbC, although both of these nuclei are known to receive sizeable inputs from the STT. 5. Many of the axons (27 of the 38 tested, 71%) that were initially antidromically activated from the contralateral posterior thalamus could also be antidromically activated with low currents (< or = 30 microA) and at increased latencies from sites located anteriorly in the contralateral hypothalamus. Such neurons are referred to as spinothalamic tract/spinohypothalamic tract (STT/SHT) neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Transcranial Direct Current Stimulation Targeting Primary Motor Versus Dorsolateral Prefrontal Cortices: Proof-of-Concept Study Investigating Functional Connectivity of Thalamocortical Networks Specific to Sensory-Affective Information Processing

“…Our findings align with previous experimental and brain imaging studies that argue that stimulating M1 mainly influences lateral thalamic projections that process sensory-discriminative information (Antal et al, 2010;Fregni et al, 2007;Mori et al, 2010). Anatomically, the lateral pathway constitutes lateral thalamic structures, like VPL, that primarily connect to cerebral cortical areas, such as S1 and M1, to convey somatosensory information (Andersson et al, 1997;Dado et al, 1994;Katter et al, 1996). The middle and posterior parts of the insular cortex also constitute the lateral pathway and receive information directly from the thalamus and from S1 (Hua et al, 2008).…”

Effects of scratching and other counterstimuli on responses of trigeminothalamic tract neurons to itch-inducing stimuli in rats

“…Lowest threshold points (Յ30 A) of each neuron were determined at all levels. Antidromic stimulation points with thresholds Յ30 A have been shown to reflect the location of examined axons within 200 m (Burstein et al 1991;Dado et al 1994a). The location of the most rostral projection of an axon was defined as the location of the most rostral LT points.…”

Thermally Identified Subgroups of Marginal Zone Neurons Project to Distinct Regions of the Ventral Posterior Lateral Nucleus in Rats

“…Antidromic mapping in the contralateral diencephalon was done as described previously by Dado et al (1994a) and Zhang et al (1995). Briefly, after unit isolation, the stimulating electrode was moved rostrally, and a row of electrode penetrations was made every 300 -500 m across the mediolateral extent of the contralateral hemisphere.…”

“…This was repeated until the most rostral point within the thalamus was found at which the MZ neuron could be antidromically activated by a current pulse Յ30 A, defined as a low-threshold point. Current pulses Յ30 A have been shown to activate spinohypothalamic tract axons at a distance of Յ400 m from the stimulating electrode (Burstein et al, 1991;Dado et al, 1994a). To resolve the putative terminal area of the axon, the most rostral low-threshold point was surrounded rostrally, medially, and laterally with stimulating electrode penetrations in which the axon could not be activated antidromically with up to 500 A.…”