Stephen J. Goldberg

Enduring suppression of hippocampal long-term potentiation following traumatic brain injury in rat

This study investigated changes in synaptic responses (population spike and population EPSP) of CA1 pyramidal cells of the rat hippocampus to stimulation of the Schaffer collateral/commissural pathways 2-3 h after traumatic brain injury (TBI). TBI was induced by a fluid percussion pulse delivered to the parietal epidural space resulting in loss of righting responses for 4.90-8.98 min. Prior to tetanic stimulation, changes observed after the injury included: (1) decreases in population spikes threshold but not EPSP thresholds; (2) decreases in maximal amplitude of population spikes as well as EPSPs. TBI also suppressed long-term potentiation (LTP), as evidenced by reductions in post-tetanic increases in population spikes as well as EPSPs. Since LTP may reflect processes involved in memory formation, the observed suppression of LTP may be an electrophysiological correlate of enduring memory deficits previously demonstrated in the same injury model.

Functional anatomy of the hypoglossal innervated muscles of the rat tongue: A model for elongation and protrusion of the mammalian tongue

This anatomical investigation in the rat was designed to illustrate the detailed organization of the tongues muscles and their innervation in order to elucidate the actions of the muscles of the higher mammalian tongue and thereby clarify the protrusor subdivision of the hypoglossal‐tongue complex. The hypoglossal innervated, extrinsic styloglossus, hyoglossus, and genioglossus and the intrinsic transversus, verticalis and longitudinalis linguae muscles were observed by microdissection and analysis of serial transverse‐sections of the tongue. Sihlers staining technique was applied to whole rat tongues to demonstrate the hypoglossal nerve branching patterns. Dissections of the tongue demonstrate the angles at which the extrinsic muscles act on the base of the tongue. The Sihler stained hypoglossal nerves demonstrate branches to the styloglossus and hyoglossus emanating from its lateral division while branches to the genioglossus muscle exit from its medial division. The largest portions of both XIIth nerve divisions can be seen to enter the body of the tongue to innervate the intrinsic muscles. Transverse sections of the tongue demonstrate the organization of the intrinsic muscle fibers of the tongue. Longitudinal muscle fibers run along the entire circumference of the tongue. Alternating sheets of transverse lingual and vertical lingual muscles can be observed to insert into the circumference of the tongue. Most importantly in clarifying tongue protrusion, we demonstrate the transversus muscle fibers enveloping the most superior and inferior portions of the longitudinalis muscles. Longitudinal muscle fascicles are completely encircled and thus are likely to be compressed by transverse muscle fascicles resulting in elongation of the tongue. We discuss our findings in relation to biomechanical studies, that describe the tongue as a muscular hydrostat and thereby define the “elongation‐protrusion apparatus” of the mammalian tongue. In so doing, we clarify the functional organization of the hypoglossal‐tongue complex. Anat Rec 260:378–386, 2000.

Organization of motoneurons in the dorsal hypoglossal nucleus that innervate the retrusor muscles of the tongue in the rat.

This anatomical investigation was prompted by the incomplete knowledge of the myotopic organization of the dorsal subdivison of the hypoglossal nucleus. Intrinsic muscle motoneurons were not segregated and labeled previously with regard to the lateral division of the hypoglossal nerve. Also, motoneuron number and cell size, in relation to the individual retrusor tongue musculature, were rarely addressed previously. Retrograde labeling of retrusor muscle motoneurons in the dorsal subdivision of the rat hypoglossal nucleus was done. Cholera toxin conjugate horseradish peroxidase (CTHRP) was injected into the retrusor tongue muscles with only the lateral division of the hypoglossal nerve intact. The dorsal subdivision of the hypoglossal nucleus contained approximately 800 motoneurons ranging in cell body size from 19 to 41 μm. When either the styloglossus, hyoglossus, superior longitudinal, or inferior longitudinal muscle was isolated and injected with CTHRP, a separate motoneuron pool for each muscle was seen. The extrinsic muscle motoneurons, styloglossus and hyoglossus, were found rostrolateral and caudolateral respectively. In contrast, the intrinsic superior and inferior longitudinal muscle motoneurons were found more central and medial in the nucleus. Extrinsic muscle motoneurons were larger (≈30 μm) than intrinsic muscle motoneurons (≈26 μm; P < .0001). Intrinsic muscle motoneurons account for a great majority of the motoneurons in the dorsal aspect of the hypoglossal nucleus and their axons have been shown to be contained in the lateral (retrusor) division of the hypoglossal nerve. This study revealed the myotopic organization of the retrusor subdivision of the rat hypoglossal nucleus. Anat Rec 254:222–230, 1999.

