Mapping of the disappearance of TIP39 fibers following selective lesion of TIP39

Bilateral lesions of TIP39 cell groups resulted in a disappearance of TIP39 fibers from their target areas (Dobolyi et al., 2003a). Unilateral lesions also caused a reduced density of TIP39 fibers ipsilateral to the lesion. We found no obvious reduction contralateral to the lesion in any brain region as compared to intact animals suggesting predominantly ipsilateral projections. The residual density was typically somewhat higher for unilateral than bilateral lesions suggesting some contribution of contralateral projection to TIP39 fibers in some brain regions (Cservenak et al., 2010; Dobolyi et al., 2003a). Still, the results of unilateral lesions are shown for demonstration because of the apparently striking difference between the two sides of the brain in the same section.

6.4.1.1. The effects of lesioning TIP39 cells in the PVG on TIP39 fibers

In the medial prefrontal cortex including the prelimbic, the infralimbic and the dorsal peduncular cortices, the TIP39-containing fibers disappeared after the lesions (Dobolyi et al., 2003a). This was best observed in the infralimbic cortex (Fig. 18A) as the normal density of TIP39 fibers is the highest in this part of the medial prefrontal cortex. In the nucleus accumbens, where TIP39-containing fibers are normally present in the shell and cone (anterior medio-dorsal part or rostral pole) portions but not in the core portion, almost all the

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fibers disappeared following PVG lesions. The high density of TIP39-containing fibers that is normally present in the lateral septum also disappeared completely in PVG lesioned rats (Fig.

18B). In the bed nucleus of the stria terminalis, the highest density of TIP39-containing fibers is in the medial division, with a particularly dense network in the anterior part, which disappeared following PVG lesions (Fig. 18C). The TIP39-containing fibers did not disappear from the hypothalamus following PVG lesions but a sharp reduction was observed in some areas including the paraventricular (Fig. 18D) and the dorsomedial nucleus. In the intact rat, the thalamus and the hippocampus contain very few TIP39-containing fibers. The greatest density is in the paraventricular thalamic nucleus and the subiculum. The density of TIP39-containing fibers showed a marked reduction in both regions following PVG lesions. There are many areas in the midbrain, and lower brainstem that normally contain TIP39-containing fibers (Dobolyi et al., 2003b), however, PVG lesions did not affect the density of TIP39-containing fibers in these regions, except the periaqueductal gray, where a moderate reduction was seen (Dobolyi et al., 2003a).

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Fig. 18. The effect of unilateral (left side) lesions of the PVG on TIP39 fibers. Disappearance of TIP39 immunoreactive fibers ipsilateral to the lesion in the dorsal peduncular and infralimbic cortices (A), lateral septum (B), bed nucleus of the stria terminalis (C), and strong

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ipsilateral reduction in the hypothalamic paraventricular nucleus (D). Scale bars = 200 µm.

The figure is from our previous publication (Dobolyi et al., 2003a).

6.4.1.2. The effects of lesioning TIP39 cells in the MPL on TIP39 fibers

Lesions in the medial paralemniscal nucleus resulted in complete, or almost complete disappearance of the TIP39-containing cells in the midbrain, lower brainstem and the spinal cord, while forebrain structures were not affected (Dobolyi et al., 2003a). Following unilateral medial paralemniscal lesions, there was an almost complete disappearance of TIP39-containing fibers ipsilaterally from the superior colliculus, the external cortex of the inferior colliculus (Fig. 19A) and the cuneiform nucleus while a moderate density of TIP39-containing fibers remained in the periaqueductal gray. In the intact pons and medulla, the ventral nucleus of the lateral lemniscus (Fig. 19B,C), the lateral parabrachial nucleus, the locus coeruleus, the subcoeruleus area, the medial nucleus of the trapezoid body (Fig. 19D), and the periolivary nuclei contain a considerable density of TIP39-containing fibers.

Following unilateral medial paralemniscal lesions, TIP39-containing fibers completely or almost completely disappeared from these pons and medulla regions ipsilateral to the lesion without any apparent change in the density of TIP39-containing fibers contralateral to the side of the lesions (Dobolyi et al., 2003a).

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Fig. 19. The effect of unilateral (right side) medial paralemniscal lesion on TIP39 fibers in brainstem auditory areas. An almost complete disappearance of TIP39 immunoreactive fibers

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ipsilateral to the lesion in the external cortex of the inferior colliculus (arrowheads) (A), in the nuclei of the lateral lemniscus (B – contralateral to the lesion, C – ipsilateral to the lesion), and in the medial nucleus of the trapezoid body (D). Scale bars = 500 µm for A, D and 250 µm for B, C. The figure is from our previous publication (Dobolyi et al., 2003a).

6.4.1.3. The effects of lesioning TIP39 cells in the PIL on TIP39 fibers

Following lesions of the PIL, TIP39 fibers almost completely disappeared from the ipsilateral amygdala, and most parts of the ipsilateral hypothalamus (Dobolyi et al., 2003a). In addition, smaller, but visible reductions in the density of TIP39 fibers were observed ipsilateral to the lesion in many other forebrain regions including the infralimbic cortex, the nucleus accumbens, the ventral subdivision of the lateral septum and the bed nucleus of the stria terminalis (Dobolyi et al., 2003a).

Since TIP39 fibers could be followed from the PIL towards the supraoptic decussations (Palkovits et al., 2010) to project in a ventromedial direction (Fig. 20A), the effect of transaction of this pathway was studied in mother rats. Transections reaching the optic tract ventrally at bregma level AP = -2.64, L = 3.0 resulted in the accumulation of TIP39 immunoreactivity immediately caudal to the transection within the fibers of the supraoptic decussations (Fig. 20B, C). In these animals, a marked reduction was found in the density of TIP39-containing fibers and terminals in the arcuate (Fig. 20D), paraventricular, and periventricular nuclei, and the preoptic area ipsilateral to the transection (Cservenak et al., 2010).

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Fig. 20. Projection of TIP39 neurons is demonstrated to the arcuate nucleus in rat dams. A:

TIP39 fibers project towards the hypothalamus in the supraoptic decussations. B: A transection perpendicular to the supraoptic decussations is shown in a coronal section. The disappearance of TIP39 fibers is observed medial to the transaction. C: A high-magnification photomicrograph showing the framed area in panel B demonstrates the accumulation of TIP39 immunoreactivity (arrows) in the supraoptic decussations immediately lateral to the transection. D: TIP39 fibers are abundant in the arcuate nucleus of rat dams (white arrow) contralaterally but disappeared from the arcuate nucleus on the side of transaction indicated by a star (*). Scale bar = 400 µm for B, 100 µm for C, and 500 µm for D. The panels are from our previous publication (Cservenak et al., 2010).

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6.4.2. Retrograde labeling of TIP39 neurons following injections into the arcuate nucleus