Organization of the hypoglossal motoneurons that innervate the horizontal and oblique components of the genioglossus muscle in the rat.

Anatomical studies have shown the genioglossus muscle of the tongue of mammals to have at least two subdivisions. One is horizontal and the other fans out obliquely. In the dog, the hypoglossal nerve appears to have separate branches for each muscle subdivision. In the rat, genioglossus muscle motoneurons have been reported in the lateral and centrolateral subnuclei of the ventral hypoglossal nucleus. Here, retrograde labeling documented that these two hypoglossal sub-nuclei separately supply the two components of the genioglossus muscle. In so doing we add new data concerning the myotopic organization of the hypoglossal nucleus and further clarify the functional organization of the hypoglossal-tongue complex into protrusor and retrusor subdivisions.

Phenotype and contractile properties of mammalian tongue muscles innervated by the hypoglossal nerve.

The XIIth cranial nerve plays a role in chewing, respiration, suckling, swallowing, and speech [Lowe, A.A., 1981. The neural regulation of tongue movements. Prog. Neurobiol. 15, 295-344.]. The muscles innervated by this nerve are functionally subdivided into three categories: those causing protrusion, retrusion, and changing the shape of the tongue. Myosin heavy chain (MHC) II isoform makes up the majority of the MHC phenotype with some variability among mammalian species and some evidence suggests between genders. In addition, there are regional differences in fiber type within some of these muscles that suggest functional compartmentalization. The transition from developmental MHC isoforms to their adult phenotype appears to vary not only from muscle to muscle but also from species to species. Motor units within this hypoglossal motor system can be categorized as predominantly fast fatigue resistant. Based on twitch contraction time and fatigue index, it appears that hypoglossal innervated muscles are more similar to fast-twitch muscles innervated by spinal nerves than, for example, extraocular muscles.

Compartmental organization of styloglossus and hyoglossus motoneurons in the hypoglossal nucleus of the rat

Surgical techniques were used to isolate the extrinsic bellies of the styloglossus and hyoglossus muscles from the body of the tongue for cholera toxin HRP injection. An average of 53 styloglossus and 121 hyoglossus motoneurons in the dorsal subdivision of the hypoglossal nucleus were demonstrated using tetramethyl benzidine histochemistry. Styloglossus motoneurons were restricted to the rostral 25% of the nucleus while hyoglossus motoneurons occupied other regions of the dorsal nucleus.

HIGH-FREQUENCY SEPTAL STIMULATION SUPPRESSES LONG-TERM POTENTIATION (LTP) IN THE CA1 REGION OF RAT HIPPOCAMPUS

The effects of high-frequency stimulation (HFS) of the medial septum/diagonal band (MSDB) on long-term potentiation (LTP) of CA1 extracellular field potentials were assessed in anesthetized rats. Ten rats received HFS of the Schaffer collateral pathway alone, and 10 received MSDB HFS 10 min prior to hippocampal HFS. Septal HFS suppressed LTP development assessed by change in population spike (PS) amplitude 60 min after hippocampal HFS (ANOVA, P less than 0.03). Septal inhibition of LTP development was most prominent when septal HFS had little direct effect on the CA1 PS. These results provide a novel demonstration of the functional heterogeneity of septohippocampal pathways and in vivo modulation of hippocampal LTP by HFS of natural afferent inputs.